A versatile platform for colorimetric, fluorescence and photothermal multi-mode glyphosate sensing by carbon dots anchoring ferrocene metal-organic framework nanosheet

A "three-in-one" detection platform based on cerium-coated metal-organic framework for multimodal glyphosate detection

Glyphosate (Glyp) is a widely used herbicide, but its through prolonged and excessive spraying residues pose significant health risks. A ratiometric multimodal sensing platform combining fluorescence, colorimetry, and photothermal detection was developed for Glyp detection using a cerium/polyacrylic acid-modified porphyrin-based metal-organic framework (PCN@PAA-Ce). The detection strategy relies on the inhibition of acetylcholinesterase by Glyp, the oxidase-like activity of PCN@PAA-Ce, and the competition between enzymatic products and 3,3',5,5'-tetramethylbenzidine (TMB). Glyp inhibits acetylcholinesterase, which prevents the hydrolysis of acetylthiocholine and the production of reduced thiocholine. The oxidase-like property of PCN@PAA-Ce facilitates the oxidation of TMB (colorless) to oxidized TMB (oxTMB) (blue-green), while fluorescence resonance energy transfer caused oxTMB to quench the red fluorescence of PCN@PAA-Ce. Under ultraviolet light, the probe solution exhibits yellow-green fluorescence as a reference signal. Additionally, the excellent photothermal conversion of oxTMB enables the probe to respond to Glyp through photothermal responses. The detection ranges in the three modes were 1 × 10-5 to 4 mg mL-1, 1 × 10-4 to 6 mg mL-1, and 1 × 10-4 to 6 mg mL-1, respectively, with detection limits of 9.85 × 10-6 mg mL-1, 8.69 × 10-5 mg mL-1, and 9.72 × 10-5 mg mL-1, respectively. Compared to a single-mode probe, the multimodal probe's self-verification function provides more accurate and stable detection, offering broader potential for application.

Portable iron-organic frameworks hydrogel for glyphosate detection based on competitive coordination with iron

The detection techniques for glyphosate residues have garnered attention due to the potential toxicity associated. Herein, we introduced a fluorescent "turn-on" strategy, leveraging competitive coordination with iron, for glyphosate detection. We synthesized iron-based metal-organic frameworks (Fe-MOFs) at room temperature. Among them, 2,5-dihydroxyterephthalic acid (DOBDC) acted as a ligand to produce strong fluorescence, and iron ions acted as a quencher to quench the fluorescence of DOBDC. Another ligand, 2-nitroterephthalic acid, contained nitro quenching of the fluorescence, giving it a lower background. Glyphosate competed with the ligands for ions, weakening the interaction between ions and the ligands. This disruption restored the fluorescence emission at 535 nm, enabling glyphosate detection. To facilitate field application, Fe-MOFs were encapsulated within agarose to create a functional hydrogel. Glyphosate penetrated the hydrogel and resulting in fluorescence "turn-on". Remarkably, this method facilitated visual detection through smartphone photography coupled with RGB (red/green/blue) analysis, offering a user-friendly and portable solution.

Nanozyme-based biosensors for food contaminants detection: advances, challenges, and prospects

The presence of food contaminants poses a growing threat to public health. Developing advanced and reliable biosensing methods with high sensitivity, specificity, and reproducibility for detecting food contaminants is an urgent requirement for food safety control. Nanozymes, recognized for their enzyme-mimicking catalytic activities and the unique physicochemical properties of nanomaterials, have been extensively utilized in the development of diverse biosensors for food safety assays. Recent years have witnessed an exponential surge in relevant publications, garnering considerable research interest. This review summarizes recent advancements in the catalytic mechanisms of peroxidase- and oxidase-like nanozymes and provides a comprehensive discussion on the construction, sensing mechanisms, and practical applications of nanozymes-based biosensors developed for detecting food contaminants over the past five years. These biosensors include colorimetric, fluorescence, chemiluminescent, electrochemical, surface-enhanced Raman scattering, multi-modal, and other types, used for detecting food contaminants such as mycotoxins, pathogens, pesticides, veterinary drugs, illegal additives, and heavy metals. The review also addresses current challenges and prospects in this field, aiming to summarize advancements and promote further exploration of nanozyme-based sensing platforms to guarantee food safety.

Iron-ferrocenedicarboxylic nanozyme based colorimetric and photothermal dual-modal signal catalytic inhibition for detection of glyphosate

A novel dual-mode colorimetric and photothermal sensing platform for glyphosate (GLP) based on iron-ferrocenedicarboxylic metal-organic framework (Fe-FcMOF) nanozyme-mediated catalysis is presented. Specifically, the synthesized Fe-FcMOF nanozyme exhibits superior peroxidase (POD)-like activity, which can oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxidized TMB (ox TMB) in the presence of H2O2. Due to the photothermal effect of oxTMB, the catalytic system composed of Fe-FcMOF, H2O2 and TMB exhibits remarkable temperature changes (ΔT) before and after being irradiated by near-infrared light at 808 nm. Subsequently, Fe-FcMOF reacts with GLP through electrostatic attraction, hydrogen bonding and specific chemical coordination between the -FeO of Fe-FcMOF and -PO3H2 of GLP, resulting in the formation of stable Fe-O-P coordination bonds. This specific interaction leads to the decrease of the POD-like activity of Fe-FcMOF and the ultraviolet absorbance and ΔT of the system. Building upon these findings, we develop a colorimetric and photothermal dual-modal sensor, with detection limits of 0.0676 µg mL-1 and 0.0856 µg mL-1 respectively. Notably, the proposed dual-mode sensing platform enhances the reliability of the assay, which offers a potential approach for the on-site visual detection of pesticide residues to guarantee food safety.

"Three-in-One" MIL@PDA-UiOL@AIEgens driven lateral flow immunosensor for multimodal detection of aflatoxin B1

The multi-modal lateral flow immunosensor (LFIS) with integrated advantages and mutual built-in calibration ability could avoid the limitations of traditional single-signal output mode to meet the growing demands for trace contaminants. In this study, an innovative "three-in-one" LFIS platform was developed for colorimetric, grayscale, and fluorescent detection of aflatoxin B1 (AFB1). It integrated polydopamine (PDA)-coated ferric metal-organic framework (MOF) (MIL@PDA) and the functionalized zirconium MOF of a UiO linker enriched with abundant AIEgens (UiOL@AIEgens) as signal probes. The synthesized MIL and UiOL with large surface area and high porosity could enrich numerous PDA and AIEgens probes, respectively, for signal amplification, not only significantly enhancing the colorimetric signal outputs, and grayscale and fluorescence responses, but also largely improving the detection sensitivity and analytical accuracy. The MIL@PDA-monoclonal antibodies (mAbs) probes could specifically identify AFB1 antigens on the test (T) line to produce a visible dark-grey band for qualitative colorimetric detection, and the grayscale intensities were monitored for the quantitation of AFB1 via a portable device. The fluorescence mode was realized through the MIL@PDA-mAbs probes quenching the fluorescence of UiOL@AIEgens on the T line, and the fluorescence intensities were recorded by using a smartphone for accurate quantitation. Under optimal conditions, this MIL@PDA-UiOL@AIEgens driven three-modal LFIS platform allowed for AFB1 detection in a wide range of 0.01-5 ng/mL with a low limit of detection of 0.01 ng/mL that was more than 59-fold lower than the traditional AuNPs-based LFIS. The feasibility and practicability of this LFIS platform was verified for AFB1 detection in lotus seeds. This study opened up a new avenue for developing high-performance LFIS platforms for the trace detection more harmful analytes in complex matrices.

Commercial reagents-based six-mode sensor: One-step detection of iodide ions without enzymes or nanomaterials

Multi-signal sensors possess immense potential for point-of-care testing, yet their widespread adoption is hindered by reliance on complex nanomaterial synthesis or fragile enzymatic systems. Herein, we propose a "six-in-one" multi-mode sensor for rapid iodide ion (I-) detection, leveraging only three commercially available reagents: chloroplatinic acid (H2PtCl6), hexadecyl trimethylammonium bromide (CTAB), and 3,3',5,5'-tetramethylbenzidine (TMB). The core innovation lies in a dynamic "on-off-on" oxidation triggered by target I- ions as follows: H2PtCl6 with strong oxidative capacity directly oxidizes TMB to its two-electron product (TMB2+) ("On" State). CTAB coordinates with H2PtCl6 thereby blocking its surface and completely inhibiting TMB oxidation ("Off" State). I- selectively displaces CTAB via competitive coordination, partially restoring H2PtCl6's oxidation activity to generate the one-electron product (TMBox) ("Reactivation" State). Remarkably, the resulting TMBox exhibits six distinct signal outputs including visual and fluorescent color, absorbance, fluorescence, temperature, and electrical current. Compared to conventional single- or dual-mode methods, our six-mode approach improves reliability of detection results. This "magic cube" signals enables dual-mode qualitative analysis and four-mode quantitative detection, achieving a nanomolar-level detection limit for I- detection. Critically, multi-mode sensor operates via one-step mixing without requiring nanomaterials, enzymes, or specialized equipment. We further demonstrate its utility in detecting I- in biological (urine, serum), food (iodized salt) and environmental (Yellow River water, tap water) samples with recovery rates of 96.3 %-110.0 %. Statistical analysis demonstrated excellent reproducibility with relative standard deviations <3.1 % across repeated measurements. This work redefines the paradigm of multi-mode sensing, offering a cost-effective, field-deployable solution for environmental monitoring and clinical diagnostics.

Self-cascade catalytic system constructed using carbon dots and Au nanoparticles co-assembled on MIL-53(Fe)-NH2 as a three-in-one fluorescent nanozyme for multimodal detection of glucose and maltose in food

Determination of glucose and maltose is crucial for food production and human health. Herein, a novel Au/CD@MIL-53(Fe)-NH2 self-cascade nanozyme was constructed via host-guest assembly with "three-in-one" features, including blue fluorescence, H2O2 production as an oxidase mimic, and •OH generation as a peroxidase mimic. Theoretical and experimental results proved that the incorporation of carbon dots renders the composite with high peroxidase-like activity and extremely high affinity for H2O2 (Km: 0.011 mM), 336 times higher than that of the natural enzyme. The self-cascade catalytic process could oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue ox-TMB, which further quenched the fluorescence and produced a photothermal effect. Consequently, colorimetric/fluorescence/photothermal-based multimodal detection of glucose and maltose was first achieved, obtaining low detection limits of 12/7.5/1.1 and 18/11.3/1.4 μM, respectively. This study offers a promising strategy for designing efficient nanozyme-based cascade systems that help enhance food quality determination.

In-situ preparation of CeO2@MIL-88B nanocomposite for improving "turn-on" fluorescent sensing toward Thiabendazole

A novel "turn-on" fluorescent sensor of CeO2@MIL-88B was constructed successfully via the facile in-situ strategy. The as-obtained CeO2@MIL-88B could be used for effectively detecting the analyte of thiabendazole (TBZ) by luminescence enhancement, which limit of detection (LOD) was as low as 0.294 μM (nearly 10.4 times smaller than that of MIL-88B). The detection behavior for TBZ exhibited the excellent selectivity and anti-interference ability. Systematic explorations were performed to shed light on the underlying mechanism of "turn-on" effect on fluorescence after adding TBZ. Moreover, the CeO2@MIL-88B was also employed for the determination of TBZ in the real samples of orange and cucumber.

Achieving ultrasensitive detection of glyphosate in fruits and vegetables using a triple-mode strategy based on carbon dots nanozymes derived from expired drugs

Rapid and sensitive detection of glyphosate (GLP) holds significant importance in the monitoring of environmental pollution and potential risks to human health. In this study, carbon dots nanozymes (CDszymes) with peroxidase-like activity were synthesized rapidly using a microwave-assisted method, employing expired drugs as raw materials. In the presence of H2O2, CDszymes catalyze the oxidation of TMB to generate blue oxTMB, which exhibits a photothermal effect under near-infrared light irradiation; an inner filter effect (IFE) may occur between oxTMB and CDszymes. By coupling the cascade catalysis of AChE and ChOx to generate H2O2, GLP effectively inhibits the activity of AChE, constructing a colorimetric/fluorescent/photothermal response platform for GLP. In colorimetry, the detection limit of GLP was 0.33 ng/mL. The detection limits of GLP by fluorescence method and photothermal method were 0.02 ng/mL and 0.41 ng/mL, respectively. The efficacy of this methodology has been successfully demonstrated in fruit and vegetable, it also provides a strategy for the high-value conversion of expired drugs.

An ultrasensitive colorimetric/fluorescent/photothermal sensing platform for the detection of D-amino acids based on carbon dots nanozymes with enhanced peroxidase-like activity

Based on the enhanced peroxidase-like activity of carbon dots nanozymes (CDszymes), with a specific oxidation reaction of D-amino acid oxidase catalysing the formation of H2O2 from D-amino acid, an ultrasensitive sensing platform, was constructed for the quantitative detection of D-amino acids in saliva. With the increase of D-amino acids concentration, the blue color of catalytic product gradually deepend, the fluorescence CDszymes gradually quenched, and the temperature gradually increased. Using D-alanine as D-amino acid models, the detection limits of D-alanine in colorimetric/photothermal/fluorescent mode were 0.3 μM, 1.8 μM, and 0.04 μM, respectively. The proposed detection platform exhibits promising application potential in clinical diagnostics. The exceptional sensing performance can be attributed to the utilization of CDszymes with outstanding POD activity. Revolving around the blind synthesis of CDszymes exhibiting high-efficiency POD activity, this study delved into the underlying mechanism governing the regulation of the POD activity of CDszymes by precursor functional groups. This work investigates the valence band theory to enhance the peroxidase-like of CDszymes, thereby offering a rational approach for designing CDszymes.

Carbon dots-based dual-mode sensor for highly selective detection of nitrite in food substrates through diazo coupling reaction

As an antioxidant and preservative agent, nitrite (NO2-) plays an essential role in the food industry to maintain freshness or inhibit microbial growth. However, excessive addition of NO2- is detrimental to health, so accurate and portable detection of NO2- is critical for food quality control. Notably, the selectivity of most carbon dots (CDs)-based fluorescence sensors was not enough due to the nonspecific interaction mechanism of hydrogen bond, electrostatic interaction and inner filter effect etc. Herein, a novel fluorescence/UV-vis absorption (FL/UV-vis) dual-mode sensor was developed on basis of mC-CDs, which were prepared by simple solvothermal treatment of m-Phenylenediamine (m-PDA) and cyanidin cation (CC). The fluorescence of these mC-CDs could be selectively responded by NO2- through the specific diazo coupling reaction between NO2- and amino groups on the surface of mC-CDs, thus effectively improving the selectivity of NO2- detection. The CDs-based fluorescence sensor possessed a low detection limit of 0.091 μM and 0.143 μM for FL and UV-vis methods and the excellent linear range of 0.0-60.0 μM. Furthermore, the mC-CDs sensor was employed to detect NO2- in real samples with a recovery rate of 97.11 %-104.15 % for quantitative addition. Moreover, the smartphone-assisted fluorescence sensing platform developed could identify the subtle color changes that could not be distinguished by the naked eye, and had the advantages of fast detection speed and intelligence. More importantly, the portable solid phase sensor based on mC-CDs had been successfully applied to the specific fluorescence identification and concentration monitoring of NO2-. Accordingly, the designed sensor provided a new strategy for the highly selective and convenient sensing of NO2- in food substrates, and paved the way for the wide application of CDs-based nanomaterials in the detection of food safety.

Design of aggregation-induced emission materials for biosensing of molecules and cells

In recent years, aggregation-induced emission (AIE) materials have gained significant attention and have been developed for various applications in different fields including biomedical research, chemical analysis, optoelectronic devices, materials science, and nanotechnology. AIE is a unique luminescence phenomenon, and AIEgens are fluorescent moieties with relatively twisted structures that can overcome the aggregation-caused quenching (ACQ) effect. Additionally, AIEgens offer advantages such as non-washing properties, deep tissue penetration, minimal damage to biological structures, high signal-to-noise ratio, and excellent photostability. Fluorescent probes with AIE characteristics exhibit high sensitivity, short response time, simple operation, real-time detection capability, high selectivity, and excellent biocompatibility. As a result, they have been widely applied in cellular imaging, luminescent sensing, detection of physiological abnormalities in the human body, as well as early diagnosis and treatment of diseases. This review provides a comprehensive summary and discussion of the progress over the past four years regarding the detection of metal ions, small chemical molecules, biomacromolecules, microbes, and cells based on AIE materials, along with discussing their potential applications and future development prospects.

Amino-functionalized HPU-23@Ru@Tb as light-driven oxidase-like nanozyme for colorimetric recognition of Hg2+ and ratiometric fluorescence sensing of ClO- and PO43

A HPU-23@Ru@Tb-NH2 sensor array with light-driven oxidase-mimicking activity and triple-emission fluorescence was developed. It was composed of a Tb3+-functionalized metal organic framework and Ru(bpy)32+ and applied to the simultaneous detection of Hg2+, ClO-, and PO43- via differently responsive channels. HPU-23@Ru@Tb-NH2 had a photoresponsive colorimetric response toward Hg2+ with a LOD as low as 4.18 nM. In addition, the three emissions of the HPU-23@Ru@Tb-NH2 sensor array were influenced by ClO- and PO43- to varying degrees, causing remarkably distinguishable responses for the fluorescence channels to discriminate ClO- and PO43- from each other. The detection limits of ClO- and PO43- were 12.26 µM and 0.197 nM, respectively. Therefore, this work demonstrates the feasibility of multi-emission and multi-mode sensing platform, which is able to combine the advantages of different strategies for solving the problems of various toxic substances coexisting in the environment while meeting the needs of accurate and precise results and no side interferences.

A colorimetric sensor for the sensitive and rapid detection of ampicillin based on CS-Cu,Fe/HS nanozyme

A novel copper and iron doped containing chitosan and heparin sodium carbon dots (CS-Cu,Fe/HS) nanozyme was formulated through a single-step microwave digestion method. CS-Cu,Fe/HS exhibits excellent peroxidase (POD)-like activity and positive charge characteristics, and it can oxidize the negatively charged 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) in the presence of H2O2 to produce a green compound (ox-ABTS). Furthermore, CS-Cu,Fe/HS enhances electron transfer and provides additional active sites through the valence state transformations of Fe2+/Fe3+ and Cu2+/Cu+. Interestingly, the POD-like activity of CS-Cu,Fe/HS is inhibited with the introduction of ampicillin (AMP), which may be because the Cu and Fe ions in CS-Cu,Fe/HS form complexes with AMP, leading to changes in the structure or surface properties of the nanozyme, thereby reducing the number of active sites on the nanozyme. Drawing from this, a straightforward and reliable colorimetric sensor was constructed for AMP detection, featuring a linear range of 0.033 to 110 μg/mL and a detection limit as low as 11.6 ng/mL. The proposed detection method for AMP performed well in real samples, with recoveries ranging from 94.8% to 110.2%.

Detection of Hg2+ Using a Dual-Mode Biosensing Probe Constructed Using Ratiometric Fluorescent Copper Nanoclusters@Zirconia Metal-Organic Framework/N-Methyl Mesoporphyrin IX and Colorimetry G-Quadruplex/Hemin Peroxidase-Mimicking G-Quadruplex DNAzyme

Mercury (Hg2+) has been recognized as a global pollutant with a toxic, mobile, and persistent nature. It adversely affects the ecosystem and human health. Already developed biosensors for Hg2+ detection majorly suffer from poor sensitivity and specificity. Herein, a colorimetric/fluorimetric dual-mode sensing approach is designed for the quantitative detection of Hg2+. This novel sensing approach utilizes nanofluorophores, i.e., fluorescent copper nanoclusters-doped zirconia metal-organic framework (CuNCs@Zr-MOF) nanoconjugate (blue color) and N-methyl mesoporphyrin IX (NMM) (red color) in combination with peroxidase-mimicking G-quadruplex DNAzyme (PMDNAzyme). In the presence of Hg2+, dabcyl conjugated complementary DNA with T-T mismatches form the stable duplex with the CuNCs@Zr-MOF@G-quadruplex structure through T-Hg2+-T base pairing. It causes the quenching of fluorescence of CuNCs@Zr-MOF (463 nm) due to the Förster resonance energy transfer (FRET) system. Moreover, the G-quadruplex (G4) structure of the aptamer enhances the fluorescence emission of NMM (610 nm). Besides this, the peroxidase-like activity of G4/hemin DNAzyme offers the colorimetric detection of Hg2+. The formation of duplex with PMDNAzyme increases the catalytic activity. This novel biosensing probe quantitatively detected Hg2+ using both fluorimetry and colorimetry approaches with a low detection limit of 0.59 and 36.3 nM, respectively. It was also observed that the presence of interfering metal ions in case of real aqueous samples does not affect the performance of this novel biosensing probe. These findings confirm the considerable potential of the proposed biosensing probe to screen the concentration of Hg2+ in aquatic products.

Ni2+ mediated oxidation and aggregation of o-phenylenediamine: an enhanced photothermal effect for direct, specific and background-free detection of thiophanate-methyl

A novel photothermal probe, o-phenylenediamine trimer (triOPD)-Ni2+ aggregates with a photothermal conversion efficiency of up to 74.4%, was prepared by CuNi-BTC catalytic oxidation and assembly of OPD. Based on the specific inhibition activity of thiophanate-methyl toward CuNi-BTC, a direct and background-free photothermal sensing platform was fabricated.

Machine learning-assisted laccase-like activity nanozyme for intelligently onsite real-time and dynamic analysis of pyrethroid pesticides

The intelligently efficient, reliable, economical and portable onsite assay toward pyrethroid pesticides (PPs) residues is critical for food safety analysis and environmental pollution traceability. Here, a fluorescent nanozyme Cu-ATP@ [Ru(bpy)3]2+ with laccase-like activity was designed to develop a versatile machine learning-assisted colorimetric and fluorescence dual-modal assay for efficient onsite intelligent decision recognition and quantification of PPs residues. In the presence of alkaline phosphatase (ALP), the laccase-like activity of Cu-ATP@ [Ru(bpy)3]2+ was enhanced to oxidize colorless o-phenylenediamine (OPD) into dark-yellow 2,3-diaminophenazine (DAP) via electron transfer, appearing a new yellow fluorescence at 550 nm. Meanwhile, the red fluorescence of Cu-ATP@ [Ru(bpy)3]2+ at 600 nm was quenched due to the internal filter effect (IFE) of DAP towards Cu-ATP@ [Ru(bpy)3]2+. However, the selective inhibition of PPs toward ALP activity enabled to observe a dual-modal response of PPs concentration-dependent decrease in colorimetric signal and enhancement in the fluorescence intensity ratio of F600 nm/F550 nm. On this basis, both the colorimetric and fluorescence images were captured and processed with a home-made WeChat applet-installed smartphone to extract the corresponding image color information, thus achieving machine learning-assisted onsite real-time and dynamic intelligent decision recognition and quantification of PPs residues in real samples, which shows a promising potential in safeguarding food safety and environmental health.

A Novel Fluorescent Chemosensor for Sensitive and Rapid Determination of Pb(II) Ions in Aqueous Environments

This investigation devised an eco-friendly spectrofluorometric Pb(II) ion measurement approach. To determine Pb(II) ions, a polymeric fluorescence sensor membrane with excellent selectivity has been developed. It contains photoinitiators, functional monomers that can be cured under UV radiation, and cross-linking agents. After the characterization of the membrane, the most suitable parameters for the measurement of Pb(II) ions were determined. The measurement was performed in a short time-roughly 40 s-at emission and excitation wavelengths of 488 nm and 277 nm, respectively, at pH 6.0. The developed method's detection limit was calculated as 1.42 × 10- 9 mol L- 1, and its calibration range was recorded as 4.83 × 10- 9 to 9.66 × 10- 8 mol L- 1. Recovery studies and the sensor's stability, lifetime, and repeatability have been evaluated. Real sample applications have been implemented using wastewater samples. The suggested approach may be used to quickly and accurately determine Pb(II) ions at low concentrations with good selectivity and sensitivity.

Europium functionalized porphyrin-based metal-organic framework heterostructure and hydrogel for visual ratiometric fluorescence sensing of sulfonamides in foods

Protecting human health and ensuring food security require the swift and accurate detection of sulfonamides (SAs) residues in foods. Herein, we proposed an Eu-postfunctionalized bimetallic porphyrin metal-organic framework (PCN-221(Zr/Ce)@Eu-DPA-H4btec) synthesized solvothermally for fluorescence sensing. The PCN-221(Zr/Ce)@Eu-DPA-H4btec fluorescent sensor demonstrated excellent stability and high selectivity to SAs, and the detection limits of sulfamethazine (SM2), sulfamerazine (SMR), and sulfamethoxydiazine (SMD) were as low as 56 nmol/L, 45 nmol/L, and 56 nmol/L, respectively. The PCN-221(Zr/Ce)@Eu-DPA-H4btec fluorescent sensor was successfully applied for the detection of SM2, SMR, and SMD in real pork and milk samples, with satisfactory recoveries (81.2-118.3%) and high precisions (RSDs <8.2, n = 3). Combining the optical properties of the nanohybrids, PCN-221(Zr/Ce)@Eu-DPA-H4btec integrated fluorescent hydrogels were innovatively prepared for visual sensing of SM2, SMR, and SMD. This study provides an uncomplicated and sensitive method for SAs detection in food matrices.

A novel fluorescent and photothermal probe based on nanozyme-mediated cascade reaction for detecting organophosphorus pesticide residues

In this study, a nanozyme (ZIF-Co-Cys) with high oxidase-like catalytic activity was prepared, and a ratiometric fluorescent/photothermal dual-mode probe was constructed for organophosphorus pesticides (OPs) detection based on the competitive effect of ZIF-Co-Cys and the enzymatic reaction product of acid phosphatase (ACP) on o-phenylenediamine and the inhibition effect of OPs on ACP activity. Using dimethyl dichloroviny phosphate (DDVP) as the model, both the fluorescence intensity ratio and the temperature change of the probe solution exhibited an excellent correlation with OPs concentration. The detection limits were 1.64 ng/mL and 0.084 ng/mL, respectively. Additionally, the detection of DDVP residues in real samples verified the outstanding anti-interference and accuracy of the probe. This work not only provided a complementary dual-mode method for the accurate and rapid detection of OPs residues in complex samples, but also supplied a new insight into the design of a multi-mode sensing platform based on the cascade reaction of nanozyme.

Rational design of cuprofullerene bipyridine nanozyme with high peroxidase-like activity for colorimetric sensing of bleomycin

The high catalytic activity of Cu-based nanozymes mainly depends on the efficient Fenton-like reaction of Cu+/ H2O2, but Cu+ cannot exist stably. Trying to find a material that can stably support Cu+ while promoting the electron cycle of Cu2+/Cu+ still faces serious challenges. C60 is expected to be an ideal candidate to solve this problem due to its unique structure and rich physicochemical properties. Here, we designed and synthesized a C60-doped Cu+-based nanozyme (termed as C60-Cu-Bpy) by loading high catalytic active site Cu+ onto C60 and coordinating with 2,2'-bipyridine (Bpy). The single crystal diffraction analysis and a series of auxiliary characterization technologies were used to demonstrate the successful preparation of C60-Cu-Bpy. Significantly, the C60-Cu-Bpy exhibited superior peroxidase-like activity during the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Then, the catalytic mechanism of C60-Cu-Bpy as peroxidase was elucidated in detail, mainly benefiting from the dual function of C60. On the one hand, C60 acted as a carrier to directly support Cu+, which has the ability to efficiently decompose H2O2 to produce reactive oxygen species. The other was that C60 acted as an electron buffer, contributing to promoting the Cu2+/Cu+ cycle to facilitate the reaction. Furthermore, a colorimetric sensor for the quantitative analysis of bleomycin was established based on the principle of bleomycin specific inhibition of C60-Cu-Bpy peroxidase-like activity, with satisfactory results in practical samples. This study provides a new strategy for the direct synthesis of Cu+-based nanozymes with high catalytic performance.

Selective dual-mode detection of glyphosate facilitated by iron organic frameworks nanozymes

To satisfy the public's urgent demand for food safety and protect the ecological environment, sensitive detection of glyphosate holds paramount importance. Here, we discovered that glyphosate can engage in specific interactions with iron organic frameworks (Fe-MOFs) nanozymes, enabling a selective detection of glyphosate. Based on this principle, an innovative colorimetric and fluorescent dual-mode detection approach was devised. Specifically, Fe-MOFs were synthesized at room temperature, exhibiting remarkable peroxidase-mimic activity. These nanozymes catalyze the conversion of colorless and fluorescent 3,3',5,5'-Tetramethylbenzidine (TMB) into blue oxidized and nonfluorescent TMB (oxTMB) in the presence of H2O2. However, the introduction of glyphosate disrupts this process by interacting with Fe-MOFs, significantly inhibiting the catalytic activity of Fe-MOFs through both physical (electrostatic and hydrogen bonding) and chemical interactions. This suppression further hindered the conversion of TMB to oxTMB, resulting in a reduction in absorbance and a corresponding enhancement in fluorescence. The method offers a colorimetric and fluorescence dual-mode detection capability with enhanced applicability. Notably, our approach avoids complex material modifications and is more stable and cost-effective than the traditional enzyme inhibition methods. This innovative detection technique holds immense potential for practical applications and provides a fresh perspective for the detection of pesticide residues.

Overview of the Design and Application of Photothermal Immunoassays

Developing powerful immunoassays for sensitive and real-time detection of targets has always been a challenging task. Due to their advantages of direct readout, controllable sensing, and low background interference, photothermal immunoassays have become a type of new technology that can be used for various applications such as disease diagnosis, environmental monitoring, and food safety. By modification with antibodies, photothermal materials can induce temperature changes by converting light energy into heat, thereby reporting specific target recognition events. This article reviews the design and application of photothermal immunoassays based on different photothermal materials, including noble metal nanomaterials, carbon-based nanomaterials, two-dimensional nanomaterials, metal oxide and sulfide nanomaterials, Prussian blue nanoparticles, small organic molecules, polymers, etc. It pays special attention to the role of photothermal materials and the working principle of various immunoassays. Additionally, the challenges and prospects for future development of photothermal immunoassays are briefly discussed.

Insights into the enhanced adsorption of glyphosate by dissolved organic matter in farmland Mollisol: effects and mechanisms of action

Dissolved organic matter (DOM) is easy to combine with residual pesticides and affect their morphology and environmental behavior. Given that the binding mechanism between DOM and the typical herbicide glyphosate in soil is not yet clear, this study used adsorption experiments, multispectral techniques, density functional theory, and pot experiments to reveal the interaction mechanism between DOM and glyphosate on Mollisol in farmland and their impact on the environment. The results show that the adsorption of glyphosate by Mollisol is a multilayer heterogeneous chemical adsorption process. After adding DOM, due to the early formation of DOM and glyphosate complex, the adsorption process gradually became dominated by single-layer chemical adsorption, and the adsorption capacity increased by 1.06 times. Glyphosate can quench the endogenous fluorescence of humic substances through a static quenching process dominated by hydrogen bonds and van der Waals forces, and instead enhance the fluorescence intensity of protein substances by affecting the molecular environment of protein molecules. The binding of glyphosate to protein is earlier, of which affinity stronger than that of humic acid. In this process, two main functional groups (C-O in aromatic groups and C-O in alcohols, ethers and esters) exist at the binding sites of glyphosate and DOM. Moreover, the complexation of DOM and glyphosate can effectively alleviate the negative impact of glyphosate on the soil. This study has certain theoretical guidance significance for understanding the environmental behavior of glyphosate and improving the sustainable utilization of Mollisol.

Glutathione-mediated copper sulfide nanoplatforms with morphological and vacancy-dependent photothermal catalytic activity for multi-model tannic acid assays

Interface engineering and vacancy engineering play an important role in the surface and electronic structure of nanomaterials. The combination of the two provides a feasible way for the development of efficient photocatalytic materials. Here, we use glutathione (GSH) as a coordination molecule to design a series of CuxS nanomaterials (CuxS-GSH) rich in sulfur vacancies using a simple ultrasonic-assisted method. Interface engineering can induce amorphous structure in the crystal while controlling the formation of porous surfaces of nanomaterials, and the formation of a large number of random orientation bonds further increases the concentration of sulfur vacancies in the crystal structure. This study shows that interface engineering and vacancy engineering can enhance the light absorption ability of CuxS-GSH nanomaterials from the visible to the near-infrared region, improve the efficiency of charge transfer between CuxS groups, and promote the separation and transfer of optoelectronic electron-hole pairs. In addition, a higher specific surface area can produce a large number of active sites, and the synergistic and efficient photothermal conversion efficiency (58.01%) can jointly promote the better photocatalytic performance of CuxS-GSH nanomaterials. Based on the excellent hot carrier generation and photothermal conversion performance of CuxS-GSH under illumination, it exhibits an excellent ability to mediate the production of reactive oxygen species (ROS) through peroxide cleavage and has excellent peroxidase activity. Therefore, CuxS-GSH has been successfully developed as a nanoenzyme platform for detecting tannic acid (TA) content in tea, and convenient and rapid detection of tannic acid is achieved through the construction of a multi-model strategy. This work not only provides a new way to enhance the enzyme-like activity of nanomaterials but also provides a new prospect for the application of interface engineering and vacancy engineering in the field of photochemistry.

A Versatile Visual Molecular Imprinting-Driven Switchable Nanozyme Activity-Based Trimodal Assay and Logic Gate Circuits of Ethyl Carbamate

Concerns regarding the hazard of the carcinogenic ethyl carbamate (EC) have driven attempts to exploit efficient, timely, straightforward, and economic assays for warning early food safety. Here, we proposed a novel molecularly imprinted polymer Co@MOF-MIP, with a high peroxidase (POD)-like activity and a bright blue fluorescence emission, to develop a versatile visual assay for colorimetric, fluorescent, and photothermal trimodal detection and logic gate outputting of EC. Briefly, the POD-like activity of Co@MOF-MIP made it to decompose H2O2 into ·OH for oxidizing colorless 3,3',5,5'-tetramethylbenzidine (TMB) into a blue oxTMB, resulting in a 660 nm irradiated photothermal effect and bursting the blue fluorescence of Co@MOF-MIP via inner filter effect, observing a decreased fluorescence signal together with an increased colorimetric and 660 nm irradiated photothermal signals. However, EC could specifically fill the imprinted cavities of Co@MOF-MIP to block the catalytic substrates TMB and H2O2 out of Co@MOF-MIP for further reacting with the inside catalytic center of Co2+, resulting in the transformation suppressing of TMB into oxTMB, yielding an EC concentration-dependent trimodal responses in fluorescence signal enhancement, colorimetric, and 660 nm irradiated photothermal signal decreases. Assisted by the portable devices such as smartphones and hand-held thermal imagers, a visual onsite portable trimodal analytical platform was proposed for EC fast and accurate detection with the low detection limits of 1.64, 1.24, and 1.78 μg/L in colorimetric, fluorescent, and photothermal modes, respectively. Interestingly, these reactive events could be programmed by the classical Boolean logic gate analysis to offer a novel promising avenue for the big data Internet of Things monitoring and warning early residual EC in a more intelligent, dynamical, fast, and accurate manner, safeguarding food safety.

Decorating Cage-Shaped Cavities with Carboxyl Groups on Two-Dimensional MOF Nanosheet for Trace Uranium(VI) Trapping

The efficient and complete extraction of uranium from aqueous solutions is crucial for safeguarding human health from potential radiotoxicity and chemotoxicity. Herein, an ultrathin 2D metal-organic framework (MOF) nanosheet with cavity structures was elaborately constructed, based on a calix[4]arene ligand. The large molecular skeleton and cup-shaped feature of the calix[4]arene enabled the as-prepared MOFs with large layer separations, which can be readily delaminated into ultrathin single-layer (∼1.25 nm) nanosheets. The incorporation of permanent cavity structures to the MOF nanosheets can fully utilize their structural features of readily accessible adsorption groups and exposed surface area in uranium removal, reaching ultrafast adsorption kinetics; the functionalized cavity structure endowed MOF nanosheets with the ability to preconcentrate and extract uranium from aqueous solutions with ultrahigh efficiencies, even at extremely low concentrations. As a result, relatively high removal ratios (>95%) can be achieved for uranium within 5 min, even in the ultralow concentration range of 75-250 ppb, and the residual uranium was reduced to below 4.9 ppb. The MOF nanosheets also exhibited extremely high anti-interference ability, which could efficiently remove the low-level uranium (∼150 ppb) from various real samples. The characterizations and density functional theory calculations demonstrated that the synergistic effects of multiple interactions between the carboxylate groups and cage-like cavities with uranyl ions can be responsible for the efficient and selective uranium extraction.

A Programmable Microfluidic Paper-Based Analytical Device for Simultaneous Colorimetric and Photothermal Visual Sensing of Multiple Enzyme Activities

New strategies for the simultaneous and portable detection of multiple enzyme activities are highly desirable for clinical diagnosis and home care. However, the methods developed thus far generally suffer from high costs, cumbersome procedures, and heavy reliance on large-scale instruments. To satisfy the actual requirements of rapid, accurate, and on-site detection of multiple enzyme activities, we report herein a smartphone-assisted programmable microfluidic paper-based analytical device (μPAD) that utilizes colorimetric and photothermal signals for simultaneous, accurate, and visual quantitative detection of alkaline phosphatase (ALP) and butyrylcholinesterase (BChE). Specifically, the operation of this μPAD sensing platform is based on two sequential steps. Cobalt-doped mesoporous cerium oxide (Co-m-CeO2) with remarkable peroxidase-like activities under neutral conditions first catalytically decomposes H2O2 for effectively converting colorless 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxidized TMB (oxTMB). The subsequent addition of ALP or BChE to their respective substrates produces a reducing substance that can somewhat inhibit the oxTMB transformation for compromised colorimetric and photothermal signals of oxTMB. Notably, these two-step bioenzyme-nanozyme cascade reactions strongly support the straightforward and excellent processability of this platform, which exhibit lower detection limits for ALP and BChE with a detection limit for BChE an order of magnitude lower than those of the other reported paper-based detection methods. The practicability and efficiency of this platform are further demonstrated through the analysis of clinical serum samples. This innovative platform exhibits great potential as a facile yet robust approach for simultaneous, accurate, and on-site visual detection of multiple enzyme activities in authentic samples.

Three-dimensional polymer phenylethnylcopper/nitrogen doped graphene aerogel electrode coupled with Fe3O4 NPs nanozyme: Toward sensitive and robust photoelectrochemical detection of glyphosate in agricultural matrix

BACKGROUND

Presently, glyphosate (Gly) is the most extensively used herbicide globally, Nevertheless, its excessive usage has increased its accumulation in off-target locations, and aroused concerns for food and environmental safety. Commonly used detection methods, such as high-performance liquid chromatography and gas chromatography, have limitations due to expensive instruments, complex pre-processing steps, and inadequate sensitivity. Therefore, a facile, sensitive, and reliable Gly detection method should be developed.

RESULTS

A photoelectrochemical (PEC) sensor consisting of a three-dimensional polymer phenylethnylcopper/nitrogen-doped graphene aerogel (PPhECu/3DNGA) electrode coupled with Fe3O4 NPs nanozyme was constructed for sensitive detection of Gly. The microscopic 3D network of electrodes offered fast transfer routes for photo-generated electrons and a large surface area for nanozyme loading, allowing high signal output and analytical sensitivity. Furthermore, the use of peroxidase-mimicking Fe3O4 NPs instead of natural enzyme improved the stability of the sensor against ambient temperature changes. Based on the inhibitory effect of Gly on the catalytic activity Fe3O4 NPs, the protocol achieved Gly detection in the range of 5 × 10-10 to 1 × 10-4 mol L-1. Additionally, feasibility of the detection was confirmed in real agricultural matrix including tea, maize seedlings, maize seeds and soil.

SIGNIFICANCE

This work achieved facile, sensitive and reliable analysis towards Gly, and it was expected to inspire the design and utilization of 3D architectures in monitoring agricultural chemicals in food and environmental matrix.

Fabrication of Carboxylate-Functionalized 2D MOF Nanosheet with Caged Cavity for Efficient and Selective Extraction of Uranium from Aqueous Solution

The efficient removal of radioactive uranium from aqueous solution is of great significance for the safe and sustainable development of nuclear power. An ultrathin 2D metal-organic framework (MOF) nanosheet with cavity structures was elaborately fabricated based on a calix[4]arene ligand. Incorporating the permanent cavity structures on MOF nanosheet can fully utilize its structural characteristics of largely exposed surface area and accessible adsorption sites in pollutant removal, achieving ultrafast adsorption kinetics, and the functionalized cavity structure would endow the MOF nanosheets with the ability to achieve preconcentration and extraction of uranium from aqueous solution, affording ultrahigh removal efficiency even in ultra-low concentrations. Thus, more than 97% uranium can be removed from the concentration range of 50-500 µg L-1 within 5 min. Moreover, the 2D nano-material exhibits ultra-high anti-interference ability, which can efficiently remove uranium from groundwater and seawater. The adsorption mechanism was investigated by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) analysis, and density functional theory (DFT) calculations, which revealed that the cavity structure plays an important role in uranium capture. This study not only realizes highly efficient uranium removal from aqueous solution but also opens the door to achieving ultrathin MOF nanosheets with cavity structures, which will greatly expand the applications of MOF nanosheets.

Biotemplated fabrication of N/O co-doped porous carbon confined spinel NiFe2O4 heterostructured mimetics for triple-mode sensing of antioxidants and ameliorating packaging properties

In this work, shrimp shell-derived magnetic NiFe2O4/N, O co-doped porous carbon nanozyme with superior oxidase (OXD)-like activity was prepared and used for colorimetric/photothermal/smartphone dual-signal triple-mode detection of antioxidants in fruits and beverages. The magnetic NiFe2O4/N, O co-doped porous carbon (MNPC) material was triumphantly fabricated using a combined in-situ surface chelation and pyrolysis method. The resultant MNPC composite exhibits a superior OXD-like activity, which can effectively oxidize 3,3',5,5'-tetramethylbenzidine (TMB) for yielding colorimetric/temperature dual-signal (CTDS) in absence of H2O2. This CTDS output sensor was successfully used for the determination of ascorbic acid and tannic acid. The proposed CTDS sensor with good specificity and high sensitivity can satisfy different on-site analysis requirements. Interestingly, the MNPC as a sustainable filler was further used for improving packaging properties of polyvinyl alcohol film. In short, this work offers a large-scale and cheap method to fabricate magnetic carbon-based nanozyme for monitoring antioxidants and ameliorating packaging properties.

Tailored Porous Ferrocene-Based Metal-Organic Frameworks as High-Performance Proton Conductors

Although crystalline metal-organic frameworks (MOFs) have gained a great deal of interest in the field of proton conduction in recent years, the low stability and poor proton conductivity (σ) of some MOFs have hindered their future applications. As a result, resolving the issues listed above must be prioritized. Due to their exceptional structural stability, MOFs with ferrocene groups that exhibit particular physical and chemical properties have drawn a lot of attention. This study describes the effective preparation of a set of three-dimensional ferrocene-based MOFs, MIL-53-FcDC-Al/Ga and CAU-43, containing both main group metals and 1,1'-ferrocene dicarboxylic acid (H2FcDC). Multiple measurements, including powder X-ray diffraction (PXRD), infrared (IR), and scanning electron microscopy (SEM), confirmed that the addition of ferrocene groups enhanced the thermal, water, and acid-base stabilities of the three MOFs. Consequently, their proton-conductive behaviors were meticulously measured utilizing the AC impedance approach, and their best proton conductivities are 5.20 × 10-3, 2.31 × 10-3, and 1.72 × 10-4 S/cm at 100 °C/98% relative humidity (RH), respectively. Excitingly, MIL-53-FcDC-Al/Ga demonstrated an extraordinarily ultrahigh σ of above 10-4 S·cm-1 under 30 °C/98% RH. Using data from structural analysis, PXRD, SEM, thermogravimetry (TG), and activation energy, their proton transport mechanisms were thoroughly examined. The fact that these MOFs are notably easy to assemble, inexpensive, toxin-free, and stable will increase the range of practical uses for them.

Galvanic Replacement Synthesis of VOx@EGaIn-PEG Core-Shell Nanohybrids for Peroxidase Mimics

The development of high-performance biosensors is a key focus in the nanozyme field, but the current limitations in biocompatibility and recyclability hinder their broader applications. Herein, we address these challenges by constructing core-shell nanohybrids with biocompatible poly(ethylene glycol) (PEG) modification using a galvanic replacement reaction between orthovanadate ions and liquid metal (LM) (VOx@EGaIn-PEG). By leveraging the excellent charge transfer properties and the low band gap of the LM surface oxide, the VOx@EGaIn-PEG heterojunction can effectively convert hydrogen peroxide into hydroxyl radicals, demonstrating excellent peroxidase-like activity and stability (Km = 490 μM, vmax = 1.206 μM/s). The unique self-healing characteristics of LM further enable the recovery and regeneration of VOx@EGaIn-PEG nanozymes, thereby significantly reducing the cost of biological detection. Building upon this, we developed a nanozyme colorimetric sensor suitable for biological systems and integrated it with a smartphone to create an efficient quantitative detection platform. This platform allows for the convenient and sensitive detection of glucose in serum samples, exhibiting a good linear relationship in the range of 10-500 μM and a detection limit of 2.35 μM. The remarkable catalytic potential of LM, combined with its biocompatibility and regenerative properties, offers valuable insights for applications in catalysis and biomedical fields.

Carbon Dots: Synthesis, Characterizations, and Recent Advancements in Biomedical, Optoelectronics, Sensing, and Catalysis Applications

Carbon nanodots (CNDs), a fascinating carbon-based nanomaterial (typical size 2-10 nm) owing to their superior optical properties, high biocompatibility, and cell penetrability, have tremendous applications in different interdisciplinary fields. Here, in this Review, we first explore the superiority of CNDs over other nanomaterials in the biomedical, optoelectronics, analytical sensing, and photocatalysis domains. Beginning with synthesis, characterization, and purification techniques, we even address fundamental questions surrounding CNDs such as emission origin and excitation-dependent behavior. Then we explore recent advancements in their applications, focusing on biological/biomedical uses like specific organelle bioimaging, drug/gene delivery, biosensing, and photothermal therapy. In optoelectronics, we cover CND-based solar cells, perovskite solar cells, and their role in LEDs and WLEDs. Analytical sensing applications include the detection of metals, hazardous chemicals, and proteins. In catalysis, we examine roles in photocatalysis, CO2 reduction, water splitting, stereospecific synthesis, and pollutant degradation. With this Review, we intend to further spark interest in CNDs and CND-based composites by highlighting their many benefits across a wide range of applications.

A sensitive lateral flow test strip sensor for visual detection of acid red 18 in food using bicentric-emission carbon dots

Hazardous synthetic colorants have found widespread use in food production, and excessive consumption of these pigments can pose potential risks to human health. In this study, we propose an ultrasensitive fluorescence method for the analysis of Acid Red 18 (AR18) in food products. The method is based on the nitrogen-doped carbon dots (N-CDs) derived from tris and resorcinol through a hydrothermal way. The as-synthesized N-CDs exhibit two emission centers at 425 nm and 541 nm, corresponding to the excitation wavelengths of 377 nm and 465 nm, respectively. Upon the addition of AR18, the fluorescence intensity at 541 nm significantly decreases with a simultaneous, though less pronounced, reduction in the intensity at 425 nm, which is attributed to the localization of fluorescence resonance energy transfer (L-FRET). Specifically, a novel ratiometric fluorescent probe was constructed based on the extracted data from the 3D fluorescence excitation-emission matrix. This probe demonstrates a wide linear range from 0.0539 to 30 μM and a low limit of detection (LOD) of 53.9 nM. For practical applications, a portable fluorescent sensor based on a lateral flow test strip (LFTS) was designed for real-time monitoring of AR18. Color channel values were determined using a smartphone application, resulting in a satisfactory LOD of 75.3 nM. Furthermore, the suitability of the proposed ratiometric fluorescent probe was validated through the detection of AR18 in real food samples, consistently achieving recovery rates in the range of 99.7-101.4%. This research not only expands the scope of CDs in sensing fields, but also provides an effective strategy for the development of an excellent platform for real-time AR18 detection, contributing to public food safety.

Dual-Mode Lateral Flow Immunoassay Based on "Pompon Mum"-Like Fe3O4@MoS2@Pt Nanotags for Sensitive Detection of Viral Pathogens

Lateral flow immunoassay (LFIA) has been widely used for the early diagnosis of diseases. However, conventional colorimetric LFIA possesses limited sensitivity, and the single-mode readout signal is easily affected by the external environment, leading to insufficient accuracy. Herein, multifunctional Fe3O4@MoS2@Pt nanotags with a unique "pompon mum"-like structure were triumphantly prepared, exhibiting excellent peroxidase (POD)-like activity, photothermal properties, and magnetic separation capability. Furthermore, the Fe3O4@MoS2@Pt nanotags were used to establish dual-mode LFIA (dLFIA) for the first time, enabling the catalytic colorimetric and photothermal dual-mode detection of severe acute respiratory syndrome coronavirus 2 nucleocapsid protein (SARS-CoV-2 NP) and influenza A (H1N1). The calculated limits of detection (cLODs) of SARS-CoV-2 NP and H1N1 were 80 and 20 ng/mL in catalytic colorimetric mode and 10 and 8 ng/mL in photothermal mode, respectively, demonstrating about 100 times more sensitive than the commercial colloidal Au-LFIA strips (1 ng/mL for SARS-CoV-2 NP; 1 μg/mL for H1N1). The recovery rates of dLFIA in simulated nose swab samples were 95.2-103.8% with a coefficient of variance of 2.3-10.1%. These results indicated that the proposed dLFIA platform showed great potential for the rapid diagnosis of respiratory viruses.

UiOL@AIEgens-assisted lateral flow immunosensor for the ultrasensitive dual-modal point-of-care detection of aflatoxin B1

Aflatoxin B1 (AFB1) contamination in food has attracted worldwide attention. The sensitive detection of AFB1 is vital for ensuring food quality and safety. This study developed an ultrasensitive signal-enhanced lateral flow immunosensor (LFIS) based on the functionalized zirconium metal-organic framework (MOF) of a UiO linker enriched with abundant aggregation-induced emission luminogen (UiOL@AIEgens) probes for the rapid dual-modal point-of-care (POC) determination of AFB1. Using UiO MOFs with numerous active sites as the carrier facilitated abundant AIEgens enrichment on the surface. After coupling with enough anti-AFB1 monoclonal antibodies (mAbs), the green-emissive UiOL@AIEgens-mAbs probes with high specificity and remarkably-enhanced fluorescence responses were obtained to competitively capture target AFB1 in the standard or sample solution and AFB1 antigen immobilized on the test (T) line of the POC LFIS. Under optimum conditions, the LFIS was capable of visual qualitative and smartphone-assisted dual-modal determination of target AFB1 within 7 min. Detection occurred in a range of 0.01-5 ng/mL at an ultra-low detection limit of 0.003 ng/mL, which was 300- and 600-fold lower than traditional immunoassays and the maximum limit set by the European Union, respectively. Moreover, the feasibility and robustness of the LFIS platform were assessed by detecting AFB1 in maize and lotus seed samples with average recoveries of 94.3-109.0%. The developed UiOL@AIEgens-based POC LFIS can be used for ultrasensitive, reliable, on-site detection in food. This study provides a new method for the real-time monitoring of AFB1 and other harmful contaminants in food and more complex matrices.

Enzyme-free ratiometric fluorescence and colorimetric dual-signal determination of glyphosate based on copper nanoclusters (ZIF/CuNCs) combined with blue carbon dots (bCDs)

A novel ratio fluorescent and colorimetric dual-signal sensing platform for detecting glyphosate based on blue carbon dots (bCDs) combined with ZIF/CuNCs nanomaterials that encapsulate copper nanoclusters (CuNCs) in a metal-organic framework (MOF). In principle, the immobilization of Cu2+ in ZIF/CuNCs results in complexation with imidazole in ZIF, leading to fluorescence quenching of ZIF/CuNCs, while the reference fluorophore bCDs remains unaffected. In addition, the colorimetric sensing strategy was based on the efficient peroxidase-like activity of bCDs binding to Cu2+, catalyzing H2O2 to generate OH. Under this condition, TMB could be oxidized to form blue oxTMB. However, when glyphosate was involved in the system, the fluorescence of ZIF/CuNCs was restored upon due to the strong chelation between Cu2+ and glyphosate, while the peroxidase-like activity of bCDs/Cu2+ decreased and resulted in the generation of fewer oxTMB, accompanied by a lighter blue color. The sensing platform was successfully applied to the determination of glyphosate in real samples of lake water and cabbage, demonstrating reliable and sensitive performance in practical applications.

A portable colorimetric sensing platform for rapid and sensitive quantification of dichlorvos pesticide based on Fe-Mn bimetallic oxide nanozyme-participated highly efficient chromogenic catalysis

BACKGROUND

Dichlorvos (DDVP), as a highly effective insecticide, is widely used in agricultural production. However, DDVP residue in foodstuffs adversely affects human health. Conventional instrumental analysis can provide highly sensitive and accurate detection of DDVP, while the need of bulky and expensive equipment limits their application in resource-poor areas and on-site detection. Therefore, the development of easily portable sensing platforms for convenient, rapid and sensitive quantification of DDVP is very essential for ensuring food safety.

RESULT

A portable colorimetric sensing platform for rapid and sensitive quantification of DDVP is developed based on nanozyme-participated highly efficient chromogenic catalysis. The Fe-Mn bimetallic oxide (FeMnOx) nanozyme possesses excellently oxidase-like activity and can efficiently catalyze oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) into a blue oxide with a very low Michaelis constant (Km) of 0.0522 mM. The nanozyme-catalyzed chromogenic reaction can be mediated by DDVP via inhibiting the acetylcholinesterase (AChE) activity. Thus, trace DDVP concentration-dependent color evolution is achieved and DDVP can be sensitively detected by spectrophotometry. Furthermore, a smartphone-integrated 3D-printed miniature lightbox is fabricated as the colorimetric signal acquisition and processing device. Based on the FeMnOx nanozyme and smartphone-integrated lightbox system, the portable colorimetric sensing platform of DDVP is obtained and it has a wide linear range from 1 to 3000 ng mL-1 with a low limit of detection (LOD) of 0.267 ng mL-1 for DDVP quantification.

SIGNIFICANCE

This represents a new portable colorimetric sensing platform that can perform detection of DDVP in foodstuffs with simplicity, sensitivity, and low cost. The work not only offers an alternative to rapid and sensitive detection of DDVP, but also provides a new insight for the development of advanced sensors by the combination of nanozyme, 3D-printing and information technologies.

Enhanced oxidase-mimic constructed by luminescent carbon dots loaded on MIL-53(Fe)-NO2 for dual-mode detection of gallic acid and biothiols in food and humans

Monitoring of gallic acid (GA) in food and biothiols in humans is crucial for body health. Nanozyme-mediated colorimetric strategy for evaluating them has been widely applied nowadays, however, the inferior efficient and susceptible single-signal recognition limit its further application. Herein, a sensitive biosensor was first constructed for bimodal detection of GA and biothiols based on CDs@MIL-53(Fe)-NO2, prepared through a facile and time-saving microwave treatment. Benefiting from the excellent fluorescent and electron transfer properties of CDs, CDs@MIL-53(Fe)-NO2 exhibited significant enhanced blue fluorescence and oxidase-like activity, which could oxide colorless 3,3',5,5'-tetramethylbenzidine without H2O2, and the blue product could quench the fluorescence of composite. The dual-mode assay based on such bifunctional nanozyme showed an extremely sensitivity towards GA/l-cysteine/homocysteine with the detection limit of 62/65/124 nM and 17/16/27 nM in colorimetric/fluorescent modes, respectively. The practicability in real samples and portability based on a smartphone of the analysis has been investigated with reliable results.

Molecular-Scale Design of Azulene-Based Triplet Photosensitizers: Insights from Time-Dependent Optimally Tuned Range-Separated Hybrid

Metal-free triplet photosensitizers are ubiquitous in photocatalysis, photodynamic therapy, photovoltaics, and so forth. Their photosensitization efficiency strongly depends on the ability of the low-lying excited spin-triplet to be populated through intersystem crossing. Small singlet-triplet gaps and considerable spin-orbit coupling between the excited spin-singlet and spin-triplet facilitate efficient intersystem crossing. Azulene (Az), a classic example of Anti-Kasha's blue emitter with considerable fluorescence quantum yield, holds great promise because of its chemical stability, rich electronic properties, and high structural rigidity. Here, we provide computationally modeled Az-derived photosensitizers, namely, Az-CHO and Az-CHS, implementing polarization consistent time-dependent optimally tuned range-separated hybrid. Calculations reveal energetic reordering of low-lying ππ* and nπ* singlet states between Az-CHO and Az-CHS and, thereby, rendering the latter to a nonfluorescent one. Importantly, a small singlet-triplet gap and large spin-orbit coupling for Az-CHX with X = O and S produce remarkably high intersystem crossing rates. Furthermore, strong nonadiabatic coupling between the S1(nπ*) and S2(ππ*) in Az-CHS due to substantially smaller energy gap causes enhanced S1 population via fast internal conversion. These research findings provide new insights into the development of functional Az and or related heavy-atom-free small organic molecule-based triplet photosensitizers.

Organic Electronics in Biosensing: A Promising Frontier for Medical and Environmental Applications

The promising field of organic electronics has ushered in a new era of biosensing technology, thus offering a promising frontier for applications in both medical diagnostics and environmental monitoring. This review paper provides a comprehensive overview of organic electronics' remarkable progress and potential in biosensing applications. It explores the multifaceted aspects of organic materials and devices, thereby highlighting their unique advantages, such as flexibility, biocompatibility, and low-cost fabrication. The paper delves into the diverse range of biosensors enabled by organic electronics, including electrochemical, optical, piezoelectric, and thermal sensors, thus showcasing their versatility in detecting biomolecules, pathogens, and environmental pollutants. Furthermore, integrating organic biosensors into wearable devices and the Internet of Things (IoT) ecosystem is discussed, wherein they offer real-time, remote, and personalized monitoring solutions. The review also addresses the current challenges and future prospects of organic biosensing, thus emphasizing the potential for breakthroughs in personalized medicine, environmental sustainability, and the advancement of human health and well-being.

MnOx In Situ Growth-Induced Luminescence and Oxidase-Like Feature Bimodulation of CePO4:Tb Nanorods: Toward Ascorbic Acid-Related Bioanalysis in a "One-Stone-Two-Birds" Manner

Nanozyme-based multimode detection is a useful means to improve the accuracy and stability of analytical methods. However, both multifunctional nanozymes and related multimodal sensing strategies are still very scarce. Besides, they require complex processes to fabricate and operate. To fill this gap, here we propose a spontaneous interfacial in situ growth strategy to prepare a new bifunctional material (CePO4:Tb@MnOx) featuring good oxidase-like activity and green photoluminescence for the dual-mode colorimetric/luminescence determination of ascorbic acid (AA)-related biomarkers specifically. CePO4:Tb@MnOx was gained through the controllable redox reaction between KMnO4 and CePO4:Tb nanorods. It was interestingly found that MnOx in situ growth not only significantly enhanced the enzyme-like activity but also could reversibly regulate the luminescence of CePO4:Tb via a dual quenching mechanism. More interestingly, CePO4:Tb@MnOx exhibited a distinctive response toward AA against other reducing species. A double-coordination regulation mechanism was further verified to clarify the catalytic activity and luminescence switching behaviors in CePO4:Tb@MnOx. Based on these findings, a dual-mode colorimetric/luminescence approach was established for AA sensing in a "one-stone-two-birds" manner, providing excellent selectivity, sensitivity, and practicability. Furthermore, the determination of AA-related biomarkers, including acid phosphatase activity and organophosphorus residue, was also validated by the sensing principle. Our work not only deepens the understanding of the coordinated regulation of the luminescence and enzyme-like features in lanthanide-based materials but also offers a novel way to design and develop multifunctional nanozymes for advanced bioanalytical applications.

Organic compound-based nanozymes for agricultural herbicide detection

Nanozymes are increasingly being used for agricultural applications, but their adoption is limited as they are generally considered toxic, have low cost-effectiveness, and pose complexity of fabrication. In this study, an organic compound-based, peroxidase-like nanozyme (OC nanozyme) was developed for use in the agricultural environment. This nanozyme was synthesized through a self-assembled one-pot particle synthesis process, interacting with urea and the metal ion to form a homogenous nanoparticle containing partially mimicked cofactors (Fe-N) of the natural enzyme. The OC nanozyme exhibited decent kinetic properties (H2O2/Km:0.056 mM and Vmax:2.19 μM s-1) and pH stability. The OC nanozyme was successfully used to detect glyphosate via integrated colorimetric assay, with a good limit of detection (LOD) of at least 0.001 ng mL-1. The authors envision that this agricultural-friendly OC nanozyme holds great potential for a wide range of agricultural applications.

Review: Synthesis of metal organic framework-based composites for application as immunosensors in food safety

Ensuring food safety continues to be one of the major global challenges. For effective food safety monitoring, fast, sensitive, portable, and efficient food safety detection strategies must be devised. Metal organic frameworks (MOFs) are porous crystalline materials that have attracted attention for use in high-performance sensors for food safety detection owing to their advantages such as high porosity, large specific surface area, adjustable structure, and easy surface functional modification. Immunoassay strategies based on antigen-antibody specific binding are one of the important means for accurate and rapid detection of trace contaminants in food. Emerging MOFs and their composites with excellent properties are being synthesized, providing new ideas for immunoassays. This article summarizes the synthesis strategies of MOFs and MOF-based composites and their applications in the immunoassays of food contaminants. The challenges and prospects of the preparation and immunoassay applications of MOF-based composites are also presented. The findings of this study will contribute to the development and application of novel MOF-based composites with excellent properties and provide insights into advanced and efficient strategies for developing immunoassays.

Glyphosate Separating and Sensing for Precision Agriculture and Environmental Protection in the Era of Smart Materials

The present article critically and comprehensively reviews the most recent reports on smart sensors for determining glyphosate (GLP), an active agent of GLP-based herbicides (GBHs) traditionally used in agriculture over the past decades. Commercialized in 1974, GBHs have now reached 350 million hectares of crops in over 140 countries with an annual turnover of 11 billion USD worldwide. However, rolling exploitation of GLP and GBHs in the last decades has led to environmental pollution, animal intoxication, bacterial resistance, and sustained occupational exposure of the herbicide of farm and companies' workers. Intoxication with these herbicides dysregulates the microbiome-gut-brain axis, cholinergic neurotransmission, and endocrine system, causing paralytic ileus, hyperkalemia, oliguria, pulmonary edema, and cardiogenic shock. Precision agriculture, i.e., an (information technology)-enhanced approach to crop management, including a site-specific determination of agrochemicals, derives from the benefits of smart materials (SMs), data science, and nanosensors. Those typically feature fluorescent molecularly imprinted polymers or immunochemical aptamer artificial receptors integrated with electrochemical transducers. Fabricated as portable or wearable lab-on-chips, smartphones, and soft robotics and connected with SM-based devices that provide machine learning algorithms and online databases, they integrate, process, analyze, and interpret massive amounts of spatiotemporal data in a user-friendly and decision-making manner. Exploited for the ultrasensitive determination of toxins, including GLP, they will become practical tools in farmlands and point-of-care testing. Expectedly, smart sensors can be used for personalized diagnostics, real-time water, food, soil, and air quality monitoring, site-specific herbicide management, and crop control.

"Three-in-one" platform based on Fe-CDs nanozyme for dual-mode/dual-target detection and NIR-assisted bacterial killing

As nanozymes, carbon dots (CDs) have attracted increasing attention due to their remarkable properties. Besides general enzyme activity, their photoluminescence and photothermal properties have been explored rarely, whereas their synergistic effects might produce CDs-based nanozymes of high performance. Here, iron-doped CDs (Fe-CDs) with tunable fluorescence and enhanced peroxidase-like activity were designed to develop a novel "three-in-one" multifunctional platform to provide dual-mode/dual-target detection and near infrared (NIR)-assisted antibacterial ability. This proposed strategy for a H₂O₂ test exhibited a wide linear relationship with a low limit of detection (LOD) of 0.16 μM (colorimetric) and 0.14 μM (ratiometric fluorescent). Furthermore, due to the nature of cholesterol being oxidized to H₂O₂ by cholesterol oxidase, sensitive and selective detection of cholesterol was realized, and the LOD was 0.42 μM (colorimetric) and 0.27 μM (ratiometric fluorescent), surpassing that reported previously. This result suggested that Fe-CDs could be used for dual-mode quantification of large family of H₂O₂-producing metabolites, thereby paving the way for developing multi-mode sensing strategies based on nanozymes. Moreover, this platform showed synergistic effects for antibacterial application, indicating great prospects for bacterial killing as well as wound disinfection and healing. Hence, this platform could contribute to the construction of multifunctional CDs with high performance.

Ultrathin C3N4 nanosheets-based oxidase-like 2D fluorescence nanozyme for dual-mode detection of organophosphorus pesticides

Engineering efficient dual-mode portable sensor with built-in cross reference correction is of great significance for onsite reliable and precise detection of organophosphorus pesticides (OPs) and evading the false-positive outputs, especially in emergency case. Currently, most nanozyme-based sensors for OPs monitoring primarily replied on the peroxidase-like activity, which involved unstable and toxic H₂O₂. In this scenario, a hybrid oxidase-like 2D fluorescence nanozyme (PtPdNPs@g-C₃N₄) was yielded by in situ growing PtPdNPs in the ultrathin two-dimensional (2D) graphitic carbon nitride (g-C₃N₄) nanosheet. When acetylcholinesterase (AChE) hydrolyzed acetylthiocholine (ATCh) to thiocholine (TCh), it ablated O₂^-• from the dissolved O₂ catalyzed by PtPdNPs@g-C₃N₄'s oxidase-like activity, hampering the oxidation of o-phenylenediamine (OPD) into 2,3-diaminophenothiazine (DAP). Consequently, with the increasing concentration of OPs which inhibited the blocking effect by inactivating AChE, the produced DAP caused an apparent color change and a dual-color ratiometric fluorescence change in the response system. Through integrating into a smartphone, a H₂O₂-free 2D nanozyme-based onsite colorimetric and fluorescence dual-mode visual imaging sensor for OPs was proposed with acceptable results in real samples, which holds vast promise for further development of commercial point-of-care testing platform in early warning and controlling of OPs pollution for safeguarding environmental health and food safety.

Development of a Dual Mode UCNPs-MB Biosensor in Combination with PCR for Sensitive Detection of Salmonella

In recent years, the high prevalence of Salmonella has emerged as a serious threat to public safety, prompting attempts to utilize accurate, rapid, and direct methods to ensure food safety. In this study, a multifunctional platform featuring dual-mode detection channels (colorimetric-fluorescence) combined with polymer chain reaction (PCR) was proposed for the sensitive and rapid detection of Salmonella. Additionally, the colorimetric measurements were achieved by color changes induced by methylene blue (MB) insertion into the double-stranded DNA, and the fluorescence measurements were performed by internal filter effect (IFE)-induced fluorescence quenching of upconversion nanoparticles (UCNPs) by MB. The results showed that the IFE and PCR amplification processes improved the sensitivity of the sensor towards Salmonella detection, with a limit of detection (LOD) of 21.8 CFU/mL. Moreover, this colorimetric-fluorescence dual-mode PCR biosensor was applied to determine Salmonella in food samples, such as chicken, egg, and fish, which produced satisfactory results. Overall, the present study results demonstrate the potential for combining PCR amplification with IFE to develop an efficient and reliable dual-mode analysis platform to safeguard food security.