A high-sensitivity thermal analysis immunochromatographic sensor based on au nanoparticle-enhanced two-dimensional black phosphorus photothermal-sensing materials

In vitro diagnosis based on SERS-LFIA: research hotspots, increase sensitivities, combined detection, multimodal detection and related patents

In recent years, the SERS-LFIA platform has gained significant traction in in vitro diagnostics. However, a comprehensive review of its advancements and applications is still lacking. This review first employing a bibliometric approach to analyze research trends. It then outlines strategies to enhance sensitivity, focusing on Raman reporter molecules, SERS tags, coupling methods, detection instruments. Additionally, the review explores the use of SERS-LFIA for diagnosing multiple disease biomarkers, highlighting its potential to improve diagnostic accuracy. The review also synthesizes the application of multimodal SERS-LFIA technology, integrating signals such as colorimetric, magnetic, photothermal, fluorescent, and catalytic modalities. This approach enhances detection versatility and broadens diagnostic capabilities. Furthermore, it examines the current patent landscape, providing insights into the technology's commercial and technological progress. Lastly, the review discusses ongoing challenges, including stability and reproducibility and quantitative detection, while suggesting directions for future research. In summary, this review consolidates the latest advancements in SERS-LFIA technology for in vitro diagnostics over the past decade. Anticipated to furnish a robust scientific foundation and theoretical underpinning for the advancement of SERS-LFIA technology, this endeavor aims to enhance its efficacy in clinical diagnostics.

A dual-mode colorimetric/photothermal lateral flow biosensor based on Au/Ti3C2TX for HIV-DNA detection

BACKGROUND

Traditional lateral flow biosensors (LFBs), which utilize colorimetric signals as output, possess the virtues of simplicity and rapidity. However, it also suffers from insufficient sensitivity and limited reliability. It is well known that the results of LFBs can be false positive, and it is difficult to perform accurate quantification under low-abundance targets. In recent years, researchers have continued to apply new nanomaterials to LFBs to obtain more sensitive detection performance and multiple signal output modes.

RESULTS

Herein, taking advantage of its excellent color intensity and photothermal properties, we synthesized a dual-functional Au/Ti3C2TX nanocomposite material by loading Au nanoparticles (Au NPs) on Ti3C2TX via the one-step self-reduction method, in which process Ti3C2TX acted as both reducing agent and carrier at the same time. Based on the prepared material, a colorimetric/photothermal dual-mode LFB was constructed for the detection of human immunodeficiency virus (HIV) DNA. In this work, the Au/Ti3C2TX nanocomposite served as a dual-signal label on the LFB platform for the first time. As a colorimetric label, Au/Ti3C2TX achieved signal amplification owing to abundant Au NPs loaded on Ti3C2TX. When playing the role of a photothermal label, the excellent photothermal effect of Au/Ti3C2TX contributed to a low limit of detection down to 0.01 nM target in human serum.

SIGNIFICANCE AND NOVELTY

Au/Ti3C2TX served as a dual-signal label on the LFB platform for the first time and showed extremely dependable analytical performance. Furthermore, this work offered a novel versatile dual-mode point-of-care testing platform in the fields of food safety, clinical diagnosis, and environmental monitoring.

Multifunctional magnetic tags with photocatalytic and enzyme-mimicking properties for constructing a sensitive dual-readout ELISA

ELISA has become the gold standard for detecting harmful substances due to its specific antibody recognition and sensitive enzyme-catalyzed reactions. In this study, multifunctional magnetic Prussian blue nanolabels (MPBNs) were synthesized using a simple gentle two-step method to achieve a dual-readout mode. The MPBNs provide a sensitive colorimetric signal by efficiently catalyzing the oxidation of TMB and exhibit prominent photocatalytic degradation activity towards Rhodamine B (RhB). Supplemented by the quenching effect of oxTMB, the fluorescence was enabled to serve as a sensitive second signal. The magnetic property of the labels facilitates the separation and enrichment of the target, thereby improving sensitivity. Utilizing the versatile MPBNs, the visual limit of detection (vLOD) for Staphylococcus aureus is as low as 100 CFU/mL, with a quantitative analysis range of 102-108 CFU/mL. The introduction of photocatalytic reactions into immunoassay has opened up a new signal response system with strong momentum for development and application.

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.

Application of photothermal effects of nanomaterials in food safety detection

Numerous nanomaterials endowed with outstanding light harvesting and photothermal conversion abilities have been extensively applied in various fields, such as photothermal diagnosis and therapy, trace substance detection, and optical imaging. Although photothermal detection methods have been established utilizing the photothermal effect of nanomaterials in recent years, there is a scarcity of reviews regarding their application in food safety detection. Herein, the recent advancements in the photothermal conversion mechanism, photothermal conversion efficiency calculation, and preparation method of photothermal nanomaterials were reviewed. In particular, the application of photothermal nanomaterials in various food hazard analyses and the newly established photothermal detection methods were comprehensively discussed. Moreover, the development and promising future trends of photothermal nanomaterial-based detection methods were discussed, which provide a reference for researchers to propose more effective, sensitive, and accurate detection methods.

An immunochromatographic strip sensor for marbofloxacin residues

Marbofloxacin (MBF) was once widely used as a veterinary drug to control diseases in animals. MBF residues in animal food endanger human health. In the present study, an immunochromatographic strip assay (ICSA) utilizing a competitive principle was developed to rapidly detect MBF in beef samples. The 50% inhibitory concentration (IC50) and the limit of detection (LOD) of the ICSAs were 2.5 ng/mL and 0.5 ng/mL, respectively. The cross-reactivity (CR) of the MBF ICSAs to Ofloxacin (OFL), enrofloxacin (ENR), norfloxacin (NOR), and Ciprofloxacin (CIP) were 60.98%, 32.05%, 22.94%, and 23.58%, respectively. The CR for difloxacin (DIF) and sarafloxacin (SAR) was less than 0.1%. The recovery rates of MBF in spiked beef samples ranged from 82.0% to 90.4%. The intra-assay and interassay coefficients of variation (CVs) were below 10%. In addition, when the same authentic beef samples were detected in a side-by-side comparison between the ICSAs and HPLC‒MS, no statistically significant difference was observed. Therefore, the proposed ICSAs can be a useful tool for monitoring MBF residues in beef samples in a qualitative and quantitative manner.

Black Phosphorus - A Rising Star in the Antibacterial Materials

Antibiotics are the most commonly used means to treat bacterial infection at present, but the unreasonable use of antibiotics induces the generation of drug-resistant bacteria, which causes great problems for their clinical application. In recent years, researchers have found that nanomaterials with high specific surface area, special structure, photocatalytic activity and other properties show great potential in bacterial infection control. Among them, black phosphorus (BP), a two-dimensional (2D) nanomaterial, has been widely reported in the treatment of tumor and bone defect due to its excellent biocompatibility and degradability. However, the current theory about the antibacterial properties of BP is still insufficient, and the relevant mechanism of action needs to be further studied. In this paper, we introduced the structure and properties of BP, elaborated the mechanism of BP in bacterial infection, and systematically reviewed the application of BP composite materials in the field of antibacterial. At the same time, we also discussed the challenges faced by the current research and application of BP, which laid a solid theoretical foundation for the further study of BP in the future.

Regulation of Near-Field Radiative Heat Transfer between Multilayer BP/hBN Heterostructures

As an allotrope of phosphorus and a promising 2D semiconductor, black phosphorus (BP) exhibits in-plane anisotropy along its armchair and zigzag crystal directions, allowing for efficient regulation of near-field radiative heat transfer (NFRHT). In this work, we investigate the NFRHT between two multilayer BP/hBN heterostructures and theoretically demonstrate that thermal regulation can be realized by tuning the electron density and rotation angle of BP. Results show that a larger electron density leads to the coupling of anisotropic surface plasmon polaritons (SPPs) of BP with hyperbolic modes of hBN, and rotation of BP changes the anisotropic characteristic of coupled SPPs on both sides, whereby a regulation ratio of 5.8 can be obtained. We also analyze the effects of period number, hBN layer thickness, and topmost-layer material on the NFRHT. This work may be beneficial for efficient nanoscale thermal management and physical understanding of radiative heat transfer based on anisotropic SPPs.

DNA-Driven Photothermal Amplification Transducer for Highly Sensitive Visual Determination of Extracellular Vesicles

Extracellular vesicles (EVs) are crucial focus of current biomedical research and future medical diagnosis. However, the requirement for specialized sophisticated instruments for quantitative readouts has limited the sensitive measurement of EVs to specialized laboratory settings, which in turn has limited bench-to-bedside translation of EV-based liquid biopsies. In this work, a straightforward temperature-output platform based on a DNA-driven photothermal amplification transducer was developed for the highly sensitive visual detection of EVs using a simple household thermometer. The EVs were specifically recognized by the antibody-aptamer sandwich immune-configuration that was constructed on portable microplates. Via a one-pot reaction, cutting-mediated exponential rolling circle amplification was initiated in situ on the EV surface, generating substantial G-quadruplex-DNA-hemin conjugates. Significant amplification in temperature was achieved from the effective photothermal conversion and regulation guided by the G-quadruplex-DNA-hemin conjugates in the 3,3',5,5'-tetramethylbenzidine-H2O2 system. Through obvious temperature outputs, the DNA-driven photothermal transducer enabled highly sensitive EV detection at close to the single-particle level and supported the highly specific identification of tumor-derived EVs directly in serum samples, without the requirement of any sophisticated instrument or labeling process. Benefiting from highly sensitive visual quantification, an easy-to-use readout, and portable detection, this photothermometric strategy is expected to be deliverable across professional on-site screening to home self-testing as EV-based liquid biopsies.

Smartphone-Based Photothermal Lateral Flow Immunoassay Using Rhenium Diselenide Nanosheet

Developing a rapid antibody-based detection method is of great importance for preventing and controlling the spread of coronavirus disease 2019 (COVID-19). Among the antibody-based methods for point-of-care (POC) detection, lateral flow immunoassay (LFIA) is the most widely used. However, LFIA still has the disadvantage of low sensitivity. In this work, an ReSe2 nanosheet with a thickness of 10-20 nm was prepared by liquid exfoliation and applied as the label in a photothermal LFIA due to its high photothermal conversion efficiency and high photothermal stability. An integrated detection device was introduced for rapid, on-site, and highly sensitive assay of the human antisevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Spike (S) protein IgG antibodies. The device mainly included a rhenium diselenide (ReSe2) nanosheet-based photothermal LFIA, a portable laser, and a smartphone with a portable thermal imager, which was used to record and analyze the thermal signal of the LFIA test zone. The human anti-SARS-COV-2 S protein IgG antibodies in buffer solution can be detected in a portable box within 10 min, with a thermal signal detection limit of 0.86 ng mL-1, which was 108-fold lower than that of the colorimetric signal. The integrated device can detect values as low as 2.76 ng mL-1 of the human anti-SARS-COV-2 S protein IgG antibodies in 50% serum. The integrated device showed great potential for rapid and home self-testing diagnosis of COVID-19.

Colorimetric-photothermal-magnetic three-in-one lateral flow immunoassay for two formats of biogenic amines sensitive and reliable quantification

Rapid, simple, sensitive and reliable approaches for biogenic amines quantification in various food samples are essential to food safety. Lateral flow immunoassay (LFIA) has been wildly utilized in point-of-care testing (POCT) owing to its advantage of flexibility and feasibility. Here, we reported a Fe₃O₄@Au nanoparticles (NPs) (Fe₃O₄@AuNPs) based multimodal readout LFIA for rapid putrescine (Put) and histamine (His) quantification with a LOD down to 10 and 10 ng/mL in naked eye mode, 2.31 and 4.39 ng/mL in photothermal mode, 0.17 and 0.31 ng/mL in magnetic mode, respectively. Such multi-mode assay has been successfully used to detect Biogenic amines (BAs) in raw aquatic foods, including fish, prawns, beef, and pork, with overall recoveries ranging from 93.68 to 109.34%. Meanwhile, it is easily expanded to detect other typical BAs with high sensitivity by simply replacing antibodies. In view of the multi-signal reading, two quantitative formats, and high sensitivity, it may greatly widen the application of lateral flow detection in food safety.

Glutathione-Capped CdTe Quantum Dots Based Sensors for Detection of H2O2 and Enrofloxacin in Foods Samples

Additives and antibiotic abuse during food production and processing are among the key factors affecting food safety. The efficient and rapid detection of hazardous substances in food is of crucial relevance to ensure food safety. In this study, a water-soluble quantum dot with glutathione as a ligand was synthesized as a fluorescent probe by hydrothermal method to achieve the detection and analysis of H₂O₂. The detection limits were 0.61 μM in water and 68 μM in milk. Meanwhile, it was used as a fluorescent donor probe and manganese dioxide nanosheets were used as a fluorescent acceptor probe in combination with an immunoassay platform to achieve the rapid detection and analysis of enrofloxacin (ENR) in a variety of foods with detection limits of 0.05-0.25 ng/mL in foods. The proposed systems provided new ideas for the construction of fluorescence sensors with high sensitivity.

A highly sensitive photothermal immunochromatographic sensor for detection of aflatoxin B1 based on Cu2-xSe-Au nanoparticles

In the study, Cu_2-xSe-Au nanoparticles (CSA) with a photothermal conversion efficiency of 60.78 % at 808 nm were applied to the construction of thermal analysis immunochromatographic test strips for the highly sensitive quantitative detection of aflatoxin B₁ (AFB₁) in grain. The CSA was coupled with the AFB₁ antibody to form a photothermal sensor probe by physical adsorption. The constructed immunosensor exhibited high sensitivity and a wide linear range from 0.01 to 10 μg/L in PBS. The detection limits of 0.00842 μg/L based on the thermal analysis was significantly improved by 11.88-fold compared with colorimetric results. No cross-reaction with the other mycotoxins was found except for aflatoxin B₂, aflatoxin M₁, aflatoxin G₁ and aflatoxin G₂. Applied to analysize grain sample, the method achieved the detection of AFB₁ ranging from 0.16 to 160 μg/kg.

Salmonella typhimurium strip based on the photothermal effect and catalytic color overlap of PB@Au nanocomposite

This work reports a sensitive and accurate multimode detection method to detect Salmonella typhimurium using inherent color, photothermal and catalytic properties of Prussian blue@gold nanoparticles (PB@Au). The inherent color of PB@Au can realize direct visual detection while the temperature increase (ΔT) of it can realize sensitive and quantitative photothermal detection. Moreover, catalytic coloration detection is applied to further amplify detection signal. The risk limit, prevention and control of Salmonella typhimurium can be more intuitively displayed through catalytic color overlap degree between PB@Au and catalytic product. The sensitivity of method is improved through photothermal and catalytic coloration detection (10¹ CFU·mL^-1) compared with direct visual detection (10² CFU·mL^-1). The multimode detection improves the accuracy of method, and exhibits good repeatability, acceptable selectivity and stability. This method is also successfully applied in real samples, displaying its good practical applicability.

Multifunctional Au@Pt@Ag NPs with color-photothermal-Raman properties for multimodal lateral flow immunoassay

Multimodal lateral flow immunoassay (LFIA) has displayed its potential to improve practicability and elasticity of point-of-care testing. Herein, multifunctional core-shell-shell Au@Pt@Ag NPs loaded with dual-layer Raman reporter molecules of 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) with a characteristic combination of color-photothermal-Raman performance were constructed for colorimetric LFIA (CM-LFIA), photothermal LFIA (PT-LFIA) and surface-enhanced Raman scattering-based LFIA (SERS-LFIA), respectively. The highly specific nanoprobes, being obtained through the combination of the resulted dual-layer DTNB modified Au@Pt@Ag NPs with the antibody, were triumphantly utilized in exploring multimodal LFIA with one visual qualitative and two optional quantitative modes with excellent sensing sensitivity. Under optimal conditions, the limit of detection (LOD) for the model hazardous analyte dehydroepiandrosterone (DHEA) were 1.0 ng mL^-1 for CM-LFIA, 0.42 ng mL^-1 for PT-LFIA, and 0.013 ng mL^-1 for SERS-LFIA, three of which were over 100-fold, 200-fold and 7 000-fold more sensitive than conventional visual AuNPs-based LFIA, respectively. In addition, the quantitative PT-LFIA and SERS-LFIA sensors worked well in spiked real samples with acceptable recoveries of 96.2 - 106.7% and 98.2 - 105.2%, respectively. This assay demonstrated that the developed multimodal LFIA had a great potential to be a powerful tool for accurate tracing hazardous analytes in complex samples.

Tunable multiplexed fluorescence biosensing platform for simultaneous and selective detection of paraquat and carbendazim pesticides

The monitoring of multiple pesticides commonly used in food is a prerequisite for public health safety. Herein, a multiplexed biosensor based on fluorescence resonance energy transfer (FRET) from multicolor upconversion nanoparticles (UCNPs)to single black phosphorus nanosheets (BPNSs) was successfully developed for simultaneous and selective detection of paraquat and carbendazim pesticides. Due to the strong π-π stacking interactions, aptamers functionalized UCNPs may adsorb on the BPNSs surface, allowing strong upconversion fluorescence quenching. In the presence of paraquat and carbendazim, the aptamers preferentially integrated with their corresponding targets and altered the aptamer's conformation, restoring the fluorescence. An excellent linear correlation was observed from 1.0 to 1.0 × 10⁵ ng/mL, with a limit of detection of 0.18 ng/mL for paraquat and 0.45 ng/mL for carbendazim. The developed aptasensor was further validated by commercial enzyme-linked immunoassays without significant differences in practical detection. Additionally, this work offers new insights into monitoring multiple targets simultaneously.

In Situ Crumpling of Gold Nanosheets into Spherical Three-Dimensional Architecture: Probing the Aggregation-Induced Enhancement in Photothermal Properties

Assembling two-dimensional noble metal nanocrystals into a three-dimensional mesoporous structure is of great value to solve the re-stacking issue for the practical application, which still remains a challenging technique. Herein, we report the one-pot fabrication of gold (Au) nanostructures with a crumpled paper ball-like morphology (Au NCPBs). The success of current work relies on the use of glutathione to crumple the branched Au nanosheets formed during the early stage, into spherical three-dimensional architecture, where the nanosheets are assembled with a mesoporous structure without intimate contact. When working as the agent toward photothermal conversion, the Au NCPBs exhibit enhanced photothermal conversion efficiency (η = 19.9%), as compared to that of flat and wrinkled Au nanosheets. Such an enhancement should be owing to the aggregation-induced effect, where the shortened inter-sheet distance contributes to an increased coupling between the plasmon oscillations/fields of the interacting Au nanosheets. The present study offers a feasible strategy to create spherical architecture of crumpled Au nanosheets and validates their structural advantage in photothermal applications, which could be potentially extended to other metals or alloys.

Ultrasensitive Competitive Lateral Flow Immunoassay with Visual Semiquantitative Inspection and Flexible Quantification Capabilities

Antibiotics abuse has caused various problems threatening human health and ecological environment. Monitoring antibiotics residual levels is of great significance, yet still challenging for quantitative point-of-need testing with high-sensitivity and visual capability. Here we developed a competitive lateral flow immunoassay (CLFIA) platform with flexible readout for enrofloxacin (ENR), a regularly added antibiotic. To overcome the limitation of low sensitivity of traditional colloidal gold-based CLFIA, the three-dimensionally assembled gold nanoparticles (AuNPs) within dendritic silica scaffold were fabricated as signal reporters. The assembly structure effectively retained the intrinsic absorption features of hydrophobic AuNPs and greatly enhanced the light extinction ability of a single label for signal amplification. The obtained CLFIA strips can not only achieve qualitative screening of ENR at a very low concentration by naked eye (cutoff value: 0.125 ng/mL), but also enable ultrasensitive quantification of ENR by an optical scanner (limit of detection: 0.00195 ng/mL) or a smartphone (limit of detection: 0.0078 ng/mL). Moreover, to elaborate the visual inspection degree of CLFIA against traditional yes/no interpretation, a novel multirange gradient CLFIA strip was prepared for visually semiquantitative identification of ENR with four concentration ranges. The novel CLFIA platform demonstrated sensitive, specific, and reliable determination of ENR with flexible signal readout and provides a potential and invigorating pathway to point-of-need immunoassay of antibiotics.

Black phosphorous quantum dots for signal-on cathodic photoelectrochemical aptasensor monoitoring amyloid β peptide

In this paper, a quantitative cathodic photoelectrochemical aptasensor is described by using black phosphorous quantum dots (BPQDs) as photoactive material and assisted by heme as electron acceptor for sensing of amyloid β peptide (Aβ). Specifically, BPQDs were synthesized by solvothermal method and characterized by various techniques. The as-prepared BPQDs were assembled on the transparent indium tin oxide electrode, and the positively charged poly-l-lysine (PLL) was then absorbed onto BPQDs via electronic interaction. Subsequently, the aptamer as the specific recognition element for Aβ oligomer was introduced on the BPQDs-PLL modified electrode. After bound with heme to form Aβ-heme complex, Aβ oligomer was simultaneously captured by the aptamer on the electrode, resulting in an enhanced photocurrent response. Under the optimized conditions, the present PEC sensor reveals a good linear response to Aβ peptide ranging from 1.0 fM to 100 nM with a detection limit of 0.87 fM. The present signal-on cathodic PEC bioassay possesses the potential to create a new paradigm in amplified PEC assays that could provide outstanding performance for bioanalysis.

Dual-mode immunoassay for diethylstilbestrol based on peroxidase activity and photothermal effect of black phosphorus-gold nanoparticle nanohybrids

Nanozyme-mediated 3,3',5,5'-tetramethylbenzidine (TMB) - H₂O₂ systems have spawned the establishment of multiple colorimetric sensing platforms that are effective but sometimes subject to low sensitivity. Taking temperature as the output signal, photothermal effects lead to new strategies for sensitive detection. In this paper, a colorimetric and photothermal dual-mode immunoassay for diethylstilbestrol (DES) was constructed. It is based on the oxidation reaction of TMB catalyzed by black phosphorus-gold nanoparticle (BP/Au) nanohybrids, and the kinetics as well as catalytic mechanism of the nanohybrids were investigated in detail for the first time. Herein, the nanohybrids playcatalytic and photothermal dual roles. Moreover, the one-electron oxidation product of TMB (oxidized TMB) not only acts as chromogenic agent but also an excellent NIR laser-driven photothermal agent. The temperature (ΔT/°C) was gauged by a portable digital thermometer. Through an indirect competition strategy, a simple, sensitive, and economic immunosensor was proposed. Higher DES content in the sample correlated with less BP/Au nanohybrids conjugated to the surface of ELISA microplate, a weaker color change, and a lower temperature variation when exposed to laser irradiation. This method was applied for DES determination in real samples with gratifying recovery rates, showing great promise in food safety inspection applications.

Conjugated bimetallic cobalt/iron polyphthalocyanine as an electrochemical aptasensing platform for impedimetric determination of enrofloxacin in diverse environments

The synthesis of bimetallic cobalt/iron polyphthalocyanine (represented by polyCoFePc) network via a modified solid-phase synthesis method is described. It was exploited as a platform for anchoring enrofloxacin (ENR)-targeted aptamer strands, thus, fabricating a label-free impedimetric aptasensor for determination of ENR. The polyCoFePc exhibited a porous two-dimensional (2D) conjugated nanostructure and rich functional groups, and showed a superior binding interaction toward aptamer strands as compared to monometallic polyFePc and polyCoPc networks. This finding was attributed to structural defects and increased active binding sites, thereby giving a highly sensitive detection ability toward ENR. By using electrochemical impedance spectroscopy (EIS), the polyCoFePc-based electrochemical aptasensor exhibited an extremely low detection limit of 0.06 fg mL^-1 within the ENR concentration from 0.1 fg mL^-1 to 100 pg mL^-1, along with high selectivity, good reproducibility, and remarkable stability. Interestingly, the constructed polyCoFePc-based aptasensor also demonstrated wide practicability in various environments. The recoveries of ENR spiked into river water, milk, and pork samples ranged within 91.2 - 107.2%, 90.5 - 109.6%, and 91.2 - 102.3%, respectively.

Multifunctional bacteria-derived tags for advancing immunoassay analytical performance with dual-channel switching and antibodies bioactivity sustaining

Constructing multifunctional immunochromatographic assays (ICA) carriers with multiple signals and retaining bioactivity of monoclonal antibodies (mAbs) are conducive to the sensitive and accurate point-of-care testing (POCT). To fulfill this pressing need, a microorganism-based microsphere mediated dual-modal ICA (DICA) was developed for sensitive and reliable detection of zearalenone (ZEN). As the key to the biosensor, a superb biotag with an intact coccus morphology was designed based on Staphylococcus aureus biosynthesized quantum dots incorporating Ru(bpy)₃²⁺ (SAQDsRu), in which SA offered a specific recognition capacity for Fc region of mAbs, QDs endowed a naked-eye discernible colorimetric signal on the SA, and robust fluorescence signal that remedied for the insufficient brightness of QDs was derived from Ru(bpy)₃²⁺. The characterization of SAQDsRu-labeled mAb (SAQDsRu-mAb) probe demonstrated strong luminescence, excellent stability and high affinity with ZEN (affinity constant was approximately 1.723 × 10⁹ M^-1), which can significantly improve the detection sensitivity. Impressively, a portable sensing system was developed by the integration of SAQDsRu-DICA with a smartphone-based readout. After optimization, this DICA indicated a limit of detection reaching down to 0.008 ng/mL (colorimetric mode) and 0.0058 ng/mL (fluorescent mode), which were much lower than that of conventional gold nanoparticles-based ICA (0.1029 ng/mL), possessing favorable specificity and repeatability (relative standard deviation (RSD) < 10%). Moreover, the feasibility of the immunoassay was further assessed by measuring ZEN in real samples with satisfactory recoveries, and the results are good consistent with liquid chromatography tandem mass spectrometry (LC-MS/MS).

A Stable Quaternized Chitosan-Black Phosphorus Nanocomposite for Synergetic Disinfection of Antibiotic-Resistant Pathogens

Antibiotics are widely used for treatment of bacterial infections, and their overuse has contributed to microbial resistance. Currently, an alternative antibiotic-free therapy for inactivating bacteria is of great interest. Black phosphorus (BP), a biocompatible and nontoxic rising-star two-dimensional layered material, has gained remarkable interest in many bioapplications including biosensing, cancer therapy, drug delivery, and also antibacterial treatment. However, BP nanosheets suffer from instability in ambient environments due to rapid oxidation and degradation. To address this issue, BP nanosheets were modified with quaternized chitosan (QCS) by electrostatic adsorption to prepare a BP-QCS composite for photothermal/pharmaco treatment of bacterial infection. The BP-QCS has obviously enhanced solubility and chemical stability in aqueous suspensions. We have demonstrated that under near-infrared (NIR) irradiation, the BP-QCS can synergistically inactivate more than 95% methicillin-resistant Staphylococcus aureus (S. aureus) (MRSA) and Escherichia coli within 10 min with a dose of only 75 μg/mL in vitro. Meanwhile, the BP-QCS composite under NIR can synergistically inactivate 98% S. aureus in vivo. Furthermore, the BP-QCS suspensions at effective antibacterial concentrations have negligible cytotoxicity and in vivo toxicity.

Black Phosphorus Nanostructure Based Highly Sensitive and Selective Surface Plasmon Resonance Sensor for Biological and Chemical Sensing: A Review

Surface plasmon resonance (SPR) is an attention-grabbing sensor type, which offers the sensitive and selective detection of biomolecules and environmentally toxic substances. Notably, the SPR sensor gives excellent rewards including real-time, in-situ, and label-free measuring capability as compared to existing sensing technologies. As a result, these noteworthy merits of the SPR sensor make it straightforward to investigate the molecular events and chemical/gas molecule interaction. Unfortunately, there are different binding events including smaller molecular mass substances, which cannot be detected at the SPR sensor. Accordingly, this downside of the SPR sensor eventually led to the design and implementation of new approaches for sensitivity and selectivity improvement for sensing applications in different fields. Recently, the black phosphorus (BP) derived 2 D nanomaterial is stand out as a distinctive nanostructure in comparison to recently reported other 2 D nanomaterials. Substantial and functional characteristics of BP including simplicity of operation, optical properties, high carrier mobility, stronger immobilization of receptors and biomolecules, electronic bridging playing important role in the highly selective and sensitive assessment of analyte. The designed BP nanostructures are mostly serving to accelerate the plasmon material signals followed by improved molecular sensing that may due to 40-times faster-sensing responses of BP nanostructure than reported 2 D nanomaterials. Therefore, the present review article sheds light on the latest significant advances in biological and toxic gas detection through 2D BP nanostructures based SPR sensors. In the future, this review will facilitate detailed insights into the development of BP-based groundbreaking frameworks for highly sensitive and selective recognition of biomolecules and environmental pollutants.

Recent Advancements in Enzyme-Based Lateral Flow Immunoassays

Paper-based lateral-flow immunoassays (LFIAs) have achieved considerable commercial success and their impact in diagnostics is continuously growing. LFIA results are often obtained by visualizing by the naked eye color changes in given areas, providing a qualitative information about the presence/absence of the target analyte in the sample. However, this platform has the potential to provide ultrasensitive quantitative analysis for several applications. Indeed, LFIA is based on well-established immunological techniques, which have known in the last year great advances due to the combination of highly sensitive tracers, innovative signal amplification strategies and last-generation instrumental detectors. All these available progresses can be applied also to the LFIA platform by adapting them to a portable and miniaturized format. This possibility opens countless strategies for definitively turning the LFIA technique into an ultrasensitive quantitative method. Among the different proposals for achieving this goal, the use of enzyme-based immunoassay is very well known and widespread for routine analysis and it can represent a valid approach for improving LFIA performances. Several examples have been recently reported in literature exploiting enzymes properties and features for obtaining significative advances in this field. In this review, we aim to provide a critical overview of the recent progresses in highly sensitive LFIA detection technologies, involving the exploitation of enzyme-based amplification strategies. The features and applications of the technologies, along with future developments and challenges, are also discussed.

Development of non-enzymatic and photothermal immuno-sensing assay for detecting the enrofloxacin in animal derived food by utilizing black phosphorus-platinum two-dimensional nanomaterials

The two-dimensional black phosphorus nanosheets (BPNSs) provide strong support for the construction of nanozymes with high catalytic performance due to the sheet structure and high electronic activity. A peroxidase-like BP-Pt nanocomposites was successfully synthesized using the instability of BPNS, a non-enzymatic immunosensing assay (NISA) was established with BP-Pt as immunosensing probe. Take the antibiotic enrofloxacin (ENR) as the target, NISA realized the highly sensitive ENR detection with detection limit (IC15) of 0.005 μg/L. In addition, based on the good photothermal performance of oxTMB at 808 nm, a photothermal immunosensing assay (PT-NISA) was established, and ENR detection results was similar to NISA were obtained. In the analysis of the samples, the same detection results as the commercially available enzyme-linked immunoassay kit were obtained. These NISA and PT-NISA provide a more rapid and promising strategy for detecting food contaminants, and was expected to be used to detect other highly sensitive biological macromolecules.

Graphite-like carbon nitride-laden gold nanoparticles as signal amplification label for highly sensitive lateral flow immunoassay of 17β-estradiol

Conventional gold nanoparticles-based lateral flow immunoassays (AuNPs-LFIA) lack sensitivity. In this work, we developed a graphite-like carbon nitride-laden AuNPs (g-C₃N₄@Au) assisted LFIA to improve sensitivity for 17β-estradiol (E2) in foods. g-C₃N₄ nanosheets were applied as carriers, because of their excellent chemical stability, large surface areas and low-cost, loading large numbers of AuNPs to amplify signals and improve the overall response of g-C₃N₄@Au-based LFIA (g-C₃N₄@Au-LFIA). The lowest visual limit of detection (vLOD) of E2 is 0.5 ng mL^-1 for g-C₃N₄@Au-LFIA, which exhibit a significantly three-fold improved analytical performance compared with that of AuNPs-LFIA. Additionally, this method was successfully used to the detection of E2 in four spiked food samples, offering a great potential of the g-C₃N₄@Au based LFIA for its application in food products.

Recent advances in sensitivity enhancement for lateral flow assay

Conventional lateral flow assay (LFA) is typically performed by observing the color changes in the test lines by naked eyes, which achieves considerable commercial success and has a significant impact on the fields of food safety, environment monitoring, disease diagnosis, and other applications. However, this qualitative detection method is not very suitable for low levels of disease biomarkers' detection. Although many nanomaterials are used as new labels for LFA, additional readers limit their application to some extent. Fortunately, a lot of work has been done for improving the sensitivity of LFA. In this review, currently reported LFA sensitivity enhancement methods with an objective evaluation are summarized, such as sample pretreatment, the change of flow rate, and label evolution, and future development direction and challenges of LFAs are discussed.

Gold nanoparticles-functionalized three-dimensional flower-like manganese dioxide: A high-sensitivity thermal analysis immunochromatographic sensor

A sensitive photothermal immunochromatographic test strip (PITS) for the detection of deoxynivalenol (DON) was developed using flower-like gold nanoparticle-deposited manganese dioxide nanocarrier (FMD-G NC) labeled antibodies (Abs) as the photothermal-sensing probe. FMD was used as a template to deposit small gold nanoparticles (GNPs) to synthesize FMD-G NC with large specific surface area and significant photothermal conversion property. The FMD-G-Ab probe was competitively captured by DON target and antigen coated on test line (T-line), forming colorimetric signals under naked eyes and photothermal signals under an 808 nm laser. Under optimal conditions, the PITS exhibited sensitive and specific detection of DON from 0.19 ng mL^-1 to 12 ng mL^-1 with detection limits of 0.013 ng mL^-1, which were over 15-fold and 58-fold more sensitive than visual FMD-G-ITS and traditional GNPs-ITS. In addition, the novel FMD-G-PITS possessed a universal applicability, which could be well applied in green bean, corn, and millet.

Multifunctional Fe3O4@Au supraparticle as a promising thermal contrast for an ultrasensitive lateral flow immunoassay

An ultrasensitive lateral flow immunoassay (LFIA) strip has been developed based on a multifunctional photothermal contrast Fe₃O₄@Au supraparticle (Fe₃O₄@Au SP) for quantitative Ochratoxin A (OTA) detection. The Fe₃O₄@Au SP composite not only shows a better photothermal effect over Fe₃O₄ and gold nanoparticles, but possesses magnetic property and excellent ability to directly adsorb protein (antibody). Under 808 nm irradiation, photothermal images of the test strips are recorded by a portable Infrared thermal camera. A quantitative analysis is easily achieved based on the thermal changes, which are proportional to the concentrations of analytes. Under an optimal condition, a wide linear detection range from 1 pg mL⁻¹ to 1μgmL⁻¹ and a limit of detection (LOD) at 0.12 pg mL⁻¹ have been achieved with OTA as a model analytes. The practical application potential has also been validated by detection of OTA in spiked corn, peanut, and soybean extractives with overall recoveries ranging from 98.6% to 115% and coefficient of variations (CVs) between 6.06% and 12.73%. The photothermal LFIA renders a rapid, sensitive, and quantitative bio-/chemo-sensing platform with only a portable laser source and a thermal camera.

Terminal-conjugated non-aggregated constraints of gold nanoparticles on lateral flow strips for mobile phone readouts of enrofloxacin

Antibiotics abuse now poses a global threat to public health. Monitoring their residual levels as well as metabolites are of great importance, still challenges remain in in situ tracing during the circulation. Herein, taking the typical antibacterial Enrofloxacin (ENR) as a subject, a paper-based aptasensor was tailored by manipulating a duo of aptameric moieties to "sandwich" the target in a lateral-flow regime. To visualize the tight-binding sandwich motif more vividly, an irregular yet robust DNA-bridged gold nanoparticles (AuNPs) proximity strategy was developed with recourse to terminal deoxynucleotidyl transferase, of which the nonaggregate constraining feature was unveiled via optical absorption and scanning probe topography. This complex performed exceptionally better in the test strip context than single-particle tags, leading to an enhanced on-chip focusing. Rather than qualitative color developing, further efforts were taken to visualize the readouts in a quantitative manner by exploiting the smartphone camera for pattern recognition along with data processing in a professional App. Overall, this prototyped contraption realized a rapid and ultrasensitive quantification of ENR down to 0.1 μg/L along with a broad linear range over 5 orders of magnitude, plus excellent selectivity and precision even for real samples. Such innovative fusion across DNA-structured nanomanufacturing and intelligent perception provides a prospective and invigorating solution to point-of-care inspection.

Recent advances in high-sensitivity detection methods for paper-based lateral-flow assay

Paper-based lateral-flow assays (LFAs) have achieved considerable commercial success and continue to have a significant impact on medical diagnostics and environmental monitoring. Conventional LFAs are typically performed by examining the color changes in the test bands by naked eye. However, for critical biochemical markers that are present in extremely small amounts in the clinical specimens, this readout method is not quantitative, and does not provide sufficient sensitivity or suitable detection limit for a reliable assay. Diverse technologies for high-sensitivity LFA detection have been developed and commercialization efforts are underway. In this review, we aim to provide a critical and objective overview of the recent progress in high-sensitivity LFA detection technologies, which involve the exploitation of the physical and chemical responses of transducing particles. The features and biomedical applications of the technologies, along with future prospects and challenges, are also discussed.

Establishment of an immunofiltration strip for the detection of 17β-estradiol based on the photothermal effect of black phosphorescence

In this study, a novel immunofiltration strip method with temperature as the readout signal based on the photothermal effect of black phosphorus nanosheets was established. The temperature was monitored by a portable temperature sensor.