Amperometric ascorbic acid biosensor based on carbon nanoplatelets derived from ground cherry husks

In this work, a novel amperometric biosensor based on carbon nanoplatelets derived from ground cherry (Physalis peruviana) husks (GCHs-CNPTs) is reported for the sensitive and selective detection of ascorbic acid (AA). The structure of the nanoplatelets, the oxygen-containing groups and edge-plane-like defective sites (EPDSs) on the GCHs-CNPTs were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The presence of GCHs-CNPTs with a high density of EPDSs effectively enhances the electron transfer between AA and the glassy carbon electrode (GCE), and thus induces a substantial decrease in the overvoltage for AA oxidation compared with both a bare GCE and a GCE modified with carbon nanotubes (CNTs/GCE). In particular, an amperometric biosensor based on GCHs-CNPTs exhibited a wider linear range (0.01–3.57 mM), higher sensitivity (208.63 μA mM^− 1 cm^− 2), a lower detection limit (1.09 μM, S/N = 3) and better resistance to fouling for AA determination compared to a CNTs/GCE. The great potential of the GCHs-CNPTs/GCE for practical and reliable AA analysis was demonstrated by the successful determination of AA in samples taken from a medical injection dose and a soft drink.     

Electrochemical biosensor based on hairpin DNA probe using 2-nitroacridone as electrochemical indicator for detection of DNA species related to Chronic Myelogenous Leukemia

In this article, a new kind of hairpin DNA Electrochemical biosensor using nitroacridone as electrochemical indicator was first designed, and used to detect BCR/ABL fusion gene in Chronic Myelogenous Leukemia (CML). The results indicated that in pH 7.0 Tris–HCl buffer solution, the oxidation peak current was linear with the concentration of complementary strand in the range of 6.2 × 10⁻⁸–3.1 × 10⁻⁷ mol/l with a detection limit of 5.3 × 10⁻⁹ mol/l. This new hairpin DNA electrochemical biosensor demonstrates its excellent specificity for single-base mismatch and complementary (dsDNA) after hybridization, and this probe has been used for assay of PCR product of a real sample with satisfactory result.     

Continuous flow hydride generation-atomic fluorescence spectrometric determination and speciation of arsenic in wine

Methods for the atomic fluorescence spectrometric (AFS) determination of total arsenic and arsenic species in wines based on continuous flow hydride generation (HG) with atomization in miniature diffusion flame (MDF) are described. For hydride-forming arsenic, l-cysteine is used as reagent for pre-reduction and complexation of arsenite, arsenate, monomethylarsonate and dimethylarsinate. Concentrations of hydrochloric acid and tetrahydroborate are optimized in order to minimize interference by ethanol. Procedure permits determination of the sum of these four species in 5–10-fold diluted samples with limit of detection (LOD) 0.3 and 0.6 μg l^− 1 As in white and red wines, respectively, with precision between 2% and 8% RSD at As levels within 0.5–10 μg l^− 1.Selective arsine generation from different reaction media is used for non-chromatographic determination of arsenic species in wines: citrate buffer at pH 5.1 for As(III); 0.2 mol l^− 1 acetic acid for arsenite + dimethylarsinate (DMA); 8 mol l^− 1 HCl for total inorganic arsenic [As(III) + As(V)]; and monomethylarsonate (MMA) calculated by difference. Calibration with aqueous and ethanol-matched standard solutions of As(III) is used for 10- and 5-fold diluted samples, respectively. The LODs are 0.4 μg l^− 1 for As(III) and 0.3 μg l^− 1 for the other three As species and precision is within 4–8% RSDs.Arsenic species in wine were also determined by coupling of ion chromatographic separation on an anion exchange column and HG-flame AFS detection. Methods were validated by means of recovery studies and comparative analyses by HG-AFS and electrothermal atomic absorption spectrometry after microwave digestion. The LODs were 0.12, 0.27, 0.15 and 0.13 μg l^− 1 (as As) and RSDs were 2–6%, 5–9%, 3–7% and 2–5% for As(III), As(V), MMA and DMA arsenic species, respectively. Bottled red and white wines from Bulgaria, Republic of Macedonia and Italy were analyzed by non-chromatographic and chromatographic procedures and the As(III), arsenite, has been confirmed as major arsenic species.     

Development of an accurate procedure for the determination of arsenic in fish tissues of marine origin by inductively coupled plasma mass spectrometry

High accuracy procedures for the determination of arsenic are needed for assigning reference values to certified reference materials (CRMs). There are a number of problems associated with the determination of total arsenic by inductively coupled plasma–mass spectrometry. Arsenobetaine (AsB) (the major species in fish) gives an enhanced response (9%) when compared to inorganic arsenic(V) and is very difficult to decompose. Chloride causes interference at m/z 75 by the formation of ArCl⁺ and chloride levels can be significant in marine fish. Also residual carbon in digests can lead to enhancement of arsenic signals by charge transfer effects. This can easily lead to erroneous quantification when compared to standards that do not contain carbon.This newly developed procedure overcomes these issues by complete mineralisation of the matrix leaving insignificant amounts of residual carbon and by removal of chlorine by evaporation. A detection limit of 30 ng/g was achieved. Recoveries for the following CRMs: DORM 2 100.1 ± 4.3%, SRM1548 96.1 ± 4.6%, BCR 422 103.6 ± 6.2% and SRM2976 105.9 ± 6.2% were obtained. The digestion procedure uses open vessel wet digestion with a mixture of sulfuric and nitric acid held at 300 °C. The decomposition of AsB was confirmed by speciation analysis of the digest. Carbon (m/z 13) was monitored to demonstrate the efficiency of the digestion. Instrumentation for the reduction of ArCl⁺ interference was not required and this view is supported by the recovery data. Measurements were performed by external calibration using tellurium as an internal standard.     

Direct electrochemistry of hemoglobin at vertically-aligned self-doping TiO2 nanotubes: A mediator-free and biomolecule-substantive electrochemical interface

The present work is dedicated to making the best of vertically-aligned TiO₂ nanotubes (TNTs) array to serve as a prospectively ideal “vessel” for protein immobilization and biosensor applications. The TNTs fabricated by electrochemical anodizing possess the advantageous of perpendicular alignment and tailored tubular architecture, as well as the good biocompatibility and hydrophilicity. But the electron-transfer resistance of the as-grown (AG-) TNTs is too large for the direct electron transfer and electrochemical biosensing. A simple strategy on controllable electrochemical reduction treatment of TNTs is adopted on it, leading TNTs in situ self-doped with Ti(III), which makes the Ti(III)–TNTs much better conductivity while the tubular and crystal structure of TNTs array still well maintained. Results show that the TNTs can be used as a super vessel for rapid and substantive immobilization of hemoglobin (Hb), with a large surface electroactive Hb coverage (Γ*) of 1.5 × 10^?9 mol cm^?2. The enhanced direct electron transfer of Hb is commendably observed on the Ti(III)–TNTs/Hb biosensor with a couple of well-defined redox peaks compared with the AG-TNTs/Hb. The biosensor further exhibits fast response, high sensitivity and stability for the amperometric biosensing of H₂O₂ with the detection limit of 1.5 × 10^?6 M, and the apparent Michaelis–Menten constant of 1.02 mM.     

Quantum dot-based electrochemical DNA biosensor using a screen-printed graphite surface with embedded bismuth precursor

This work reports the development of screen-printed quantum dots (QDs)-based DNA biosensors utilizing graphite electrodes with embedded bismuth citrate as a bismuth precursor. The sensor surface serves both as a support for the immobilization of the oligonucleotide and as an ultrasensitive voltammetric QDs transducer relying on bismuth nanoparticles. The utility of this biosensor is demonstrated for the detection of the C634R mutation through hybridization of the biotin-tagged target oligonucleotide with a surface-confined capture complementary probe and subsequent reaction with streptavidin-conjugated PbS QDs. The electrochemical transduction step involved anodic stripping voltammetric determination of the Pb(II) released after acidic dissolution of the QDs. Simultaneously with the electrolytic accumulation of Pb on the sensor surface, the embedded bismuth citrate was converted in situ to bismuth nanoparticles enabling ultra-trace Pb determination. The biosensor showed a linear relationship of the Pb(II) peak current with respect to the logarithm of the target DNA concentrations from 0.1 pmol L^− 1 to 10 nmol L^− 1, and the limit of detection was 0.03 pmol L^− 1. The biosensor exhibited effective discrimination between a single-base mismatched sequence and the fully complementary target DNA. These “green” biosensors are inexpensive, lend themselves to easy mass production, and hold promise for ultrasensitive bioassay formats.     

MgO polyhedral nanocages and nanocrystals based glucose biosensor

MgO polyhedral nanocages and nanocrystals, synthesized by non-catalytic simple thermal evaporation process, were used to fabricate high-sensitive amperometric glucose biosensor which showed a high and reproducible sensitivity of 31.6 μA μM^?1 cm^?2 with a response time less than 5 s, linear dynamic range from 1.0 to 9.0 μM and correlation coefficient of R = 0.9993. The detection limit of fabricated biosensor (based on S/N ratio = 3) was estimated to be 68.3 ± 0.02 nM. To the best of our knowledge, this is the first report which demonstrates the use of MgO nanostructures for the fabrication of glucose biosensor; hence, this work opens a new way to utilize MgO nanostructures as an efficient electron mediator to fabricate efficient glucose biosensors.     

Direct electrochemistry of single-stranded DNA on an ionic liquid modified carbon paste electrode

Electrochemical oxidation of thermally denatured single-stranded DNA (ssDNA) was studied on a room temperature ionic liquid N-butylpyridinium hexafluorophosphate (BPPF₆) modified carbon paste electrode (IL-CPE). A distinct oxidation peak appeared at +0.772 V (vs. SCE) on the IL-CPE after preconcentration of ssDNA at +0.35 V for 160 s in pH 7.0 phosphate buffer solution (PBS), which was attributed to the oxidation of guanine residue on the ssDNA molecular structure. The results showed an apparent negative shift of the oxidation peak potential and a great enhancement of the oxidation peak current on the IL-CPE compared with that of CPE. The electrochemical parameters of ssDNA on the IL-CPE were further calculated. Under the selected conditions, a linear calibration curve for ssDNA detection was obtained in the concentration range from 10.0 to 110.0 μg mL⁻¹ with the detection limit of 1.5 μg mL⁻¹(3σ).     

Amperometric enzyme biosensor for hydrogen peroxide via Ugi multicomponent reaction

A novel strategy based on the Ugi multicomponent reaction was employed for immobilizing horseradish peroxidase on sodium alginate-coated gold electrode. The electrode was employed for constructing an amperometric biosensor device using 1 mM hydroquinone as electrochemical mediator. The electrode showed linear response (poised at −300 mV vs Ag/AgCl) toward H₂O₂ concentration between 70 μM and 8.8 mM at pH 7.0. The biosensor reached 95% of steady-state current in about 12 s and its sensitivity was 33.8 mA/M cm². The electrode retained full initial activity after 30 days of storage at 4 °C in 50 mM sodium phosphate buffer, pH 7.0.     

Synthesis,characterizations of silica-coated gold nanorods and its applications in electroanalysis of hemoglobin

Gold nanorods (GNRs) were synthesized by a seed–mediated growth approach followed by TEOS polymerization leading to the formation of silica layer surrounding the gold nanorod core. TEM images showed that the silica-coated gold nanorods (GNRs@SiO₂) were dispersed with an average aspect ratio of 3.1 for the GNRs cores and a uniform thickness of the silica shell. The core/shell nanocomposites were further used as efficient supports for the immobilization of hemoglobin (Hb) to fabricate a novel biosensor. The immobilized Hb showed an enhanced electron transfer for its heme Fe(III) to Fe(II) redox couple. This biosensor showed an excellent bioelectrocatalytic activity towards H₂O₂ with a linear range from 8.0 × 10⁻⁷ to 6.1 × 10⁻⁵ M, and the detection limit was 6.0 × 10⁻⁸ M at 3σ. The apparent Michaelis–Menten constant of the immobilized hemoglobin was calculated to be 0.13 mM.     

Dual-signal anodic stripping voltammetric determination of trace arsenic(III) at a glassy carbon electrode modified with internal-electrolysis deposited gold nanoparticles

A glassy carbon electrode (GCE) modified with internal-electrolysis deposited gold nanoparticles (AuNPs_ied) was applied to sensitively and selectively detect As(III) by anodic stripping linear sweep voltammetry (ASLSV). The AuNPs_ied/GCE was prepared based on the redox replacement reaction between a supporting-electrolyte-free aqueous HAuCl₄ and a copper sheet in saturated KCl separated by a salt bridge. Under optimum conditions (0.5 M aqueous H₂SO₄, 300-s preconcentration at − 0.4 V), the ASLSV peak current for the As(0)–As(III) oxidation responded linearly to As(III) concentration from 0.02 to 3 μM with a limit of detection (LOD) of 0.9 nM (0.07 μg L^− 1) (S/N = 3), while that for the As(III)–As(V) oxidation was linear with As(III) concentration from 0.02 to 1 μM with a LOD of 4 nM (0.3 μg L^− 1) (S/N = 3). An appropriate high-scan-rate for ASLSV can enhance both the sensitivity and signal-to-noise ratio. This method was applied for analyses of As(III) in real water samples.     

A high-performance DNA biosensor using polyhydroxylated fullerenol as 3D matrix for probe immobilization

A novel electrochemical DNA biosensor has been developed using water-soluble polyhydroxylated fullerenols as 3D matrix platform for probe DNA immobilization. Owing to the multiple merits including the unique spherical 3D nanostructure, rich OH on the outside surface, and good water-solubility of fullerenol platform, the developed biosensor revealed high probe loading density (2.24 × 10¹³ strands cm^− 2) and fast hybridization kinetics. Also, a wide linear range from 1.0 fM to 1.0 nM with a detection limit down to 0.17 fM in target DNA detection was obtained.     

Deoxyribonucleic acid modified poly(dimethylsiloxane) microfluidic channels for the enhancement of microchip electrophoresis

In this paper, deoxyribonucleic acid (DNA) was employed to construct a functional film on the PDMS microfluidic channel surface and apply to perform electrophoresis coupled with electrochemical detection. The functional film was formed by sequentially immobilizing chitosan and DNA to the PDMS microfluidic channel surface using the layer-by-layer assembly. The polysaccharide backbone of chitosan can be strongly adsorbed onto the hydrophobic PDMS surface through electrostatic interaction in the acidic media, meanwhile, chitosan contains one protonatable functional moiety resulting in a strong electrostatic interactions between the surface amine group of chitosan and the charged phosphate backbone of DNA at low pH, which generates a hydrophilic microchannel surface and reveals perfect resistance to nonspecific adsorption of analytes. Aminophenol isomers (p-, o-, and m-aminophenol) served as a separation model to evaluate the effect of the functional PDMS microfluidic chips. The results clearly showed that these analytes were efficiently separated within 60 s in a 3.7 cm long separation channel and successfully detected on the modified microchip coupled with in-channel amperometric detection mode at a single carbon fiber electrode. The theoretical plate numbers were 74,021, 92,658 and 60,552 N m^?1 at the separation voltage of 900 V with the detection limits of 1.6, 4.7 and 2.5 μM (S/N = 3) for p-, o-, and m-aminophenol, respectively. In addition, this report offered an effective means for preparing hydrophilic and biocompatible PDMS microchannel surface, which would facilitate the use of microfluidic devices for more widespread applications.     

Determination of gallium at trace levels using a spectrofluorimetric method in synthetic U–Ga and Ga–As solutions

A simple, easy to use and selective spectrofluorimetric method for the determination of trace levels of gallium has been developed. A new Schiff base, N-o-vanillidine-2-amino-p-cresol (OVAC) was synthesized and its fluorescence activity with gallium investigated. Based on this chelation reaction, a spectrofluorimetric method has been developed for the determination of gallium in synthetically prepared Ga–U and Ga–As samples buffered at pH 4.0 using acetic acid–sodium acetate. The chelation reaction between Ga(III) and N-o-vanillidine-2-amino-p-cresol was very fast, requiring only 30 min at room temperature to complex completely. The limit of detection (LOD) (3σ) for Ga(III) was 7.17 nM (0.50 μg L^?1), determined from the analysis of 11 different solutions of 20 μg L^?1 Ga(III).     

Ultra-sensitive cholesterol biosensor based on low-temperature grown ZnO nanoparticles

A high-sensitive cholesterol amperometric biosensor based on the immobilization of cholesterol oxidase (ChOx) onto the ZnO nanoparticles has been fabricated which shows a very high and reproducible sensitivity of 23.7 μA mM^?1 cm^?2, detection limit (based on S/N ratio) 0.37 ± 0.02 nM, response time less than 5 s, linear range from 1.0 to 500.0 nM and correlation coefficient of R = 0.9975. A relatively low value of enzyme’s kinetic parameter (Michaelis–Menten constant) ～4.7 mM has been obtained which indicates the enhanced enzymatic affinity of ChOx to Cholesterol. To the best of our knowledge, this is the first report in which such a very high-sensitivity and low detection limit has been achieved for the cholesterol biosensor by using ZnO nanostructures modified electrodes.     

Validated voltammetric method for the determination of some antiprotozoa drugs based on the reduction at an activated glassy carbon electrode

A sensitive electrochemical procedure based on reduction of secnidazole (I), tinidazole (II) and ornidazole (III) at a glassy carbon electrode (GCE) was introduced. A study of the variation of the peak current with solution variables such as pH, ionic strength, concentration of drugs, possible interference, and instrumental variables such as scan rate, pulse amplitude, preconcentration time, accumulation potential, has resulted in the optimization of the reduction signal for analytical purposes. Linear calibration plots were obtained over the concentration ranges of 50–800, 50–750 μg mL^?1 for I, and both (II, III) respectively, in Britton–Robinson buffer of pH 7. The relative standard deviations of five replicate measurements of 1.0 and 10.0 μg mL^?1 of I, II and III concentrations were 4.7%, 4.9% and 5.3%, and 2.2%, 2.6% and 2.8%, respectively. The limits of detection (LOD) for I, II and III were found to be 2 × 10^?10, 3 × 10^?10 and 2.5 × 10^?10 mol L^?1 and limits of quantification (LOQ) for I, II and III were found to be 4.0 × 10^?8, 1.2 × 10^?8 and 4.4 × 10^?8 mol L^?1, respectively. The optimal conditions were: E_acc = ?0.9 V, t_acc = 30 s, scan rate = 20 mV s^?1, pulse-height = 90 mV and Britton–Robinson buffer of pH 7. The method was applied for the determination of the cited drugs both in raw materials and in pharmaceutical preparations with satisfactory results and compared with the official reference method. Complete validation of the proposed method was also done.     

Electrochemiluminescent biosensor based on multi-wall carbon nanotube/nano-Au modified electrode

The electrochemiluminescent (ECL) behavior of lucigenin on a multi-wall carbon nanotube/nano-Au modified glassy carbon electrode (MWNT/nano-Au/GCE) was studied in this paper. Compared with the bare GCE, the ECL intensity of lucigenin can be greatly enhanced at MWNT/nano-Au/GCE. Based on the fact that superoxide dimutase (SOD) could obviously inhibit the ECL of lucigenin at MWNT/nano-Au/GCE, a sensitive ECL biosensor for determination of SOD was developed with a wide linear range of 5.0 × 10⁻⁸–5.0 × 10⁻⁶ mol/L with detection limit of 2.5 × 10⁻⁸ mol/L.     

Novel poly (neutral red) nanowires as a sensitive electrochemical biosensing platform for hydrogen peroxide determination

Poly (neutral red) nanowires (PNRNWs) have been synthesized for the first time by the method of cyclic voltammetric electrodeposition using porous anodic aluminum oxide (AAO) template and were examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Moreover, horseradish peroxidase (HRP) was encapsulated in situ in PNRNWs (denoted as PNRNWs–HRP) by electrochemical copolymerization for potential biosensor applications. The PNRNWs showed excellent efficiency of electron transfer between the HRP and the glassy carbon (GC) electrode for the reduction of H₂O₂ and the PNRNWs–HRP modified GC electrode showed to be excellent amperometric sensors for H₂O₂ at −0.1 V with a linear response range of 1 μM to 8 mM with a correlation coefficient of 0.996. The detection limit (S/N = 3) and the response time were determined to be 1 μM and <5 s and the high sensitivity is up to 318 μA mM⁻¹ cm⁻².     

Ferrocene-modified Fe3O4@SiO2 magnetic nanoparticles as building blocks for construction of reagentless enzyme-based biosensors

A novel amperometric glucose biosensor was developed by entrapping glucose oxidase (GOD) in chitosan (CS) composite doped with ferrocene monocarboxylic acid-modified magnetic core-shell Fe₃O₄@SiO₂ nanoparticles (FMC-AFSNPs). It is shown that the obtained magnetic bio-nanoparticles attached to the surface of a carbon paste electrode (CPE) with the employment of a permanent magnet showed excellent electrochemical characteristics and at the same time acted as mediator to transfer electrons between the enzyme and the electrode. Under optimal conditions, this biosensor was able to detect glucose in the linear range from 1.0 × 10⁻⁵ to 4.0 × 10⁻³ M with a detection limit of 3.2 μM (S/N = 3). This immobilization approach effectively improved the stability of the electron transfer mediator and is promising for construction of biosensor and bioelectronic devices.     

Direct electron transfer of cytochrome c and its biosensor based on gold nanoparticles/room temperature ionic liquid/carbon nanotubes composite film

A robust and effective composite film based on gold nanoparticles (GNPs)/room temperature ionic liquid (RTIL)/multi-wall carbon nanotubes (MWNTs) modified glassy carbon (GC) electrode was prepared by a layer-by-layer self-assembly technique. Cytochrome c (Cyt c) was successfully immobilized on the RTIL-nanohybrid film modified GC electrode by electrostatic adsorption. Direct electrochemistry and electrocatalysis of Cyt c were investigated. The results suggested that Cyt c could be tightly adsorbed on the modified electrode. A pair of well-defined quasi-reversible redox peaks of Cyt c was obtained in 0.10 M, pH 7.0 phosphate buffer solution (PBS). RTIL-nanohybrid film showed an obvious promotion for the direct electron transfer between Cyt c and the underlying electrode. The immobilized Cyt c exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis currents increased linearly to the H₂O₂ concentration in a wide range of 5.0 × 10⁻⁵– 1.15 × 10⁻³ M. Based on the multilayer film, the third-generation biosensor could be constructed for the determination of H₂O₂.