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In this work, a simple label-free electrochemical immunosensor for the detection of carcinoembryonic antigen (CEA) was developed. At first, the GC electrode was coated with partially reduced graphene oxide (rGO) to form a platform to bind the antibody. After activating the carboxyl groups of rGO through the EDC/NHS linker, the electrode surface was covered with the antibody. Then, the electrochemical behavior of the antibody-modified electrode and the parameters of the interactions of antibody-antigen immune complexes were investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). This immune-complex layer was found to attenuate the electrochemical current which can be used as a good signal to determine the antigen concentration. The proposed immunosensor exhibited a good amperometric response to CEA within a concentration range of 0.1-5 ng mL -1 with a detection limit of 0.05 ng ml -1 . Furthermore, the developed method was evaluated for the detection of CEA in the real sample (human blood serum), and the results were comparable with the reference values obtained by the standard enzyme-linked immunosorbent assay (ELISA). Our findings suggest the present immunosensor as a good candidate for application in clinical screening., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Herein, we report the fabrication of a novel label-free impedimetric biosensor employing porous graphene oxide (PrGO) nanostructures for the specific detection of cardiac troponin-I (cTnI) to establish the myocardial infarction (MI). This nano-immunosensor demonstrates an outstanding selectivity and high sensitivity towards the human-cTnI analyte. An excellent detection limit of 0.07ngmL(-1) and dynamic linear range of 0.1-10ngmL(-1) were calculated for anti-cTnI/PrGO/GC. Finally, this biosensor was employed to check the concentration of the MI biomarker in real clinical samples and the results are in good agreement with standard enzyme-linked fluorescence assay (ELFA) method., (Copyright © 2016 Elsevier B.V. All rights reserved.)

In the present work we report a facile method for fabrication of glucose oxidase immobilized on the partially reduced graphene-gold nanocomposite (PRGO-AuNPs/GOx) as a novel biosensor for determination of glucose concentration. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the morphology of PRGO and PRGO-AuNPs. Also, fast Fourier transformation infrared spectroscopy (FTIR) and UV-Vis spectroscopy were used to confirm formation of graphene and graphene-gold composite. Then, the electrochemical behavior of PRGO-AuNPs/GOx modified electrode was studied by cyclic voltammetry (CV). Our electrochemical studies, especially chronoamperometry (CA), showed that the PRGO-AuNPs/GOx modified electrode has excellent electrocatalytic activity towards the glucose. The limit of detection and sensitivity towards glucose were estimated as 0.06μM and 15.04mAmM(-1), respectively., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In this article we report the application of non-Faradaic mode of electrochemical impedance spectroscopy (EIS) for determination of potassium ion (K(+)) concentration using a guanine rich K(+)-selective aptasensor (K(+)-aptasensor). This is a simple, electroactive probe free, sensitive and reproducible method allowing determination of K(+) ion concentration without any disturbance from electroactive probes used in similar works based on the Faradaic EIS method. Herein, a wide linear range of K(+) ion concentrations (1 μM-0.1mM) with a 200 nM limit of detection was achieved which is better than most of the previously reported Faradaic biosensing methods. The proposed method maintains valuable applications when it is used for K(+) determination in the presence of potentially important interferences in biological media. Thus, application of the non-Faradaic EIS method for sensing the concentration of K(+) ion with the presented K(+)-aptasensor can find an important role in clinical assay., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In the present work, gold electrode modified with novel aldehyde-terminated self-assembled monolayers (SAMs) was used for controllable load and release of dopamine molecules by pH triggering. Electrochemical techniques including cyclic voltammetry (CV) and electrochemcial impedance spectroscopy (EIS) were employed to investigate the SAMs characteristic on the gold electrode surface. The electrochemical experiments indicated Faradaic behavior for the electrode surface after its modification with dopamine. Notably, it was observed that decreasing the conditioning pH, results in a decrease of peak currents, presumably due to the hydrolysis of the terminal imine bonds and releasing the dopamine moiety into the solution. Moreover, the preliminary kinetics studies were done for dopamine release from the SAMs surface as a model to design future drug delivery systems. Finally, the rate constant of dopamine release from the SAMs modified surface estimated to be 0.167 day(-1) at pH=3., (© 2013.)

A double-stranded calf thymus DNA (dsDNA) was physisorbed onto a polypyrrole (PPy) nanofiber film that had been electrochemically deposited onto a Pt electrode. The surface morphology of the polymeric film was characterized using scanning electron microscopy (SEM). The electrochemical characteristics of the PPy film and the DNA deposited onto the PPy modified electrode were investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Then the interaction of DNA with salicylic acid (SA) and acetylsalicylic acid (ASA), or aspirin, was studied on the electrode surface with DPV. An increase in the DPV current was observed due to the oxidation of guanine, which decreased with the increasing concentrations of the ligands. The interactions of SA and ASA with the DNA follow the saturation isotherm behavior. The binding constants of these interactions were 1.15×10(4)M for SA and 7.46×10(5)M for ASA. The numbers of binding sites of SA and ASA on DNA were approximately 0.8 and 0.6, respectively. The linear dynamic ranges of the sensors were 0.1-2μM (r(2)=0.996) and 0.05-1mM (r(2)=0.996) with limits of detection of 8.62×10(-1) and 5.24×10(-6)μM for SA and ASA, respectively., (Copyright © 2011 Elsevier Inc. All rights reserved.)