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Here, a novel rapid and ultrasensitive aptamer biosensor was designed for target-induced activation of AIE effect and followed by the activation of Crispr Cas12a (LbCpf1)-mediated cleavage to achieve dual-signal detection. The prepared DNA building blocks contain the target aptamer, ssDNA-Fc, and Activator1. In this system, the activation mode was divided into two steps. First, when the target interacts with the aptamers, the DNA building blocks would be disintegrated rapidly, releasing a mass of Ac1, generating ETTC-dsDNA aggregated to produce a fluorescence signal by the AIE effect. Second, with the release of Ac2, LbCpf1-crRNA was activated, which greatly improves the ssDNA-Fc cleavage efficiency to render signal amplification and ultrasensitive detection of the target. Satisfactorily, using this approach to detect gliotoxin, optimal conditions for detection was achieved for reducing the detection time to 55 min, achieving a low detection limit of 2.4 fM and a satisfactory linear in the range of 50 fM to 1 nM, which addressed the shortcoming of a weak electrochemical signal in previous sensors. The water-insoluble AIE material was coupled with DNA to obtain water-soluble ETTC-dsDNA and successfully introduced into the sensor system, with a low detection limit of 5.6 fM. Subsequently, the biosensor combined with handheld electrochemical workstation was successfully applied in the detection of gliotoxin in five actual samples, with a detection range of 32.0 to 2.09 × 10 8 pM. This strategy not only provides a novel and effective detection platform for mycotoxins in complex food matrices but also opens a promising avenue for various molecules detection in imaging and disease diagnosis.

Patulin (PAT) is an unsaturated lactone mycotoxin primarily produced by Penicillium expansum and Aspergillus clavatus. Given the potential health risks and economic losses associated with PAT, the rapid detection of PAT using fluorescent aptasensors is of significant importance in evaluating food safety. However, it easily increases the cost and complexity caused by signal labeling. We combined TCPP/BDC-NH 2 mixed ligands functionalized Zr metal-organic frameworks (Zr-MOF mix ) and terminated three-stranded DNA gates (ttsDNA gates) to fabricate a label-free fluorescent aptasensor for PAT detection. The Zr-MOF mix system was synthesized via a one-pot strategy and could be used to address the problem of pore size limitation and increase the loading amounts of dyes. TtsDNA gate was integrated into the Zr-MOF mix system to control the release of dyes, exhibiting a high signal-to-background ratio. The single-stranded aptamer region in ttsDNA gate situated away from the surface of the Zr-MOF mix , resulting in a natural release of dyes in the absence of PAT. While binding to PAT resulted in target-induced conformational changes that helped form the hairpin structure of the aptamer. This structure hindered the release of dyes from the pores of Zr-MOF mix , thus reducing the fluorescence signals intensity. The stimuli-responsive DNA-gated material provides a platform for PAT analysis under conditions of a low limit of detection (0.871 pg/mL). Furthermore, the excellent specificity and anti-interference of the fluorescent aptasensor make the system suitable for the analysis of apple juice samples. This label-free strategy is cheaper and simper compared with labeled detection, especially for the development of multi-target-detection., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Ochratoxin A (OTA), a toxic secondary metabolite produced via various fungus, poses a serious threat to the health of human beings and animals. In this paper, an aptasensor for OTA detection based on gold nanoparticles decorated molybdenum oxide (AuNPs-MoO x ) nanocomposites, hybridization chain reaction (HCR) and a restriction endonuclease (Nb.BbvCI)-aided walker DNA machine was successfully constructed. In this electrochemical platform, the HCR was also used to embed more electrical signal molecules of methylene blue (MB) on silver nanoparticles (AgNPs) to achieve signal amplification. Under the optimum conditions, after adding OTA and Nb.BbvCI in turn and responding adequately under appropriate conditions, aptamer-DNA (6-DNA) carries the OTA away from the electrode surface, and walker DNA was hybridized autonomously with 5-DNA, releasing a large amount of 5'-DNA with the help of Nb.BBVCI. Finally, the electrochemical signal obtained by differential pulse voltammetry (DPV) was weakened. As an artificial and popular signal amplification technique, the DNA walking machine greatly improved the sensitivity. The proposed biosensor exhibited excellent analytical performance in the range of 0.01-10000 pg mL -1 with a detection limit as low as 3.3 fg mL -1 . Furthermore, direct comparison with ultraperformance liquid chromatography (UPLC) indicates excellent agreement to actual samples such as apple juice, orange juice, red wine and serum., (Copyright © 2021 Elsevier B.V. All rights reserved.)

In this article, we introduce an innovative and practically promising fiber-optic sensing platform (FOSP) that we proposed and demonstrated recently. This FOSP relies on a silicon Fabry-Perot interferometer (FPI) attached to the fiber end, referred to as Si-FOSP in this work. The Si-FOSP generates an interferogram determined by the optical path length (OPL) of the silicon cavity. Measurand alters the OPL and thus shifts the interferogram. Due to the unique optical and thermal properties of the silicon material, this Si-FOSP exhibits an advantageous performance in terms of sensitivity and speed. Furthermore, the mature silicon fabrication industry endows the Si-FOSP with excellent reproducibility and low cost toward practical applications. Depending on the specific applications, either a low-finesse or high-finesse version will be utilized, and two different data demodulation methods will be adopted accordingly. Detailed protocols for fabricating both versions of the Si-FOSP will be provided. Three representative applications and their according results will be shown. The first one is a prototype underwater thermometer for profiling the ocean thermoclines, the second one is a flow meter to measure flow speed in the ocean, and the last one is a bolometer used for monitoring exhaust radiation from magnetically confined high-temperature plasma.

Cardiac troponin I (cTnI) is a specific and sensitive biomarker for the early diagnosis of acute myocardial infarction and for the subsequent clinical treatments. In this work, novel electrochemical sensing platform for sensing of cTnI based on aptamer-MoS 2 nanoconjugates was proposed. For comparison, core-shell Au@SiO 2 @Au nanoparticles were also used for sensing of cTnI. The sensing schemes and electrochemical responses of the proposed sensors were investigated by electrochemical impedance spectroscopy (EIS) in 5.0 mM K 3 [Fe(CN) 6 ]/K 4 [Fe(CN) 6 ] (1:1) solution containing 0.1 M KCl, respectively. Results showed that the aptamer-Au@SiO 2 @Au based aptasensor shows a linear rage of 10 pM-10.0 μM with the detection limits of 1.23 pM For the aptamer-MoS 2 nanosheets based aptasensor, the linear range for cTnI detection was from 10 pM to 1.0 μM with a lower detection limit of 0.95 pM Meanwhile, both the sensors were successfully applied for detection of cTnI in human blood samples. The two kinds of aptsensors have been successfully used for detecting of cTnI in human blood serums. Moreover, no negligible signal changes could be observed in the presence of non-targets of CK-MB and Myo, suggesting the good potential for clinic diagnosis., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Nanopore-based devices have recently become popular tools to detect biomolecules at the single-molecule level. Unlike the long-chain nucleic acids, protein molecules are still quite challenging to detect, since the protein molecules are much smaller in size and usually travel too fast through the nanopore with poor signal-to-noise ratio of the induced transport signals. In this work, we demonstrate a new type of nanopore device based on atomic layer deposition (ALD) Al2O3 modified track-etched conical nanochannels for protein sensing. These devices show very promising properties of high protein (bovine serum albumin) capture rate with well time-resolved transport signals and excellent signal-to-noise ratio for the transport events. Also, a special mechanism involving transient process of ion redistribution inside the nanochannel is proposed to explain the unusual biphasic waveshapes of the current change induced by the protein transport.

An ultrasensitive cytosensor based on DNA-rolling-circle-amplification-directed enzyme-catalyzed polymerization is demonstrated. As a proof of concept, the cytosensor shows excellent sensitivity for MCF-7 cell detection with a lower detection limit of 12 cells per mL.

The direct electrochemistry of hemoglobin (Hb) immobilized by a fullerene-nitrogen doped carbon nanotubes and chitosan (C60-NCNTs/CHIT) composite matrix is demonstrated. The cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the modified electrode. In the deaerated buffer solution, the cyclic voltammogram of the Hb/C60-NCNTs/CHIT composite film modified electrode showed a pair of well-behaved redox peaks with the E°'=-0.335 (± 0.3) V (vs. SCE). The redox peaks are assigned to the redox reaction of Hb(Fe(III)/Fe(II)) and confirm the effective immobilization of Hb on the composite film. The large value of ks = 1.8 (± 0.2)s(-1) suggests that the immobilized Hb achieved a relative fast electron transfer process. The fast electron transfer interaction between protein and electrode surface suggested that the C60-NCNTs/CHIT composite film may mimic some physiological process and further elucidate the relationship between protein structures and biological functions. Moreover, the resulting electrode exhibited excellent electrocatalytic ability towards the reduction of hydrogen peroxide (H2O2) with the linear dynamic range of 2.0-225.0 μM. The linear regression equation was Ip/μA=7.35 (± 0.08)+0.438 (± 0.007)C/μM with the correlation coefficient of 0.9993. The detection limit was estimated at about 1 μM (S/N=3). The sensitivity was 438.0 (± 2.5) μA mM(-1). It is expected that the method presented here can not only be easily extended to other redox enzymes or proteins, but also be used as an electrochemical sensing devices for the determination of H2O2 in cell extracts or urine., (Copyright © 2013 Elsevier B.V. All rights reserved.)

We report on the direct electrochemistry of myoglobin (Mb) immobilized on a composite matrix based on chitosan (CHIT) and titanium carbide nanoparticles (TiC NPs) underlying on glassy carbon electrode (GCE). The cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the modified electrode. In deaerated buffer solutions, the cyclic voltammetry of the composite films of Mb-TiC NPs-CHIT showed a pair of well-behaved redox peaks that are assigned to the redox reaction of Mb, confirming the effective immobilization of Mb on the composite film. The electron transfer rate constant was estimated to be 3.8 (±0.2)·s(-1), suggested that the interaction between the protein and certain electrode surfaces may mimic some physiological situations and may elucidate the relationship between the protein structures and biological functions. The linear dynamic range for the detection of hydrogen peroxide was 0.5-50 μM with a correlation coefficient of 0.999 and the detection limit was estimated at about 0.2 μM (S/N=3). The calculated apparent Michaelis-Menten constant was 0.07 (±0.01) mM, which suggested a high affinity of the redox protein-substrate. The immobilized Mb in the TiC NPs-CHIT composite film retained its bioactivity. Furthermore, the method presented here can be easily extended to immobilize and obtain the direct electrochemistry of other redox enzymes or proteins., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Unique monkshoodvine root-bark like morphology carbon materials (MLC) have been successfully synthesized under hydrothermal conditions. Utilizing the merits of high surface area and good electron conductivity of the MLC, a layered biosensor designed by assembling the MLC, hemoglobin (Hb) and gold nanoparticles was further developed. Scanning electron microscope and transmission electron microscope showed that the morphology of carbon materials can be successfully controlled simply by moderating the initiator amount of precursor and reaction temperature. The results indicated that the MLC was formed at the reaction condition of 5 mg Ferrocene + 6 mL CCl(4) at 280 °C. Electrochemical methods, such as cyclic voltammetry and electrochemical impedance spectroscopy, were used to characterize the layered biosensor and its application for sensitive detection of hydrogen peroxide (H(2)O(2)). Under optimized experimental condition, the linear range for the determination of H(2)O(2) was 0.06 μM to 1.6 mM with a detection limit of 0.03 μM (S/N = 3). Furthermore, the biosensor also showed a fast response (within 2 s) and high stability.

Thermally two-dimensional lattice graphene (GR) and biocompatibility chitosan (CS) act as a suitable support for the deposition of palladium nanoparticles (PdNPs). A novel hydrogen peroxide (H(2)O(2)) biosensor based on immobilization of hemoglobin (Hb) in thin film of CS containing GR and PdNPs was developed. The surface morphologies of a set of representative membranes were characterized by means of scanning electron microscopy and showed that the PdNPs are of a sphere shape and an average diameter of 50 nm. Under the optimal conditions, the immobilized Hb showed fast and excellent electrocatalytic activity to H(2)O(2) with a small Michaelis-Menten constant of 16 μmol L(-1), a linear range from 2.0 × 10(-6) to 1.1 × 10(-3) mol L(-1), and a detection limit of 6.6 × 10(-7) mol L(-1). The biosensor also exhibited other advantages, good reproducibility, and long-term stability, and PdNPs/GR-CS nanocomposites film would be a promising material in the preparation of third generation biosensor.

Thulium hexacyanoferrate (TmHCF) nanoparticles (NPs) were in situ synthesized within the chitosan film on the electrode surface by a biocatalyzed reaction. The properties of the obtained nanoparticles are characterized with scanning electron microscope (SEM) and energy-dispersive X-ray (EDX). The optimized conditions for the formation of TmHCF NPs were 16 mM Fe(CN)(6)(3-) and 1.5 mM Tm(3+) with an accumulation time of 20 min. Based on process of in situ synthesis of TmHCF NPs, a novel biosensor for glucose was designed, and there is a linear relationship between the current response of TmHCF NPs and glucose concentration. The linear range for glucose detection was 0.02-0.4 mM (r=0.9975, n=5) and 0.4-13.6 mM (r=0.9935, n=10) and the detection limit was 6 μM at a signal-to-noise ratio of 3., (Copyright © 2011 Elsevier B.V. All rights reserved.)

A novel H(2)O(2) sensor based on enzymatically induced deposition of electroactive polyaniline (PANI) at a horseradish peroxide (HRP)/aligned single-wall carbon nanotubes (SWCNTs) modified Au electrode is fabricated, and its electrochemical behaviors are investigated. Electrochemical impedance spectroscopy of the sensor confirmed the formation of PANI on SWCNTs through the HRP catalytic reaction. Cyclic voltammograms of PANI/HRP/SWCNTs modified Au electrodes showed a pair of well-defined redox peaks of PANI with reduction peak potentials of 0.211 and oxidation peak potentials of 0.293 V in 0.1 M HOAc-NaOAc (pH 4.3) solution. The oxidation peak current response of PANI is linearly related to H(2)O(2) concentration from 2.5 μM to 50.0 μM with a correlation coefficient of 0.9923 and a sensitivity of 200 μA mM(-1). The detection limit is determined to be 0.9 μM with a signal-to-noise ratio of 3. Thus, the synergistic performance of the enzyme, the highly efficient polymerization of PANI, and the templated deposition of SWCNTs provided an extensive platform for the design of novel electrochemical biosensors.

This paper reported the enzymatic deposition of Au nanoparticles (AuNPs) on the designed 3-mercapto-propionic acid/glucose oxidase/chitosan (MPA/GOD/Chit) modified glassy carbon electrode and its application in glucose detection. Chit served as GOD immobilization matrix and interacted with MPA through electrostatic attraction. AuNPs, without nano-seeds presented on the electrode surface, was produced through the glucose oxidase catalyzed oxidation of glucose. The mechanism of production of AuNPs was confirmed to be that enzymatic reaction products H(2)O(2) in the solution reduce gold complex to AuNPs. The characterizations of the electrode modified after each assembly step was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. Scanning electron microscopy showed the average particle size of the AuNPs is 40nm with a narrow particle size distribution. The content of AuNPs on the electrode surfaces was measured by differential pulse stripping voltammetry. The electrochemical signals on voltammogram showed a linear increase with the glucose concentration in the range of 0.010-0.12mM with a detection limit of 4μM. This provided a method to the determination of glucose., (Copyright © 2010 Elsevier B.V. All rights reserved.)

A novel electrochemical aptasensor for the detection of thrombin was developed on basis of the thrombin-binding aptamer (TBA) as a molecular recognition element and multi-walled carbon nanotubes (MWCNTs) as a carrier of the electrochemical capture probe. Amine-modified capture probe (12-mer) was covalently conjugated to the MWCNTs modified glassy carbon electrode (GCE). The target aptamer probe (21-mer) contains TBA (15-mer) labeled with ferrocene (Fc), which is designed to hybridize with capture probe and specifically recognize thrombin, is immobilized on the electrode surface by hybridization reaction. Introduction of the analyte thrombin triggered the dissociation of the aptamer probe labeled with Fc from the biosensors, led to a significant decrease in peak current intensity. Differential pulse voltammetry (DPV) was employed to detect the target analyte with different concentrations. The decreased peak current was in proportion to the concentration of thrombin in a range from 1.0x10(-12) to 5.0x10(-10)M with a detection limit of 5x10(-13)M. The present work demonstrates that using MWCNTs as a carrier for electrochemical capture probe is a promising way to amplify the electrochemical signal and to improve the sensitivity of the electrochemical aptasensor.

An ultrasensitive assay for electrical biosensing of syphilis DNA was proposed by using target-guided formation of polyaniline (PANI) based on an enzymatically catalyzed method. The sensitive biodetection relies on the DNA hybridization and biotin-streptavidin interaction. After coupling of biotinylated catalase with streptavidin-modified hybrids, a head-to-tail structure of PANI templated by hybridized DNA was formed. The current response of PANI was linearly related to target DNA concentration between 1.0 pM and 1.0 nM with a correlation coefficient of 0.998. The detection limit was determined to be 0.5 pM with the signal-to-noise ratio of 3. The synergistic performances of DNA hybridization, strong biotin-streptavidin binding ability, and highly efficient polymerization provide a general platform for simple, highly sensitive and selective biosensor for the detection of the specific polA gene fragment of T. pallidum. It is expected that the proposed biosensor holds great promise for diagnosing disease in practice., (2010 Elsevier B.V. All rights reserved.)

A novel method based on covalent attachment of two enzymes, glucose oxidase (GOD) and horseradish peroxide (HRP), onto carboxylic-derived multiwalled carbon nanotubes (MWNTs) for the deposition of electroactive polyaniline (PANI) under ambient conditions is described. Ultraviolet-visible spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and transmission electron microscopy were used to characterize the assembling of bienzyme and the morphology of PANI|MWNTs. Under the bienzyme biocatalytic condition, a head-to-tail structure of PANI templated by MWNTs was formed. The voltammetric characteristics of the resulting biosensor were investigated by cyclic voltammetry in the presence of glucose. The current response of PANI was linearly related to glucose concentration between 0.05 and 12.0mM with a correlation coefficient of 0.994. The synergistic performance of bienzyme, highly efficient polymerization, and templated deposition provide a general platform for the synthesis of nanowires and nanocircuits, the construction of bioelectronic devices, and the design of novel biosensors.

The direct electrochemistry of glucose oxidase (GOx) immobilized on a composite matrix based on chitosan (CHIT) and NdPO(4) nanoparticles (NPs) underlying on glassy carbon electrode (GCE) was achieved. The cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the modified electrode. In deaerated buffer solutions, the cyclic voltammetry of the composite films of GOx/NdPO(4) NPs/CHIT showed a pair of well-behaved redox peaks that are assigned to the redox reaction of GOx, confirming the effective immobilization of GOx on the composite film. The electron transfer rate constant was estimated to be 5.0 s(-1). The linear dynamic range for the detection of glucose was 0.15-10 mM with a correlation coefficient of 0.999 and the detection limit was estimated at about 0.08 mM (S/N=3). The calculated apparent Michaelis-Menten constant was 2.5 mM, which suggested a high affinity of the enzyme-substrate. The immobilized GOx in the NdPO(4) NPs/CHIT composite film retained its bioactivity. Furthermore, the method presented here can be easily extended to immobilize and obtain the direct electrochemistry of other redox enzymes or proteins.

The formation of neodymium hexacyanoferrate (NdHCF) nanoparticles (NPs) on the surface of glucose oxidase/chitosan (GOx/CHIT) modified glass carbon electrode induced by enzymatic reaction was described and characterized. CHIT can be used not only as enzyme immobilizer, but also to provide active sites for NPs growth. Results showed that the optimized conditions of the GOx/CHIT film induced NdHCF NPs for the biosensing of glucose were 1.0mM Nd(3+) and 20.0mM Fe(CN)(6)(3-). The biocatalyzed generation of NdHCF NPs enabled the development of an electrochemical biosensor for glucose. The calculated apparent Michaelis-Menten constant was 7.5mM. The linear range for glucose detection was 0.01-10.0mM with the correlation coefficient of 0.9946, and the detection limit was 5 microM (S/N=3). Furthermore, this system avoids the interferences of other species during the biosensing process and can be used for the determination of glucose in human plasma samples.

A glucose biosensor based on polyvinylpyrrolidone (PVP) protected Prussian blue nanoparticles (PBNPs)-polyaniline/multi-walled carbon nanotubes hybrid composites was fabricated by electrochemical method. A novel route for PBNPs preparation was applied in the fabrication with the help of PVP, and from scanning electron microscope images, Prussian blue particles on the electrode were found nanoscaled. The biosensor exhibits fast current response (<6 s) and a linearity in the range from 6.7x10(-6) to 1.9x10(-3) M with a high sensitivity of 6.28 microA mM(-1) and a detection limit of 6x10(-7) M (S/N=3) for the detection of glucose. The apparent activation energy of enzyme-catalyzed reaction and the apparent Michaelis-Menten constant are 23.9 kJ mol(-1) and 1.9 mM respectively, which suggests a high affinity of the enzyme-substrate. This easy and controllable construction method of glucose biosensor combines the characteristics of the components of the hybrid composites, which favors the fast and sensitive detection of glucose with improved analytical capabilities. In addition, the biosensor was examined in human serum samples for glucose determination with a recovery between 95.0 and 104.5%.