Enhancing Electrochemiluminescence Efficiency through Introducing Atomically Dispersed Ruthenium in Nickel-Based Metal-Organic Frameworks

Development of Pt/Au/PPy-COOH multisegmental nanowires modified label-free impedimetric immunosensor to determine mucin 1 (MUC1)

In this study, a label-free nanowire-based impedimetric immunosensor was developed for the purpose of determining cancer biomarkers mucin 1 (MUC1). Nanowires were selected for sensor modification due to their high catalytic properties and high enzyme loading capacity. The synthesis, characterization, and application of Pt/Au/PPy-COOH nanowires to modify SPE electrodes were conducted. The nanowire-based immunosensors developed as a result of this research demonstrated a broad linear working range for MUC1 (20-3000 fg/mL), a low LOD value (0.244 fg/mL), and a low LOQ value (0.815 fg/mL). The nanowire-based immunosensor exhibited several notable characteristics. Firstly, it demonstrated excellent reproducibility, selectivity, and long-term stability. Furthermore, it demonstrated notable regenerative capabilities. It is noteworthy that the sensor exhibited the capability to detect MUC1 in commercial human serum samples, even in the presence of interfering agents. The affordability, simplicity, and expeditious analysis of nanowire-based immunosensors render them more appealing than alternative commercial kits. Consequently, these sensors hold considerable promise for clinical applications.

Enhanced "Off-On" Electrochemiluminescent Biosensor Based on a Multivalent Aptamer-Induced Spatial Confinement Strategy for Ultrasensitive Detection of Membrane Protein (PTK-7)

"Off-on" electrochemiluminescence (ECL) techniques have garnered considerable interest in the biosensing field owing to its high sensitivity, low background signal, high signal-to-noise ratio, and avoidance of false-positive signals. However, a significant hurdle that prevents its further application is the lack of nontoxic, label-free, and easily synthesized ECL luminophores. In addition, achieving high quenching efficiency on these luminophores still requires strategy renewal. In this study, we propose novel Tb-DNA nanoparticles (NPs) as an emerging luminophore with low environmental risk and easy synthesis, which were synthesized in a facile coordination-driven approach. Taking advantage of the sequence programmability of these luminophores conferred by DNA molecules, we further construct an ultralow background "off-on" ECL platform by anchoring a multivalent aptamer on these nanoparticles, which facilitates close proximity with electron acceptors (e.g., dopamine (DA) oxidized by K2S2O8, DAOx) and enables efficient electron transfer between the excited state of Tb-DNA NPs and DAOx. Using the membrane protein protein tyrosine kinase-7 (PTK-7) as a sensing target, our "off-on" ECL strategy of spatially confined electron acceptors by multivalent aptamer-anchored Tb-DNA NPs displayed good detection performance, exhibiting a detection range of 90 to 106 cells/mL and a detection limit as low as a single-digit number of cells. This work not only puts forward novel Tb-DNA-based ECL luminophores but also proposes a multivalent aptamer-recognized acceptor strategy with high sensitivity, low background noise, and high specificity, which might hold great potential for ultrasensitive membrane protein detection.

An "on-off" electrochemical immunosensor for the detection of the glycan antigen CA125 by amplification signals using electropositive COFs

Cancer Antigen 125 (CA125), is a high molecular weight mucinous glycoprotein found on the surface of ovarian cancer cells. Generally, 90 % of women may appear a high concentration of CA125 when they got the cancer; thus, CA125 can act as a marker for ovarian cancer diagnosis and therapeutic evaluation. COFs have been widely used for disease detection due to their structural stability, high loading capacity and biocompatibility. However, the limited variety of electroactive COFs used as signal probes, fewer enriched signaling molecules, weaker electrical signals generated, and higher oxidation or reduction potentials of electroactive substances, a series of side reactions are easily triggered causing serious interference. To solve the above problems, [Fe(CN)6]3/4- as a signal probe and COFs for signal amplification were selected to creating a highly sensitive electrochemical immunosensor for glycan antigen CA125. Firstly, two-dimensional (2D) EP-TD-COF with ultra-high specific surface area was modified on bare GCE, which could covalently bound numerous Ab1 molecules due to the epoxy-rich functional groups. Then, the electropositive AuNPs@2DCOFBTT-DGMH was prepared by the in situ growth of AuNPs, proved an effective platform for loading Ab2 molecules via Au-S bonds. Based on the positively charged AuNPs@COFBTT-DGMH/Ab2 and negatively charged [Fe(CN)6]3/4- of electrostatic interactions, which could significantly enchaned signal for quantitative and sensitive detection of CA125. The constructed immunosensor exhibits excellent stability performance and high sensitivity, enabling ultrasensitive detection of trace glycan antigens. This study provided a new idea for the use of non-electroactive substances for the construction of electrochemical immunosensors and provided an effective signal amplification strategy.

Ultrasensitive photoelectrochemical detection of cancer markers based on heterojunctions constructed from Bi2O3 star-like flower nanoclusters and CdS hollow nanorods

CYFRA21-1 is a tumor marker for lung cancer, and its rapid and accurate detection can provide evidence for the early diagnosis of lung cancer. In this work, Bi-Fe turnbull blue analogues (Bi-Fe-TBA) were synthesized by the self-templating method. Bi2O3-SFNs was prepared by simple oxidation in air using Bi-Fe-TBA as a template. Bi2O3 Star-like Flower Nanoclusters (Bi2O3-SFNs) and CdS Hollow Nanorods (CdS-HNRs) were used to form a unique type II heterojunction for the first time. The arrangement of energy levels between CdS-HNRs and Bi2O3-SFNs, along with their hollow structure and star shape, effectively suppressed the recombination of photogenerated electrons and holes while shortening carrier transport distance. An ultra-sensitive PEC biosensor was developed to detect the lung cancer marker CYFRA21-1, leveraging the superior photoelectric conversion capabilities of Bi2O3-SFNs/CdS-HNRs. The sensor demonstrates outstanding stability, specificity, reproducibility as well as a wide linear range (10-4 - 10 ng mL-1) and low detection limit (4.23 × 10-5 ng mL-1). This study is valuable for the preparation of other functional materials using TBA as a template.

Interactions of metal-based nanozymes with aptamers, from the design of nanozyme to its application in aptasensor: Advances and perspectives

Nanozymes, characterized by enzyme-like activity, have been extensively used in quantitative analysis and rapid detection due to their small size, batch fabrication, and ease of modification. Researchers have combined aptamers, an emerging molecular probe, with nanozymes for biosensing to address the limited reaction specificity of nanozymes. Nanozyme aptasensors are currently experiencing significant growth, offering a promising solution to the lack of rapid detection methods across various fields. Unlike traditional nanozyme research, the development of nanozyme aptasensors is challenging as it requires the design of highly active nanozymes as well as the establishment of efficient and agile interactions between aptamers and nanozymes. Therefore, this review summarizes the active species and catalytic mechanisms of various nanozymes along with classical design options, discussing the future development of nanozyme aptasensors. It is anticipated that this review will inspire researchers in this domain, leading to the design of more enzymatically active nanozymes and advanced nanozyme aptasensors.

A mixed-organic ligands Ru(bpy)32+@Zn mMOFs-NH2 nanoreactors integrated co-reaction accelerator and morphologic regulator for the electrochemiluminescence detection of ATP

The functionalized architecture within the nanoreactor could dramatically change the electron transport and reaction efficiency of ECL during electrochemical processes. Here, we've devised a novel mixed-ligand strategy that combines co-reaction accelerator and morphologic regulator onto the same metal node. This innovative approach effectively addressed the critical issue that some co-reactants cannot be covalently linked due to their special states, while enhancing the stability and electroactivity of MOFs nanoreactors. Ru(bpy)32+ was in-situ encapsulated within Zn mMOFs-NH2 nanocages in which the 2-aminoterephthalic acid (NH2-BDC) ligand functioned as an effective co-reaction accelerator. While S2O82- underwent electron exchange on the surface of GCE to form SO4•-, Zn mMOFs-NH2 was electrochemically oxidized to Zn mMOFs-NH•, which could significantly catalyze S2O82- to form SO4•-. This greatly increased the local concentration of SO4•- in the vicinity of Ru(bpy)32+, thus achieving self-enhancing ECL. At the same time, 1,4-benzenedicarboxylic acid (BDC) ligands were used as morphologic regulator, yielding ultra-thin MOFs nanosheets that significantly boosted the loading capacity for Ru(bpy)32+ and enhanced electrical conductivity. The luminous efficiency of Ru(bpy)32+ is further enhanced by this synergy. A highly sensitive ECL biosensor was crafted for the detection of ATP. Optimal conditions allowed a robust linear correlation between the ECL intensity and the logarithm of ATP concentration, enabling a sensitive detection limit down to 1.18 nM. Our findings underscore the exceptional self-enhanced ECL properties of the devised Ru(bpy)32+@Zn mMOFs-NH2 nanoreactors, presenting a novel and promising platform for biomolecular analysis.

Research progress on the synthesis, performance regulation, and applications of Prussian blue nanozymes

Nanocatalytic medicine offers a novel solution to address the issues of low efficacy, potential side effects, and the development of drug resistance associated with traditional therapies. Therefore, developing highly efficient and durable nanozymes is of great significance for treating diseases related to oxidative stress. In recent years, prussian blue nanoparticles (PBNPs) have been demonstrated to possess multiple enzyme-like catalytic activities and are thus referred to as prussian blue nanozymes (PBNZs). Their excellent biocompatibility and biodegradability make PBNZs promising candidates as biomedical materials. Due to their remarkable catalytic activities, PBNZs have shown great potential in various biomedical applications, such as heavy metal detoxification, antioxidative damage, and anticancer therapies. This paper systematically summarizes the Synthetic strategies of PBNZs, analyzes the regulatory factors of their catalytic performance, and highlights the corresponding modulation methods. Furthermore, the biomedical applications of PBNZs are also reviewed. This study aims to provide researchers with insights and inspirations for the design and preparation of high-performance PBNZs.

Ultrasensitive detection of holoTC for analysis of Vitamin B12 levels using Ag2MoO4 deposited PEDOT sensing platform

Vitamin B12 is an essential micronutrient required for the proper functioning of the human body. Vitamin B12 deficiency is primarily causative of various neurolological disorders alongwith recurrence of oral ulcers and burning sensations which are early signs of condition such as pernicious anemia. Other complications associated with Vitamin B12 deficiency include risk of heart failure due to anemia, risk of developing autoimmune disorders and gastric cancer. Therefore, to obstruct these communal health issues, early detection of Vit B12 is highly needed. However, screening of vitamin B12 insufficiency is hindered by the low sensitivity of the conventional vitamin B12 test. Holotranscobalamin (holoTC) is an early indicator of the negative vitamin B12 balance as it is the first protein to decline in the serum. We report a novel impedimetric immunosensor based on flower-like poly (3,4-ethylenedioxythiophene) (PEDOT) nanostructural film impregnated with silver molybdate nanoparticles (Ag2MoO₄ NPs) deposited on fluorine-doped tin oxide electrode. The prepared electrodes were characterized by Field emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and electrochemical studies. The activated anti-holoTC antibody was immobilized and optimized to capture the target in a response time of 15 min. The electrochemical performance of the sensor was carried out by using the electrochemical impedance spectroscopy technique (EIS) and a good linear relationship between ΔRct and holoTC was obtained in the range from 0.1 pg mL-1 to 100 ng mL-1 with a detection limit of 0.093 pg mL-1. The proposed sensor was successfully applied in human serum samples for holoTC detection. The experimental results showed that the immunosensor is highly selective towards holoTC and presented an acceptable stability of 20 days with reproducibility RSD ≤4%. To the best of our knowledge, this is the first developed electrochemical immunosensor for holoTC detection.

AuPt/NF prepared with the lattice induction of substrate was applied to construct the electrochemical immunosensor for PCT detection

For the electrodeposition, the conductivity and lattice structure of substrate is important to the morphology and lattice of the deposited material. In this study, gold-platinum (AuPt) nanopartical was deposited on nickel foam (NF) based on the lattice induced orientation of the Ni substrate, and the obtained AuPt/NF was applied to construct electrochemical impedimetric immunosensor for procalcitonin (PCT) detection. As a new immunosensor matrix, NF with higher electrical conductance, flexibility and specific surface area, which can improve the plasticity, sensitivity and universality of the immunoelectrode. Due to the lattice matching between Au and Ni, ultrathin AuPt nanolayer with good biocompatibility and large surface area can be modified on the NF surface, which can bind more biomolecules and amplifies the change of impedance signal. Based on the synergistic effect between AuPt and NF, PCT detection based on this electrochemical impedimetric immunosensor with a wide linear range (0.2 pg mL-1 to 20 ng mL-1) and low detection limit (0.11 pg mL-1). In addition, this impedimetric immunosensor exhibits high recovery in the PCT detection of serum samples. This work provides a new thought and method for the construction of electrochemical immunosensor.

A novel and facile oxygen-activated time-temperature indicator with wide temperature monitoring range and good stability based on the laccase-like nanozyme

BACKGROUND

Time-Temperature Indicator (TTI) is an indicator device for real-time monitoring of the thermal history of the product. Due to the enzymatic reactions are affected by both time and temperature, enzymatic TTIs have been extensively studied and developed in recent years. However, enzymatic TTIs contain biologically active molecules (enzymes), which require high storage and use conditions. Most of them are designed to mix the system species together and irreversible reaction is undertaken. Nanozymes are the synthetic nanomaterials with similar biocatalytic functions as natural enzymes, which have extensive applications in analytical chemistry, biosensing, and environmental protection due to their facile synthesis, low cost, high stability and durability.

RESULTS

This work proposed to replace the natural laccase to laccase-like nanozyme, designed a novel and facile O2-activated time-temperature indicator for the first time. Nanozyme had excellent thermal and storage stability, which could maintain fabulous catalytic activity in the wide temperature range of 10-80 °C and after a long-term storage. Based on the O2 was required to participate in the oxidation of laccase-catalyzed substrates, a squeeze-type O2-activated TTI was designed by controlling O2 in the TTI system. The TTI was activated through extruding the O2-coated airbag ruptured and producing an irreversible color reaction. Combined with a smartphone to extract the chromaticity for portable visual real-time monitoring. Five sets of TTIs were prepared based on the concentration of nanozyme, and the activation energies (Ea) ranging from 28.45 to 72.85 kJ mol-1, which were able to be fitted to products with Ea ranging from 3.45 to 97.8 kJ mol-1 and the monitoring-time of less than 7 days.

SIGNIFICANCE

Compared to the traditional enzymatic TTI, the TTIs designed based on nanozyme has the advantages of controlled activation, wider temperature monitor range and good stability. Providing a new approach to the development of real-time monitoring of smart devices.

N-doped carbon quantum dots for the selective detection of OCl- ions, bioimaging, and the production of Fe3O4 nanoparticles utilized in the synthesis of substituted imidazole

Nitrogen-doped quantum dots (NCQD) were synthesized by solvothermal means using o-phenylenediamine and l-tartaric acid. The resultant NCQD produced a high quantum yield (40.3%) and a vivid green fluorescence. They were about 6 nm in size. The NCQD is useful in HeLa cell bioimaging investigations and is used for the fluorescence detection of OCl- ions. The quantum dots' Limit of Detection (LoD) was discovered to be 40 nM. Additionally, cytotoxicity testing was conducted, and we found out that HeLa cells safely endured up to 6.5 mg ml-1 of NCQD. Furthermore, NCQDs were employed to synthesize Fe3O4 nanoparticles, with the quantum dots acting as a reducing and stabilizing agent. The nanoparticles exhibited remarkable catalytic activity towards organic processes due to their size of 11 nm and surface area of 67.360 m2 g-1. Excellent yields of tri-substituted imidazole derivatives were produced using Fe3O4 nanoparticles as nanocatalysts in a solvent-free method.

Electrochemical detection of myoglobin using an ultrasensitive label-free sensor derived from cubic-ZIF67@Au-rGOF-NH2 composite of MOF and GOF

Markers of myocardial injury, such as myoglobin (Mb), are substances swiftly released into the peripheral bloodstream upon myocardial cell injury or altered cardiac activity. During the onset of acute myocardial infarction, patients experience a significant surge in serum Mb levels. Given this, precise detection of Mb is essential, necessitating the development of innovative assays to optimize detection capabilities. This study introduces the synthesis of a three-dimensional hierarchical nanocomposite, Cubic-ZIF67@Au-rGOF-NH2, utilizing aminated reduced graphene oxide and zeolite imidazolium ester framework-67 (ZIF67) as foundational structures. Notably, this novel material, applied in a label-free electrochemical immunosensor, presents a groundbreaking approach for detecting myocardial injury markers. Experimental outcomes revealed ZIF67 and AuNPs exhibit enhanced affinity and growth on the 3D-rGOF-NH2 matrix, thus amplifying electrical conductivity while preserving the inherent electrochemical attributes of ZIF67. As a result, the Cubic-ZIF67@Au-rGOF-NH2 label-free electrochemical immunosensor exhibited a broad detection range and high sensitivity for Mb. The derived standard curve was ΔIp = 16.67552lgC+275.245 (R = 0.993) with a detection threshold of 3.47 fg/ml. Moreover, recoveries of standards spiked into samples ranged between 96.3% and 108.7%. Importantly, the devised immunosensor retained notable selectivity against non-target proteins, proving its potential clinical utility based on exemplary sample analysis performance.

Comparative study of optical fiber immunosensors based on traditional antibody or nanobody for detecting HER2

In this study, we present a novel biomarker detection platform employing a modified S-tapered fiber coated with gold nanoparticle/graphene oxide (GNP/GO) for quantifying human epidermal growth factor receptor-2 (HER2) concentrations, using antibodies as sensing elements. The fabrication of this device involves implementing an in-situ layer-by-layer technique coupled with a chemical adsorption step to achieve the self-assembly of GNP, GO, and antibodies on the STF surface. The detection mechanism relies on monitoring the refractive index changes induced by the adsorption of HER2 onto the immobilized antibodies. For comparative analysis, both monoclonal antibody (mAb) and the novel nanobody (Nb) were employed in constructing the STF immunosensor, referred to as the mAb immunosensor and Nb immunosensor, respectively. Spectral analysis results highlight that the Nb immunosensor exhibits twice the sensitivity of the mAb immunosensor. This enhanced sensitivity is attributed to the small size, high antigen affinity, strong specificity, and structural stability of Nb. The Nb immunosensor demonstrated an impressive detection limit of 0.001 nM for HER2, surpassing the detection limit of the mAb immunosensor. These findings underscore the potential of the proposed Nb immunosensor as a promising and sensitive tool for HER2 detection, contributing to the diagnosis and prognosis of breast cancer. Furthermore, the simplicity of production and excellent optical performance position the Nb immunosensor as a prospective real-time biosensor with minimal cytotoxicity.

Aggregation-induced electrochemiluminescence based on intramolecular charge transfer and twisted molecular conformation for label-free Immunoassay

Organic emitters with exceptional properties exhibit significant potential in the field of aggregation-induced electrochemiluminescence (AIECL); however, their practicality is impeded by limited ECL efficiency (ΦECL). This paper investigates a novel type of AIECL emitter (BDPPA NPs), where an efficient intramolecular charge transfer (ICT) effect and highly twisted conformation contribute to a remarkable enhancement of ECL. The ICT effect reduces the electron transfer path, while the twisted conformation effectively restricts π-π stacking and intramolecular motions. Intriguingly, compared to the standard system of [Ru(bpy)32+]/TPrA, bright emissions with up to 54 % ΦECL were achieved, enabling direct visual observation of ECL through the co-reactant route. The label-free immunosensor exhibited distinguished performance in detecting SARS-CoV-2 N protein across an exceptionally wide linear range of 0.001-500 ng mL-1, with a remarkably low detection limit of 0.28 pg mL-1. Furthermore, this developed ECL platform exhibited excellent sensitivity, specificity, and stability characteristics, providing an efficient avenue for constructing platforms for bioanalysis and clinical diagnosis analysis.

One-step detection of procollagen type III N-terminal peptide as a fibrosis biomarker using fluorescent immunosensor (quenchbody)

BACKGROUND

Procollagen type III N-terminal peptide (P-III-NP) is a fibrosis biomarker associated with liver and cardiac fibrosis. Despite the value of P-III-NP as a biomarker, its analysis currently relies on enzyme-linked immunosorbent assays (ELISA) and radioimmunoassays (RIA), which require more than 3 h. To facilitate early diagnosis and treatment through rapid biomarker testing, we developed a one-step immunoassay for P-III-NP using a quenchbody, which is a fluorescence-labeled immunosensor for immediate signal generation.

RESULTS

To create quenchbodies, the total mRNA of P-III-NP antibodies was extracted from early-developed hybridoma cells, and genes of variable regions were obtained through cDNA synthesis, inverse PCR, and sequencing. A single-chain variable fragment (scFv) with an N-terminal Cys-tag was expressed in E. coli Shuffle T7, resulting in a final yield of 9.8 mg L-1. The fluorescent dye was labeled on the Cys-tag of the anti-P-III-NP scFv using maleimide-thiol click chemistry, and the spacer arm lengths between the maleimide-fluorescent dyes were compared. Consequently, a TAMRA-C6-labeled quenchbody exhibited antigen-dependent fluorescence signals and demonstrated its ability to detect P-III-NP at concentrations as low as 0.46 ng mL-1 for buffer samples, 1.0 ng mL-1 for 2 % human serum samples.

SIGNIFICANCE

This one-step P-III-NP detection method provides both qualitative and quantitative outcomes within a concise 5-min timeframe. Furthermore, its application can be expanded using a 96-well platform and human serum, making it a high-throughput and sensitive method for testing fibrotic biomarkers.

Tetrahedral DNA-linked aptamer-antibody-based sandwich-type electrochemical sensor with Ag@Au core-shell nanoparticles as a signal amplifier for highly sensitive detection of α-fetoprotein

The conventional electrochemical detection strategy for alpha-fetoprotein (AFP) is limited by the antigen-antibody (Ag-Ab) reactions and suffers from low sensitivity and poor reproducibility due to the inconsistency of Ab-modified electrodes. Herein, we designed and explored a sandwich-type electrochemical sensor for highly sensitive detection of AFP based on aptamer (Apt)-AFP-Ab interaction mode with silver@gold (Ag@Au) core-shell nanoparticles (NPs) as a signal amplifier. AuNPs were electrodeposited onto MXene (Ti3C2TX)-modified glassy carbon electrode (GCE) to get AuNPs/MXene/GCE and further used as the signal amplification substrate. The tetrahedral DNA-linked AFP aptamers were immobilized onto AuNPs/MXene/GCE surface via Au-S bonds and used as the sensing and recognition platform for AFP capturing. Ag@AuNPs with core-shell structures were synthesized, characterized, and bound with Ab as detection elements by catalyzing H2O2 reduction. In the presence of AFP, a stable Apt-AFP-Ab sandwich structure was formed owing to the high affinities of aptamer and Ab toward the target AFP. The catalytic current produced by H2O2 reduction increased linearly with the logarithm of AFP concentration from 5 × 10-4 ng/mL to 1 × 105 ng/mL, accompanied by a low detection limit (1.6 × 10-4 ng/mL). Moreover, the novel sandwich-type electrochemical sensor shows high sensitivity, outstanding selectivity, and promising performance in the analysis of actual samples, displaying a broad application prospect in bioanalysis.

An ultrasensitive unlabeled electrochemical immunosensor for the detection of cardiac troponin I based on Pt/Au-B,S,N-rGO as the signal amplification platform

In this study, an ultrasensitive unlabeled electrochemical immunosensor for the detection of cardiac troponin I (cTnI) was developed based on Pt/Au modified B,S,N co-doped reduced graphene oxide (Pt/Au-B,S,N-rGO) as a signal amplification platform. First-principles calculations were employed to analyze the electron density of states of Pt/Au-B,S,N-rGO, revealing an increase in the electron density of the graphene oxide (GO) states. Furthermore, scanning electron microscopy (SEM), X-ray photoelectron diffraction spectroscopy (XPS), and electrochemical detection were used to successfully construct and analyze Pt/Au-B,S,N-rGO. The results showed that B,S,N-rGO exhibited good electrochemical activity, and the Au/Pt NPs demonstrated excellent catalytic properties, which provided a strong foundation for achieving high-sensitivity detection. Moreover, the constructed unlabeled electrochemical immunosensor had an ideal linear range (0.1 pg/mL∼50 ng/mL) and detection limit (0.082 pg/mL). In human serum detection, the results of this immunosensor were essentially similar to the ELISA results for the same samples, which suggested that the immunosensor had a promising clinical application prospect for the detection of cTnI.

Luminescent Metal-Organic Frameworks for Electrochemiluminescent Detection of Water Pollutants

The modern lifestyle has increased our utilization of pollutants such as heavy metals, aromatic compounds, and contaminants that are of rising concern, involving pharmaceutical and personal products and other materials that may have an important environmental impact. In particular, the ultimate results of the intense use of highly stable materials, such as heavy metals and chemical restudies, are that they turn into waste materials, which, when discharged, accumulate in environmental water bodies. In this context, the present review presents the application of metal-organic frameworks (MOFs) in electrochemiluminescent (ECL) sensing for water pollutant detection. MOF composites applied as innovative luminophore or luminophore carriers, materials for electrode modification, and the enhancement of co-reaction in ECL sensors have enabled the sensitive monitoring of some of the most common contaminants of emerging concern such as heavy metals, volatile organic compounds, pharmaceuticals, industrial chemicals, and cyanotoxins. Moreover, we provide future trends and prospects associated with ECL MOF composites for environmental sensing.

COF-300-AR@CRL as a two-in-one nanocatalyst for one-step chemiluminescent detection of diphenyl ether herbicide residues in vegetable and fruit samples

A sensitive and accurate chemiluminescence (CL) method was developed for one-step determination of diphenyl ether herbicides at trace level with nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) as a model analyte. Candida rugosa lipase (CRL) was immobilized on a nanocarrier of amine-linked covalent organic framework (named as COF-300-AR) through a self-assembly strategy. The formed nanocomposite of COF-300-AR@CRL owns dual enzymatic catalytic activities. It can directly catalyze luminol-dissolved oxygen reaction to produce an intense CL emission by virtue of oxidase mimic activity of COF-300-AR but also effectively decompose nitrofen to release phenolic compounds by the immobilized CRL. The released phenolic compounds own strong reducing capacity and in turn decrease the CL signal sharply. Under the optimal conditions, the decreased CL intensity presents a good linear response to nitrofen concentration in the 0.02-50.0 μM range. The limit of detection (LOD, 3sb/S) is 11 nM and the precision is 2.0% for replicate measurements of 50.0 nM nitrofen solution (n = 11). This method has the advantages of rapid analytical efficiency, good selectivity, satisfactory stability, and recyclability. Recovery experiments were conducted on spiked vegetable and fruit samples with the recoveries falling in the range 90.0-107.0%.

A machine learning strategy-incorporated BiFeO3/Ti3C2 MXene electrochemical platform for simple, rapid detection of Pb2+ with high sensitivity

The electrochemical technique has been increasingly used for the detection of heavy metal ions in the water system. However, the process for determining the optimum experimental conditions was cumbersome, time-consuming, and unsynchronized, resulting in unsatisfactory detection efficiency. Herein, a new machine learning (ML) strategy combined with BiFeO3/Ti3C2 MXene (BiFeO3/MXene) was used to fabricate a simple but efficient electrochemical Pb2+ sensor. The interconnected BiFeO3/MXene composites prepared by a hydrothermal method possessed an interconnected conductive framework, abundant active sites, and a large surface area, which gave them excellent electronic conductivity and high accumulation of Pb2+. Meanwhile, ML methods such as back-propagation artificial neural network (BPANN) and genetic algorithm (GA) combined with orthogonal experimental design (OED) were used to optimize sensor parameters such as the pH of the supporting electrolyte, the BiFeO3/MXene content, deposition potential, and deposition time. Compared with OED and the one factor at a time (OFAT) methods, the OED-ML method greatly simplified the experimental procedures and improved the electrochemical detection performance. The developed sensor showed superior detection performance for Pb2+ with a detection limit of 0.0001 μg L-1 using the OED-ML method, which was much lower than that of the OED and OFAT methods (0.0003 μg L-1). In addition, the sensor showed good repeatability, reproducibility, stability, and interference capability. The feasibility of the method was verified by detecting Pb2+ in lake samples with recoveries ranging from 98.79% to 101.3%. To our knowledge, the ML strategy was introduced for the first time in an electrochemical sensor for Pb2+ detection, which proved the feasibility and practicality of ML.

Novel Ultralow-Potential Electrochemiluminescence Aptasensor for the Highly Sensitive Detection of Zearalenone Using a Resonance Energy Transfer System

An ultralow-potential electrochemiluminescence (ECL) aptasensor has been designed for zearalenone (ZEN) assay based on a resonance energy transfer (RET) system with SnS2 QDs/g-C3N4 as a novel luminophore and CuO/NH2-UiO-66 as a dual-quencher. SnS2 QDs were loaded onto g-C3N4 nanosheets and enhanced the ECL luminescence via strong synergistic effects under an ultralow potential. The UV-vis absorption spectrum of CuO/NH2-UiO-66 exhibits considerable overlap with the ECL emission spectrum of SnS2 QDs/g-C3N4, an important consideration for the RET process. In order to stimulate RET, the ZEN aptamer and complementary DNA are introduced for conjugation between the donor and the acceptor. With the binding interaction between ZEN by its aptamer, CuO/NH2-UiO-66 is removed from the electrode surface, resulting in the inhibition of the RET system and an increase in the ECL signal. Under optimal conditions, the as-prepared aptasensor quantified ZEN from 0.5 μg·mL-1 to 0.1 fg·mL-1 with a low limit of detection of 0.085 fg·mL-1, and it exhibited good stability, excellent specificity, high reproducibility, and desirable practicality. The sensing strategy provides a method for mycotoxins assay to monitor food safety.

Machine learning-guided the fabrication of nanozyme based on highly-stable violet phosphorene decorated with phosphorus-doped hierarchically porous carbon microsphere for portable intelligent sensing of mycophenolic acid in silage

Violet phosphorene (VP) have been proved to be more stable than black phosphorene, but few reports for its application in electrochemical sensors. In this study, a highly-stable VP decorated with phosphorus-doped hierarchically porous carbon microsphere (PCM) with multiple enzyme-like activities as a nanozyme sensing platform for portable intelligent analysis of mycophenolic acid (MPA) in silage with machine learning (ML) assistance is successfully fabricated. The pore size distribution on the PCM surface is discussed using N2 adsorption tests, and morphological characterization indicates that the PCM is embedded in the layers of lamellar VP. The affinity of the VP-PCM nanozyme obtained under the guidance of the ML model reaches Km = 12.4 μmol/L for MPA. The VP-PCM/SPCE for the efficient detection of MPA exhibits high sensitivity, a wide detection range of 2.49 μmol/L - 71.14 μmol/L with a low limit of detection of 18.7 nmol/L. The proposed ML model with high prediction accuracy (R2 = 0.9999, MAPEP = 0.0081) assists the nanozyme sensor for intelligent and rapid quantification of MPA residues in corn silage and wheat silage with satisfactory recoveries of 93.33%-102.33%. The excellent biomimetic sensing properties of the VP-PCM nanozyme are driving the development of a novel MPA analysis strategy assisted by ML in the context of production requirements of livestock safety.

A portable microfluidic electrochemical sensing platform for rapid detection of hazardous metal Pb2+ based on thermocapillary convection using 3D Ag-rGO-f-Ni(OH)2/NF as a signal amplifying element

Heavy metal pollution is causing a great threat to ecological environment and public health, which needs an efficient strategy for monitoring. A portable microfluidic electrochemical sensing system was developed for the determination of heavy metal ions. Herein, the detection of Pb²⁺ was chosen as a model, and a microfluidic electrochemical sensing chip relying on a smartphone-based electrochemical workstation was proposed for rapid detection Pb²⁺ with the assistance of thermocapillary convection result from the formed temperature gradient. The 3D Ag-rGO-f-Ni(OH)₂/NF composites, prepared by one-step hydrothermal method without any Ni precursor salt, were used to further amplify electrochemical signals under the synergistic effect of thermocapillary convection. The thermocapillary convection could accelerate the preconcentration process and shorten the detection time (save 300 s of preconcentration time). The fabricated system exhibited the exceptional competence for monitoring of Pb²⁺ range from 0.01 μg/L to 2100 μg/L with a low detection limit (LOD) of 0.00464 μg/L. Furthermore, this portable system has been successfully demonstrated for detecting Pb²⁺ (0.01 μg/L to 2100 μg/L) in river water (LOD = 0.00498 μg/L), fish (LOD = 0.00566 μg/L) and human serum samples (LOD = 0.00836 μg/L), and the results were consistent with inductively coupled plasma-mass spectrometry (ICP-MS). The proposed novel sensing platform provides a cost-effectiveness, rapidly responding and ease-to-use pathway for analysis of heavy metal ions in real samples and shows great potential in point-of-care testing.

Novel design constructed In2S3@SnO2 hollow heterojunctions by insufficiently etched MOFs as framework for photoelectrochemical bioanalysis

Compared to sufficiently etched MOFs materials, insufficiently etched MOFs materials tend to display unsatisfactory performance due to their immature structure and have been eliminated from scientific research. Herein, this work reported a novel In₂S₃@SnO₂ heterojunction (In₂S₃@SnO₂-HSHT) materials, which were stably synthesized in high temperature aqueous environment and equipped extraordinary photoelectrochemical (PEC) properties, fabricated by a succinct hydrothermal synthesis method using insufficiently etched MIL-68 as a self-sacrificing template. Compared with the control groups and In₂S₃@SnO₂ heterojunctions with collapse morphology synthesized by sufficiently etched MIL-68 in high temperature aqueous environment, In₂S₃@SnO₂-HSHT synthesized from insufficiently etched MIL-68 as a template had a massively enhanced light-harvesting capability and generated more photoinduced charge carriers due to its well-preserved hollow structure. Therefore, based on outstanding PEC performance of In₂S₃@SnO₂-HSHT, the established PEC label-free signal-off immunosensor to detect CYFRA 21-1, revealing vivid selectivity, stability, and reproducibility. This novel strategy adopted the insufficient chemical etching method neglected by the mainstream chemical etching approaches, which solved the challenge that the stability of the sufficient etched MOFs with hollow structure cannot be maintained under the subsequent high temperature aqueous reaction conditions, and was further applied to the design of hollow heterojunction materials for photoelectrochemical fields.

A photoelectrochemical immunosensing platform for ultrasensitive detection of alpha-fetoprotein based on a signal amplification strategy

For the first time, a PEC immunosensor based on a signal amplification strategy is successfully constructed to quantitatively detect alpha-fetoprotein in serum sample. Three favorable factors explain the ultra-high sensitivity of this method. Firstly, compared with pure BiPO₄, the BiPO₄/BiOBr heterojunction has a narrower band gap, which expands the light absorption range and enables the light energy to be fully utilized. Secondly, the separation of photogenerated electrons and hole pairs during PEC detection is due to the efficient matching of energy levels among BiPO₄, BiOBr and CdS, inhibiting the recombination of photogenerated electrons, which improves the performance of PEC immunosensor. Thirdly, due to the presence of CdS, the light absorption capability of the sensor is enhanced, more electron-hole pairs are generated, and the photocurrent signal is increase. Under the optimal conditions, the PEC immunosensor shows a wide linear range of 0.001-1000 ng/mL for AFP and a low detection limit of 0.82 pg/mL. The PEC immunosensor developed in this experiment has excellent reproducibility, stability and high sensitivity, and also achieves satisfactory results in the analysis of human serum samples, establishing a new analytical method for biomarker detection.

Electrochemical aptasensor based on carboxylated graphene oxide modified carbon paste electrode for strontium ultrasensitive detection

Determination of strontium ions (Sr²⁺) is crucial with regard to human health and environmental protection. In this work, an electrochemical aptasensor was designed using carboxylated graphene oxide (CGO)-modified carbon paste electrode (CGO/CPE) for ultrasensitive determination of Sr²⁺ ions. The electrochemical determination was accomplished with employing the constructed G-quadruplex (G4) aptamer at the surface of aptasensor in presence of carmoisine (CA) as an electrochemical label. Moreover, NH₂-functionalized aptamer was immobilized onto CGO/CPE via carboxylic group. Hence, differential pulse voltammetry was applied for detection of any possible signal changes of CA on the aptasensor surface. The reduction peak currents of CA in the absence and presence of Sr²⁺ in solution were different and this difference was linearly dependent to the concentration of Sr²⁺ in solution. The analytical results revealed that our novel aptasensor showed two appropriate linear ranges (0.1-8.0 pM and 3.0-20.0 nM) versus to Sr²⁺ ion concentrations with the limit of detection of 0.06 pM (S/N = 3). Excellent stability, selectivity and reproducibility were achieved with this new electrochemical aptasensor. Additionally, the aptasensor showed good achievements in analysis of Sr²⁺ in aqueous and urine real samples, which making this proposed method a promising candidate for electrochemical detection of Sr²⁺ in real samples.

In situ synthesis of Cu nanoclusters/CeO2 nanorod as aggregated induced ECL probe for triple-negative breast cancer detection

Cu nanoclusters (NCs) have attracted a lot of attention due to the excellent properties. However, the low luminescence and poor stability limited the Cu NC-based sensing research. In this work, Cu NCs were in situ synthesized on CeO₂ nanorods. On the one hand, the aggregated induced electrochemiluminescence (AIECL) of Cu NCs has been observed on the CeO₂ nanorods. On the other hand, the substrate of CeO₂ nanorods acted as catalysis, which reduced the excitation potential and further enhanced the ECL signal of Cu NCs. It was noticed that CeO₂ nanorods also greatly improved the stability of Cu NCs. The resulted high ECL signals of Cu NCs can be kept constant for several days. Furthermore, MXene nanosheets/Au NPs has been employed as electrode modification materials to construct the sensing platform to detect miRNA-585-3p in triple negative breast cancer tissues. Au NPs@MXene nanosheets not only enlarged the specific interface area of the electrodes and the number of reaction sites, but also modulated electron transfer to amplify the ECL signal of Cu NCs. The biosensor had a low detection limit (0.9 fM) and a wide linear range (1 fM to 1 μM) for the detection of miRNA-585-3p in the clinic tissues.