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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]

Human telomerase RNA (hTR), works as a template for synthesis of telomeric DNA repeats at the ends of linear eukaryotic chromosomes, is overexpressed in tumor cells and its concentration has a positive correlation with telomerase activity. The lack of facile and reliable method for detection of hTR in complex matric limited its application for clinical diagnosis. To address the limitation, herein, we proposed a facile and reliable flow cytometric assay for sensitive and specific detection of hTR by combing magnetic enrichment with signal amplification of DNA toehold strand displacement reaction (TSDR). Two hairpin DNA probes of TSDR are ingeniously designed, including biotinylated hairpin DNA1 (H1) and carboxyfluorescein (FAM)-labeled hairpin DNA2 (F-H2). Firstly, H1 was immobilized on streptavidin-functionalized magnetic beads (STV-MBs) through biotin-avidin interaction. In the presence of hTR DNA, TSDR between H1 and F-H2 was triggered to continuously form H1/H2 duplex, resulting in a “turn on” fluorescence on the surface of MBs. Due to fluorescence amplification of TSDR and magnetic enrichment, hTR-DNA can be sensitively, specifically and facile analyzed by flow cytometry and fluorescence microscopy imaging. The detection limit of flow cytometry is 0.3 pM, which is superior to those of most existing approaches. Moreover, the proposed strategy can be successfully utilized to detect hTR in complex biological media as well. Therefore, an enzyme-free amplification approach is provided for robust and rapid detecting hTR DNA, which offers a facile, reliable and sensitive method for studying disease-related gene. [ABSTRACT FROM AUTHOR]

DNAzyme motor systems using gold nanoparticles (AuNPs) as scaffolds are useful for biosensing and in situ amplification because these systems are free of protein enzymes, isothermal, homogeneous, and sensitive. However, detecting different targets using the available DNAzyme motor techniques requires redesigns of the DNAzyme motor. We report here a toehold-exchange translator and the translator-mediated DNAzyme motor systems, which enable sensitive responses to various nucleic acid targets using the same DNAzyme motor without requiring redesign. The translator is able to efficiently convert different nucleic acid targets into a specific output DNA that further activates the pre-silenced DNAzyme motor and consequently initiates the autonomous walking of the DNAzyme motor. Simply adjusting the target-binding region of the translator enables the same DNAzyme motor system to respond to various nucleic acid targets. The translator-mediated DNAzyme motor system is able to detect as low as 2.5 pM microRNA-10b and microRNA-21 under room temperature without the need of separation or washing. We further demonstrate the versatility of the translator and the DNAzyme motor by successful construction and operation of four logic gates, including OR, AND, NOR, and NAND logic gates. These logic gates use two microRNA targets as inputs and generate amplified fluorescence signals from the operation of the same DNAzyme motor. Incorporation of the toehold-exchange translator into the DNAzyme motor technology improves the biosensing applications of DNA motors to diverse nucleic acid targets. [Display omitted] • Toehold exchange translators enhanced applicability of DNAzyme motors. • Translator-mediated DNAzyme motors achieved sensitive detection of microRNAs. • Two translators facilitated a DNAzyme motor to operate four logic gates. • OR, AND, NOR, and NAND logic gates responded to input miR10b and miR21. [ABSTRACT FROM AUTHOR]

As a universal biomarker for cancer diagnostics and cancer therapeutics, telomerase has attracted extensive attention concerning its detection and discovery of its inhibitors. Herein, we developed a PCR-free and label-free fluorescent strategy for facile, reliable and highly sensitive assay of human telomerase activity from crude cancer cell extracts. A G-quadruplex-selective fluorescent dye, N-methyl mesoporphyrin IX (NMM), was utilized as signal probe. Two hairpin probes with hidden G-quadruplex strand in their stem were designed as assembly components of strand displacement reaction (SDR). In this strategy, one telomerase elongation product contains several hexamer repeats which can hybridize with numerous assistant DNA to release a lot of trigger DNA (T-DNA) of SDR for achieving first step amplification. Then, strand displacement reaction led to the formation of G-quadruplex at the both end of two hairpin DNA probes for realizing second step amplification. Finally, the re-released T-DNA initiated another cycle of SDR, resulting in a significant increase in the fluorescence intensity of NMM. By taking advantage of triple signal amplification, the telomerase activity in the HeLa extracts equivalent to 1-3000 cells was detected in homogeneous solution. Telomerase activities of different cell lines, including cancer cells and normal cell, were also successfully evaluated. Meanwhile, the inhibition effect of 3′-azido-3′-deoxythymidine (AZT) was also investigated. Therefore, it offers a simple and reliable method for detecting telomerase activity at single-cell level without complex pre-modification of probe and enzyme auxiliary signal amplification, which has the merits of simplicity, rapid response, low cost and high reliability. [ABSTRACT FROM AUTHOR]

Due to its important biological and clinical roles of polynucleotide kinase (PNK), accurate monitoring of PNK activity and inhibition is highly desirable. Herein, a homogeneous and sensitive fluorescence assay has been proposed for the detection of PNK activity by integrating target recycling signal amplification of DNA toehold strand displacement reaction (TSDR) with gamma-cyclodextrin (γ-CD) enhancement of pyrene excimer. A label-free hairpin DNA1 (H1) and two singly pyrene-labelled DNA, H2 and H3, are designed. Accompanying the occurrence of the efficient enzyme reactions, namely phosphorylation-actuated λ exonuclease reaction, a single-stranded DNA as a trigger DNA (tDNA) of TSDR can be released from H1. Then, tDNA drives circulatory interactions between H2 and H3 to continuously form H2/H3 duplex, resulting in formation of pyrene excimer and a “turn on” fluorescence signal of pyrene excimer. Furthermore, the fluorescence of pyrene excimer is further amplified by introducing gamma-cyclodextrin (γ-CD), which can regulate the space proximity of two pyrene molecules. Thus, TSDR-induced cyclic formation of pyrene excimer and γ-CD enhancement can specifically up-regulate the fluorescence of pyrene excimer for detection of PNK activity, the detection limit is 9.3×10 −5 U mL −1 , which is superior to those of most existing approaches. Moreover, the proposed strategy can also be successfully utilized to study inhibition efficiency of different PNK inhibitors as well. Therefore, a dual amplification approach is provided for nucleic acid phosphorylation related researches. [ABSTRACT FROM AUTHOR]

Most conducting polymer/graphene composites have excellent electrical conductivity. However, the background currents of these composites modified electrodes are much larger. In order to improve the sensitivities of these methods, it is necessary to decrease the background signal. In this paper, porous structure films of overoxidized polypyrrole/graphene (PPyox/GR) have been electrochemically coated onto glassy carbon electrode (GCE) and successfully utilized as an efficient electrode material for the quantitive detection of adenine and guanine, two of the most important components of DNA and RNA. The permselective polymer coatings with low background current could improve the selectivity and sensitivity of microelectrodes for the electropositive purine bases. The GRs into these polymers would further improve sensitivity by increasing the electroactive surface area. The electrochemical sensor can be applied to the quantification of adenine and guanine with a linear range covering 0.06-100µM and 0.04-100µM, and a low detection limit of 0.02μM and 0.01μM, respectively. More importantly, the proposed method was applied to quantify adenine and guanine in calf thymus DNA with satisfactory results. [ABSTRACT FROM AUTHOR]

Abstract: Herein, functionalized PEDOT films were prepared by incorporation of two electroactive species, ferrocenecarboxylic acid (Fc−) and ferricyanide (Fe(CN)6 4−) as doping anions during the electropolymerization of PEDOT at glassy carbon electrodes (GCEs) from aqueous solution. The electrochemically synthesized electroactive species-doped PEDOT films have been carefully characterized by scanning electron microscopy (SEM), FTIR and UV/Vis spectra and various electrochemical techniques. Such nanostructured films combined the advantages of PEDOT (high conductivity and stability) together with electroactive species (good electrochemical activity) and were applied as electrochemical sensors for simultaneous determination of vitamin B2 (VB2), vitamin B6 (VB6) and vitamin C (VC). The results showed that the oxidation peak currents of vitamins obtained at the GCEs modified with electroactive species-doped PEDOT films were much higher than those at the ClO4 −-doped PEDOT films and bare GCEs. The experiment results also illustrated that the sensors possessed high selectivity with no interference from other potential competing species. Moreover, the proposed sensors were successfully employed for the determination of vitamins in orange juice samples with satisfactory results. [Copyright &y& Elsevier]

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: We report a simple approach for the selectively electrochemical sensing of cysteine (CySH) using β-MnO2 nanowires modified glassy carbon (GC) electrode via a direct and facile electrochemical co-deposition process with chitosan hydrogel. The electrode showed excellent electrocatalytic effect toward cysteine oxidation. A possible reaction mechanism related to the formation of surface complexes was proposed: the –SH group is the reacting group in the reaction between cysteine and MnO2, while the –NH2 group acts as an anchor to stabilize the surface complexes. The electrocatalytic behavior is further developed as a sensitive detection scheme for cysteine by amperometric measurement, which shows a large determination range of 0.5–630μM and a low detection limit of 70nM. Other nineteen amino acids in a 20-fold concentration do not interfere in the detection of cysteine. Furthermore, other biological species containing –SH group or Ssuch as glutathione, cystine, and bovine serum albumin (BSA), show no interferences because of steric hindrance and inactive S/ce:simple-para> [Copyright &y& Elsevier]

Abstract: Dopamine-coordinated photoactive TiO2 nanoporous films with a wide excitation range of light in the visible region (up to 580nm) were prepared and used for sensitive detection of NADH. Colloidal TiO2 was firstly covered on an indium–tin oxide (ITO) electrode surface and sintered at 450°C to form a nanoporous TiO2 film, then the electrode was dipped in a dopamine solution to form a dopamine–TiO2 charge transfer complex via coordinating dopamine with undercoordinated titanium atoms on the electrode surface. This charge transfer complex provided an anodic photocurrent under visible light and the photocurrent could be largely enhanced by NADH. The photocurrent enhancement might be due to the electron transfer between NADH and the holes localized on dopamine. A new photoelectrochemical methodology for sensitive detection of NADH at a relatively low potential was developed. The detection limit of NADH was 1.4×10−7 M, and the detection range could extend up to 1.2×10−4 M. The dopamine–TiO2 modified electrode exhibits its major advantages such as effective electronic transducer, fast response and easy fabrication for photoelectrochemical determination of NADH. This strategy largely reduces the destructive effect of UV light and the photogenerated holes of illuminated TiO2 to biomolecules and opens a new avenue for the applications of TiO2 in photoelectrochemical biosensing. [Copyright &y& Elsevier]

Abstract: Using chitosan as an effective linker between CMK-3 and glassy carbon electrode surface, {Hb/CMK-3} n multilayer film-modified electrodes were constructed through layer-by-layer assembly. The morphology of thus-formed {Hb/CMK-3} n film was characterized by scanning electron micrographs, and the interaction of hemoglobin (Hb) with CMK-3 was studied by UV–vis spectroscopy and electrochemical methods. Under optimal conditions, {Hb/CMK-3}6 film showed a couple of stable and well-defined redox peaks at about −377 and −296mV in pH 7.0 buffers. Furthermore, the {Hb/CMK-3}6 film displayed excellent electrocatalysis to the reduction of both H2O2 and O2. Based on thus-formed film and its direct electron transfer behavior, a novel biosensor was presented for the determination of H2O2 ranging from 1.2 to 57μM with the detection limit of 0.6μM at S/N=3. CMK-3 provided a desirable matrix for protein immobilization and biosensor preparation. [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 new strategy for immobilization of horseradish peroxidase (HRP) has been presented by self-assembling gold nanoparticles on chitosan hydrogel modified Au electrode. From a mildly acidic chitosan solution, a chitosan film is electrochemically deposited on Au electrode surface via a negative voltage bias. This process is accompanied by the hydrogen evolution reaction, and the released hydrogen gas made the deposited chitosan film with porous structure, which facilitates the assembly of gold nanoparticles and HRP. The resulting substrates were characterized by atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). The immobilized HRP displayed an excellent catalytic property to the reduction of H2O2 in the presence of methylene blue mediator. The resulting biosensor (HRP-modified electrode) showed a wide dynamic range of 8.0μM–15mM H2O2, and the linear ranges were 8.0μM–0.12mM and 0.50–12mM, with a detection limit of 2.4μM estimated at a signal-to-noise ratio of 3. Moreover, the biosensor remained about 85% of its original sensitivity after four weeks’ storage. [Copyright &y& Elsevier]

A glucose detection approach based on the concept of electrochemical depletion of electroactive species in diffusion layer was established, using scanning electrochemical microscopy (SECM). By controlling the glucose oxidase (GOD) modified electrode (substrate electrode) at a proper potential of electrochemical oxidation of interfering electroactive species, i.e., ascorbic acid (AA), an interference-free microcircumstance was formed in the diffusion layer of the substrate electrode. Consequently, we could successfully sense hydrogen peroxide generated from an enzymatic reaction by locating a Pt ultramicroelectrode (UME) (tip electrode, 5 μm in radius) into the diffusion layer of the substrate electrode. Properties of this interference-removing approach based on electrochemical depletion were systematically investigated. Results showed that the interference-removing efficiency was significantly determined by the tip-substrate distance and substrate potential. When the tip-substrate distance was 11 μm (2.2 times of the tip electrode radius) and the substrate potential was 0.5 V, nearly 90% of AA (0.5 mM) could be depleted within 30 s without consumption of H2O2. Under these conditions, 0.1 mM AA showed no influence on the detection of 0.5 mM glucose. The linear range of glucose detection is 0.01–1 mM with a detection limit (DL) of 0.005 mM (correlation coefficient is 0.9948). This research will open a new way for developing selective micro-biosensors. [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]

Generally a glucose-sensitive enzyme field-effect transistor (ENFET) is based on local pH change in biomembranes resulted from the formation of gluconic acid. Here we proposed a glucose ENFET based on a new principle. The glucose ENFET was fabricated by coimmobilizing glucose oxidase (GOD) and MnO2 nanoparticles on the gate of an ion-sensitive field-effect transistor (ISFET). The proposed glucose biosensor shows a significant local pH increase in the sensitive membrane with the increase of glucose concentration. The driving force of the pH change in our sensor is essentially different from all the other glucose ENFETs, including those prepared by bulk MnO2. The special reaction ability of MnO2 nanoparticles with hydrogen peroxide might be the main cause of the pH change. In addition, the influence of buffer concentration, pH and ionic strength on the glucose ENFET is investigated in detail. It is found that the ionic strength has little effect on the performance of the ENFET. Under optimal conditions, the proposed ENFET exhibits a linear response with glucose in the range of 0.025–1.90 mM, an extended dynamic upper limit of 3.5 mM glucose, and considerable good reproducibility and stability. [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]

In this work, we developed a visual ECL ratiometry on a closed bipolar electrode (BPE) for the detection of prostate specific antigen (PSA), prostate cancer biomarker. High efficient CdTe QDs was synthesized which emitted visualized red light at BPE cathode. Integrating with the anodic ECL emitters, luminol, visual emission of red-blue ratiometric ECL was achieved in BPE array chips. As a sensing probe, Au NRs nanocomposite was assembled on the surface of the cathode and acted as both the quencher of the CdTe QDs ECL and the promoter of the luminol ECL. After incubated with PSA, the Au NRs nanocomposite was peeled off from the electrode surface due to the specific recognition between PSA and aptamer. Consequently, the cathode ECL partly recovered and the anode ECL turned off. By measuring the ratio of visual ECL intensity at two poles of BPE, sensitive detection of PSA was achieved with a linear range from 1.0 ng/mL to 1.0 μg/mL and detection limit of 0.5 ng/mL (S/N=3). This strategy combining the BPE-ECL and visual ratiometry provided an accurate and intrinsic way for the sensing of PSA and showed good perspective in the clinical diagnosis. [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]

Near-infrared (NIR) aggregation induced-emission luminogens (AIEgens) circumvent the noisome aggregation-caused quenching (ACQ) effect in physiological milieu, thus holding high promise for real-time and sensitive imaging of biomarkers in vivo. β-Galactosidase (β-Gal) is a biomarker for primary ovarian carcinoma, but current AIEgens for β-Gal sensing display emissions in the visible region and have not been applied in vivo. We herein propose an NIR AIEgen QM-TPA-Gal and applied it for imaging β-Gal activity in vitro and in ovarian tumor model. After being internalized by ovarian cancer cells (e.g. , SKOV3), the hydrophilic nonfluorescent QM-TPA-Gal undergoes hydrolyzation by β-Gal to yield hydrophobic QM-TPA-OH , which subsequently aggregates into nanoparticles to turn NIR fluorescence "on" through the AIE mechanism. In vitro experimental results indicate that QM-TPA-Gal has a sensitive and selective response to β-Gal with a limit of detection (LOD) of 0.21 U/mL. Molecular docking simulation confirms that QM-TPA-Gal has a good binding ability with β-Gal to allow efficient hydrolysis. Furthermore, QM-TPA-Gal is successfully applied for β-Gal imaging in SKOV3 cell and SKOV3-bearing living mouse models. It is anticipated that QM-TPA-Gal could be applied for early diagnosis of ovarian cancers or other β-Gal-associated diseases in near future. • A near-infrared AIEgen QM-TPA-Gal was designed and synthesized for the first time. • QM-TPA-Gal presented highly sensitive and selective response to β-Gal in vitro, with a limit of detection (LOD) of 0.21 U/mL. • QM-TPA-Gal was successfully applied for β-Gal imaging in vivo with superior sensitivity, specificity, and biosafety. [ABSTRACT FROM AUTHOR]

Abstract: This work demonstrates an aptasensor for ultrasensitive electrochemiluminescence (ECL) detection of thrombin based on an “off–on–off” approach. The system is composed of an Eu3+-doped CdS nanocrystals (CdS:Eu NCs) film on glassy carbon electrode (GCE) as ECL emitter. Then gold nanoparticles (AuNPs) labeled hairpin-DNA probe (ssDNA1) containing thrombin-binding aptamer (TBA) sequence was linked on the NCs film, which led to ECL quenching (off) as a result of Förster-resonance energy transfer (FRET) between the CdS:Eu NC film and the proximal AuNPs. Upon the occurrence of hybridization with its complementary DNA (ssDNA2), an ECL enhancement (on) occurred owing to the interactions of the excited CdS:Eu NCs with ECL-induced surface plasmon resonance (SPR) in AuNPs at large separation. Thrombin could induce ssDNA1 forming a G-quadruplex and cause the AuNPs to be close to CdS:Eu NCs film again, which resulted in an enhanced ECL quenching (off). This “off–on–off” system showed a maximum 7.4-fold change of ECL intensity due to the configuration transformation of ssDNA1 and provides great sensitivity for detection of thrombin in a wide detection range from 50aM to 1pM. [Copyright &y& Elsevier]

Abstract: An electrochemical method for the simultaneous detection of two different tumor markers, carcinoembryonic antigen (CEA) and α-fetoprotein (AFP), in one-pot, using CdS/DNA and PbS/DNA nanochains as labels was developed. Herein, magnetic beads (MBs) as bimolecule immobilizing carriers, were used for co-immobilization of primary anti-CEA and anti-AFP antibodies. The distinguishable signal labels were synthesized by in situ growth of CdS and PbS nanoparticles on DNA chains, respectively, which were further employed to label the corresponding secondary antibodies. A sandwich-type immunoassay format was formed by the biorecognition of the antigens and corresponding antibodies. The assay was based on the peak currents of Cd2+ and Pb2+ dissolved from CdS and PbS nanoparticles by HNO3 using square wave stripping voltammetry. Experimental results show that the multiplexed electrochemical immunoassay has enabled the simultaneous monitoring of CEA and AFP in a single run with wide working ranges of 0.1–100ngmL−1 for CEA and 0.5–200ngmL−1 for AFP. The detection limits reach to 3.3pgmL−1 for CEA and 7.8pgmL−1 for AFP. [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: A novel microfluidic immunoassay system for specific detection of hemoglobin A1c (HbA1c) was developed based on a three-component shell/shell/core structured magnetic nanocomposite Au/chitosan/Fe3O4, which was synthesized with easy handling feature of Fe3O4 by magnet, high affinity for gold nanoparticles of chitosan and good immobilization ability for anti-human hemoglobin-A1c antibody (HbA1c mAb) of assembled colloidal gold nanoparticles. The resulting HbA1c mAb/Au/chitosan/Fe3O4 magnetic nanoparticles were then introduced into microfluidic devices coupled with a gold nanoband microelectrode as electrochemical detector. After that, three-step rapid immunoreactions were carried out in the sequence of HbA1c, anti-human hemoglobin antibodies (Hb mAb) and the secondary alkaline phosphatase (AP)-conjugated antibody within 20min. The current response of 1-naphtol obtained from the reaction between the secondary AP-conjugated antibody and 1-naphthyl phosphate (1-NP) increased proportionally to the HbA1c concentration. Under optimized electrophoresis and detection conditions, HbA1c responded linearly in the concentration of 0.05–1.5μgmL−1, with the detection limit of 0.025μgmL−1. This system was successfully employed for detection of HbA1c in blood with good accuracy and renewable ability. The proposed method proved its potential use in clinical immunoassay of HbA1c. [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]

Photoelectrochemical (PEC) bioanalysis is a newly developed methodology that provides an exquisite route for innovative biomolecular detection. Quantum dots (QDs) are semiconductor nanocrystals with unique photophysical properties that have attracted tremendous attentions among the analytical community. QDs-based PEC bioanalysis comprises an important research hotspot in the field of PEC bioanalysis due to its combined advantages and potentials. Currently, it has ignited increasing interests as demonstrated by increased research papers. This review aims to cover the most recent advances in this field. With the discussion of recent examples of QDs-PEC bioanalysis from the literatures, special emphasis will be placed on work reporting on fundamental advances in the signaling strategies of QDs-based PEC bioanalysis from 2013 to now. Future prospects in this field are also discussed. [ABSTRACT FROM AUTHOR]

This work reports the use of compositionally heterogeneous asymmetric Ag@Au core–satellite nanoassembly functionalized with DNA sequence as unique signaling nanoprobes for the realization of new energy-transfer-based photoelectrochemical (PEC) immunoassay of prostate- specific antigen (PSA). Specifically, the Ag@Au asymmetric core–satellite nanoassemblies (Ag@Au ACS) were fabricated on a two-dimensional glass substrate by a modified controlled assembly technique, and then functionalized with DNA sequences containing PSA aptamers as signaling nanoprobes. Then, the sandwich complexing between the PSA, its antibodies, and the signaling nanoprobes was performed on a CdS QDs modified indium tin oxide (ITO) electrode. The single stranded DNA can server as a facile mediator that place the Ag@Au ACS in proximity of CdS QDs, stimulating the interparticle exciton–plasmon interactions between Ag@Au ACS and CdS QDs and thus quenching the excitonic states in the latter. Since the damping effect is closely related to the target concentration, a novel energy-transfer-based PEC bioanalysis could be achieved for the sensitive and specific PSA assay. The developed biosensor displayed a linear range from 1.0×10 −11 g mL −1 to 1.0×10 −7 g mL −1 and the detection limit was experimentally found to be of 0.3×10 –13 g mL −1 . This strategy used the Ag@Au ACS-DNA signaling nanoprobes and overcame the deficiency of short operating distance of the energy transfer process for feasible PEC immunoassay. More significantly, it provided a way to couple the plasmonic properties of the Ag NPs and Au NPs in a single PEC bioanalytical system. We expected this work could inspire more interests and further investigations on the advanced engineering of the core–satellite or other judiciously designed nanostructures for new PEC bioanalytical uses with novel properties. [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]

A real-time self-powered biosensor is designed for ultrasensitive detection of microRNA-21 based on electrochemical energy device capacitor and target-induced recycling double amplification strategy, which greatly improves the output signal by converting a small number of targets into two glucose oxidase labeled output strand DNAs, and the squeezed-out output strand is recycled by the cathode to fix more signal [Ru(NH 3) 6 ]3+ to further improve the detection signal. A digital multimeter (DMM) is connected to computer for real-time displaying the output signal of the self-powered biosensing system, which improves the accuracy of the sensing platform. The sensitivity of the proposed biosensor is 116.15 μA/pM for target microRNA-21, which is 32.26 times higher than that of pure EBFC (3.6 μA/pM). The target concentration is proportional to the open-circuit voltage value in a wide linear range of 0.1–10000 fM with a low detection limit of 0.04 fM (S/N = 3). The method shows high sensitivity and excellent selectivity, and can be applied to detect tumor marker microRNA-21 in biological matrix. [ABSTRACT FROM AUTHOR]

Herein, a spatial-resolved electrochemiluminescene (ECL) ratiometry based on a closed biopolar electrode (BPE) is reported for the highly sensitive detection of prostate specific antigen (PSA). Au@g-C 3 N 4 NCs as one ECL emitter were firstly coated on the cathode of BPE, while the anode of the BPE served for calibration via another ECL substance, Ru(bpy) 3 2+ . The electroneutrality across the BPE makes the reactions on each pole of BPE electrically coupled. Thus one electrochemical sensing reaction at one pole of BPE could be quantified at both ends. A composite, Pt-PAMAM-DNAzyme was assembled on the surface of cathode via DNA hybridization between probe DNA and PSA aptamer. It acted as an ECL quencher of g-C 3 N 4 via resonance energy transfer (RET) and catalyzing the reduction of O 2 , the co-reactant of g-C 3 N 4 . Meanwhile, it could promote the ECL of Ru(bpy) 3 2+ at anode, since the catalytic reduction of O 2 at the cathode increased the faradiac current flowing through the BPE. Based on this signal composite, an ECL “off-on” phenomenon was observed at the cathode, after Pt-PAMAM-DNAzyme was “peeled off” by PSA. Conversely, at the anode, an “on-off” ECL changing was obtained. Therefore, a sensitive ratiometry for PSA detection was achieved with a linear range from 0.10 to 200 ng/mL. Since the two ECL emitters were physically separated, the ratiometric system was relatively simple and neither optical filters nor spectrometer were required. The strategy combining the ECL ratiometry and BPE broadens the applications of BPE-ECL and shows good perspective in clinical application. [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]

Herein the influence of ultrasmall Ag nanoclusters (Ag NCs) against CdS quantum dots (QDs) in a photoelectrochemical (PEC) nanosystem was exploited for the first time, based on which a novel PEC bioanalysis was successfully developed via the efficient quenching effect of Ag NCs against the CdS QDs. In a model system, DNA assay was achieved by using molecular beacon (MB) probes anchored on a CdS QDs modified electrode, and the MB probes contain two segments that can hybridize with both target DNA sequence and the label of DNA encapsulated Ag NCs. After the MB probe was unfolded by the target DNA sequence, the labels of oligonucleotide encapsulated Ag NCs would be brought in close proximity to the CdS QDs electrode surface, and efficient photocurrent quenching of QDs could be resulted from an energy transfer process that originated from NCs. Thus, by monitoring the attenuation in the photocurrent signal, an elegant and sensitive PEC DNA bioanalysis could be accomplished. The developed biosensor displayed a linear range from 1.0 pM to 10 nM and the detection limit was experimentally found to be of 0.3 pM. This work presents a feasible signaling principle that could act as a common basis for general PEC bioanalysis development. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H 2 S) is an essential intracellular gasotransmitter undertaking numerous signaling roles and physiological effects. Herein, an ingenious anisotropic gold (Au)-silver (Ag) Janus plasmonic nanoprobe was constructed based on the dark-field light scattering imaging for the detection of exogenous and endogenous H 2 S. In the presence of sulfide, the Ag islands as the sensing agent were susceptible to oxidation to Ag 2 S, which induced changes in the longitudinal localized surface plasmon resonance (LSPR) properties of Au-Ag Janus nanoparticles (JNPs), resulting in remarkable and distinctive scattering color changes as well as spectral shifts. The JNPs exhibited satisfying anti-interference capability and a good linear relationship with a low detection limit of 0.11 nM. Additionally, this distinct nanoprobe was successfully applied to monitor endogenous H 2 S as well as map local variations of H 2 S in real-time with its unique intuition and sensitivity in intracellular imaging applications. This work provided a promising application in the plasmonic detection of intracellular H 2 S and paved insight into the H 2 S-related biological process. • A Janus Au-Ag-PLA plasmonic nanoprobe is successfully prepared. • The nanoprobe owns excellent anti-interference performances with a striking red-orange scattering color under DFM. • Modification of positively charged polymers enables more efficient endocytosis. • The nanoprobe was applied to monitor endogenous H 2 S and map local variations of H 2 S in real-time. [ABSTRACT FROM AUTHOR]

In this work, a dual-signaling electrochemiluminescence (ECL) ratiometric sensing approach for the detection of HL-60 cancer cells was reported for the first time. G-C 3 N 4 nanosheets and Ag–PAMAM–luminol nanocomposits (Ag–PAMAM–luminol NCs) were prepared and served as reductive–oxidative and oxidative–reductive ECL emitters respectively. DNA probe functionalized Ag–PAMAM–luminol NCs would hybridize with aptamers modified onto magnetic beads. In the presence of HL-60 cells, the aptamer would conjugate with the target cell and release Ag–PAMAM–luminol NCs. After magnetic separation, released Ag–PAMAM–luminol NCs would hybridize with capture DNA on g-C 3 N 4 nanosheets. ECL from g-C 3 N 4 nanosheets coated on ITO electrode at −1.25 V (vs SCE) could be quenched by Ag–PAMAM–luminol NCs due to the resonance energy transfer (RET) from g-C 3 N 4 nanosheets to Ag NPs. Meanwhile, Ag–PAMAM–luminol brought the ECL signal of luminol at +0.45 V (vs SCE). Thus, the concentration of HL-60 cancer cells could be quantified by both the quenching of ECL from g-C 3 N 4 nanosheets and the enhancement of ECL from luminol. By measuring the ratio of ECL intensities at two excitation potentials, this approach could achieve sensitive and reliable detection for cancer cells in a wide range from 200 cells/mL to 9000 cells/mL with the detection limit of 150 cells ( S / N =3). [ABSTRACT FROM AUTHOR]

Abstract: Detection of phytohormones in situ has gained significant attention due to their critical roles in regulating developmental processes and signaling for defenses in plants at low concentration. As one type of plant hormones, salicylic acid has recently been found to be one of pivotal signal molecules for physiological behaviors of plants. Here we report the application of paper-based electroanalytical devices for sensitively in situ detection of salicylic acid in tomato leaves with the sample volume of several microliters. Specifically, disposable working electrodes were fabricated by coating carbon tape with the mixture of multiwall carbon nanotubes and nafion. We observed that the treatment of the modified carbon tape electrodes with oxygen plasma could significantly improve electrochemical responses of salicylic acid. The tomato leaves had a punched hole of 1.5mm diameter to release salicylic acid with minor influence on continuous growth of tomatoes. By incorporating the tomato leaf with the paper-based analytical device, we were able to perform in situ determination of salicylic acid based on its electrocatalytic oxidation. Our experimental results demonstrated that the amounts of salicylic acid differed statistically in normal, phytoene desaturase (PDS) gene silent and diseased (infected by Botrytis cinerea) tomato leaves. By quantifying salicylic acid at the level of several nanograms in situ, the simple paper-based electroanalytical devices could potentially facilitate the study of defense mechanism of plants under biotic and abiotic stresses. This study might also provide a sensitive method with spatiotemporal resolution for mapping of chemicals released from living organisms. [Copyright &y& Elsevier]

Abstract: Here we report a novel approach for the detection of adenosine in cancer cells by electrochemiluminescence (ECL) on a wireless indium tin oxide bipolar electrode (BPE). In this approach, ferrocene (Fc) which is labeled on adenosine aptamer is enriched on one pole of the BPE by hybridization with its complementary DNA (ssDNA) and oxidized to Fc+ under an external voltage of 5.0V at the two ends of BPE. Then, a reversed external voltage was added on the BPE, making Fc+ enriched pole as cathode. The presence of Fc+ promotes the oxidation reaction on the anodic pole of the BPE, resulting in a significant increase of ECL intensity using Ru(bpy)3 2+/tripropylamine (TPA) system as test solution. The presence of target adenosine was reflected by the ECL signal decrease on the anodic pole caused by the target-induced removal of ferrocene-aptamer on the cathodic pole. The decrease of ECL signal was logarithmically linear with the concentration of ATP in a wide range from 1.0fM to 0.10μM. This ECL biosensing system could accurately detect the level of adenosine released from cancer cells. [Copyright &y& Elsevier]

Abstract: In this paper, we demonstrate a new strategy for replaceable enzymatic microreactor based on a switchable wettability interface of poly(N-isopropylacrylamide) (PNIPAAm). PNIPAAm porous polymer monolith (PPM) with 3D macroporous framework is photopolymerized in glass microchip within 30s. The PNIPAAm PPM not only shows its reversible swelling/shrinking property at the different temperature around the lower critical solution temperature (LCST), but also shows reversible hydrophilicity/hydrophobicity corresponding to its swelling/shrinking status. Based on these properties, a biocompatible and replaceable on-chip enzymatic microreactor has been successfully built by means of the reversible adsorption and release of glucose oxidase (GOx) on the robust and stable matrix. Coupled with a carbon fiber microelectrode as electrochemical detector, the microreactor has been successfully employed for detection of glucose with a linear range from 0.05 to 5mM. This approach may provide a promising way for high efficient and renewable microreactors that will find wide application in clinical diagnosis, biochemical synthesis/analysis, and proteomic research. [Copyright &y& Elsevier]

Abstract: In this work, we firstly enunciated the presence of synergy effect between the electron and energy transfer in an electrochemiluminescence (ECL) system involving the CdS NCs and Au NPs, based on which an amplified ECL biosensor was constructed for sensitive detection of DNA–protein interactions. Specifically, Au NPs modified on electrode, following by assembled probe DNA. Then the modified GCE was hybridized with SiO2@CdS/DNA conjugates. With DNA duplex as a rigid spacer, Au NPs could not only accelerate the electron transfer but also produce the surface plasma resonance upon excited ECL of CdS NCs. However, the enhanced ECL could be greatly suppressed by the binding of target protein. The prepared biosensor possesses excellent analytical performance with the linear range of target protein from 0.015 to 150nM. [Copyright &y& Elsevier]

Abstract: A novel DNAzyme-functionalized Pt nanoparticles/carbon nanotubes (DNAzyme/Pt NPs/CNTs) bioconjugate was fabricated as trace tag for ultrasensitive sandwich DNA detection. The Pt NPs/CNTs were prepared via layer-by-layer (LBL) assembly of the Pt NPs and polyelectrolyte on the carboxylated CNTs, followed by the functionalization with the DNAzyme and reporter probe DNA through the platinum—sulfur bonding. The subsequent sandwich-type DNA specific reaction would confine numerous DNAzyme/Pt NPs/CNTs bioconjugate onto the gold electrode surface for amplifying the signal. In the presence of 3,3′,5,5′ tetramethylbenzidine (TMB) which could be oxidized by the DNAzyme, electrochemical signals could be generated by chronoamperometry via the interrogation of reduction electrochemical signal of oxidized TMB. The constructed DNA sensor exhibited a wide linear response to target DNA ranging from 1.0fM to 10pM with the detection limit down to 0.6fM and exhibited excellent selectivity against even a single base mismatch. In addition, this novel DNA sensor showed fairly good reproducibility, stability, and reusability. [Copyright &y& Elsevier]

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 novel and simple method for preparing cadmium sulfide nanoparticles (CdS NPs) functionalized colloidal carbon particles (CPs) has been successfully developed by in situ growing abundant CdS NPs on the surfaces of monodisperse carbon particles (CdS/CPs). The obtained CdS/CPs conjugates as signal amplification labels were further used for the ultrasensitive determination of thrombin. The CdS/CPs conjugates were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–visible absorption spectrum (UV). The protein electrical detection involves a dual binding event, based on thrombin linked to the CdS/CPs tags and glass surface by the specific aptamer–protein affinity interactions and a succedent electrochemical stripping transduction. Owing to the high-content CdS NPs on carbon particles, this assay allowed a desirable detection limit of 6.0×10−17 M, which was 1000 times lower than that of only using CdS NPs as labels in the control experiments. This protocol exhibited excellent selectivity against these common proteins such as bovine plasma albumin, lysozyme and hemoglobin. The signal amplification approach proposed here provides a facile, cost-effective method for the ultrasensitive determination of thrombin in the practical samples. [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]

Abstract: Based on the newly discovered artificial enzyme formed by mixing hemin with supramolecular hydrogels via the self-assembly of amphiphilic oligopeptides, we prepared a novel organic phase artificial enzyme electrode by coating the artificial enzyme on an electrode which was then covered with sodium alginate for protection. Scanning electron micrograph showed that the supramolecular hydrogel kept its nanofibers structure on the electrode surface. Hemin dispersed in the supermolecular hydrogel as monomer greatly promotes its direct electrochemistry behavior in organic solvents. At the same time, this electrode exhibited higher electrocatalytic ability to tert-butyl hydroperoxide (TBHP) than free hemin modified electrode (free hemin mainly present as dimer). As low as 27μM TBHP could be detected with a linear range from 6.6×10−5 to 1.27×10−2 M via amperometric method. The biosensor can reach 95% of the steady-state current in about 10±2s. More importantly, it can be applied in both hydrophilic and hydrophobic solvents without adding extra buffer or mediators to them that cannot be received by most traditional organic phase enzyme electrodes. This unique property greatly promotes the development of the organic phase enzyme electrodes by facilitating the detection of different kinds of substrates of the hemin-based artificial enzyme soluble in hydrophilic and hydrophobic solvents. The artificial enzyme electrode was successfully used to determine organic peroxides in body lotion samples. [Copyright &y& Elsevier]