Photoelectrochemical bioanalysis of antibiotics on rGO-Bi2WO6-Au based on branched hybridization chain reaction

Centrifugated lateral flow assay strips based on dual-emission carbon dots modified with europium ions for ratiometric determination and on-site discrimination of tetracyclines in environment

Due to the serious detrimental impact on human health, antibiotic pollution particularly tetracyclines residues has become a serious problem. Herein, a multiple response fluorescent probe consisted of dual-emission carbon dots and Eu3+ (D-CDs@Eu3+) is designed for the determination and discrimination of tetracyclines (TCs). Specifically, the carboxyl and amidogen group of dual-emission carbon dots (D-CDs) can coordinate with Eu3+ to form the D-CDs@Eu3+. Upon adding TCs, the fluorescence intensities of D-CDs at 405 nm and 495 nm are quenched due to inner filter effect (IFE) and the localization of fluorescence resonance energy transfer (L-FRET) between the D-CDs@Eu3+ and TC. Simultaneously, the D-CDs@Eu3+ may chelate with TCs to enhance the occurrence of antenna effect, while the characteristic peaks of Eu3+ at 590 nm and 615 nm are enhanced. On these bases, the TCs detection is achieved with low detection limits from 46.7 to 72.0 nM. Additionally, through the distinct efficiencies of L-FRET, the discrimination of TCs is achieved. Moreover, a novel centrifugated lateral flow assay strips (CLFASs) device is developed by integrating the D-CDs@Eu3+, lateral flow assay strips and smartphone using RGB variations for TCs detection, achieving remarkable recoveries (98.6-103.7 %) in real samples. Therefore, this CLFASs device provides a reliable approach for the TCs detection, demonstrating potential applications.

Foldable paper-based photoelectrochemical biosensor based on etching reaction of CoOOH nanosheets-coated laser-induced PbS/CdS/graphene for sensitive detection of ampicillin

Timely and rapid detection of antibiotic residues in the environment is conducive to safeguarding human health and promoting an ecological virtuous cycle. A foldable paper-based photoelectrochemical (PEC) sensor was successfully developed for the detection of ampicillin (AMP) based on glutathione/zirconium dioxide hollow nanorods/aptamer (GSH@ZrO2 HS@apt) modified cellulose paper as a reactive zone with laser direct-writing lead sulfide/cadmium sulfide/graphene (PbS/CdS/LIG) as photoelectrode and cobalt hydroxide (CoOOH) as a photoresist material. Initially, AMP was introduced into the paper-based reaction zone as a biogate aptamer, which specifically recognized the target and then left the ZrO2 HS surface, releasing glutathione (GSH) encapsulated inside. Subsequently, the introduction of GSH into the reaction region and etching of CoOOH nanosheets to expose the PbS/CdS/LIG photosensitive material increased photocurrent. Under optimal conditions, the paper-based PEC biosensor showed a linear response to AMP in the range of 5.0 - 2 × 104 pM with a detection limit of 1.36 pM (S/N = 3). In addition, the constructed PEC sensing platform has excellent selectivity, high stability and favorable reproducibility, and can be used to assess AMP residue levels in various real water samples (milk, tap water, river water), indicating its promising application in environmental antibiotic detection.

Citizen science in action: Time-resolved immunofluorescence-based field detection of antibiotics with portable analytical kit

Citizen scientist-based environmental monitoring and public education are becoming increasingly popular. However, current technologies for antibiotic-based novel contaminant identification are still restricted to laboratory sample collection and analysis due to detection methodologies and apparatus limitations. This study developed a time-resolved immunofluorescence-based simultaneous field-based assay for ciprofloxacin (CIP) and enrofloxacin (ENR) that matches test results to geographic locations. The assay helps the public understand the potential levels of antibiotic exposures in their environments and helps them take appropriate action to reduce risk. The assay was developed using smartphones and social software in addition to rapid testing. The method uses a portable, low-cost analytical kit with a smartphone app to build a field-based detection platform for the detection and analysis of ENR and CIP in water and aquatic products. The methodological evaluation was good, with detection limits of 0.4 ng/mL and 0.5 ng/g for ENR in water and fish, and quantification limits of 1.2 ng/mL and 1.4 ng/g, with recoveries of 89.0 %-101.0 % and 78.0 %-97.0 %. For CIP in water and fish, the limits of detection were 0.3 ng/mL and 0.4 ng/g, the limits of quantification were 0.9 ng/mL and 1.2 ng/g, and the recoveries were 75.0 %-91.0 % and 72.0 %-89.0 %, both with coefficients of variation <15 %. These limits were sufficient to prevent the two antibiotics from crossing over during simultaneous detection. The assay was validated using real samples to assess the effectiveness of the assay platform in field deployments, and the results were consistent with those obtained through liquid chromatography-tandem mass spectrometry (LC-MS) and enzyme-linked immunoassay (ELISA) techniques. In addition, the TRFIA assay process requires less time, uses more portable instruments, and is less complex than traditional methods. This study provides a new scientific, accurate, and rapid detection method for antibiotic detection by citizen scientists, helping scientists to obtain a wider range of data and providing more opportunities to solve scientific problems.

Ratiometric fluorescence platform for the ultrasensitive detection of kanamycin based on split aptamer co-recognition triggers Mg2+-DNAzyme-driven DNA walker systems

In this work, a novel 3D-DNA walker signal amplification strategy was designed to construct a fluorescent aptasensor for the detection of kanamycin (KAN). The aptasensor utilizes split aptamers for the synergistic recognition of KAN. The presence of KAN induces the split aptamers recombination to form the Mg2+-DNAzyme structure, which is activated by Mg2+ to drive the 3D-DNA walker process for cascading signal amplification. Employing gold nanoflowers (AuNFs) as walking substrate material increases the local DNA concentration to enhance the walker efficiency. The prepared fluorescent aptasensor achieved efficient and sensitive detection of KAN with satisfactory results in the concentration range of 1 × 10-8 - 1 × 10-3 μg/kg and the detection limit of 5.63 fg/kg. Meanwhile, the designed fluorescent aptasensor exhibited favorable specificity, anti-interference, storage stability and reproducibility, and verified the feasibility of its application in milk samples. The present work provides an effective tool for the regulation of KAN contamination in animal-derived foods with promising prospects.

A new strategy based on a cascade amplification strategy biosensor for on-site eDNA detection and outbreak warning of crown-of-thorns starfish

Population outbreaks of the crown-of-thorns starfish (COTS) seriously threaten the sustainability of coral reef ecosystems. However, traditional ecological monitoring techniques cannot provide early warning before the outbreaks, thus preventing timely intervention. Therefore, there is an urgent need for a more accurate and faster technology to predict the outbreaks of COTS. In this work, we developed an electrochemical biosensor based on a programmed catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR) cyclic amplification strategy for sensitive and selective detection of COTS environmental DNA (eDNA) in water bodies. This biosensor exhibited excellent electrochemical characteristics, including a low limit of detection (LOD = 18.4 fM), low limit of quantification (LOQ = 41.1 fM), and wide linear range (50 fM - 10 nM). The biosensing technology successfully allowed the detection of COTS eDNA in the aquarium environment, and the results also demonstrated a significant correlation between eDNA concentration and COTS number (r = 0.990; P < 0.001). The reliability and accuracy of the biosensor results have been further validated through comparison with digital droplet PCR (ddPCR). Moreover, the applicability and accuracy of the biosensor were reconfirmed in field tests at the COTS outbreak site in the South China Sea, which has shown potential application in dynamically monitoring the larvae before the COTS outbreak. Therefore, this efficient electrochemical biosensing technology offers a new solution for on-site monitoring and early warning of the COTS outbreak.

One-tube B7-H3 detection based on isothermal exponential amplification and dendritic hybridization chain reaction

We have developed a one-tube fluorescence strategy for the detection of B7-H3 based on a proximity hybridization-mediated protein-to-DNA signal transducer, isothermal exponential amplification (EXPAR), and dendritic hybridization chain reaction (D-HCR). In this assay, a protein signal transducer was employed to convert the input protein to output single-stranded DNA with a nicking site. Antibody-conjugated DNA1 was first hybridized with the output DNA (DNA3). The binding of antibodies conjugated DNA1 and DNA2 to the same protein was able to increase the local concentrations, resulting in strand displacement between DNA3 and DNA2. DNA3 with a nicking endonuclease recognition sequence at the 5' end then hybridized with hairpin probe 1 to mediate EXPAR in the presence of nicking endonuclease and DNA polymerase. A large number of single-strand DNA were produced in the circle of nicking, polymerization, and strand displacement. The resulting ssDNA products were further amplified by D-HCR to produce many large-molecular concatemers. The resulting DNA products can be monitored in real-time fluorescence signaling. Our proposed assay can realize one-tube detection due to the same reaction temperature of the protein-to-DNA signal transducer, EXPAR, and DHCR. This assay has a linear range from 100 fg mL-1 to 1 μg mL-1 with a detection limit down to 100 fg mL-1. This work shows a good performance in clinical specimen detection.

A double defects-dominated flexible TiO2 matrix for in-situ SERS sensing of antibiotic residues in aquatic ecosystem (fish & fishpond water) and their on-site degradation in flowing water

High-performance flexible semiconductor material can be used as an excellent multifunctional matrix for in-situ ultrasensitive surface-enhanced Raman scattering (SERS) detection and synchronous photocatalytic degradation of antibiotic residues in aquatic ecosystem. Here, a calcium-doped TiO2 flexible matrix with double defects (surface oxygen vacancy defect and Ti3+ energy level defect) was developed by its "in-situ one-step" hydrothermal synthesis on cotton fabric for the above purposes. Due to the joint contribution of double defects, a multi-channel charge transfer mode and a high-efficiency carrier separation are achieved, which endows flexible cotton fabric/Ca-doped TiO2 (Cot/Ca-TiO2) substrate with the greatly boosted SERS effect for in-situ detection of antibiotic residues on fish body surface and in fishpond water by a simple wiping or dipping sampling method, even for simultaneous identification of multi-component residues. The detection limits of three antibiotic residues (enrofloxacin, ciprofloxacin and enoxacin) are as low as 10-9 M, which are far lower than the EU standard. More meaningfully, the flexible Cot/Ca-TiO2 can be used as a multifunctional filter-membrane type photocatalyst for efficient on-site degradation of antibiotic residues in flowing fishpond water by a multi-grade photocatalysis means. Moreover, the flexible matrix exhibits good recyclability in both actual detection and photocatalysis.

Rapid antibiotic screening based on E. coli apoptosis using a potentiometric sensor array

Phenotypic antimicrobial susceptibility testing enables reliable antibiotic screening but requires multiple strategies to identify each phenotypic change induced by different bactericidal mechanisms. Bacteria apoptosis with typical phenotypic features has never been explored for antibiotic screening. Herein, we developed an antibiotic screening method based on the measurement of antibiotic-induced phosphatidylserine (PS) exposure of apoptotic bacteria. Phosphatidylserine externalization of E. coli that can be widely used as an apoptosis marker for antibiotics with different antibacterial mechanisms was explored. A positively charged PS-binding peptide was immobilized on magnetic beads (MBs) to recognize and capture apoptotic E. coli with PS externalization. Apoptotic E. coli binding led to the charge or charge density change of MBs-peptide, resulting in a potential change on a magneto-controlled polymeric membrane potentiometric sensor. Based on the detection of apoptotic E. coli killed by antibiotics, antibiotic screening for different classes of antibiotics and silver nanoparticles was achieved within 1.5 h using a potentiometric sensor array. This approach enables sensitive, general, and time-saving antibiotic screening, and may open up a new path for antibiotic susceptibility testing.

A novel electrochemiluminescence biosensor based on Ru(bpy)32+-functionalized MOF composites and cycle amplification technology of DNAzyme walker for ultrasensitive detection of kanamycin

An electrochemiluminescence (ECL) sensing platform for ultrasensitive and highly selective detection of kanamycin (KANA) was developed based on the prepared Ru(bpy)32+-functionalized MOF (Ru@MOF) composites by hydrothermal synthesis and Ag+-dependent DNAzyme. In this sensor, the stem-loop DNA (HP) with the ferrocene (Fc) was used as substrate chain to quench the ECL emission generated by the Ru@MOF. Using the specific recognition effect between KANA and the KANA aptamer (Apt) and the DNAzyme dependence on Ag+, the KANA aptamer as the pendant strand of the DNAzyme was assembled on Ru@MOF/GCE with the aptamer. When both Ag+ and KANA were present simultaneously, KANA specifically was binded to KANA aptamer as a pendant chain. Subsequently, Ag+-dependent DNAzyme walker continuously cleaved the HP chain and released the modified end of Fc to restore the ECL signal of Ru@MOF composites, thus achieving selective and ultrasensitive detection of KANA. The constructed KANA biosensor exhibits a wide detection range (30 pM to 300 μM) accompanied by a low detection limit (13.7 pM). The KANA in seawater and milk samples are determined to evalute the practical application results of the sensor. This ECL detection strategy could be used for detecting other similar analytes and has broad potential application in biological analysis.

Dual-mode colorimetric and photothermal aptasensor for detection of kanamycin using flocculent platinum nanoparticles

Chitosan (CS)-stabilized platinum nanoparticles (CS/PtNPs) were employed to develop a novel aptamer-based dual-mode colorimetric and photothermal biosensor for selective detection of kanamycin (KAN). As a peroxidase-like catalyst, the CS/PtNPs showed outstanding catalytic activity for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). As a stabilizing agent, CS excelled at fixing the KAN binding aptamer on the surface of the CS/PtNPs, amplifying their catalytic activity and enhancing colloidal dispersion and stability. The oxidized TMB (TMBox) functioned as a signal for the colorimetric, photothermal aptasensor because of its observable absorbance of light in the visible and near-infrared (NIR) regions. When light from a NIR laser was absorbed by the TMBox in the reaction solution, heat was generated in inverse proportion to the KAN concentration. The developed colorimetric and photothermal modes of the aptasensor showed a linear detection range of 0.1-50 and 0.5-50 μM, with a limit of detection (LOD) of 0.04 and 0.41 μM, respectively. Moreover, the aptasensor successfully determined KAN concentrations in spiked milk samples, verifying the reliability and reproducibility in practical applications. The dual-mode aptasensor based on CS/PtNPs for KAN detection, utilizing both color change and heat generation signals through a single probe (TMBox), demonstrates rapid response, simplicity in operation, cost-effectiveness, and high sensitivity. In addition, unlike typical immunoassays, this aptamer-based peroxidase-like nanozyme activation and inhibition strategy required no washing process, which was very effective in terms of reducing the time required for an assay and sustaining a high sensitivity.

MicroRNA Sensors Based on CRISPR/Cas12a Technologies: Evolution From Indirect to Direct Detection

MicroRNA (miRNA) has emerged as a promising biomarker for disease diagnosis and a potential therapeutic targets for drug development. The detection of miRNA can serve as a noninvasive tool in diseases diagnosis and predicting diseases prognosis. CRISPR/Cas12a system has great potential in nucleic acid detection due to its high sensitivity and specificity, which has been developed to be a versatile tool for nucleic acid-based detection of targets in various fields. However, conversion from RNA to DNA with or without amplification operation is necessary for miRNA detection based on CRISPR/Cas12a system, because dsDNA containing PAM sequence or ssDNA is traditionally considered as the activator of Cas12a. Until recently, direct detection of miRNA by CRISPR/Cas12a system has been reported. In this review, we provide an overview of the evolution of biosensors based on CRISPR/Cas12a for miRNA detection from indirect to direct, which would be beneficial to the development of CRISPR/Cas12a-based sensors with better performance for direct detection of miRNA.

Programmable DNA barcode-encoded exponential amplification reaction for the multiplex detection of miRNAs

Multiple analysis of miRNAs is essential for the early diagnosis and monitoring of diseases. Here, a programmable, multiplex, and sensitive approach was developed for one-pot detection of miRNAs by melting temperature encoded sequences and exponential isothermal amplification (E-EXPAR). In the presence of target miRNAs, the corresponding templates initiate the cycles of nicking and polymerization/displacement, generating numerous barcode strands with unique encoding sequences. Subsequently, generated barcode strands hybridize with fluorescent probes and quench the fluorophore by a triplet of G base through a photo-induced electron transfer mechanism. Finally, a melting curve analysis is performed to quantify miRNAs by calculating the rate of fluorescence change at the corresponding melting temperature. Based on this, miRNA-21, miRNA-9, and miRNA-122 were detected with the detection limits of 3.3 fM, 2.9 fM, and 1.7 fM, respectively. This E-EXPAR was also employed to simultaneously detect three miRNAs in biological samples, showing consistent results with RT-qPCR. Overall, this study provides a programmable and universal platform for multiplex analysis of miRNAs, and holds great promise as an alternative to the multiplex analysis in clinical diagnostics and prognostics for nucleic acid detection.

Exonuclease-catalyzed recycling and annular four-footed DNA walking amplification-assisted "on-off-super on" signal transitions for photoelectrochemical biosensing of kanamycin

Photoelectrochemical (PEC) biosensors have exhibited a promising potential for assays of a large variety of analytes; however, how to realize their low background-based "super on" signal output is still a great challenge. Herein, we report a novel multiple nucleic acid amplification-assisted "on-off-super on" signal transition mechanism for the PEC biosensing of kanamycin antibiotics. The biosensing platform was constructed on a perylene-3,4,9,10-tetracarboxylic dianhydride-based photoelectrode, and its strong photocurrent could be well inhibited by an anchored ferrocene (Fc)-labeled hairpin DNA to produce a low background signal. Two target biorecognition-triggered exonuclease III-catalytic reactions were adopted to produce an annular four-footed DNA walker (AFW) and a methylene blue (MB)-labeled DNA strand. By using their synergistic effect to release Fc quenchers and simultaneously capture MB sensitizers, a "super on" signal output was realized. As a result, a very wide linear range from 10 fg mL-1 to 10 ng mL-1 and an ultra-low detection limit of 7.8 fg mL-1 were obtained. Meanwhile, the aptamer recognition-based homogeneous reaction and AFW-based multiple nucleic acid amplification effectively simplified the assay manipulation and well ensured the repeatability of the method. The satisfactory sample experiment results indicated its good reliability and accuracy for the antibiotic residue analysis application.

Contactless photoelectrochemical biosensors based on hierarchical MXene/Bi2S3 nanosheets with the branched hybridization chain reaction

Ethyl carbamate, a substance frequently occurring in fermented foods, seriously affects people's health; however, poor sensitivity constrains the development of ethyl carbamate sensors. In this work, hierarchical Bi2S3/MXene nanosheets were synthesized using a hydrothermal method, and experimentally their coupled UV light is an efficient NH3 sensing material. Meanwhile, the density functional theory (DFT) confirms that the MXene/Bi2S3 nanosheet interface has an excellent ability to adsorb NH3, resulting in a change of photocurrent. As a proof-of-concept, a highly sensitive ethyl carbamate photoelectrochemical (PEC) biosensor was constructed based on the ammonia generation strategy of glutamate dehydrogenase coupled to the branched hybridization chain reaction (bHCR). Specifically, the target-triggered bHCR enriches a large number of enzyme-encapsulated liposomes, while the enzymatic NH3-generation reaction will cause a change in the Bi2S3/MXene photocurrent, which completes the target detection process. Under optimal conditions, the constructed PEC biosensors exhibited superior analytical performance toward ethyl carbamate in the range of 0.01 μg/mL to 1 μg/mL and limit of detection (LOD) down to 0.001 μg/mL. In addition, it offers an effective method for food safety monitoring due to its excellent stability, fast response, and maneuverability on real samples (red wine, yellow wine, and brandy).

Ultrasensitive fluorescence immunoassay of pepsinogen I based on enzyme-triggered decomposition of AuNCs/MnO2

Gastric cancer is a prevalent malignant tumor of the gastrointestinal tract accompanied by a high mortality rate; therefore, early gastric cancer screening is critical for improving patient survival. In this study, we present a facile fluorescence immunoassay for highly sensitive screening of pepsinogen I (PG I) based on a one-pot biomimetic mineralization process for the synthesis of gold nanocluster-anchored manganese dioxide (AuNCs/MnO2) nanosheets. MnO2 first quenches the fluorescence of AuNCs through the Förster resonance energy transfer effect, whereas the introduction of ascorbic acid (AA) leads to the decomposition of MnO2 and rapidly recovers the fluorescence of AuNCs. Based on the above principles and phenomena, we developed a sensitive fluorescence immunoassay for the in situ generation of AA to detect PG I. Specifically, in the presence of PG I, the sandwich-type immunoreactivity-enriched alkaline phosphatase-labeled secondary antibody catalyzes the production of AA from the substrate, which enhances the fluorescence intensity. Under optimized conditions, the fluorescence intensity increased linearly with the concentration of PG I (0.05 to 200 ng mL-1) with a limit of detection (LOD) of 0.013 ng mL-1 (S/N = 3). The designed sensing platform has good stability (more than one year) and excellent anti-interference capability and demonstrates satisfactory accuracy for detection in real samples compared to commercial ELISA kits.

Accelerated Hybridization Chain Reaction Kinetics Using Poly DNA Tetrahedrons and Its Application in Detection of Aflatoxin B1

Traditional hybridization chain reaction (HCR) as a popular isothermal amplification technique shows some inevitable disadvantages in bioanalysis due to its relatively slow kinetics, which could be markedly promoted when the HCR initiator occurs under tension. Herein, a poly DNA tetrahedrons (pTDNs)-mediated HCR was successfully constructed to make its initiator in a stretched state by long-range electrostatic forces owing to the superimposed electrostatic interactions derived from the synthesized pTDNs, and it was hypothesized that it could remarkably enhance HCR performance, which was testified by theoretical simulations and experimental studies. Consequently, pTDNs-mediated HCR was applied to develop a novel immunoassay for rapid and sensitive detection of aflatoxin B1 as a proof-of-concept, and its signal amplification was attributed to the increased G4 DNAzyme that loaded on the second antibody. Our work paves a promising way using simple DNA frameworks alone to heighten HCR kinetics for reaction speed improvement and signal amplification in bioanalysis.

Analytical Methodologies for the Estimation of Oxazolidinone Antibiotics as Key Members of anti-MRSA Arsenal: A Decade in Review

Gram-positive bacterial infections are among the most serious diseases related with high mortality rates and huge healthcare costs especially with the rise of antibiotic-resistant strains that limits treatment options. Thus, development of new antibiotics combating these multi-drug resistant bacteria is crucial. Oxazolidinone antibiotics are the only totally synthetic group of antibiotics that showed activity against multi-drug resistant Gram positive bacteria including MRSA because of their unique mechanism of action in targeting protein synthesis. This group include approved marketed members (tedizolid, linezolid and contezolid) or those under development (delpazlolid, radezolid and sutezolid). Due to the significant impact of this class, larger number of analytical methods were required to meet the needs of both clinical and industrial studies. Analyzing these drugs either alone or with other antimicrobial agents commonly used in ICU, in the presence of pharmaceutical or endogenous biological interferences, or in the presence of matrix impurities as metabolites and degradation products poses a big analytical challenge. This review highlights current analytical approaches published in the last decade (2012-2022) that dealt with the determination of these drugs in different matrices and discusses their advantages and disadvantages. Various techniques have been described for their determination including chromatographic, spectroscopic, capillary electrophoretic and electroanalytical methods. The review comprises six sections (one for each drug) with their related tables that depict critical figures of merit and some experimental conditions for the reviewed methods. Furthermore, future perspectives about the analytical methodologies that can be developed in the near future for determination of these drugs are suggested.

Photoelectrochemical biosensor for DNA demethylase detection based on enzymatically induced double-stranded DNA digestion by endonuclease-exonuclease system and Bi4O5Br2-Au/CdS photoactive material

A novel photoelectrochemical (PEC) biosensor for the detection of DNA demethylase MBD2 was developed based on Bi₄O₅Br₂-Au/CdS photosensitive material. Bi₄O₅Br₂ was firstly modified with gold nanoparticles (AuNPs), following with the modification onto the ITO electrode with CdS to realize the strong photocurrent response as a result of AuNPs had good conductibility and the matched energy between CdS and Bi₄O₅Br₂. In the presence of MBD2, double-stranded DNA (dsDNA) on the electrode surface was demethylated, which triggered the digestion activity of endonuclease HpaII to cleave dsDNA and induced the further cleavage of the dsDNA fragment by exonuclease III (Exo III), causing the release of biotin labeled dsDNA and inhibiting the immobilization of streptavidin (SA) onto the electrode surface. As a results, the photocurrent was increased greatly. However, in the absence of MBD2, HpaII digestion activity was inhibited by DNA methylation modification, which further caused the failure in the release of biotin, leading to the successful immobilization of SA onto the electrode to realize a low photocurrent. The sensor had a detection of 0.3-200 ng/mL and a detection limit was 0.09 ng/mL (3σ). The applicability of this PEC strategy was assessed by studying the effect of environmental pollutants on MBD2 activity.

A sensitive label-free biosensor based on Ag2S-sensitived Bi2WO6/BiOBr heterojunction for photoelectrochemical immunoassay of prostate specific antigen

Prostate cancer is one of the most common cancers in the world, and its early diagnosis can effectively reduce mortality. A new label-free photoelectrochemical (PEC) immunosensor on the basis of Bi₂WO₆/BiOBr nanocomposite materials has been successfully prepared for the test of prostate-specific antigen (PSA) in human serum in this work. The Ag₂S-sensitized Bi₂WO₆/BiOBr heterojunction was used as a photosensitive material, which effectively improved the photocurrent response. On Bi₂WO₆/BiOBr surface, dopamine immobilized PSA antibody by self-polymerizing to form polydopamine membrane. Antigen and antibody are specifically combined to achieve quantitative detection of PSA according to the current changes at different concentrations of antigen. Under the optimal experimental conditions, the PEC immunosensor has an ideal linear relationship between 1 pg/mL - 50 ng/mL, and the detection limit is 0.084 pg/mL. In addition, the prepared immunosensor has good stability, reproducibility and selectivity, providing a new method for the detection of PSA in actual sample analysis.

The development of a fluorescence/colorimetric biosensor based on the cleavage activity of CRISPR-Cas12a for the detection of non-nucleic acid targets

Nano-biosensors are of great significance for the analysis and detection of important biological targets. Surprisingly, the CRISPR-Cas12a system not only provides us with excellent gene editing capabilities, it also plays an important role in biosensing due to its high base resolution and high levels of sensitivity. However, most CRISPR-Cas12a-based sensors are limited by their recognition and output modes, are therefore only utilized for the detection of nucleic acids using fluorescence as an output signal. In the present study, we further explored the potential application of CRISPR-Cas12a and developed a CRISPR-Cas12a-based fluorescence/colorimetric biosensor (UCNPs-Cas12a/hydrogel-MOF-Cas12a) that provides an efficient targeting system for small molecules and protein targets. These two sensors yield multiple types of signal outputs by converting the target molecule into a deoxyribonucleic acid (DNA) signal input system using aptamers, amplifying the DNA signal by catalyzed hairpin assembly (CHA), and then combining CRISPR-Cas12a with various nanomaterials. UCNPs-Cas12a/hydrogel-MOF-Cas12a exhibited prominent sensitivity and stability for the detection of estradiol (E2) and prostate-specific antigen (PSA), and was successfully applied for the detection of these targets in milk and serum samples. A major advantage of the hydrogel-MOF-Cas12a system is that the signal output can be observed directly. When combined with aptamers and nanomaterials, CRISPR-Cas12a can be used to target multiple targets, with a diverse array of signal outputs. Our findings create a foundation for the development of CRISPR-Cas12a-based technologies for application in the fields of food safety, environmental monitoring, and clinical diagnosis.

Dual-sensitized heterojunction PDA/ZnO@MoS2 QDs combined with multilocus domino-like DNA cascade reaction for ultrasensitive photoelectrochemical biosensor

In this work, by integrating with a highly efficient multilocus domino-like cascade reaction on DNA nanonet, an ultrasensitive PEC biosensor based on dual-sensitized PDA/ZnO@MoS₂ QDs photoactive material as signal probe was proposed for detection of miRNA-182-5p. The dual-sensitized PDA/ZnO@MoS₂ QD composed by both of p-n and S-scheme heterojunctions on electrode generated an extremely high initial PEC signal, which however quenched by CdTe QDs decorated on DNA nanonet owing to the significant p-n quenching effect. Thereafter, the output DNA (RS) from DSN enzyme-assisted target recycling amplification triggered an ingenious multilocus domino-like DNA cascade reaction on DNA nanonet for releasing numerous CdTe QDs. Thanks to the multilocus domino-like mode that owned abundant binding sites for increasing trigger efficiency and drove cascade reaction automatically advance along four stated pathways, the target conversion rate could be improved effectively compared with that of traditional approaches, significantly enhancing the detection sensitivity. Consequently, the developed PEC biosensor exhibited a low detection limit to 0.17 fM, providing a new avenue for sensitive, fast and reliable sensing of various DNA/RNA.

Detection of Hepatitis C virus RNA using a novel hybridization chain reaction method that competitively dampens cascade amplification

The hybridization chain reaction (HCR) is widely used for biosensing. However, HCR does not provide the required sensitivity. In this study, we reported a method to improve the sensitivity of HCR by dampening the cascade amplification. First, we designed a biosensor based on HCR, and an initiator DNA was used to trigger the cascade amplification. Optimization of the reaction was then performed, and the results showed that the limit of detection (LOD) for the initiator DNA was about 2.5 nM. Second, we designed a series of inhibitory DNAs to dampen the HCR cascade amplification, and DNA dampeners (50 nM) were applied in the presence of the DNA initiator (50 nM). One of the DNA dampeners (D5) showed the best inhibitory efficiency of greater than 80%. This was further applied at concentrations ranging from 0 nM to 10 nM to prohibit the HCR amplification caused by a 2.5 nM initiator DNA (the limit of detection for this initiator DNA). The results showed that 0.156 nM of D5 could significantly inhibit the signal amplification (p<0.05). Additionally, the limit of detection for the dampener D5 was 16 times lower than that for the initiator DNA. Based on this detection method, we achieved a detection limit as low as 0.625 nM for HCV-RNAs. In summary, we developed a novel method with improved sensitivity to detect the target designed to prohibit the HCR cascade. Overall, this method could be used to qualitatively detect the presence of single-stranded DNA/RNA.

Snowflake-like CdS@ZnIn2S4 heterojunction-based photocatalyst-electrolyte effect: An innovative mode for photoelectrochemical immunoassay

Exploiting innovative strategies with signal amplification in photoelectrochemical (PEC) biosensing systems to realize sensitive screening of low-abundance proteins has become one of the mainstream research orientations. Herein we reported a new strategy to amplify photocurrent signal employing a photocatalyst-electrolyte effect in alkaline media for the sensitive monitoring of prostate-specific antigen (PSA) using snowflake-liked CdS@ZnIn2S4 heterojunction as photosensitizer. In this strategy, both the band-edge position and surface redox reaction process were subtly altered by modulating the alkalinity of electrolyte. The hydroxyl anions (OH-) from NaOH could be oxidized to hydroxyl radicals (·OH) by the holes in CdS@ZnIn2S4, thus accelerating the scavenging of holes and promoting the photocurrent. Based on the above-mentioned mechanism, a sensitive split-type glucose oxidase-mediated PEC immunosensor for PSA detection was fabricated. Upon target PSA introduction, the glucose acid was generated through the sandwich-type immunoreaction to affect the alkalinity of PEC detection environment, thereby suppressing the photocurrent intensity. The CdS@ZnIn2S4-based PEC immunosensor exhibited satisfactory photocurrent responses with a good linear range of 0.04-40 ng mL-1 at a limit of detection of 14 pg mL-1. Significantly, this research not only introduces an effective strategy to detect PSA with good sensitivity and specificity, but also provides a new insight to amplify the signal by regulating the electrolyte.

Sensitive fluorescent aptasensing of tobramycin on graphene oxide coupling strand displacement amplification and hybridization chain reaction

An ultrasensitive biosensor was designed and constructed for tobramycin detection. As a target recognition component, the DNA probe consists of an aptamer region for tobramycin binding and a template for amplification. In the absence of tobramycin, the probe was locked to form a stem-loop structure. In the presence of the target, the binding of tobramycin led to a conformational change in the probe. The released 3' end was used as a primer for the strand displacement amplification (SDA) to produce a large amount of single-stranded trigger DNA, which then efficiently initiated the following hybridization chain reaction (HCR) to produce a long duplex DNA with many fluorophores. The signals were detected after the addition of graphene oxide (GO) to quench the fluorescence from excess hairpin DNA. Through sequence and reaction condition optimization, the biosensor exhibited high selectivity for tobramycin. The linearity range and limit of detection (LOD) were 0.5-30 nM and 0.06 nM, respectively. Moreover, the application of detecting tobramycin in milk and lake water samples showed that this method is reliable and could be further used in food safety control and environmental monitoring.

Spectrophotometric Detection of the BRCA1 Gene via Exponential Isothermal Amplification and Hybridization Chain Reaction of Surface-Bound Probes

In this work, we demonstrated an ultrasensitive approach with a dual-amplification strategy for DNA assay based on isothermal exponential amplification (EXPAR) and the hybridization chain reaction (HCR). In the presence of target DNA, the hairpin probe DNA (HP1) recognized and partially hybridized with the target DNA to form double-stranded structures containing the full recognition sequences for nicking endonuclease and then initiated EXPAR. Under the reaction of EXPAR, a large number of single-stranded DNA (ssDNA) was produced in the circle of nicking, polymerization, and strand displacement. The resulting ssDNA can bind to the surface-bound probe on the well of the microplate and trigger the hybridization chain reaction, resulting in the production of numerous double-stranded DNA concatamers with biotin labeling. In the presence of streptavidin-conjugated horseradish peroxidase (HRP), the amplified signal can be detected by a spectrophotometer via HRP-catalyzed substrate 3,3'5,5'-tetramethylbenzidine (TMB). This proposed dual-amplification method provides a detection limit of 74.48 aM, which also exhibits good linearity ranging from 0.1 fM to 100 pM.

Perspectives and Trends in Advanced MXenes-Based Optical Biosensors for the Recognition of Food Contaminants

Fabricating novel biosensing constructs with high sensitivity and selectivity is highly demanded in food contaminants detection. In this prospect, various nanostructured materials were envisaged to build (bio)sensors with superior sensitivity and selectivity. The desirable biocompatibility, brilliant mechanical strength, ease of surface functionalization, as well as tunable optical and electronic features, portray 2D MXenes as versatile scaffolds for biosensing. In this review, we overviewed the state-of-the-art MXenes-based optical biosensing devices to detect mycotoxins, pesticide residues, antibiotic residues, and food borne-pathogens from foodstuff and environmental matrices. Firstly, the synthesis methods and surface functionalization/modification of MXenes are discussed. Secondly, according to the target analytes, we categorized and presented a detailed account of the newest research progress of MXenes-based optical probes for food contaminants monitoring. The efficiency of all the surveyed probes was assessed on the basis of important factors like response time, detection limit (DL), and sensing range. Lastly, the necessity and requirements for future advances in this emerging MXenes material are also given, followed by challenges and opportunities. We hope that this study will bridge the gap between nanotechnology and food science, offering insights for engineers or scientists in both areas to accelerate the progress of MXenes-based materials for food safety detection.

Cuprous oxide coated silver/graphitic carbon nitride/cadmium sulfide nanocomposite heterostructure: Specific recognition of carcinoembryonic antigen through sandwich-type mechanism

The development of the effective diagnostic method for the determination of cancer biomarkers is one of the most promising strategies for early clinical diagnosis of cancer. Here, based on the preparation of heterogeneous cuprous oxide coated silver (Ag@Cu₂O) nanocomposites/graphitic carbon nitride (g-C₃N₄)/cadmium sulfide (CdS) nanoarrays structure, a highly sensitive photoelectrochemical (PEC) biosensor for the examination of carcinoembryonic antigen (CEA) has been constructed successfully. The combination of photoactive semiconductor materials g-C₃N₄ and CdS increases the electron transfer rate between them and enhances their photocurrent response, thus greatly increasing the concentration detection range. At the same time, the specific recognition between antigen and antibody is used to form a sandwich structure secondary antibody (Ab₂)/CEA/antibody (Ab₁). And because Ag@Cu₂O has the function of absorbing light and consuming electron donor. Therefore, the successful measurement of CEA was achieved by labeling Ag@Cu₂O on Ab₂ and finally immobilizing it on the sensor to correlate the current reduction with the CEA concentration. The sandwich PEC biosensor proposed by this signal amplification strategy under optimal conditions has good analytical performance for CEA, with a wide linear detection range (from 10^-5 to 1 ng/mL) and a low detection limit of 0.0011 pg/mL. The PEC biosensor constructed by this method showed high sensitivity, excellent anti-interference ability, favourable repeatability, and good stability.

A highly sensitive homogeneous electrochemiluminescence biosensor for flap endonuclease 1 based on branched hybridization chain reaction amplification and ultrafiltration separation

A sensitive homogeneous electrochemiluminescence (ECL) biosensor for flap endonuclease 1 (FEN1) detection was developed by combining highly sensitive ECL detection, high efficiency of branched hybridization chain reaction (BHCR) amplification, a convenient homogeneous strategy, and simple ultrafiltration separation. Magnetic beads were first modified with well-designed double flap DNAs containing 5'-flaps. In the presence of FEN1, the 5'-flap can be cleaved, and a large amount of single-stranded DNA can be produced, which can be separated easily from the double-flap DNA-modified beads by a magnet. Then, the cleaved 5'-flap can be used to initiate BHCR amplification to produce a large amount of long-strand dsDNA. Ru(phen)₃²⁺ can insert dsDNA to form Ru-dsDNAs, which can be easily separated from the main solution through ultrafiltration. The ECL signal from the separated Ru-dsDNAs has a good linear relationship with the logarithm of the FEN1 concentration ranging from 6.5 × 10^-2 ∼ 6.5 × 10³ U/L with a detection limit of 2.2 × 10^-2 U/L. The proposed biosensor was used to evaluate FEN1 activity in real samples with satisfactory results.

A cascade amplification strategy for ultrasensitive Salmonella typhimurium detection based on DNA walker coupling with CRISPR-Cas12a

Salmonella typhimurium (S. typhimurium) infection is one of leading causes of severe foodborne illness, which poses grievous threats to public health. Thus, the detection with ultra-sensitivity is highly demanded for timely prevention and diagnosis of S. typhimurium. In this study, we developed a novel detection machinery based on DNA walker and CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)-Cas12a technologies. Mechanistically, the S. typhimurium specific sequence triggers Nt.AlwI nicking endonuclease and produces particular signaling nucleotide, which further activates Cas12a for strong fluorescence signal output. This cascade amplification strategy exhibits excellent specificity and successfully decreases the limit of detection (LOD) of DNA walker by 2,000 folds to 5 CFU/mL. Collectively, this combinatorial approach offers great promises to effectively reduce foodborne diseases by ultrasensitive detection of S. typhimurium. As a proof of concept, this innovative design also shows prominent potential in detections of other biomolecules, cells and pathogens.

Size-Controlled Engineering Photoelectrochemical Biosensor for Human Papillomavirus-16 Based on CRISPR-Cas12a-Induced Disassembly of Z-Scheme Heterojunctions

Photoelectrochemical (PEC) biosensors incorporating biomolecular recognition with photon-to-electron conversion capabilities of the photoactive species have been developed for molecular diagnosis, but most involve difficulty in adjusting band gap positions and are unsuitable for PEC biodetection. In this work, an innovative PEC biosensor combined with quantum size-controlled engineering based on quantum confinement by controlling the quantum size was designed for the detection of human papillomavirus-16 (HPV-16) through CRISPR-Cas12a (Cpf1)-induced disassembly of Z-scheme heterojunction. To the best of our knowledge, quantum size-controlled engineering that precisely tunes the properties of photoactive materials is first utilized in the PEC bioanalysis. Based on the quantum size effect, the light absorption efficiency and charge-transfer rate were tuned to suitable levels to obtain the best PEC performance. After incubation with target HPV-16, the binding of Cas12a-crRNA to the target double-stranded DNA (dsDNA) stimulated the activity of indiscriminate cleavage toward single-stranded DNA (ssDNA), resulting in a decrease in photocurrent due to the blocking of electron transfer through the heterojunction. By optimizing experimental conditions, the Z-scheme sensing system exhibited incredible photocurrent response to HPV-16 in the range from 3.0 pM to 600 nM with a detection limit of 1.0 pM. Impressively, the application of the quantum size effect could stimulate more interest in the precise design of band gap structure to improve PEC performance.

Development of label-free fluorescent biosensor for the detection of kanamycin based on aptamer capped metal-organic framework

The abuse of antibiotics has caused serious threat to human health, so it is of great significance to develop a simple and sensitive method for the detection of trace residues of antibiotics in the environment and food. Herein, a novel label-free fluorescent biosensing platform based on the fluorescence change of aptamers-capped zeolitic imidazolate framework-8 (ZIF-8) @ 2,2',2″,2‴-((ethene-1,1,2,2-tetrayltetrakis (benzene-4,1-diyl)) tetrakis (oxy)) tetraacetic acid (TPE) through ATP-assisted competitive coordination reaction was designed for such an end. ZIF-8@TPE/Aptamer (Apt) emits strong fluorescence at 425 nm in HEPES buffer due to the aggregation induced luminescence properties of TPE molecules in confined state. Once kanamycin was added, the conformation of aptamer capped on the surface of ZIF-8@TPE changes because of the specific recognition of kanamycin with aptamer, leading to the collapse of ZIF-8 and release of TPE, accompanied with a dramatic decrease of fluorescence intensity. Under the optimal conditions, a good correlation was obtained between the fluorescence intensity of ZIF-8@TPE/Apt and the concentration of kanamycin ranging from 10 to 10³ ng/mL with a detection limit of 7.3 ng/mL. The satisfactory analytical performance of the assay for kanamycin detection suggests good prospect for its application in food safety analysis.

Sensitivity of photoelctrocehmical aptasensor using spiral nanorods for detecting antiobiotic levels in experimental and real samples

Given increasing concern regarding antibiotic environmental contamination, there is immediate need to monitor antibiotic levels to effectively control pollution. In this study, we used a photoelectrochemical aptasensor based on TiO₂@MoS₂ spiral nanoarrays to detect chloramphenicol (CAP) in antibiotics. Nanoarrays were directly grown on fluorine-doped tin oxide (FTO) conductive glass with excellent biochemical stability, while aptamer-SH were immobilized by chemical binding on a synthetic TiO₂@MoS₂ nanoarray. Results show that the photocurrents were reduced in the presence of photoelectrochemistry associated with specific selection of aptamer for CAP. When the measurement of the fabricated nanomaterial chip was carried out using a three-electrode system, we found a highly specific and stable detection of chloramphenicol that ranged between 0.1 pM and 1 μM, with the detection limit of 0.1 pM. In addition, we obtained satisfactory results when real sample were used to validate the potential of photoelectrochemical (PEC) aptasensor for detecting chloramphenicol content in milk. Our results demonstrate that photoelectrochemical aptasensor is conducive to the development of less toxic multifunctional nanomaterials, making the biosensor more robust and environmentally friendly. Therefore, photoelectrochemical aptasensor can be widely applied in the field of environmental monitoring.

Ultrasensitive electrochemical aptasensor based on palindromic sequence mediated bidirectional SDA and a DNAzyme walker for kanamycin detection

An electrochemical biosensing platform for kanamycin analysis based on SDA and a DNA walker.

Optimizing the hybridization chain reaction-fluorescence in situ hybridization (HCR-FISH) protocol for detection of microbes in sediments

Fluorescence in situ hybridization (FISH) is a canonical tool commonly used in environmental microbiology research to visualize targeted cells. However, the problems of low signal intensity and false-positive signals impede its widespread application. Alternatively, the signal intensity can be amplified by incorporating Hybridization Chain Reaction (HCR) with FISH, while the specificity can be improved through protocol modification and proper counterstaining. Here we optimized the HCR-FISH protocol for studying microbes in environmental samples, particularly marine sediments. Firstly, five sets of HCR initiator/amplifier pairs were tested on the laboratory-cultured bacterium Escherichia coli and the archaeon Methanococcoides methylutens, and two sets displayed high hybridization efficiency and specificity. Secondly, we tried to find the best combination of sample pretreatment methods and HCR-FISH protocol for environmental sample analysis with the aim of producing less false positive signals. Various detachment methods, extraction methods and formulas of hybridization buffer were tested using sediment samples. Thirdly, an image processing method was developed to enhance the DAPI signal of microbial cells against that of abiotic particles, providing a reliable reference for FISH imaging. In summary, our optimized HCR-FISH protocol showed promise to serve as an addendum to traditional FISH for research on environmental microbes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-021-00098-8.

Applications of scaffold-based advanced materials in biomedical sensing

There have been many efforts to synthesize advanced materials that are capable of real-time specific recognition of a molecular target, and allow the quantification of a variety of biomolecules. Scaffold materials have a porous structure, with a high surface area and their intrinsic nanocavities can accommodate cells and macromolecules. The three-dimensional structure (3D) of scaffolds serves not only as a fibrous structure for cell adhesion and growth in tissue engineering, but can also provide the controlled release of drugs and other molecules for biomedical applications. There has been a limited number of reports on the use of scaffold materials in biomedical sensing applications. This review highlights the potential of scaffold materials in the improvement of sensing platforms and summarizes the progress in the application of novel scaffold-based materials as sensor, and discusses their advantages and limitations. Furthermore, the influence of the scaffold materials on the monitoring of infectious diseases such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and bacterial infections, was reviewed.

Ultrasensitive dual-quenching electrochemiluminescence immunosensor for prostate specific antigen detection based on graphitic carbon nitride quantum dots as an emitter

Early monitoring of prostate-specific antigen (PSA) is crucial in diagnosis and proactive treatment of prostate disease. Herein, a dual-quenching ternary ECL immunosensor was designed for PSA detection based on graphitic carbon nitride quantum dots (g-CNQDs, as an emitter), potassium persulfate (K2S2O8, as a coreactant), and silver nanoparticles doped multilayer Ti3C2 MXene hybrids (Ag@TCM, as a coreaction accelerator). First, Ag@TCM was immobilized on the surface of a glassy carbon electrode, then g-CNQDs was further adsorbed on Ag@TCM to acquire a higher initial ECL signal at a potential window from - 1.3 to 0.0 V (vs. Ag/AgCl). Ag@TCM not only acted as the coreaction accelerator, but also as a matrix to load enormous g-CNQDs and prostate-specific capture antibody via Ag-N bond. Meanwhile, prostate-specific detection antibody was marked by gold nanoparticles modified manganese dioxide as a dual-quenching probe (Ab2- Au@MnO2). When Ab2-Au@MnO2 was introduced into the ternary ECL system via sandwiched immuno-reaction, the high-sensitive detection of PSA was achieved by the dual-quenching effect, caused by the resonant energy transfer from g-CNQDs (energy donor) to Au@MnO2 (energy acceptor). As a result, this ECL immunosensor showed a good dynamic concentration range from 10 fg·mL-1 to 100 ng·mL-1 with a detection limit of 6.9 fg·mL-1 for PSA detection. The dual-quenching ECL strategy presented high stability and good specificity to open up a new pathway for ultrasensitive immunoassay.

Rapid and sensitive detection of Salmonella in milk based on hybridization chain reaction and graphene oxide fluorescence platform

Salmonella is a foodborne pathogen that has contributed to numerous food safety accidents worldwide, making it necessary to detect contamination at an early stage. A pair of specific primers based on the invA gene of Salmonella was designed for PCR. Target double-stranded DNA (dsDNA) from PCR was purified and denatured at high temperature to obtain target single-stranded DNA (ssDNA). Two carboxyfluorescein-labeled hairpin probes (H1-FAM and H2-FAM) were designed with complementary portions to the ssDNA sequence so that binding could trigger H1-FAM and H2-FAM hybridization chain reaction (HCR) to produce a long dsDNA complex. In this study, graphene oxide (GO) was used in the development of a homogeneous fluorescence detection platform for Salmonella. Using this HCR-GO assay platform, Salmonella detection was completed in 3.5 h. Salmonella was reliably and specifically detected with a limit of detection (LOD) of 4.2 × 10¹ cfu/mL in pure culture. Moreover, this new HCR-GO assay platform was successfully applied to the detection of Salmonella in artificially contaminated milk with a LOD of 4.2 × 10² cfu/mL.

Graphene-coated copper-doped ZnO quantum dots for sensitive photoelectrochemical bioanalysis of thrombin triggered by DNA nanoflowers

This work reports a photoelectrochemical (PEC) biosensing platform for the sensitive and specific screening of thrombin by using graphene oxide-coated copper-doped zinc oxide quantum dots (Cu_0.3Zn_0.7O-GO QDs) as the photoactive materials and glucose oxidase-encapsulated DNA nanoflowers (GOx-DFs) for signal amplification. Interestingly, the coated graphene oxide nanosheets on the surface of the Cu_0.3Zn_0.7O QDs could cause the charge to transfer rapidly and ameliorate the photocorrosion. The doped copper into the quantum dots could enhance the absorption of visible light by tuning the band gap of ZnO QDs, therefore increasing the photocurrent under visible irradiation. Upon addition of target thrombin, a sandwiched reaction was carried out between thrombin aptamer and GOx-DFs, accompanying the formation of nanocomposites with the magnetic microparticles (MMPs)/thrombin/GOx-DFs. Followed by magnetic separation, the carried GOx oxidized glucose to H₂O₂, thus resulting in the increasing photocurrent of the Cu_0.3Zn_0.7O-GO QD-modified electrode. Under optimum conditions, the developed PEC biosensing platform exhibited good analytical performance with a linear range of 50-10 000 fM thrombin and a limit of detection of 29 fM. Impressively, our strategy offers a new horizon in developing bridge-connected graphene-coated nanomaterials and novel signal amplification strategy for the development of PEC biosensors.

CRISPR/Cas12a-mediated liposome-amplified strategy for the photoelectrochemical detection of nucleic acid

This study reports a photoelectrochemical biosensor for dopamine-loaded liposome-encoded magnetic beads cleaved by clustered regularly interspaced short palindromic repeats (CRISPR)/Cas 12a system for the quantification of human papilloma virus (HPV)-related DNA using neodymium-doped BiOBr nanosheets (Nd-BiOBr) as a photoactive matrix. Magnetic beads and dopamine-loaded liposomes are covalently attached to the both ends of ssDNA to construct dumbbell-shaped dopamine-loaded liposome-encoded magnetic bead (DLL-MB) probes. When the guide RNA binds to the target HPV-16, the ssDNA will be cleaved by Cas12a, thereby degrading the double dumbbell probes. After magnetic separation, the dissolved DLLs are treated with Triton X-100 to release the dopamine (as an electron donor), which was then detected by an amplified photocurrent using the Nd-BiOBr-based photoelectrode.

Electrochemical micro-aptasensors for exosome detection based on hybridization chain reaction amplification

Exosomes are cell-derived nanovesicles that have recently gained popularity as potential biomarkers in liquid biopsies due to the large amounts of molecular cargo they carry, such as nucleic acids and proteins. However, most existing exosome-based analytical sensing methods struggle to achieve high sensitivity and high selectivity simultaneously. In this work, we present an electrochemical micro-aptasensor for the highly sensitive detection of exosomes by integrating a micropatterned electrochemical aptasensor and a hybridization chain reaction (HCR) signal amplification method. Specifically, exosomes are enriched on CD63 aptamer-functionalized electrodes and then recognized by HCR products with avidin-horseradish peroxidase (HRP) attached using EpCAM aptamers as bridges. Subsequently, the current signal that is generated through the enzyme reaction between the HRP enzyme and 3,3',5,5'-tetramethylbenzidine (TMB)/H2O2 directly correlates to the amount of bound HRP on the HCR products and thus to the number of target exosomes. By introducing anti-EpCAM aptamers, micro-aptasensors can detect cancerous exosomes with high specificity. Due to the micropatterned electrodes and HCR dual-amplification strategy, the micro-aptasensors achieve a linear detection response for a wide range of exosome concentrations from 2.5×103 to 1×107 exosomes/mL, with a detection limit of 5×102 exosomes/mL. Moreover, our method successfully detects lung cancer exosomes in serum samples of early-stage and late-stage lung cancer patients, showcasing the great potential for early cancer diagnosis.

Simultaneous Quantification of Ampicillin and Kanamycin in Water Samples Based on Lateral Flow Aptasensor Strip with an Internal Line

In this work, a simple and rapid method based on the lateral flow assay (LFA) has been developed for the detection of dual antibiotics. To achieve the quantitative assay and to reduce the non-specific adsorption, an internal system has been developed. A non-specific DNA was exploited as an internal standard and could be recognized by the DNA marker that was coated at the internal line. Two different kinds of aptamers were applied to recognize ampicillin (AMP) and kanamycin (KAM), and the distance between the detection line and conjugate pad was then optimized. Under the optimum conditions, the quantitative assays of AMP (R² = 0.984) and KAM (R² = 0.990) were achieved with dynamic ranges of 0.50 to 500.0 ng/L, and of 0.50 to 1000.0 ng/L, respectively. The LOQs of AMP and KAM were 0.06 ng/L and 0.015 ng/L, respectively. Finally, the proposed method has been successfully applied to analyze aquaculture water, tap water, and lake water, and hospital wastewater, indicating the established method could be used to monitor the environment.