A sandwich-type photoelectrochemical biosensor based on Ru(bpy)32+ sensitized In2S3 for aflatoxin B1 detection.

Aflatoxin B1 (AFB1), classified as a class I carcinogen, is a widespread mycotoxin that poses a serious threat to public health and economic development, and the food safety problems caused by AFB1 have aroused worldwide concern. The development of accurate and sensitive methods for the detection of AFB1 is significant for food safety monitoring. In this work, a sandwich-type photoelectrochemical (PEC) biosensor for AFB1 detection was constructed on the basis of an aptamer-antibody structure. A good photocurrent response was obtained due to the sensitization of In2S3 by Ru(bpy)32+. In addition, this sandwich-type sensor constructed by modification with the antibody, target detector, and aptamer layer by layer attenuated the migration hindering effect of photogenerated carriers caused by the double antibody structure. The aptamer and antibody synergistically recognized and captured the target analyte, resulting in more reliable PEC response signals. CdSe@CdS QDs-Apt were modified as a signal-off probe onto the sensor platform to quantitatively detect AFB1 with a "signal-off" response, which enhanced the sensitivity of the sensor. The PEC biosensor showed a linear response range from 10-12 to 10-6 g mL-1 with a detection limit of 0.023 pg mL-1, providing a feasible approach for the quantitative detection of AFB1 in food samples.

An electrochemiluminescence aptasensor based on highly luminescent silver-based MOF and biotin-streptavidin system for mercury ion detection.

In this study, for the first time, a silver-based metal-organic framework (Ag-MOF) was synthesized and used as the electrochemiluminescence (ECL) emitter for building an ECL sensor. After modification with chitosan (CS) and gold nanoparticles (Au NPs), the ECL stability of Ag-MOF was improved. To detect mercury ions, a biosensor was constructed using the mercury ion aptamer and steric effect of streptavidin. First, the capture strand (cDNA) with terminal-modified sulfhydryl group was attached to the electrode surface by the Au-S bond. Then, the mercury-ion aptamer (Apt-Hg) modified with biotin was anchored to the electrode by complementary pairing with cDNA. Streptavidin (SA) could be fixed on the electrode by linking with biotin, thereby reducing the ECL signal. However, in the presence of mercury ions, the aptamer was removed and streptavidin could not be immobilized on the electrode. Hence, the ECL signal of the sensor increased with the concentration of mercury ions, which was linear in the range from 1 µM to 300 fM. The detection limit could reach 66 fM (S/N = 3). The sensor provided a new method for the detection of mercury ions.

An Iron(III)-Based Metal-Organic Gel-Catalyzed Dual Electrochemiluminescence System for Cytosensing and In Situ Evaluation of the VEGF165 Subtype.

The recent surge of interest in metal-organic gels (MOGs) has emerged for their soft porous structure, large surface area, and abundant active metal sites, making them a promising candidate for building catalyst matrices. In this work, facilely synthesized Fe(III)-organic gel was directly used as a robust electrode matrix. Detailed studies illustrated that their Fe(III) centers can speed up the electro-oxidation/reduction of the H2O2 coreactant to produce reactive oxygen species for enhancing a potential-resolved dual electrochemiluminescence (ECL) emission. Among them, the anodic signal of luminol varied with the cell concentration based on the impedance ECL mechanism, while the cathodic signal of CdS quantum dots traced the VEGF165 subtype at cell surface by specific aptamer recognition. Based on this, a ratiometric strategy was proposed for accurate cytosensing by eliminating environmental interference. Moreover, by cooperating these two signals, a novel strategy was developed for direct evaluation of the VEGF165 subtype, further realizing rapid drug screening and subtype assessment on different cell lines. This work not only opens up the promising application of MOGs as an effective catalyst matrix but also develops reliable cell assays and protein subtype identification for clinical diagnosis and research.

Coupled electrochemiluminescent and resonance energy transfer determination of microRNA-141 using functionalized Mxene composite.

The electrochemiluminescence and resonance energy transfer (ECL-RET) method was adopted to detect miRNAs, in which the two-dimensional Ti3C2 Mxenes with high surface area modified with CdS:W nanocrystals (CdS:W NCs) were used as ECL signal emitter. Mxenes with a specific surface area of 5.2755 m2/g carried more emitters and promote ECL intensity. As an energy acceptor, BiOCl nanosheets (BiOCl NSs) have a wide UV-Vis absorption peak in the range 250 nm-700 nm, including the emission band of CdS:W NCs with 520 nm emission wavelength. Hence, BiOCl NSs are covalently bound to hairpin DNA 2 by amide bond to quench the ECL signal of CdS:W NCs. In the presence of miRNA-141, the hairpin DNA 1 modified on the GCE was unfold and then paired with hairpin DNA 2 to release miRNA-141 and quench the signal of the ECL biosensor. Then, the concentration signal of miRNA-141 was amplified by catalytic hairpin assembly. The novel specific biosensor demonstrated a satisfactory linear relationship with miRNA-141 in the range 0.6 pM to 4000 pM; the detection limit was as low as 0.26 pM (3 s/m) under the potential of 0 ~ -1.3 V and showed outstanding RSD of 1.19%. The findings of the present work with high accuracy and sensitivity will be of positive significance for the clinical diagnosis of miRNA in the future work. The construction process of the biosensor and electrochemiluminescence mechanism.

A label-free photoelectrochemical immunosensor for carcinoembryonic antigen detection based on a g-C3N4/CdSe nanocomposite.

Herein, a label-free photoelectrochemical immunosensor based on a g-C3N4/CdSe nanocomposite was established and applied to detect carcinoembryonic antigen (CEA). The prepared nanocomposite materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), ultraviolet-visible absorption spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectrometer (FT-IR) and photoluminescence spectroscopy (PL). The results indicate that g-C3N4/CdSe nanocomposite materials were successfully synthesized. In a typical assembly process, the immunosensor was constructed by modifying a fluorine-doped tin oxide (FTO) electrode with poly dimethyl diallyl ammonium chloride (PDDA), the g-C3N4/CdSe nanocomposite, the anti-carcinoembryonic antigen antibody (Ab) and the blocking agent bovine serum albumin (BSA) successively. In the presence of CEA, the photocurrent signal of the prepared immunosensor decreased significantly. Accordingly, under the optimal conditions, a label-free photoelectrochemical immunosensor was established, and it exhibited excellent selectivity and repeatability for CEA detection. The detection limit was 0.21 ng mL-1, and the range was 10 ng mL-1-100 µg mL-1. Simultaneously, the immunosensor also provides a likely sensing device for detecting other protein targets, which is of great significance for early clinical diagnosis.

Highly sensitive electrochemiluminescence biosensor for VEGF165 detection based on a g-C3N4/PDDA/CdSe nanocomposite.

In this work, an electrochemiluminescence (ECL) biosensor was fabricated for the selective detection of vascular endothelial growth factor (VEGF165). g-C3N4/PDDA/CdSe nanocomposites were used as the ECL substrate. Then, DNA labeled at the 5' end with amino groups (DNA1) was immobilized on the surface of g-C3N4/PDDA/CdSe nanocomposite-modified glassy carbon electrode (GCE) by amido linkage. AuNP-labeled target DNA (Au-DNA2) could hybridize with DNA1 to form a double strand. The ECL of the g-C3N4/PDDA/CdSe nanocomposite was efficiently quenched due to the resonance energy transfer between CdSe QDs and Au NPs. After VEGF165 was recognized and bound by Au-DNA2, the double helix was disrupted, and the energy transfer was broken. In this case, Au-DNA2 was released from the electrode surface, and the ECL intensity recovered to a higher level. Under optimal conditions, this ECL biosensor possesses excellent selectivity, accuracy, and stability for VEGF165 detection in a linear range of 2 pg mL-1 to 2 ng mL-1 with a detection limit of 0.68 pg mL-1. In addition, this assay has been successfully applied to the determination of VEGF165 in serum samples. Graphical abstract Schematic representation of the electrochemiluminescence sensor based on a g-C3N4/PDDA/CdSe nanocomposite, which can be determined in the concentration of vascular endothelial growth factor in serum.

A two-dimensional zinc(II)-based metal-organic framework for fluorometric determination of ascorbic acid, chloramphenicol and ceftriaxone.

A two-dimensional zinc(II)-based metal-organic framework [Zn • (BA) • (BBI)] was synthesized from 1,2-benzenediacetic acid and 1,1'-(1,4-butanediyl) bis(imidazole) via a solvothermal reaction. The crystal exhibits good chemical stability in the pH range from 2 to 12, and strong fluorescence with excitation/emission maxima of 270/290 nm. The crystal is shown to by a viable fluorescent probe for the detection of ascorbic acid (AA) and the antibiotics chloramphenicol (CHL) and ceftriaxone (CRO). Fluorescence intensity of crystal dispersion is significantly quenched with increasing concentrations of AA/CHL/CRO. Quenching occurs even in the presence of other substances. The assay is fast (5 s) and has a low detection limit (1.6 ppb for AA, 12 ppb for CHL and 3.9 ppb for CRO). The crystal still has a good quenching effect on AA/CHL/CRO after washing and using for five times. The response of the probe is related to the interplay between the MOF and analytes via energy absorption competition. Graphical abstractSchematic diagram of preparing Zn • (BA) • (BBI) and responding to target analytes. BA: 1,2-phenyldiacetic acid; BBI: 1,1'-(1,4-butanediyl)bis(imidazole); Zn • (BA) • (BBI): Crystal chemical formula.

An electrochemiluminescence biosensor for p53 antibody based on Zn-MOF/GO nanocomposite and Ag+-DNA amplification.

An ultrasensitive electrochemiluminescence biosensor was established based on the Zn-MOF/GO nanocomposite. Ag(I)-embedded DNA complexes were used as a signal amplification reagent. In this work, 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP) and Zn2+ were integrated into a porphyrin paddlewheel framework (Zn-MOF) by a hydrothermal method. The synthesized Zn-MOF material has electrochemiluminescence property, and the luminescence intensity is improved after being composited with graphene oxide (GO). Based on the composite material, we constructed an ultrasensitive ECL biosensor for the p53 antibody detection. The composite material acted as an admirable substrate and then loaded plenty of p53 antigens to recognize the target (p53 antibody) accurately. Because of the bridging effect of streptavidin and biotin-conjugated goat anti-rabbit IgG (bio-ab2), the rich-C DNA with positive correlation with the target was modified on the electrode and then captured the co-reactant accelerator Ag+ to amplify the signal. Therefore, the ECL biosensor response increases with increasing p53 antibody concentration. In the range 0.1 fg/mL-0.01 ng/mL, the response signal of the biosensor has a good linear relationship with the p53 antibody concentration. The detection limit is 0.03 fg/mL (S/N = 3). Impressively, the biosensor not only featured high sensitivity, good stability, and excellent specificity for the detection of p53 antibody, but also provides a new way for early detection of cancer. Graphical abstract Schematic representation of the electrochemiluminescence sensor based on a Zn-MOF/GO nanocomposite, which can be applied to the determination of p53 antibody.

Electrochemiluminescence immunoassay for the prostate-specific antigen by using a CdS/chitosan/g-C3N4 nanocomposite.

An electrochemiluminescence (ECL) biosensor was fabricated for the evaluation of prostate specific antigen (PSA). The sensor was developed by successively modifying glassy carbon electrode (GCE) electrodes with CdS/Chito/g-C3N4 nanocomposites and DNA1 was labeled at the 5' end with thiol. The aptamer DNA was labeled at the 3' end with a quencher ferrocene (Fc) was ligated to DNA1 by the principle of complementary base pairing. In the absence of PSA, the ECL intensity signal is effectively quenches through the energy transfer and photoexcitation electron transfer between CdS/Chito/g-C3N4 emitter and quencher Fc. After incubation with target PSA, the aptamer DNA interacts with PSA and then moved away from the electrode surface together, which will recover the ECL intensity. Under the optimal conditions, the ECL intensity increases linearly with the logarithm of PSA concentration in the range of 1 pg·mL-1 to 100 ng·mL-1, and the detection limit is 0.14 pg·mL-1 (S/N = 3). The biosensor has been successfully applied to the determination of PSA in serum sample. Graphical abstractSchematic representation of the electrochemiluminescence sensor based on a CdS/chitosan/g-C3N4 nanocomposite, which can be applied to the determination of prostate specific antigen in serum.

TiO2/g-C3N4/CdS Nanocomposite-Based Photoelectrochemical Biosensor for Ultrasensitive Evaluation of T4 Polynucleotide Kinase Activity.

Herein, an efficient photoelectrochemical (PEC) platform was constructed by a cosensitization strategy with a cascade energy level arrangement for the ultrasensitive evaluation of T4 polynucleotide kinase (T4 PNK). Based on CdSe quantum dots (QDs) with an extremely narrow bandgap, this cosensitization strategy offered a highly efficient sensitizer with a matching band-edge level of a ternary TiO2/g-C3N4/CdS nanocomposite. In this protocol, the ternary nanocomposite was first prepared to serve as the matrix to construct the PEC sensing platform. On the other hand, a well-designed hairpin DNA1 probe with 5'-hydroxyl termini was specifically phosphorylated by T4 PNK which would be selectively cleaved with lambda exonuclease (λ-Exo) outputting the 3'-thiol end ssDNA2. After tagged with CdSe QDs, ssDNA2 was captured by the complementary capture DNA3 on the electrode surface. As a result, CdSe QDs were in close contact with the ternary nanocomposite matrix, leading to an enhanced photocurrent response. Therefore, this proposed PEC platform displayed an analytical performance with a wide linear range from 0.0001 to 0.02 U mL-1 and a low detection limit down to 6.9 × 10-5 U mL-1. Moreover, this ternary nanocomposite-based platform exhibited excellent selectivity, good reproducibility, and remarkable storage stability, which shows great potential for T4 PNK detection and inhibitor screening.

A Cd-MOF as a fluorescent probe for highly selective, sensitive and stable detection of antibiotics in water.

Recently, the pollution and damage caused by antibiotics in water have aroused serious concerns. In this situation, it is extremely important to develop a highly effective approach to detect antibiotics in water. In this contribution, we built a Cd-MOF material with stable fluorescence properties, using bbi = 1,4-bis(2-methyl-imidazol-1-yl)butane and H2L = 1,2-phenylenediacetic acid as organic ligands and Cd(NO3)2·4H2O as the metal node. The highly selective response of this MOF probe to ceftriaxone sodium (an antibiotic) can reach up to the ppb level in water, along with a fast response time, acid and alkali resistance, and anti-interference ability.

Photoelectrochemical immunoassay for human interleukin 6 based on the use of perovskite-type LaFeO3 nanoparticles on fluorine-doped tin oxide glass.

A film of perovskite-type LaFeO3 nanoparticles (NPs) was deposited on fluorine-doped tin oxide (FTO) conducting glass via dipping-lifting and calcination. Scanning electron microscopy shows that the NPs are evenly distributed on the surface of the glass. The modified glass was further coated with antibody against human interleukin 6 (IL-6) to result in a photoelectrochemical immunosensor for IL-6. The well-established photoelectrochemical immunoassay has a linear current response in the range of 0.1 pg·mL-1 to 0.1 µg·mL-1 and a detection limit as low as 33 fg·mL-1. Graphical abstract Schematic of a novel photoelectochemical immunoassay for the measurement of IL-6 based on perovskite-type LaFeO3 nanoparticles. The immunoassay had a higher sensitivity and may also be applied to other bioanalysis and environment monitoring.

Synthesis of TiO2-loaded Co0.85Se thin films with heterostructure and their enhanced catalytic activity for p-nitrophenol reduction and hydrazine hydrate decomposition.

P-nitrophenol (4-NP) and hydrazine hydrate are considered to be highly toxic pollutants in wastewater, and it is of great importance to remove them. Herein, TiO2-loaded Co0.85Se thin films with heterostructure were successfully synthesized by a hydrothermal route. The as-synthesized samples were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy and selective-area electron diffraction. The results demonstrate that TiO2 nanoparticles with a size of about 10 nm are easily loaded on the surface of graphene-like Co0.85Se nanofilms, and the NH3 · H2O plays an important role in the generation and crystallization of TiO2 nanoparticles. Brunauer-Emmett-Teller measurement shows that the obtained nanocomposites have a larger specific surface area (199.3 m(2) g(-1)) than that of Co0.85Se nanofilms (55.17 m(2) g(-1)) and TiO2 nanoparticles (19.49 m(2) g(-1)). The catalytic tests indicate Co0.85Se-TiO2 nanofilms have the highest activity for 4-NP reduction and hydrazine hydrate decomposition within 10 min and 8 min, respectively, compared with the corresponding precursor Co0.85Se nanofilms and TiO2 nanoparticles. The enhanced catalytic performance can be attributed to the larger specific surface area and higher rate of interfacial charge transfer in the heterojunction than that of the single components. In addition, recycling tests show that the as-synthesized sample presents stable conversion efficiency for 4-NP reduction.

Self-catalytic polymerization of a water-soluble selenium/polypyrrole nanocomposite and its nonlinear optical properties.

A facile one-step method for the synthesis of a water-soluble selenium/polypyrrole (Se/PPy) nanocomposite was developed. In the aqueous synthesis process, the pyrrole acted as a reductant for the reduction of H2SeO3, and then the elemental Se formed in situ acted as a catalyst for the polymerization of pyrrole. The characterization results show that the as-obtained composite (Se/PPy) is a spherical (Φ80 nm) product that is made up of amorphous Se particles coated by PPy layers. The formation mechanism and influence factors of the products were discussed, based on a series of experiments. It is proposed that remainder H2SeO3 adsorbed on the PPy chains increased the water-solubility and conductivity of the Se/PPy nanocomposite. Significantly, relying on the synergistic effect of photo-conductive Se nanoparticles and electric-conductive PPy molecules, the Se/PPy nanocomposite possesses a large two-photon absorption (2PA) cross-section and good optical limiting properties, which were demonstrated by the Z-scan technique using a femtosecond laser. We believe that this work should be an interesting strategy for developing polymer composites with excellent optoelectrical properties.

Strong cathode electroluminescence biosensor based on CeO2 functionalized PCN-222@Ag NPs for sensitive detection of p-Tau-181 protein.

Electrochemiluminescence (ECL) biosensors provide a convenient and high sensitivity method for early disease diagnosis. However, creating luminophore arrays relying on powerful ECL signals remains a daunting task. Porphyrin-centered metal organic frameworks (MOFs) exhibit remarkable potential in ECL sensing applications. In this paper, based on a simple one-pot synthesis method, PCN-222@Ag NPs doped with CeO2 was synthesized to enhance the ECL performance. Due to the strong catalytic ability of CeO2, the ECL signal strength of the new material PCN-222@CeO2@Ag NPs is much higher than that of the PCN-222@Ag NPs and PCN-222. The luminous properties of PCN-222@CeO2@Ag NPs become more intense and stable due to the excellent electronic conductivity of Ag NPs. Based on the fact that CuS@PDA composite can quench the ECL signal of PCN-222@CeO2@Ag NPs, we constructed a novel sandwich ECL immune sensor for the detection of phosphorylated Tau 181 (p-Tau-181) protein. The ECL sensor has a great linear relationship with p-Tau-181 protein concentration, ranging from 1 pg/mL to 100 ng/mL. The detection limit is as low as 0.147 pg/mL. This work provides new ideas for developing sensitive ECL sensors for the p-Tau-181 protein, the marker of Alzheimer's disease.

Rapid synthesis and electrochemiluminescence behavior of CdTe nanoribbons.

A rapid chemical method has been developed for the synthesis of the CdTe nanoribbons with cubic crystalline phase. The method is based on the template-engaged synthesis in which the Te nanowires were used as template reagents. On the basis of a series of experiments and characterizations, the electrochemical property of CdTe nanoribbons was determined by the voltammetric technique. Furthermore, electrochemiluminescence property of CdTe nanoribbons was investigated. The results show that CdTe nanoribbons are helpful to obtain stable electrochemiluminescence emission for 1200 seconds.

A photoelectrochemical biosensor based on b-TiO2/CdS:Eu/Ti3C2 heterojunction for the ultrasensitive detection of miRNA-21.

A novel photoelectrochemical (PEC) biosensor based on b-TiO2/CdS:Eu/Ti3C2 heterojunction was developed for ultrasensitive determination of miRNA-21. In this device, the b-TiO2/CdS:Eu/Ti3C2 heterojunction with excellent energy level arrangement effectively facilitated photoelectric conversion efficiency and accelerated the separation of the photogenerated electron hole pairs, which because that the structure of heterojunction overcomes the drawbacks of single material, such as narrow light absorption range, wide band gap, short carrier lifetime, etc., improves light utilization, extends the lifetime of photogenerated electron hole pairs, and promotes electron transfer. Herein, hairpin DNA1 (H1) decorated on the b-TiO2/CdS:Eu/Ti3C2 electrode surface by Cd-S bonds, after H2/miRNA-21 heterduplex was introduced, the strand-displacement reaction (SDR) was triggered between H1 and H2/miRNA-21, accordingly, miRNA-21 was discharged from the H2/miRNA-21 heterduplex, forming the H1/H2 duplex, and the reuse of miRNA-21 was realized. As a signal amplification factor, the signal amplification factor H3-CdSe was hybridized with H1/H2 duplex, which greatly enhanced the sensitivity of the PEC biosensor. Under optimal conditions, the designed PEC biosensor displayed outstanding sensitivity, selectivity and stability with a wide liner range from 1.0 µM to 10.0 fM and a low detection limit of 3.3 fM. The preparation of the optoelectronic material affords a new direction for the progress of heterojunction photovoltaic materials and the construction of the proposed biosensor also provides a new thought for the PEC detection of human miRNA-21 with superior performance. Simultaneously, the established biosensor exhibiting tremendous possibility for detecting other biomarkers and biomolecules in clinical diagnosis fields.

A ZnIn2S4@ReS2/AgInS2-based photoelectrochemical aptasensor for the ultrasensitive detection of kanamycin.

An ultrasensitive photoelectrochemical (PEC) aptasensor was originally designed by using ZnIn2S4/ReS2 as a photoactive material and AgInS2 as a signal amplifier. The signal amplifier AgInS2 was incubated on the terminal of H-DNA (immobilized on the ZnIn2S4/ReS2/FTO surface), leading to an enhanced photocurrent response. Then, due to the introduction of DNA2, the formation of a double-stranded structure caused AgInS2 to keep away from the electrode surface, and the photocurrent was reduced. In the presence of kanamycin, DNA2 was released from the system due to the competition relationship, and a restored photocurrent response was obtained. The combination of ZnIn2S4/ReS2 and AgInS2 accelerated the electron transfer and enhanced the separation efficiency of photogenerated electron-hole pairs, resulting in an improved performance of the PEC aptasensor, which was capable of accurate and sensitive detection of kanamycin in actual samples.

Site-selective heat boosting electrochemiluminescence for single cell imaging.

In operando visualization of local electrochemical reactions provides mechanical insights into the dynamic transport of interfacial charge and reactant/product. Electrochemiluminescence is a crossover technique that quantitatively determines Faraday current and mass transport in a straightforward manner. However, the sensitivity is hindered by the low collision efficiency of radicals and side reactions at high voltage. Here, we report a site-selective heat boosting electrochemiluminescence microscopy. By generating a micron-scale heat point in situ at the electrode-solution interface, we achieved an enhancement of luminescence intensity up to 63 times, along with an advance of 0.2 V in applied voltage. Experimental results and finite element simulation demonstrate that the fundamental reasons are accelerated reaction rate and thermal convection via a photothermal effect. The concentrated electrochemiluminescence not only boosts the contrast of single cells by 20.54 times but also enables the site-selective cell-by-cell analysis of the heterogeneous membrane protein abundance. This electrochemical visualization method has great potential in the highly sensitive and selective analysis of local electron transfer events.

Direct electrochemistry and electrocatalytic behavior of hemoglobin entrapped in Ag@C nanocables/gold nanoparticles nanocomposites film.

Direct electrochemistry of hemoglobin (Hb) was successfully fabricated by immobilizing Hb on the nanocomposites containing of Ag@C nanocables and Au nanoparticles (AuNPs) modified glassy carbon electrode (GCE). The immobilized Hb retained its biological activity and shown high catalytic activities to the reduction of H2O2 by circular dicroism (CD) spectrum, fourier transform infrared (FT-IR) spectrum and cyclic voltammetry (CV). Experimental conditions such as scan rate and pH Value were studied and optimized. The results indicated that the resulting biosensor are linear to the concentrations of H2O2 in the ranges of 6.67 x 10(-7)-2.40 x 10(5) M, and the detection limit is 2.02 x 10(-7) M. The electrochemical biosensor has also high stability and good reproducibility.