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Modern optical detection technology plays a critical role in current clinical detection due to its high sensitivity and accuracy. However, higher requirements such as extremely high detection sensitivity have been put forward due to the clinical needs for the early finding and diagnosing of malignant tumors which are significant for tumor therapy. The technology of isothermal amplification with nucleic acids opens up avenues for meeting this requirement. Recent reports have shown that a nucleic acid amplification-assisted modern optical sensing interface has achieved satisfactory sensitivity and accuracy, high speed and specificity. Compared with isothermal amplification technology designed to work completely in a solution system, solid biosensing interfaces demonstrated better performances in stability and sensitivity due to their ease of separation from the reaction mixture and the better signal transduction on these optical nano-biosensing interfaces. Also the flexibility and designability during the construction of these nano-biosensing interfaces provided a promising research topic for the ultrasensitive detection of cancer diseases. In this review, we describe the construction of the burgeoning number of optical nano-biosensing interfaces assisted by a nucleic acid amplification strategy, and provide insightful views on: (1) approaches to the smart fabrication of an optical nano-biosensing interface, (2) biosensing mechanisms via the nucleic acid amplification method, (3) the newest strategies and future perspectives. [ABSTRACT FROM AUTHOR]

A dual target-recycling amplification strategy for sensitive detection of microRNAs based on duplex-specific nuclease and catalytic hairpin assembly was reported for the first time. [ABSTRACT FROM AUTHOR]

The development of sensitive and selective small molecular probes that enable real-time detection of endogenous cysteine (Cys) has become an attractive topic because of the essential roles played by Cys in controlling the cellular nitrogen balance and in maintaining biological redox homeostasis. Herein, we report a Cys-specific probe, 2-cyanobenzothiazol-6-yl acrylate (CBTOA), that shows not only fluorescence turn-on for sensitive detection of endogenous Cys but also enhanced probe retention inside cells for real-time monitoring of Cys levels upon external stimulation. Cys-mediated intracellular formation of luciferin from CBTOA was the key strategy leading to this new type of fluorogenic probe. CBTOA showed fast response to Cys in living cells and liver tissue slices with high sensitivity and selectivity. By using CBTOA as a real-time probe, we were able to monitor the change in Cys levels in living HeLa cells under ROS-induced oxidative stress as well as in human mesenchymal stem cells during adipogenic differentiation. [ABSTRACT FROM AUTHOR]

Based on the assay of DNA binding proteins upon visible light irradiation, a photoelectrochemical sensor was constructed for successfully probing a DNA–protein interaction for the first time. [ABSTRACT FROM AUTHOR]

The evolution of photoelectrochemical (PEC) bioanalysis has resulted in substantial progress in its analytical performance and biodetection applications. The aim of this review is to provide a panoramic snapshot of the state of the art in this dynamically developing field, with special emphasis on PEC DNA analysis, immunoassay, enzymatic biosensing and cell-related detection. The future prospects in this area are also evaluated and discussed. This work will serve as a useful source to inform the interested audience of the latest developments and applications in the field of PEC bioanalysis. [ABSTRACT FROM AUTHOR]

There has been great interest in developing new nucleic acid and protein detection methods for both clinical and numerous non-clinical applications. In a long-lasting effort to improve the detection ability of bioassays, functional nanomaterials have been actively explored to greatly enhance the sensitivity during the last two decades. This tutorial reviewfocuses on recent progress in biosensor development by exploiting several unique optical, electronic and catalytic properties of a range of nanomaterials, such as gold nanoparticles, quantum dots, silicon nanowires, carbon nanotubes and graphene. In addition, a perspective on new opportunities offered by emerging technologies (e.g.DNA nanotechnology) is provided. [ABSTRACT FROM AUTHOR]

We have developed a novel nitric oxide (NO) cellular biosensor based upon the immobilization of red blood cells (RBCs) onto nanometer‐size colloidal gold that is attached to an electrochemically pretreated glassy carbon electrode via the bridging of an ethylenediamine monolayer. The biosensor has been characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and electrochemistry. The immobilized RBCs display an excellent electrocatalytic response to nitric oxide. The electrocatalytic currents are proportional to the NO concentration in the range from 1.0×10–8 to 1.0×10–6 M and the detection limit is as low as 5.0×10–9 M (S/N=3). Furthermore, the biosensor is very stable and relatively free of potential interference. [ABSTRACT FROM AUTHOR]

A novel reagentless NO biosensor based on hemoglobin (Hb) immobilized on nanometer-sized gold colloid particles associated with a cysteamine monolayer on gold electrode surface was presented. The experimental optimization was studied in detail. The immobilized Hb displayed an excellent electrocatalytic response to NO. The electrocatalytic currents were proportional to the NO concentration from 1.2 × 10[sup -8] to 5.0 × 10[sup -6] M and the detection limit was as low as 4.0 × 10[sup -9] M (S/N = 3) with good stability. Arginine, ascorbate, nitrite, uric acid, epinephrine and cystine didn't interfere with the determination of NO. The Michaelis-Menten constant (K[sub m]) was determined to be 0.19 mM. This resulting biosensor has been applied to the direct determination of trace NO in raw blood. [ABSTRACT FROM AUTHOR]

A dual-functional electrochemical biosensor for adenosines and hydrogen peroxide from cancer cells was developed based on a traditional switchable electrochemical sensing format and ATP improved G-quadruplex DNAzyme as a biolabel. [ABSTRACT FROM AUTHOR]

Based on the K-doped graphene–CdS:Eu NC composites and the nicking endonuclease (NEase) assisted strand-scission cycle, we have developed an ultrasensitive and selective electrochemiluminescence (ECL) DNA biosensor using the G-quadruplex–hemin-based DNAzyme which acts as an electrocatalyst for the reduction of H2O2, the coreactant of CdS:Eu NCs ECL. [ABSTRACT FROM AUTHOR]

A reusable potassium ion biosensor was reported for the first time based on the reversible DNA structural change and the interaction between surface plasmons of Au nanoparticles (NPs) and the ECL emission of CdS nanocrystals (NCs). [ABSTRACT FROM AUTHOR]

This work is the first report on the energy transfer between CdS quantum dots and Au nanoparticles for photoelectrochemical biosensing applications. [ABSTRACT FROM AUTHOR]

Transconductance (gm) is one important figure of merit for benchmarking organic electrochemical transistor (OECT) biosensors, which nevertheless experiences undesired fluctuation instead of keep constant during the target detection of varied concentrations. Light‐matter interplay is recently shown as a potential way to regulate the OECT characteristics, e.g. maximum gm at zero gate bias is achieved. In this work, the challenge of unstable gm is addressed by using a unique metal‐organic framework (MOF)‐derived hollow tube indium sulfide (m‐In2S3) as the photogate. Interestingly, the light irradiation on m‐In2S3 generate a straight transfer curve, leading to a stable gm that is desirable for biological application. Exemplifying by an aptasening, such a device is then tested for protein quantification with a stable sensitivity during the detection. This work features the feasibility of light‐matter interplay to achieve a stable gm in organic electronics. [ABSTRACT FROM AUTHOR]

Enzymatic biosensors have been valuable bioanalytical devices for analysis of diverse targets in disease diagnosis, biological and biomedical research, etc. Photoelectrochemical (PEC) bioanalysis is a recently emerged method that promptly becoming a subject of new research interests due to its attractive potential for future bioanalysis with high sensitivity and specificity. PEC enzymatic biosensors integrate the inherent sensitivities of PEC bioanalysis and the selectivity of enzymes and thus share their both advantages. Currently, PEC enzymatic biosensors have become a hot topic of significant research and the recent impetus has grown rapidly as demonstrated by increased research papers. Given the pace of advances in this area, this review will make a thorough discussion and survey on the fundamentals, sensing strategies, applications and the state of the art in PEC enzymatic biosensors, followed by future prospects based on our own opinions. We hope this work could provide an accessible introduction to PEC enzymatic biosensors for any scientist. [ABSTRACT FROM AUTHOR]

Abstract: A novel photoelectrochemical immunosensor based on TiO2/CdS hybrid modified electrode was developed. The TiO2/CdS hybrid modified electrode was obtained by alternately dipping the TiO2 modified indium–tin oxide (ITO) electrode into the [Cd(NH3)4]2+ and S2− solution repeatedly. Compared with the routine method using Cd2+ solution for CdS deposition, the as obtained TiO2/CdS electrode showed enhanced photocurrent intensity with fewer coating times. After the ITO/TiO2/CdS electrode was coated with chitosan (CS), α-fetoprotein (AFP) antibodies were covalently conjugated on the surface of the electrode. Thus, a label-free photoelectrochemical immunosensor for the detection of AFP was developed by monitoring the changes in the photocurrent signals of the electrode resulting from the immunoreaction. The immunosensor displayed a linear response to AFP in the ranges from 50pg/mL to 50ng/mL with a relatively low detection limit of 40pg/ml. The photoelectrochemical results for the detection of AFP in five human sera showed acceptable accuracy. The method is simple, sensitive and specific. Moreover, the studied immunosensor possessed acceptable reproducibility and storage stability. The proposed methodology was potentially attractive for clinical immunoassay. [Copyright &y& Elsevier]

Abstract: A simple one-step biomimetic coprecipitation method is reported to prepare a protein based biosensor by immobilizing calcium phosphate/hemoglobin composite nanoparticles directly onto glassy carbon electrode surface. Atomic force microscopy (AFM), attenuated total reflection spectra (ATR) and electrochemical method were used to characterize the as-prepared composite nanoparticles. Hb in the composite film kept their biological activity well, realized its direct electrochemistry with the formal potential of −0.363V in pH 7.0 phosphate buffer solution and gave excellent electrocatalytic performance to the reduction of hydrogen peroxide, by which the mediator-free biosensors could be fabricated. Compared to other immobilization methods, this system not only avoids the tedious synthesis of nanoparticles and the use of reagent detrimental to biomolecules but also possesses the advantages of simple preparation and low cost. [Copyright &y& Elsevier]

Abstract: Here we reported a novel microfluidic biosensor with an on-column immobilized enzyme microreactor. The fabrication approach of this biosensor is simple and the enzyme microreactors with controlled sizes can be placed at any desired position on the microchip. Taking glucose oxidase (GOx) as an example, electroosmotic flow (EOF) as a driving force and amperometry as a detection method, the performance of biosensors were modulated by changing the length of enzyme reactor from 0.5cm to 3cm, and the linear ranges were changed from 0–8.0mM to 0–30.0mM with the detection limits from 42μM to 6.5μM. The enzyme reactor remained its 65% activity after 23 days storage. It also showed good anti-interference ability and was used to quantify glucose in human serum samples. [Copyright &y& Elsevier]

Abstract: We report on the formation of colloidal biocomposites resulting from the electrostatic self-assembly of negatively charged lactate oxidase (LOD) and oppositely charged nanoscaled cobalt phthalocyanine (NanoCoPc) colloid under enzyme-friendly conditions. The biocomposites were further used to fabricate lactate biosensors due to their excellent film-forming ability and strong adsorbability on the surface of glassy carbon electrode. The electrochemical assays of such films revealed a large capacity of NanoCoPc for the retention of LOD. Here, NanoCoPc colloid was not only used as carriers for immobilization of LOD, but also displayed intrinsic electrocatalytic activity for the oxidation of H2O2, a product of enzymatic reaction. A chitosan film containing MnO2 nanoparticles was further electrodeposited as an external layer, which could effectively eliminate the interference from ascorbic acid. Under optimal conditions, the biosensor showed a wide linear response to lactate in the range of 0.020–4.0mM, with high sensitivity (3.98μAcm−2 mM−1), as well as good reproducibility and long-term stability. The biosensor has been used for the determination of lactate in real samples with an acceptable accuracy. [Copyright &y& Elsevier]

We report on the utilization of a novel nanoscaled cobalt phthalocyanine (NanoCoPc)–glucose oxidase (GOD) biocomposite colloid to create a highly responsive glucose biosensor. The biocomposite colloid is constructed under enzyme-friendly conditions by adsorbing GOD molecules on CoPc nanoparticles via electrostatic interactions. The glucose biosensor can be easily achieved by casting the biocomposite colloid on a pyrolytic graphite electrode (PGE) without any auxiliary matter. It has been found that GOD can be firmly immobilized on PGE surface and maintain its bioactivity after conjugating with NanoCoPc. NanoCoPc displays intrinsic electrocatalytic ability to the oxidation of the product of enzymatic reaction H2O2 and shows a higher catalytic activity than that of bulk CoPc. Under optimal conditions, the biosensor shows a wide linear response to glucose in the range of 0.02–18 mM, with a fast response (5 s), high sensitivity (7.71 μA cm-2 mM-1), as well as good thermostability and long-term life. The detection limit was 5 μM at 3σ. The general interferences coexisted in blood except ascorbic acid and l-cysteine do not affect glucose determination, and further coating Nafion film on the surface of the biosensor can effectively eliminate the interference from ascorbic acid and l-cysteine. The biosensor with Nafion film has been used for the determination of glucose in serum with an acceptable accuracy. [Copyright &y& Elsevier]

A new type of sol–gel/organic hybrid composite material based on the cross-linking of natural polymer chitosan with (3-aoryloxypropyl) dimethoxymethylsilane was developed for the fabrication of an amperometric H2O2 biosensor. The composite film was used to immobilize horseradish peroxidase (HRP) on a gold disk electrode. The properties of sol–gel/chitosan and sol–gel/chitosan-HRP films have been carefully characterized by atomic force microscopy and Fourier transform infrared. By using fluorescent label, a protein density on sol–gel/chitosan has been calculated to be 3.14×1012 molecules cm−2. With the aid of catechol mediator, the biosensor had a fast response of less than 2 s with linear range of 5.0×10−9–1.0×10−7 mol l−1 and a detection limit of 2×10−9 mol l−1. Its current response shows a typical Michaelis-Menten mechanism. The apparent Michaelis-Menten constant KMapp is found to be 1.30 μmol l−1. The activation energy for enzymatic reaction is calculated to be 8.22 kJ mol−1. The biosensor retained approximately 75% of its original activity after about 60 days of storage in a phosphate buffer at 4 °C. [Copyright &y& Elsevier]

Two different glucose biosensors for the amperometric determination of glucose, based on poly(p-chlorophenylamide) (PCPA) and bilayer film of PCPA and Nafion (PCPA/Nafion), are successfully developed. These two biosensors show linear amperometric responses to glucose ranging from 2.0×10−4 to 3.5×10−2 mol l−1 and 5.0×10−4 to 7.5×10−2 mol l−1, respectively, with the same correlation coefficient of 0.9988. Effects of polymerization potential and polymerization time on the performance of enzyme sensors are studied. It is found that PCPA, as a non-conducting polymer, can largely reduce the influence of electroactive interferents. Introduction of inner Nafion membrane not only further eliminates the influence of ascorbic acid on the sensor response but also increases electrode stability. [Copyright &y& Elsevier]

In this study, on the basis of hierarchical CuInS 2 -based heterostructure, a novel cathodic photoelectrochemical (PEC) enzymatic bioanalysis of the sarcosine detection was reported. Specifically, heterostructured CuInS 2 /NiO/ITO photocathode was prepared and sarcosine oxidases (SOx) were integrated for the construction of the enzymatic biosensor. In the bioanalysis, the O 2 -dependent suppression of the cathodic photocurrent can be observed due to the competition between the as-fabricated O 2 -sensitive photocathode and the SOx-catalytic event toward O 2 reduction. Based on the sarcosine-controlled O 2 concentration, a novel photocathodic enzymatic biosensor could be realized for the sensitive and specific sarcosine detection. This work manifested the great potential of CuInS 2 -based heterostructure as a novel platform for future PEC bioanalytical development and also a PEC method for sarcosine detection, which could be easily extended to numerous other enzymatic systems and to our knowledge has not been reported. This work is expected to stimulate more interest in the design and implementation of numerous CuInS 2 -based heterostructured photocathodic enzymatic sensing. [ABSTRACT FROM AUTHOR]

A critical challenge in surface-based DNA assembly amplification is the reduced accessibility of DNA strands arranged on a heterogeneous surface compared to that in homogeneous solution. Here, a novel in situ surface-confined DNA assembly amplification electrochemiluminescence (ECL) biosensor based on DNA nanostructural scaffold was presented. In this design, a stem-loop structural DNA segment (Hairpin 1) was constructed on the vertex of DNA nanostructural scaffold as recognition probe. In the present of target DNA, the hairpin structure changed to rod-like through complementary hybridization with target DNA, resulting in the formation of Hairpin 1:target DNA. When the obtained Hairpin 1:target DNA met Hairpin 2 labeled with glucose oxidase (GOD), the DNA cyclic amplification was activated, releasing target DNA into homogeneous solution for the next recycling. Thus, the ECL signal of Ru(bpy) 3 2+ -TPrA system was quenched by H 2 O 2 , the product of GOD catalyzing glucose. As a result, this proposed method achieved a linear range response from 50 aM to 10 pM with lower detection limit of 20 aM. [ABSTRACT FROM AUTHOR]

Nanochannels have brought new opportunities for biosensor development. Herein, we present the novel concept of a nanochannels photoelectrochemical (PEC) biosensor based on the integration of a unique CuxO-nanopyramid-islands (NPIs) photocathode, an anodic aluminum oxide (AAO) membrane, and alkaline phosphatase (ALP) catalytic chemistry. The CuxO-NPIs photocathode possesses good performance, and further assembly with AAO yields a designed architecture composed of vertically aligned, highly ordered nanoarrays on top of the CuxO-NPIs film. After biocatalytic precipitation (BCP) was stimulated within the channels, the biosensor was used for the successful detection of ALP activity. This study has not only provided a novel paradigm for an unconventional nanochannels PEC biosensor, which can be used for general bioanalytical purposes, but also indicated that the new concept of nanochannel -- semiconductor heterostructures is a step toward innovative biomedical applications. [ABSTRACT FROM AUTHOR]

Proximal metallic nanoparticles (NPs) could quench the electrochemiluminescence (ECL) emission of semiconductor quantum dots (QDs) due to Förster energy transfer (FRET), but at a certain distance, the coupling of light-emission with surface plasmon resonance (SPR) result in enhanced ECL. Thus, the modification strategies and distances control between QDs and metallic NPs are critical for the ECL intensity of QDs. In this strategy, a SPR enhanced ECL sensor based on DNA tetrahedral scaffolds modified platform was reported for the detection of telomerase activity. Due to the rigid three-dimensional structure, DNA tetrahedral scaffolds grafting on the electrode surface could accurately modulate the distance between CdS QDs and luminol labelled gold nanoparticles ( L -Au NPs), meanwhile provide an enhanced spatial dimension and accessibility for the assembly of multiple L -Au NPs. The ECL intensities of both CdS QDs (−1.25 V vs. SCE) and luminol (+0.33 V vs. SCE) gradually increased along with the formation of multiple L -Au NPs at the vertex of DNA tetrahedral scaffolds induced by telomerase, bringing in a dual-potential ECL analysis. The proposed method showed high sensitivity for the identification of telomerase and was successfully applied for the differentiation of cancer cells from normal cells. This work suggests that DNA tetrahedral scaffolds could serve as an excellent choice for the construction of SPR-ECL system. [ABSTRACT FROM AUTHOR]

Here, a mass-sensitive microRNA sensing surface is developed by utilizing a probe DNA/gold nanoparticles (GNP)/dendrimer composite coupling with an enzymatic amplification process. The probe DNA/GNP/dendrimer composite is prepared via the covalent coupling between the NH 2 groups in PAMAM or DNA and the COOH group on GNP. Target microRNA binds to a stem-loop-structured DNA on maganatic NPs, forming a heteroduplex. By enzyme recycling amplification, a large number of linker sequences are produced on MNPs. Via the combination of probe DNA, the linker DNA on MNPs and a capture DNA on gold chip, the DNA/GNP/dendrimer probe could be assembled on the surface of gold chip inducing a sensitive frequency response. It presents an excellent performance in microRNA-203 quantification with a detection linear range of 1.0×10 −11 –1.0×10 −9 M. Both the success in discriminating expressing miroRNA-203 in MCF-7 cell and the well agreement with the commercial qRT-PCR detection method implied its potential application in early cancer diagnosis for future. [ABSTRACT FROM AUTHOR]

Herein, on the basis of the alkaline phosphate (ALP) induced reaction, a simultaneous photoelectrochemical (PEC) and visualized immunoassay has been established for the detection of β-human chorionic gonadotrophin (β-HCG). Specifically, in the proposed system, ALP stimulated the oxidative hydrolyzing transformation of 5-bromo-4-chloro-3-indoyl phosphate (BCIP) to an indigo precipitation, generating an insulating layer that impeded the interfacial mass and electron transfer and thus the photocurrent production. Meanwhile, a visualized detection could be performed according to the change of color intensity. Upon proper experimental conditions, the protocol possessed a detection range of 0.5–1000 IU/L with a detection limit of (0.20±0.011) IU/L toward β-HCG. With high sensitivity and specificity, this work presents the first general protocol for simultaneous PEC and visualized detection, which could be easily extended to addressing numerous other targets. [ABSTRACT FROM AUTHOR]

A highly sensitive electrogenerated chemiluminescence (ECL) biosensor was developed on the basis of a closed bipolar electrode (BPE) apparatus for the analysis of prostate specific antigen (PSA). Bipolar modifications bring up two different stages of enhancement on the same electrode. Anodic enhancement was conducted by modifying gold nanoparticles (Au NPs) to catalyze the anodic ECL reaction between luminol and hydrogen peroxide. Cathodic introduction of thionine tagged PSA antibody led to a further pertinently enhancement synchronized with the PSA amount variation, because the existence of thionine greatly increased the rate of electron gains on cathode, leading to the corresponding acceleration of anodic ECL reaction. The more thionine modified target molecules were introduced, the faster luminol was oxidized, the higher faraday current approached, and sensitive quantification was realized in correlation with the responsive ECL intensity differences. The quantification resulted in a good determination range between 0.1 pg/mL and 0.1 µg/mL. This strategy mainly took advantage of the special structure of closed BPE to realize a simultaneous amplification on both ends of BPE. Moreover, the platform had a potential of providing a multi-functional strategy for the realization of other bio-detections by simply substituting the PSA sandwich structure with other bio-structures. [ABSTRACT FROM AUTHOR]

Quantifying the interactions of bacteria with external ligands is fundamental to the understanding of pathogenesis, antibiotic resistance, immune evasion, and mechanism of antimicrobial action. Due to inherent cell-to-cell heterogeneity in a microbial population, each bacterium interacts differently with its environment. This large variability is washed out in bulk assays, and there is a need of techniques that can quantify interactions of bacteria with ligands at the single bacterium level. In this work, we present a label-free and real-time plasmonic imaging technique to measure the binding kinetics of ligand interactions with single bacteria, and perform statistical analysis of the heterogeneity. Using the technique, we have studied interactions of antibodies with single Escherichia coli O157:H7 cells and demonstrated a capability of determining the binding kinetic constants of single live bacteria with ligands, and quantify heterogeneity in a microbial population. [ABSTRACT FROM AUTHOR]

Abstract: On the basis of aptamer-based rolling circle amplification (RCA) and magnetic beads (MBs), a highly sensitive electrochemical method was developed for the determination of Ochratoxin A (OTA). Initially, an amino-modified capture DNA was immobilized onto MBs for the following hybridization with an OTA aptamer and a phosphate labeled padlock DNA. In the presence of OTA, the aptamer would dissociate from the bioconjugate, and the padlock DNA would subsequently hybridize with the capture DNA to form a circular template with the aid of the T4 ligase. Next, capture DNA would act as primer to initiate a linear RCA reaction and hence generate a long tandem repeated sequences by phi29 DNA polymerase and dNTPs. Then, two quantum dots (QDs) labeled DNA probes were tagged on the resulted RCA product to indicate the OTA recognition event by electrochemical readout. This strategy, based on the novel design of OTA-mediated DNA circularization, the combination of RCA and double signal probes introduction, could detect OTA down to the level of 0.2pgmL−1 with a dynamic range spanning more than 4 orders of magnitude. The proposed approach is tested to determine OTA in red wines and shows good application potential in real samples. [Copyright &y& Elsevier]

Abstract: A new “signal-on” aptasensor for ultrasensitive detection of Ochratoxin A (OTA) in wheat starch was developed based on exonuclease-catalyzed target recycling. To construct the aptasensor, a ferrocene (Fc) labeled probe DNA (S1) was immobilized on a gold electrode (GE) via Au–S bonding for the following hybridization with the complementary OTA aptamer, with the labeled Fc on S1 far from the GE surface. In the presence of analyte OTA, the formation of aptamer-OTA complex would result in not only the dissociation of aptamer from the double-strand DNA but also the transformation of the probe DNA into a hairpin structure. Subsequently, the OTA could be liberated from the aptamer-OTA complex for analyte recycling due to the employment of exonuclease, which is a single-stranded DNA specific exonuclease to selectively digest the appointed DNA (aptamer). Owing to the labeled Fc in close proximity to the electrode surface caused by the formation of the hairpin DNA and to the analyte recycling, differential pulse voltammetry (DPV) signal could be produced with enhanced signal amplification. Based on this strategy, an ultrasensitive aptasensor for the detection of OTA could be exhibited with a wide linear range of 0.005–10.0ngmL−1 with a low detection limit (LOD) of 1.0pgmL−1 OTA (at 3σ). The fabricated biosensor was then applied for the measurement of OTA in real wheat starch sample and validated by ELISA method. [Copyright &y& Elsevier]

Abstract: We demonstrated herein a newly developed photoelectrochemical cell-sensor for the determination of SMMC-7721 human hepatoma carcinoma cells (SMMC-7721 cells) by using a photosensitive CdS-polyamidoamine (G4) nano-composite film (CdS-PAMAM). The film was generated by electrodeposition method. The presence of PAMAM in the film eliminated the surface defects of CdS nanoparticles and therefore resulted in a greatly enhanced photocurrent and a reduced dark current. In the presence of the electron donor ascorbic acid (AA), the photoexcitation of this modified electrode potentiostated at 0V versus Ag/AgCl led to an anodic photocurrent. As a result of the covalent coupling reactions, a layer of concanavalin A (ConA) was firmly bound to the functionalized CdS-PAMAM film via glutaraldehyde bridges. The resulting modified electrodes were tested as sensors for SMMC-7721 cell capture and detection via affinity interactions between ConA and mannosyl groups on cell surface. The cell concentration was measured from 5.0×103 to 1.0×107 cellsmL−1 through the decrease in photocurrent intensity resulting from its specific binding onto the photosensitive film, the detection limit being 5.0×103 cellsmL−1. [Copyright &y& Elsevier]

CRISPR-Cas12a system exhibits tremendous potential in accurate recognition and quantitation of nucleic acids and non-nucleic-acid targets thanks to the discovery of its cleavage capability toward single-stranded DNA (ssDNA). In this study, we developed an efficient electrochemiluminescence (ECL) sensing platform based on CRISPR-Cas12a for the analysis of adenosine triphosphate (ATP). In the presence of the target, the successful release of the DNA activator is specially recognized by Cas12a-crRNA duplex and activates the cleavage of ferrocene (Fc) labeled–ssDNA (Fc-ssDNA) modified on the cathode of bipolar electrode (BPE), resulting in a decrease of ECL intensity of [Ru(bpy) 3 ]2+/TPrA in the anodic cell of BPE. By means of the unique combination of Cas12a with ECL technique based on BPE, it can convert the recognition of target ATP into a detectable ECL signal. The detection limit of ATP was determined to be 0.48 nM under the optimal conditions. This work will expand the application of CRISPR-Cas detection system and propose a potential method for the analysis of non-nucleic-acid targets. Sensing mechanism for ATP detection. [Display omitted] • The paper provides an efficient ECL biosensing system based on CRISPR-Cas12a for the determination of ATP. • CRISPR-Cas12a can convert the recognition of target ATP into detectable ECL signals on bipolar electrodes. • Sensitive quantitative analysis of ATP was achieved with the detection limit of 0.48 nM. [ABSTRACT FROM AUTHOR]

Abstract: An interesting mode of reactivity of MnO2 nanoparticles modified electrode in the presence of H2O2 is reported. The MnO2 nanoparticles modified electrodes show a bi-direction electrocatalytic ability toward the reduction/oxidation of H2O2. Based on this property, a choline biosensor was fabricated via a direct and facile electrochemical deposition of a biocomposite that was made of chitosan hydrogel, choline oxidase (ChOx) and MnO2 nanoparticles onto a glassy carbon (GC) electrode. The biocomposite is homogeneous and easily prepared and provides a shelter for the enzyme to retain its bioactivity. The results of square wave voltammetry showed that the electrocatalytic reduction currents increased linearly with the increase of choline chloride concentration in the range of 1.0×10−5 –2.1×10−3 M and no obvious interference from ascorbic acid and uric acid was observed. Good reproducibility and stability were obtained. A possible reaction mechanism was proposed. [Copyright &y& Elsevier]

Abstract: Boron-doped diamond has drawn much attention in electrochemical sensors. However there are few reports on non-doped diamond because of its weak conductivity. Here, we reported a glucose biosensor based on electrochemical pretreatment of non-doped nanocrystalline diamond (N-NCD) modified gold electrode for the selective detection of glucose. N-NCD was coated on gold electrode and glucose oxidase (GOx) was immobilized onto the surfaces of N-NCD by forming amide linkages between enzyme amine residues and carboxylic acid groups on N-NCD. The anodic pretreatment of N-NCD modified electrode not only promoted the electron transfer rate in the N-NCD thin film, but also resulted in a dramatic improvement in the reduction of the dissolved oxygen. This performance could be used to detect glucose at negative potential through monitoring the current change of oxygen reduction. The biosensor effectively performs a selective electrochemical analysis of glucose in the presence of common interferents, such as ascorbic acid (AA), acetaminophen (AP) and uric acid (UA). A wide linear calibration range from 10μM to 15mM and a low detection limit of 5μM were achieved for the detection of glucose. [Copyright &y& Elsevier]

Abstract: A novel organic–inorganic nanocomposite of methylene blue (MB) and silicon oxide was synthesized and characterized by TEM, FTIR, and UV–vis. The as-prepared material was able to transfer the electron of the MB to electrode and was different from other SiO2 spheres structurally. It can be used as mediator to construct a biosensor with horseradish peroxidase (HRP) coimmobilized in the gelatine matrix and cross-linked with formaldehyde. The resulting biosensor exhibited fast amperometric response and good stability to hydrogen peroxide (H2O2). The linear range for H2O2 determination was from 1×10−5 to 1.2×10−3 M, with a detection limit of 4×10−6 M based on S/N=3. Moreover, the lifetime is more than 3 months under dry conditions at 4°C. [Copyright &y& Elsevier]

An amperometric biosensor for the quantitative measurement of glucose is reported. The biosensor is based on a biocomposite that is homogeneous and easily prepared. This biocomposite is made of chitosan hydrogel, glucose oxidase, and gold nanoparticles by a direct and facile electrochemical deposition method under enzyme-friendly conditions. The resulting biocomposite provided a shelter for the enzyme to retain its bioactivity at considerably extreme conditions, and the decorated gold nanoparticles in the biocomposite offer excellent affinity to enzyme. The biosensor exhibited a rapid response (within 7s) and a linear calibration range from 5.0μM to 2.4mM with a detection limit of 2.7μM for the detection of glucose. The combination of gold nanoparticles affinity and the promising feature of the biocomposite with the onestep nonmanual technique favor the sensitive determination of glucose with improved analytical capabilities. [Copyright &y& Elsevier]

A chitosan film containing MnO2 nanoparticles was introduced to amperometric glucose biosensors for the elimination of the interference from ascorbic acid. Chitosan was mixed with MnO2 nanoparticles and electrochemically deposited on electrodes previously modified with glucose oxidase. MnO2 nanoparticles incorporated in the chitosan film was very stable and can effectively oxidize AA to electrochemical inactive product, and thus eliminate the interference of AA on the glucose biosensors based on the direct oxidation of hydrogen peroxide. The effect of the content of MnO2 nanoparticles and the deposition time on the characteristics of the film, as well as the stability of the film during continuous exposure to AA was investigated. Glucose biosensors deposited with the film containing MnO2 nanoparticles were suitable for determination of glucose in the presence of AA. [Copyright &y& Elsevier]

While remarkable progress has been made in developing enzyme field-effect transistors (ENFETs), the immobilization of enzymes remains a significant challenge. Recently, nanometer materials such as gold, silver and metal oxide nanoparticles have been widely used in biosensors because of their big surface area and good biocompatibility. However, there are few reports about fabricating biocatalytic layer on ENFETs with nanoparticles. Here, SiO2 nanoparticles were introduced into the construction of ENFET. A glucose-sensitive ENFET was fabricated based on the modification of the gate surface of ion-sensitive field-effect transistors (ISFETs) with SiO2 nanoparticles and glucose oxidase (GOD). Compared with the one without SiO2 nanoparticles, the proposed sensor shows obviously enhanced sensitivity and extended lifetime. It infers that SiO2 nanoparticles can provide a biocompatible environment and improve the enzyme activity, and prevent the immobilized enzymes from leakage as well. The linear range of the ENFET is 0.05–1.8 mM, and the detection limit is ca. 0.025 mM. The effects of buffer concentration, pH and ionic strength were also examined. The biosensor has good stability and reproducibility, and it can be used for the determination of glucose. [Copyright &y& Elsevier]

A novel tyrosinase biosensor has been developed for a subpicomolar detection of phenols, which is based on the immobilization of tyrosinase in a positively charged chitosan film on a glassy carbon electrode. It was found that chitosan cross-linked with (3-aminooryloxypropyl) dimethoxymethylsilane is beneficial for the immobilization of tyrosinase. The large microscopic surface area and porous morphology of chitosan matrix lead to high enzyme loading, and the enzyme entrapped in this matrix can retain its bioactivity and the positively charged surface of chitosan can also display a good anti-interference ability to the substances with positive charge. Hence, the resulting sensor offers a high-sensitivity (150 nA·nM−1) for the monitoring of phenols, and the detection limit is as low as 5.0×10−11 M. Its response time is less than 2 s reaching 95% of the steady-state value. It may retain 75% of the activity for at least 70 days. [Copyright &y& Elsevier]

Abstract: The coupling of biocatalytic precipitation (BCP) to photoelectrochemical (PEC) biosensing for the development of rapid PEC sensors with ultrahigh sensitivity and excellent anti-interference ability is successfully realized. Horseradish peroxidase (HRP) was immobilized on the matrix of TiO2/CdS and 4-chloro-1-naphthol (4-CN) was chosen for the BCP-amplified PEC detection of H2O2. The HRP accelerated oxidation of 4-CN by H2O2 would yield insoluble product on the photoelectrode surface, on the basis of which the photocurrent be influenced. The detection limit of 5.0×10−10 M (S/N=3) for the determination of H2O2 was achieved. [Copyright &y& Elsevier]