Unmodified Screen Printed Carbon Electrode Research Articles

A portable microfluidic electrochemical sensor with nonlinear fit strategy for wide-range uric acid detection

In this work, we have developed a portable electrochemical sensing device controlled by a smartphone through Bluetooth, which was applied for regular uric acid (UA) monitoring in prevention and healthcare management. On the core lies a nonlinear fitting model (I = k·(N − exp(−K·cbulk + b))) which is proposed for the first time and given from the differential equation based on the theoretical analysis. We believe this model can reflect the intrinsic relationship between the obtained current and the bulk analyte concentration, therefore leading to an expanding UA detection range (10-fold) compared to the widely used linear standard curve model and reducing the requirements for the modification of the electrode materials. Besides, the integration of the microfluidic chip promoted the removal of UA oxidation products at the electrode surface, yielding excellent sensing stability with a relative standard deviation (RSD) lower than 1 % during 10 consecutive runs. Consequently, we acquired the relationship between Square Wave Voltammetry (SWV) current and UA concentration (I = 15.27*(2.05 − exp(−0.00108*(cbulk − 663.5))), R2 = 0.9999) in the range of 5 to 1000 μM with a limit of detection (LoD) of 2.4 μM using a completely unmodified screen-printed carbon electrode (SPCE). Proof of concept experiments using 25× diluted human urine spiked with UA yielded a recovery rate of 87.5–101.4 % and a satisfactory selectivity result, which is within the value expected for clinical use, indicating the potential of the developed instrument and nonlinear fitting model for urinary UA detection.

Electrochemical detection of heavy metal ions in water using MWCNT/ZnO nanocomposite

A nanocomposite of multi-walled carbon nanotubes (MWCNTs) decorated with zinc oxide nanoparticles (ZnO NPs) was fabricated via an in-situ hydrothermal approach and implemented as a modified electrode for stripping voltammetric detection of dissolved heavy metal ions. The MWCNT/ZnO exhibited a high specific surface area of 53 m2/g and charge transfer conductivity amplified to 26 S/cm. By square wave voltammetry, the nanocomposite sensor achieved wide linear detection of Cu(II) from 1 to 800 ppb, Pb(II) from 5 to 1000 ppb, and Hg(II) from 1 to 900 ppb, along with low limits of detection reaching 0.8, 1.2, and 0.7 ppb, respectively. The 3–5X enhanced sensitivity versus an unmodified screen-printed carbon electrode confirms performance gains supplied by the tailored hybrid interface. Selectivity testing produced distinct, well-resolved oxidation peaks for each metal ion target that remained unaffected by high off-target concentrations of Mn(II), Co(II), and Fe(III) interferents. Accurate spike recoveries between 95% and 102% were obtained from quantifying ternary mixtures across various Cu(II):Pb(II):Hg(II) compositions, substantiating the capability for simultaneous multianalyte analysis. The simple preparation, high sensitivity and selectivity, and accuracy for direct water testing validates the nanocomposite as a practical portable sensor for on-site toxic heavy metal detection.

Electrochemical determination of riboflavin in pharmaceuticals using unmodified screen printed carbon electrodes.

In this study, we have devised an efficient and rapid approach to detect riboflavin (also known as Vitamin B2 or VB2) utilizing an unaltered screen-printed carbon electrode (SPCE). The unmodified screen-printed electrodes are created within the laboratory, where carbon ink is applied to a ceramic substrate. All experiments pertaining to the investigation of electrochemical behavior and the fine-tuning of crucial experimental parameters were conducted through cyclic voltammetry (CV). For quantitative assessments, square wave voltammetry (SWV) was employed. The findings indicate that unaltered SPCEs exhibit robust current signals during the riboflavin redox reaction. Riboflavin displays a distinct oxidation peak at -0.136V (vs. Ag/AgCl, 3.0M KCl) in a Britton-Robinson buffer solution (BRBS) at pH 2, which was employed for quantification. The electrode demonstrates a broad linear range from 0.05 to 10µM, boasting a detection limit of 0.03µM. Repeatability stands at 1.45%, while reproducibility is 6.61%. Testing the influence of common interfering compounds yielded negligible results. The sensor effectively determines riboflavin content in pharmaceutical formulations without any prior treatment. This method presents an economical, modifier-free sensor with exceptional sensitivity and cost-effectiveness, making it suitable for rapid riboflavin quantification.

Gold nanoparticles enhanced molecularly imprinted poly(3-aminophenylboronic acid) sensor for myo-inositol detection

Myo-inositol (MI) is a secondary messenger that can be used to treat a variety of metabolic syndromes (MS), from diabetes to cancer, and ongoing research is reassuring a bright future for therapies. In this study, two molecular imprinting polymer (MIP) sensor matrixes were created and investigated for the determination of MI; (i) 3-aminophenylboronic acid (3-APBA) electropolymerization with MI as the template on the SPCE surface (ii) gold nanoparticles (AuNPs) initially electrodeposited on a screen-printed carbon electrode (SPCE) surface and further the molecularly imprinted poly-3-aminophenylboronic acid (PAPBA) sensor film was electropolymerized with MI on the modified AuNPs/SPCE surface. Here, the surface modification with AuNPs on SPCE better enhances the electrochemical signal compared with unmodified SPCE. The electrochemical characterization of molecularly imprinted sensors was evaluated via Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and Differential Pulse Voltammetry (DPV) techniques. The morphological changes of the modified electrodes were analyzed by Scanning Electron Microscope (SEM). The performances of the imprinted sensors (such as extraction of the template, rebinding conditions, and interference study) were investigated and optimized. The overall analytical data of the MI/PAPBA/AuNPs/SPCE based imprinted sensor (linear range: 500 nM to 60 μM; limit of detection: 1.0 nM; sensitivity: 0.042 μA μM−1) was better than the MI/PAPBA/SPCE (linear range: 500 nM to 50 μM; limit of detection: 4.7 nM; sensitivity: 0.019 μA μM−1). Further, the MI/PAPBA/AuNPs/SPCE imprinted sensor was successfully validated by applying for the sensitive and selective detection of myo-inositol in human plasma samples, and the results agreed well with the HPLC literature data.

Enhanced Electrochemical Response of Isoniazid Electrocatalytic Oxidation on RGO‐PPD‐SiW Modified Electrode

AbstractThe electroactive composites based on reduced graphene oxide (RGO), poly‐o‐phenylenediamine (PPD) and heteropolyacids – H4SiW12O40nH2O (SiW) and H3[PW12O40] ⋅ nH2O (PW) was applied to a screen‐printed carbon electrode (SPCE) as a planar three‐electrode cell as the first step to creating various devices, in particular, sensors and catalysts. We studied potential use of the modified and unmodified SPCE planar electrode in determining the concentration of antitubercular antibiotic isoniazid (isonicotinic acid hydrazide C6H7N3O or INH). The best result was observed for SPCE+RGO‐PPD‐SiW. CV of normal saline with various concentrations of C6H7N3O demonstrated linear dependence of the relevant anodic peak current either in the bulk solution upon immersion of the modified electrode or in a droplet on the electrode surface.

RGO/MWCNTs-COOH 3D hybrid network as a high-performance electrochemical sensing platform of screen-printed carbon electrodes with an ultra-wide detection range of Cd(II) and Pb(II)

• Developed a high-performance SPCE sensor based on rGO-MWCNTs-COOH 3D hybrid. • The detection of Cd 2+ and Pb 2+ with an ultra-wide linear range was performed. • The electrochemical behaviour of modified SPCE reveals the sensing mechanism. • Shows an application potential for directly detecting high-concentration samples. In this study, we develop a high-performance screen-printed carbon electrodes (SPCE) based on reduced graphene oxide (rGO) - carboxy-functionalized multi-walled carbon nanotubes (MWCNTs-COOH) hybrids for simultaneous detection cadmium ions (Cd 2+ ) and lead ions (Pb 2+ ). The surface morphology and electrochemical behaviour of the modified SPCE was characterised by SEM, AFM, EIS and CV. The control steps of the redox reaction on the modified SPCE and the influence of the morphology of modified SPCE on the shape of stripping peak have also been studied. In addition, Nafion and in-situ bismuth film (BFE) methods were introduced in this detection system to enhance the stability and stripping performance. Under the optimal experimental conditions, the Nafion/rGO-MWCNTs-COOH/SPCE showed excellent catalytic activity towards Cd 2+ and Pb 2+ (pH = 4.5) with a significantly increased SWASV peak current compared to the unmodified SPCE. The developed sensor obtains an ultra-wide dynamic concentration range from 0.1 to 1350 μg·L −1 due to the introduction of 3D hybrid material and the optimisation of the detection parameters. The limit of detection (S/N = 3) for Cd 2+ and Pb 2+ was 0.04 μg·L −1 and 0.02 μg·L −1 , respectively. Furthermore, the applicability of the developed SPCE was demonstrated by detecting Cd 2+ and Pb 2+ in tap water and lake water.

Electrochemical Determination of Tartrazine in Foods by Voltammetry with a Screen‐printed Carbon/Chitosan‐MnO2 Microcomposite Electrode

AbstractThis paper presents a new application for a screen‐printed carbon electrode (SPCE) modified with chitosan (Cs) and manganese oxide (II). This new electrode (Cs‐MnOX/SPCE) was applied in the detection of tartrazine (TZ) by linear scan voltammetry (LSV). The anodic peak current for TZ increased by nearly 500 % compared with Cs/SPCE and unmodified SPCE. The surface of the electrode was characterized by cyclic voltammetry. The detection limit was 0.06 μmol/L. The relative standard deviations (RSDs) were between 1.0 and 6.0 % (n=15). The accuracy of the new method was evaluated with real samples spiked with known quantities of TZ.

The Effect of Preconditioning Strategies on the Adsorption of Model Proteins onto Screen-Printed Carbon Electrodes.

The preconditioning and modification of the supporting electrode surface is an essential step in every biosensor architecture. In particular, when using screen-printed carbon electrodes (SPEs) as inexpensive and convenient disposable sensor substrates, their somewhat lower electrochemical (surface) reproducibility might represent a complex hurdle. Herein, we investigated the effect of selected preconditioning strategies, such as cyclic voltammetric pretreatment, in H2SO4 and H2O2 and plasma pretreatment with a positive and negative glow discharge, which all improved the electrochemical stability of the unmodified SPEs. Furthermore, we studied the influence of preconditioning strategies on the adsorption kinetics of the two most commonly used building blocks for biosensor preparation, i.e., bovine serum albumin (BSA) and protein A. We observed an advantageous effect of all the examined preconditioning strategies for the modification of SPEs with protein A, being the most effective the negative glow discharge. On the other hand, BSA exhibited a more complex adsorption behavior, with the negative glow discharge as the only generally beneficial preconditioning strategy providing the highest electrochemical stability. Protein A revealed a more substantial impact on the electrochemical signal attenuation than BSA considering their same concentrations in the modification solutions. For both BSA and protein A, we showed that the concentrations of 5 and 10 μg mL−1 already suffice for an electrochemically satisfactorily stable electrode surface after 60 min of incubation time, except for BSA at the positive-plasma-treated electrode.

Simultaneous determination of iron and copper using screen-printed carbon electrodes by adsorptive stripping voltammetry with o-phenanthroline

The simultaneous voltammetric determination of iron and copper was accomplished by an unmodified screen-printed carbon electrode based on the complexation with o-phenanthroline assisted by the reducing agent ferrocyanide. The detection limits were 3.74 and 0.34 µg L−1 for iron and copper, respectively, and a linear response was observed from 12.5 to 400 µg L−1 for iron and from 1.14 to 400 µg L−1 for copper. This method successfully avoids interferences between iron and copper while allowing the simultaneous determination of both low and high metal concentrations usually found in the environment. Finally, a certified wastewater reference material was successfully analyzed, confirming the precision and accuracy of the proposed method.

Quantification of Myoinositol in Serum by Electrochemical Detection with an Unmodified Screen-Printed Carbon Electrode.

Simple, rapid, and accurate detection of myoinositol (MI) concentration in blood is crucial in diagnosing polycystic ovary syndrome, neurological disorders, and cancer. A novel electrochemical detection (IED) method was established to quantify MI in human serum using a disposable unmodified screen-printed carbon electrode (SPCE) for the first time. MI was detected indirectly by the reaction product of myoinositol dehydrogenase (IDH) and cofactor β-nicotinamide adenine dinucleotide (NAD+). Good linear calibration curves were obtained at the concentration range from 5.0 μM to 500.0 μM (R2 = 0.9981) with the lower limits of detection (LOD) and quantification (LOQ) of 1.0 μM and 2.5 μM, respectively. Recoveries were calculated at three spiked concentrations, and the values were between 90.3 and 106%, with relative standard deviation values of 3.2–6.2% for intraday precision and 7.1–9.0% for interday precision. The SPCE-electrochemical biosensor is simple, accurate, and without modification, showing great potential for point-of-care testing (POCT) of serum MI in clinical samples.

Rational design of manganese oxide/tin oxide hybrid nanocomposite based electrochemical sensor for detection of prochlorperazine (Antipsychotic drug)

The development of hybrid metal oxides nanocomposite has been utilized for the electrochemical sensor with low detection limits, and excellent sensitivity. In this present study, the co-precipitation synthesis of manganese oxide/tin oxide (Mn2O3/SnO2) hybrid nanocomposite was developed and applied for prochlorperazine (PCP) electrochemical detection. The structural and morphological properties of the prepared hybrid nanocomposite were characterized with various analytical techniques. The synthesized Mn2O3/SnO2 was modified on a screen-printed carbon electrode (SPCE) surface and utilized cyclic voltammetric (CV) and differential pulse voltammetric (DPV) analysis. The linking advantages of Mn2O3, SnO2, and SPCE show superior electrochemical performance in PCP detection, displaying high oxidation response than that of the unmodified SPCE and other modified electrodes (Mn2O3 and SnO2). The optimized voltammetric results exhibited that the hybrid modified electrode shows a broad linear range of 0.03–421.45 µM, the lowest limit of detection, and the limit of quantification of 8 nM, and 29 nM with high sensitivity of 1.415 µA µM−1 cm−2 for PCP oxidation. Besides, the constructed sensor reveals excellent selectivity, stability, and precision for the detection of PCP. Finally, the viability of the hybrid sensor was performed to PCP determination in real human samples with satisfactory results.

Sensitive and selective electrochemical sensor for serotonin detection based on ferrocene-gold nanoparticles decorated multiwall carbon nanotubes

Serotonin, or 5-hydroxytryptamine (5-HT), is a neurotransmitter that plays a crucial role in neural activities. 5-HT deficiency is clinically related to several psychiatric disorders. Therefore, sensitive 5-HT detection is critical in the diagnosis of diseases associated with neurological disorders. Here we developed a sensitive electrochemical sensor utilizing ferrocene covalently linked gold nanoparticles on multiwall carbon nanotubes (FeC-AuNPs-MWCNT), electrocatalytic nanocomposites, to enhance 5-HT detection. FeC-AuNPs-MWCNT modified screen-printed carbon electrodes (SPCEs) provide catalytic activity towards 5-HT oxidation from both FeC and AuNPs along with the high conductance from the carbon nanotube network. The FeC-AuNPs-MWCNT was synthesized by chemically reducing AuNPs on MWCNT surfaces and covalently attaching FeC to the AuNPs. Square wave voltammetry analyses confirmed that the electrocatalytic nanocomposite modified electrodes improved the electrocatalytic activity towards 5-HT oxidation, 61 times higher than the unmodified SPCE. The sensor exhibited a sensitive response to 5-HT over a wide dynamic range from 0.05 µM to 20 µM, a limit of detection of 17 nM (S/N = 3), excellent reproducibility, and high selectivity towards 5-HT against several interferers, including ascorbic acid, urea, uric acid, dopamine, and glucose. The sensor was successfully demonstrated to detect sub-µM 5-HT in urine samples with satisfactory recoveries (98.3–104.9%) and a low relative standard deviation of less than 3%. This sensitive, selective, and cost-effective electrochemical sensor shows great promise in direct 5-HT analysis for clinical applications.

A new electroanalytical methodology for the determination of formaldehyde in wood-based products

A new electroanalytical methodology was developed for the sensitive and selective determination of formaldehyde in wood-based products (WBPs), featuring an extraction process using a Headspace Liquid Acceptor System (HLAS), and detection by square-wave voltammetry (SWV) on unmodified screen-printed carbon electrodes (SPCEs). HLAS, here presented for the first time, captures and derivatizes formaldehyde released from the sample by using the acetylacetone reagent as acceptor solution. The product of formaldehyde with acetylacetone, in the presence of ammonium salt, is 3,5-diacetyl-1,4-dihydrolutidine (DDL) which we have found to be electrochemically active at unmodified SPCEs, generating a selective oxidation peak at +0.4 V. Detection and quantification limits of 0.57 and 1.89 mg kg−1 were obtained, together with intra- and inter-day precisions below 10% (as relative standard deviation, RSD). The methodology was used to determine formaldehyde content in seven WBPs, with similar results being obtained by the developed HLAS-SPCE method and the European standard method EN 717–3, with a profound reduction of total analysis time.The developed HLAS-SPCE combines the use of a new sample preparation procedure for volatiles with, as far as we know, the first determination of formaldehyde (as the derivative product, DDL) on unmodified SPCEs, offering a promising alternative for the determination of formaldehyde in WBPs and other samples.

Polyphenol Detection in Mate Tea Samples Using Iron Tetrasulfonated Phthalocyanine Modified Screen-Printed Electrode

Fast, inexpensive, and efficient methods to determine polyphenols content are of interest to the food industry. Here, we propose an easy and fast sensor for the determination of polyphenol content in tea samples from a green and roasted mate. The screen-printed carbon electrodes (SPCEs) were modified with iron tetrasulfonated phthalocyanine (FeTsPc) solutions prepared at different pHs (2.5, 6.0, and 9.0). The modification in different pHs showed only small changes on catechol oxidation. However, all modified electrodes decreased the oxidation potential of catechol in comparison with unmodified SPCE. The SPCE/FeTsPc was evaluated as a sensor in catechol standard solution, showing a limit of detection and quantification of 0.6 and $2.0~\mu $ mol/L, respectively. The determination of polyphenols in the tea samples is in agreement with the Folin-Ciocalteu method; both methods used catechol as standard. The statistics results indicate SPCE modified with FeTsPc showed a high level of confidence to the application as a sensor for polyphenol content in mate tea samples.

A simple and sensitive electrochemical method for the determination of capsaicinoids in chilli peppers

Total capsaicinoids content is a main parameter that reflects the spicy degree of chilli peppers. Capsaicin and dihydrocapsaicin are the most abundant components in capsaicinoids, which are responsible for about 90% of the spicy taste of chilli peppers. The determination of capsaicinoids becomes important for the increasing demand for spicy foods by consumers. To analyze the capsaicinoids, a sensitive and simple electrochemical method was established in this study. The adsorptive stripping voltammetry (AdSV) method was used to enrich samples. The detection was performed using differential pulse voltammetry (DPV) method combined with the disposable unmodified screen-printed carbon electrode (SPCE). The results showed that capsaicin and dihydrocapsaicin had similar electrochemical behaviors. The linearity of capsaicinoids was from 0.16 to 16.37 μmol/L at the optimal experimental conditions and the detection limit (LOD, S/N = 3) was 0.05 μmol/L. The established electrochemical method presented satisfactory precision and accuracy and the variations were both below 8.9%. After a simple pretreatment of chilli pepper samples, the content of capsaicinoids could be finally determined. This method is sensitive, simple, cost-effective and with satisfactory selectivity for the capsaicinoids in chilli peppers, which provides a promising tool in food industry.

Screen printed carbon electrode modified with magnetic core shell manganese ferrite nanoparticles for electrochemical detection of amlodipine

In the present work, a rapid and sensitive detection of the amlodipine (AML) based on the modified screen printed carbon electrode (SPCE) is developed. At first, SPCE was modified with magnetic core shell manganese ferrite nanoparticles (MCSNP). Cyclic voltammetry (CV) was used to study the electrochemical behaviour of AML and its determination was conducted by applying differential pulse voltammetry (DPV). The results were showed that, the modified SPCE in comparison with unmodified SPCE exhibited the enhanced electrocatalytic activity toward the oxidation of AML. A single irreversible oxidation peak was observed at a potentials of 600 and 725 mV (on the scale of Ag/AgCl electrode) on the modified SPCE and unmodified SPCE, respectively. Under the optimized conditions, the anodic peak current of AML recorded by DPV varies linearly with AML concentration in the range 0.5?400 ?M with a detection limit of 0.1 ?M. The modified SPCE was used for the quantitative analysis of AML in AML tablet and urine samples and the results indicated the feasibility of the developed method for AML analysis in routine detection.

Novel electrochemical sensing platform based on a nanocomposite of PVA/PVP/RGO applied to IgG anti- Toxoplasma gondii antibodies quantitation

This article describes the development of a new electrochemical platform composed by a polymer mixture and graphene oxide (GO). The working electrode of a screen-printed carbon electrode (SPCE) was modified with nanocomposite constituted by poly-vinyl alcohol (PVA), poly-vinylpyrrolidone (PVP) and GO, which was electrochemically reduced to obtain PVA/PVP/RGO/SPCE. The interactions and morphology of the PVA/PVP/GO nanocomposite were investigated by SEM, FTIR and UV–Vis. SEM images indicated an excellent dispersion of the GO sheets in the polymer matrix. Besides, FTIR and visible UV studies revealed strong interactions between polymer mixture and GO sheets. According to electrochemical studies, the new platform increased the electroactive surface area by a factor of 20.46 compared to the unmodified SPCE. Also, the PVA/PVP/RGO/SPCE had a fast electron kinetics transfer process with a value of ks = 9.6 s−1.The modified electrode was applied to the determination of IgG anti-T. gondii antibodies for the serological diagnosis of toxoplasmosis. The IgG anti-T. gondii antibodies quantification showed a detection limit of 0.012 U mL−1, and the coefficients of variation intra-day and inter-day assays were lower than 4.5% and 6.2%, respectively. The electrochemical platform proved to be a sensitive and easily applicable tool applied to the serological diagnosis of toxoplasmosis. Therefore, the developed nanocomposite represents an excellent alternative for the electrochemical biosensor fabrication.

A Disposable Electrochemical Sensing Platform for Acetaminophen Based on Graphene/ZrO2 Nanocomposite Produced via a Facile, Green Synthesis Method

In this paper, a disposable electrochemical sensor was fabricated using graphene/zirconium dioxide (ZrO2)-modified screen printed carbon electrode (SPCE). The implemented synthesis route is simple, cost feasible, and abolish the usage of harsh chemical. A green approach using single step exfoliation of graphite in mild sonochemical ethanol–water treatment and hydrothermal synthesis method were employed to prepare the graphene/ZrO2 nanocomposites. Characterization methods, such as X-ray diffraction, scanning electron microscope (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM) and energy dispersive x-ray spectroscopy (EDX), were used to study the crystallinity, surface characteristics, morphology and elemental composition of the synthesized nanocomposites. All the results evidently suggested that pristine graphene was successfully produced without attachment of any undesirable functional groups and ZrO2 nanoparticles of approximately 10.4 nm were homogeneously distributed on the graphene sheet. The electrochemical performance of the graphene/ZrO2/SPCE was assessed with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Both tests suggested improved electron transfer kinetic of graphene/ZrO2/SPCE as compared with bare SPCE. Effect of ZrO2 precursor loading was investigated, in which nanocomposites containing different ratios of graphene and ZrO2 precursors were prepared. CV and EIS results indicated that ratio 1:8 (graphene: ZrO2 precursor) was the optimum composition, exhibiting the highest current response and lowest charge transfer resistance. The potential application of graphene/ZrO2/SPCE for electroanalytical purposes was demonstrated with acetaminophen detection. The graphene/ZrO2/SPCE sensor was calibrated with differential pulse voltammetry and demonstrated better electrocatalytic activity toward acetaminophen with lower oxidation potential and higher peak current than the unmodified SPCE. The sensor exhibited a linear range of 10– $100~\mu \text{M}$ , detection limit of 75.5 nM, reproducibility of <5 % relative standard deviation (RSD), repeatability of < 3% RSD, and good selectivity to acetaminophen in the presence of dopamine and ascorbid acid. The graphene/ZrO2/SPCE sensor was applied to determine acetaminophen in pharmaceutical tablets and yielded satisfactory results. The simple, low cost, and green method reported here can be further exploited to provide a biocompatible platform for electrochemical sensing application.

A novel electrochemical biosensor for ultrasensitive detection of serum total bile acids based on enzymatic reaction combined with the double oxidation circular amplification strategy

Serum total bile acids (TBA) level is used as a sensitive and reliable index for hepatobiliary diseases in clinics. Herein, a novel electrochemical biosensor was fabricated using enzymatic reaction coupling with the double oxidation circular amplification strategy for the detection of human serum TBA. With the catalysis of 3α-hydroxysteroid dehydrogenase (3α-HSD), 3α-bile acids reacted specifically with nicotinamide adenine dinucleotide (NAD+). And then, the reduced nicotinamide adenine dinucleotide (NADH) was produced. After that, the NADH reacted with the electron mediator of tris(2,2'-bipyridine) ruthenium(Ⅲ) (Ru(bpy)33+), which was then transformed to Ru(bpy)32+. Ultimately, Ru(bpy)32+ was further oxidized to Ru(bpy)33+ under a certain voltage, which was detected by the chronoamperometry assay. The detection was performed using a disposable unmodified screen-printed carbon electrode (SPCE) without sample preparation. The proposed biosensor showed high sensitivity and accuracy with the linear range from 5.0 to 150.0 pmol/L in 106-fold dilution serum. The established method had a good correlation with the enzymatic cycling method (r = 0.9372, P < 0.001, n = 72) commonly used in clinic. The electrochemical biosensor is simple, ultrasensitive and without sample pretreatment, showing great potential for point-of-care testing (POCT) of serum TBA in clinical samples. In addition, the biosensor is cost-effective with a small volume of samples, especially suitable for those who have difficulties in blood collection, such as infants, children and some small animals.

Electrocatalytic Oxidation and Flow Injection Analysis of Isoniazid Drug Using an Unmodified Screen Printed Carbon Electrode in Neutral pH

AbstractIn this work we report electrocatalytic oxidation and flow injection analysis of tuberculostatic drug isoniazid (INZ) based on a disposable and unmodified screen printed carbon electrode (SPCE). Instead of using chemically modified electrode to increase the sensitivity at low overpotential, the same purpose can be achieved simply by preanodization of a bare SPCE in a suitable electrolyte medium. Surface characterization of the as‐preanodized electrode by X‐ray photoelectron spectroscopy and Raman spectroscopy indicate that both oxygen functionalities and edge/defect sites effectively assist the INZ oxidation. Flow injection analysis extends its applicability with a wide linear range up to 1 mM and an enhanced sensitivity of 100 nA μM−1 with a low detection limit of 2.7 nM (S/N=3). These good analytical features accomplished with disposable and economical devices could make possible the implementation of this methodology for INZ on‐line monitoring in pharmaceuticals.