Wide Linear Working Range Research Articles

Designing and construction of carboxyl functionalised MWCNTs/Co-MOFs-based electrochemical sensor for the sensitive detection of nitrite

ABSTRACT A simple and sensitive electrochemical sensor based on metal-organic framework carboxyl functionalised MWCNTs/Co-MOFs have been successfully fabricated towards nitrite detection. Electrochemical techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) experiments were conducted on carboxyl functionalised MWCNTs/Co-MOFs electrochemical sensor to decipher the electrochemical sensing performance. Several important electrochemical sensor parameters have been evaluated for nitrite oxidation, such as pH, deposition potential and preconcentration time. The observed results showed that the proposed electrochemical sensor provide a wide linear working range i.e. 80–1160 µM with a detection limit (3σ) of 18.8 µM and sensitivity of 0.01 µA µm−1 cm−2. Furthermore, the proposed sensor also applied to determine the nitrite level in beverage and water samples with satisfactory recoveries.

Fabrication of high-performance wearable strain sensors by using CNTs-coated electrospun polyurethane nanofibers

In this work, a new kind of composite nanofiber-based strain sensor with superior electromechanical properties was fabricated by using aligned thermal plastic polyurethane (TPU) nanofibers coated with multi-wall carbon nanotubes (CNTs). In order to improve the deposition efficiency and the fastness of CNTs coating on TPU nanofibers, bio-inspired dopamine (DA) was employed to modify the surface of the TPU nanofiber via a fast deposition method. (The composite nanofibers obtained were denoted as DATPU.) The electromechanical tests showed that DATPU/CNTs nanofiber membrane had a wide linear working range of 370% in the direction parallel to the nanofibers (P-DATPU/CNTs), a high gauge factor of 22.0 and a high linear coefficient of determination (r2) of 0.997. P-DATPU/CNTs nanofibers also exhibited excellent durability during stretching–releasing test for 5000 cycles. The P-DATPU/CNTs composite nanofibers demonstrated high sensing performance in detecting human motions of finger and elbow bendings.

Determination of bisphenol S, simultaneously to bisphenol A in different water matrices or solely in electrolyzed solutions, using a cathodically pretreated boron-doped diamond electrode

A simple, accurate, and environmentally friendly method for the simultaneous determination of the analog endocrine disruptors bisphenol S (BPS) and bisphenol A (BPA) was developed and validated. The determination was performed by square-wave voltammetry using a cathodically pretreated boron-doped diamond (BDD) as the working electrode, with 0.1 mol L−1 H2SO4 as the supporting electrolyte. Under optimized conditions, a wide linear working range (R2 = 0.999) from 0.20 to 80.0 mg L−1 with a limit of detection (S/N = 3) of 0.060 mg L−1 was attained for BPS. For BPA, a linear correlation (R2 = 0.992) was attained from 0.10 to 50.0 mg L−1, with a limit of detection of 0.030 mg L−1. As far as we could ascertain, these are the lowest limits of detection and the widest linear ranges in the literature for this determination. The method was applied to the simultaneous determination of BPS and BPA in real water samples, with minimum sample preparation processes (dilution and acidification only). Excellent recovery values were achieved, ranging from 95 to 99%. Additionally, the method was successfully applied to the monitoring of the electrochemical degradation (anodic oxidation) of BPS using a recirculating flow system fitted with a BDD anode. The decay of [BPS] with time was also checked by an HPLC method, with results statistically similar to those obtained by the proposed electroanalytical method. Hence, the proposed method is a reliable, greener, and low-cost alternative to monitor simultaneously BPS and BPA in aquatic matrices or only BPS in wastewater treatment processes.

Giant piezoresistive gauge factor in vein-membrane/graphene sensors with a wide linear working range

Here, a piezoresistive sensor was fabricated by combining graphene and the veins ofMagnolia henryi.

Sensitive electrochemical platform based on nano-cylindrical strontium titanate/N-doped graphene hybrid composite for simultaneous detection of diphenhydramine and bromhexine

Herein, we report a nano-cylindrical strontium titanate/N-doped graphene (SrTiO3/N-GNS) hybrid composite synthesized by a solvothermal method. The composite material has been explored by various physicochemical and electrochemical characterization techniques. It is found that the nano-cylindrical SrTiO3 nanoparticles with highly crystalline mesoporous structure are consistently present in between as well as on the surface of N-GNS sheets resulted in 3-dimensional continuous structure. The electrochemical investigations reveal that SrTiO3/N-GNS hybrid composite displays excellent electrocatalytic behavior towards simultaneous electro-oxidation of two commonly encountered anti-allergic drugs viz. Diphenhydramine (DPH) and Bromhexine (BRO) in phosphate buffer of pH 7.0 employing adsorptive stripping differential pulse voltammetry. The new application of SrTiO3/N-GNS hybrid as an electrochemical sensor shows wide linear working range from 0.038 to 100.0 μM for DPH and 0.030–90.0 μM for BRO with detection limit of 2.1 and 1.9 nM respectively. Also, the developed sensor manifests adequate recoveries in synthetic pharmaceutical samples and human body fluids. These findings suggest that SrTiO3/N-GNS composite is and could serve as a potential candidate for highly sensitive electrochemical sensing applications.

Au/ERGO nanoparticles supported on Cu-based metal-organic framework as a novel sensor for sensitive determination of nitrite

In this work, an electrode which comprises Au nanoparticles (AuNPs) and electrochemically reduced graphene oxide (ERGO) recombined Cu based metal-organic framework (Cu-TDPAT) was prepared for nitrite detection. The structure and constituent of the modified material were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and FT-IR. The electrochemical behavior of nitrite at the modified electrode was performed by cyclic voltammetry and electrochemical impedance spectroscopy. The results indicated that the oxidation process of nitrite happened at recommended electrode had a superior response. The proposed electrode showed high electrocatalytic capacity toward nitrite oxidation with a wide linear working range (0.001–1000 μmol·L−1) and a detection limit of 0.006 μmol·L−1. Finally, the sensor was successfully applied to detect nitrite in real sample and achieved desirable recovery rate, showing its potential application in real-time detection of food.

A dual template imprinted polymer modified electrochemical sensor based on Cu metal organic framework/mesoporous carbon for highly sensitive and selective recognition of rifampicin and isoniazid

A highly sensitive and selective doubly imprinted polymer modified electrochemical sensor based on copper metal organic framework/mesoporous carbon (Cu-MOF/MC) composite was developed for simultaneous determination of Rifampicin (RIF) and Isoniazid (INZ). The molecularly imprinted polymer (MIP) film was formed on the surface of Cu-MOF/MC modified glassy carbon electrode (GCE) by incorporating RIF and INZ as template molecules during electropolymerization of pyrrole, followed by removal of both the template molecules. During this process of sensor fabrication, large numbers of complementary binding sites for template molecules are created on the surface of MIP sensor due to high surface area offered by Cu-MOF/MC composite. Various parameters influencing the performance of MIP sensor such as number of electropolymerization cycles and template: monomer ratio were optimized during the study. Based on the optimized parameters, the electrochemical response of Cu-MOF/MC/MIP/GCE towards determination of RIF and INZ was studied in a wide linear working range of 0.08 μM to 85 μM employing adsorptive stripping differential pulse voltammetry in aqueous as well as real samples. The limit of detection was found to be 0.28 nM and 0.37 nM for RIF and INZ respectively. In addition, the MIP sensor showed good stability, acceptable reproducibility and high selectivity for RIF and INZ over other common interferents. Moreover, the developed sensor was successfully applied for simultaneous determination of RIF and INZ in pharmaceutical formulations, blood serum and urine samples with satisfactory recoveries.

Electrochemical Biochip Assays Based on Anti-idiotypic Antibodies for Rapid and Automated On-Site Detection of Low Molecular Weight Toxins.

Phycotoxins and mycotoxins, such as paralytic shellfish poisoning toxins, type A trichothecenes, and aflatoxins are among the most toxic low molecular weight toxins associated with human poisoning incidents through the consumption of naturally contaminated food. Therefore, there is an utmost need for rapid and sensitive on-site detection systems. Herein, an electrochemical biochip for fast detection of saxitoxin, T-2 toxin as well as aflatoxin M1 and their corresponding congeners, respectively, using a portable and fully automated detection platform (pBDi, portable BioDetector integrated) was developed. Toxin analysis is facilitated upon the biochip via an indirect competitive immunoassay using toxin-specific antibodies combined with anti-idiotypic antibodies. The developed biochips enable detection in the low ng/mL-range within 17 min. Moreover, the assays cover a wide linear working range of 2–3 orders of magnitude above the limit of detection with an inter-chip coefficient of variation lower than 15%. The broad specificity of the employed antibodies which react with a large number of congeners within the respective toxin group allows efficient screening of contaminated samples for the presence of these low molecular weight toxins. With respect to the analysis of human urine samples, we focused here on the detection of saxitoxin, HT-2 toxin, and aflatoxin M1, all known as biomarkers of acute toxin exposure. Overall, it was proved that the developed biochip assays can be used to rapidly and reliably identify severe intoxications caused by these low molecular weight toxins.

A wearable strain sensor based on the ZnO/graphene nanoplatelets nanocomposite with large linear working range

Flexible strain sensors are attracting more and more attentions in wearable devices and electronic skins. Currently, the fabrication of flexible strain sensor with features of high sensitivity and wide linear working range is still a great challenge. Herein, a stretchable and wearable strain sensor is fabricated with the ZnO nanoparticles (NPs)/graphene nanoplatelets nanocomposite (ZnO/GNP NC) as both the sensing element and reinforcement phase. The ZnO/GNP NC strain sensor exhibits fascinating performance, including high mechanical properties (fracture strength of 0.6 MPa and elongation of ~ 90%), large working range of 0–44%, high sensitivity (gauge factor of 8.8–12.8), and good reproducibility over 1700 cycles. Importantly, the ZnO/GNP NC strain sensor holds perfect linearity (R2 = 0.999) in the whole working range, which can be attributed to the coupling effect between the ZnO NPs and the GNP. The ZnO/GNP NC strain sensor can not only detect large human motions such as elbow rotation, wrist rotation, clenching fist, and waving badminton racket, but also monitor subtle human motions in real time, such as pulse, phonation, coughing, and swallowing. The wide linear working range of the ZnO/GNP NC strain sensor makes it a potential choice for the application of wearable devices.

Silver Nanoparticles-Chitosan Composite Embedded Graphite Screen-Printed Electrodes as a Novel Electrochemical Platform in the Measurement of Trace Level Nitrite: Application to Milk Powder Samples

Background:Nitrites can exert acute toxic effects in humans. It is widely used as a preservative in dairy and meat products. The nitrites form N-nitrosamines, which are potential carcinogens and cause detrimental health effects. Herein we report a disposable graphite screen-printed sensor developed using silver metal nano particle embedded chitosan composite in the quantification of nitrite at trace level.Methods:Conventional methods possess various limitations. Electrochemical methods provide an ideal platform for trace nitrite analysis. The prepared composite has been characterized by UV-Visible spectrometry, SEM, EDS and XRD techniques. The proposed sensor has been fabricated by using graphite screen-printed electrodes through drop coating of the composite material. The redox behavior and its application of the fabricated electrode have been studied using cyclic and anodic stripping voltammetric methods.Results:Graphite screen-printed electrodes after modification have been used to identify the electrocatalytic behavior of nitrite oxidation in an aqueous medium. All the parameters influencing the analytical signal have been optimized and incorporated in the recommended procedure. The proposed sensor has been used to measure the nitrite levels from commercially available milk powder samples and the results have been compared with the standard protocol. The results of the proposed sensor are in good agreement with the standard protocol.Conclusion:Ag metal nanoparticles have been embedded in chitosan matrix and used as a composite material in the chemical modification of graphite screen-printed electrodes. GSPEs are easy to fabricate. They provide wide linear working range i.e. 30 - 1140 µM of nitrite. The sensor is highly stable, reproducible and provides a very low detection limit of 1.84 µM. The method has been applied to measure trace level nitrite from milk powder samples.

Electroanalytical Determination of Cysteine Using the Electrodes Based on Ternary Silver-Copper Sulfides.

The amperometric determination of cysteine, using an electrode based on ternary silver-copper sulfide, is presented. Electrochemical characterizations (using cyclic voltammetry) of three electrode materials revealed that the electrode based on the material that consists of jalpaite (Ag3CuS2), doped with a small amount of metallic silver, has the best electrocatalytical performance for cysteine oxidation. For the amperometric determination, 0.142 V at pH 5 and 0.04 V at pH 7 vs. Ag/AgCl, related to the electrocatalytical oxidation of thiol group, were chosen. Electrochemical impedance spectroscopy together with Fourier transform infrared spectroscopy (FTIR) revealed that oxidation takes place on the electrode surface with fouling effect, which does not affect a wide linear working range between 1 μM and 100 μM. Sensitivities, at pH 5 and pH 7, are calculated to be 0.11 μA μM−1 and 0.10 μA μM−1, respectively. The detection limits were determined to be 0.036 μM and 0.024 μM for pH 5 and pH 7, respectively. In the presence of uric acid, folic acid, ascorbic acid, and glucose no interference was noticed. This electrode showed remarkable stability and excellent reproducibility. The electrode was exploited for the determination of cysteine in a dietary supplement with the excellent recoveries.

Comprehensive monitoring of specific metabolites of tri-(2-ethylhexyl) trimellitate (TEHTM) in urine by column-switching liquid chromatography-tandem mass spectrometry.

Tri-(2-ethylhexyl) trimellitate (TOTM or TEHTM) is a substitute for the plasticizer di-(2-ethylhexyl) phthalate (DEHP). Here, a fast and robust HPLC method is presented for the first time enabling the simultaneous quantification of several TEHTM metabolites in urine. These are the three TEHTM monoester isomers 1-mono-(2-ethylhexyl) trimellitate (1-MEHTM), 2-mono-(2-ethylhexyl) trimellitate (2-MEHTM), and 4-mono-(2-ethylhexyl) trimellitate (4-MEHTM) as well as several selected side chain oxidized monoesters of TEHTM, namely, 1-mono-(2-ethyl-5-hydroxyhexyl) trimellitate (5OH-1-MEHTM), 2-mono-(2-ethyl-5-hydroxyhexyl) trimellitate (5OH-2-MEHTM), 1-mono-(2-ethyl-5-oxohexyl) trimellitate (5oxo-1-MEHTM), 2-mono-(2-ethyl-5-oxohexyl) trimellitate (5oxo-2-MEHTM), 1-mono-(2-ethyl-5-carboxypentyl) trimellitate (5cx-1-MEPTM), 2-mono-(2-ethyl-5-carboxypentyl) trimellitate (5cx-2-MEPTM), 2-mono-(2-carboxymethylhexyl) trimellitate (2cx-2-MMHTM), and 1-mono-(2-carboxymethylhexyl) trimellitate (2cx-1-MMHTM). The method is characterized by a short sample preparation, for which the urine samples are enzymatically hydrolyzed and cleaned up by an online column arrangement. Separation of the analytes is enabled using liquid chromatography coupled with tandem mass spectrometry. Thus, in less than 30min, 11 postulated metabolites of TEHTM can be selectively and sensitively quantified. The method is distinguished by its wide linear working range of up to 1800μg/L with detection limits ranging from 0.3μg/L (for 5oxo-1-MEHTM) to 1.5μg/L (for 1-MEHTM). Precision and repeatability of the method were proven with determined relative standard deviations between 2.5 and 11.3%. The selection of the analytes of this method was based on a pilot study, by which several potential TEHTM metabolites were investigated in human urine of an orally exposed volunteer. Thus, the here presented method is a perfect tool for human biomonitoring of TEHTM exposure. Graphical abstract Analysis of several postulated TEHTM metabolites in human urine using LC-MS/MS.

Glutathione-Capped Gold Nanoparticles-Based Photoacoustic Sensor for Label-Free Detection of Lead Ions

The photoacoustic signal generated by laser-induced nanobubbles (PA-LINB) proved to be a sensitive tool to monitor the aggregation of gold nanoparticles. Here, a simple and label-free photoacoustic method for the rapid detection of Pb2+ in the aqueous phase was developed. Due to the high affinity of Pb2+ ions to glutathione, the presence of Pb2+ led to the aggregation of glutathione-conjugated gold nanoparticles (GSH-GNPs). Hence, by measuring the variation of the PA-LINB signal after the aggregation of GSH-GNPs, Pb2+ can be quantified. A low detection limit for Pb2+ (42 nM) and a wide linear working range (~42–1000 nM) were achieved. Furthermore, the proposed method showed good selectivity against other metal ions.

Naked eye and smartphone applicable detection of toxic mercury ions using fluorescent carbon nanodots

Chitosan passivated carbon nanodots (C-Dots$_{CHIT})$ were synthesized from expired molasses via a simple and green thermal synthesis procedure. As-synthesized C-Dots were nitrogen-doped (NC-Dots$_{CHIT})$ by posttreatment with liquid ammonia and used as nanoprobes for fluorometric detection of mercury ions (Hg(II)$_{aq.})$. Fluorescence response of NC-Dots$_{CHIT}$ in the presence of mercury was evaluated and compared with that of the polyethylene glycol passivated C-Dots$_{PEG}$. This sensing strategy using NC-Dots$_{CHIT}$ displayed a wide linear working range from 1.25 $\mu $g/mL to 43.54 $\mu $g/mL with a detection limit of 1.41 $\mu $g/mL. The fluorescence of C-Dots$_{PEG}$ did not show any significant change upon mercury addition. Selectivity of as-synthesized NC-Dots$_{CHIT}$ to Hg(II)$_{aq.}$ was assessed by comparing the level of fluorescence quenching in the presence of four other divalent cations (cadmium(II), zinc(II), nickel(II), and copper(II)). Finally, synthesized nanoprobes were embedded into the cross-linked alginate hydrogels and test strips were formed on the FTO-coated glass. Images captured under a UV light source (λexc: 365 nm) were successfully processed by a smartphone application. Color codes generated by the app showed a close resemblance to the data gathered from fluorescence spectroscopy. The proposed detection system was applied satisfactorily to both a certified calibration standard and real water samples. The methodology developed within this study could be a potential candidate for detection of mercury concentration in water samples with high recovery rates reaching up to 98%. This smartphone applicable detection platform that uses carbon nanodots as cheap yet sensitive nanoprobes could lead to more advanced lab-on-site systems for water or food sample analysis that can be performed by anyone, anywhere, anytime.

Multivariate optimisation of a rapid and simple automated method for bismuth determination in well water samples exploiting long path length spectrophotometry

ABSTRACTAn automated spectrophotometric system is proposed for the determination of bismuth in well water samples, using multi-syringe flow injection analysis (MSFIA) and exploiting a liquid waveguide capillary cell (LWCC). This method is based on the colorimetric reaction of bismuth and methylthymol blue (MTB) in the presence of polyvinylpyrrolidone (PVP) in acid medium (0.1 mol L−1 HNO3). The Bi(III)–MTB complex was measured at 600 nm. The method was optimised by multivariate techniques. Some figures of merit of the proposed system are worth being highlighted, such as its wide linear working range (between 4.9 and 600 μg L−1), its low detection limit (1.5 μg L−1 of bismuth) and its high intra-day precision and inter-day precision (0.7% (n = 12) and 1.4% (n = 5), respectively, both expressed as RSD). Moreover, a high injection frequency of 30 h−1 is achieved, as the proposed analyser is a powerful tool for fast Bi(III) determination. The method developed was successfully validated by analysing reference samples (pharmaceutical samples) by comparing the results with those obtained by ICP-OES and it was satisfactorily applied to well water samples. Besides, the present system is miniaturised allowing in situ measurements in control processes and field analysis.

Ethanol fuel adulteration with methanol assessed by cyclic voltammetry and multivariate calibration

Abstract In this work, it is proposed the one-voltammogram simultaneous determination of methanol and ethanol in hydrated ethyl alcohol fuel (HEAF) samples by cyclic voltammetry and multivariate calibration. To perform the determination, different multivariate calibration approaches were tested namely partial least-squares regression (PLS) and multivariate linear regression (MLR). To minimize collinearity problems in MLR, three variable selection algorithms were evaluated: the successive projections algorithm (SPA), the stepwise (SW) formulation, and the genetic algorithm (GA). Variable selection could also provide an improvement in prediction results when compared to full-voltammogram PLS. In this sense, genetic algorithm PLS (GA-PLS), interval PLS (iPLS), and synergy interval PLS (siPLS) were evaluated. An excellent analytical performance was obtained for both alcohols (RMSEP −1 ) with GA-MLR performed on data transformed by standard normal variate (SNV). The developed method presented a wide linear working range for both alcohols and a LOD = 0.9% w.w −1 for methanol sufficient to assess the adulteration of HEAF samples in accordance to Brazilian regulatory agency. The proposed method is simple (with no sample pre-treatment), accurate, rapid, presents low-cost, and can be conducted at distribution sites using a portable potentiostat.

Rapid determination of four short-chain alkyl mercapturic acids in human urine by column-switching liquid chromatography-tandem mass spectrometry.

We developed and validated an analytical method for the simultaneous determination of methyl mercapturic acid (MeMA), ethyl mercapturic acid (EtMA), n-propyl mercapturic acid (PrMA) and iso-propyl mercapturic acid (iPrMA) in human urine. These alkyl mercapturic acids are known or presumed biomarkers of exposure to several alkylating agents including methyl bromide, dimethyl sulfate, ethyl bromide, 1-bromopropane and 2-bromopropane. The method involves a column switching arrangement for online solid phase extraction of the analytes with subsequent analytical separation and detection using liquid chromatography and tandem mass spectrometry. Within day and day-to-day imprecision was determined to range from 4.5 to 12.2%. The analytical method is distinguished by its wide linear working range of up to 2,500 μg/L with detection limits ranging from 2.0 μg/L (for PrMA) to 5.1 μg/L (for MeMA) that render possible the application in various biomonitoring studies regarding exposure to alkylating agents. The results of a pilot study on urine samples of 30 individuals occupationally non-exposed to alkylating agents using the new procedure confirmed the background excretion of MeMA (<5.1-35.6 μg/L) and PrMA (<2.0-95.7 μg/L).

A highly sensitive and wide-ranged electrochemical zinc(II) aptasensor fabricated on core–shell SiO2-Pt@meso-SiO2

In this work, bi-functional SiO2-Pt@meso-SiO2 core–shell nanoparticles were designed to prepare a highly sensitive and selective electrochemical zinc(II) aptasesnor. This core–shell structure boasts its SiO2 mesoporous shell and the inside Pt nanoparticles. SiO2 mesoporous shell can fix aptamer without affecting its configuration and can admit electrolyte through the shell. SiO2 core inside can be the substrate of larger amount of Pt nanoparticles that improve the conductivity of the modified electrode dramatically. Due to the application of such a special bi-functional structure and the aptamer's strong combination capacity with Zn2+, Zn2+ is pre-enriched onto the electrode effectively and specifically, so that it can be determined sensitively and selectively. Results have shown that the zinc(II) aptasensor can be utilized at a wide linear working range from 100pM to 50μM and a low detection limit of 65pM, which makes it practical in both biological samples and environment monitoring. This method has been successfully applied in Zn2+ monitoring in human blood and disrupted human cells (MCF-7).

Electropreparation of (±)‐10‐camphorsulfonate‐doped poly(o‐phenylenediamine) in acetonitrile and its use in determination of glucose

ABSTRACTPoly(o‐phenylenediamine) (PoPD) film has been electrochemically prepared on Pt electrode in an acetonitrile–water medium containing o‐phenylenediamine (oPD) monomer and (±)‐10‐camphorsulfonic acid (HCSA) by using the cyclic voltammetry (CV). The PoPD film (PoPD–CSA) has been characterized by FTIR, CV, EIS, FESEM, and conductivity measurement. The glucose biosensor (Pt/PoPD–CSA/GOx) has been prepared from the PoPD coated electrode by immobilizing glucose oxidase (GOx) enzyme using glutaraldehyde. The biosensor shows a low detection limit and wide linear working range, a good reusability, long‐term stability, and anti‐interference ability. The Pt/PoPD–CSA/GOx has possesses higher sensitivity (2.05 μA/mmol L−1) and affinity to glucose due to the use of CSA ion as dopant. The linear concentration ranges of Pt/PoPD–CSA/GOx have been found to be 9.6 × 10−3 to 8.2 mmol L−1 from calibration curve and 4.6 × 10−2 to 100 mmol L−1 from the relationship between the (1/glucose concentration) and (1/current difference). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39864.

Real-time electrochemical monitoring of adenosine triphosphate in the picomolar to micromolar range using graphene-modified electrodes.

We report on a competitive electrochemical detection system that is free of wash steps and enables the real-time monitoring of adenosine triphosphate (ATP) in a quantitative manner over a five-log concentration range. The system utilizes a recognition surface based on ATP aptamer (ATPA) capture probes prebound to electroactive flavin adenine dinucleotide (FAD) molecules, and a signaling surface utilizing graphene (Gr) and gold nanoparticle (AuNP) modified carbon paste electrode (Gr-AuNP-CPE) that is optimized to enhance electron-transfer kinetics and signal sensitivity. Binding of ATP to ATPA at the recognition surface causes the release of an equivalent concentration of FAD that can be quantitatively monitored in real time at the signaling surface, thereby enabling a wide linear working range (1.14 × 10(-10) to 3.0 × 10(-5) M), a low detection limit (2.01 × 10(-11) M using graphene and AuNP modified glassy carbon), and fast target binding kinetics (steady-state signal within 12 min at detection limit). Unlike assays based on capture probe-immobilized electrodes, this double-surface competitive assay offers the ability to speed up target binding kinetics by increasing the capture probe concentration, with no limitations due to intermolecular Coulombic interactions and nonspecific binding. We utilize the real-time monitoring capability to compute kinetic parameters for target binding and to make quantitative distinctions on degree of base-pair mismatch through monitoring target binding kinetics over a wide concentration range. On the basis of the simplicity of the assay chemistry and the quantitative detection of ATP within fruit and serum media, as demonstrated by comparison of ATP levels against those determined using a standard high-performance liquid chromatography (HPLC)-UV absorbance method, we envision a versatile detection platform for applications requiring real-time monitoring over a wide target concentration range.