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Graphene, emerging as a true two-dimensional (2D) material, has attracted increasing attention due to its unique physical and electrochemical properties such as high surface area, excellent conductivity, high mechanical strength, and ease of functionalization and mass production. The entire scientific community recognizes the significance and potential impact of graphene. Electrochemical detection strategies have advantages such as being simple, fast, and low-cost. The use of graphene as an excellent interface for electrode modification provides a promising way to construct more sensitive and stable electrochemical (bio)sensors. The review presents sensors based on graphene and its derivatives for electrochemical drug assays from pharmaceutical dosage forms and biological samples. Future perspectives in this rapidly developing field are also discussed. In addition, the interaction of several important anticancer drug molecules with deoxyribonucleic acid (DNA) that was immobilized onto graphene-modified electrodes has been detailed in terms of dosage regulation and utility purposes.

In the present work, preparation of titanium dioxide coated graphene (TiO2/graphene) and the use of this nanocomposite modified electrode for electrochemical biosensing applications were detailed. The nanocomposite was prepared with radio frequency (rf) rotating plasma method which serves homogeneous distribution of TiO2 onto graphene. TiO2/graphene was characterized with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis. Then, this nanocomposite was dissolved in phosphate buffer solution (pH 7.4) and modified onto disposable pencil graphite electrode (PGE) by dip coating for the investigation of the biosensing properties of the prepared electrode. TiO2/graphene modified PGE was characterized with SEM, EDS and cyclic voltammetry (CV). The sensor properties of the obtained surface were examined for DNA and DNA-drug interaction. The detection limit was calculated as 1.25mgL(-1) (n=3) for double-stranded DNA (dsDNA). RSD% was calculated as 2.4% for three successive determinations at 5mgL(-1) dsDNA concentration. Enhanced results were obtained compared to the ones obtained with graphene and unmodified (bare) electrodes., (Copyright © 2016 Elsevier B.V. All rights reserved.)

In this work, Cibacron Blue F3GA (CB) modified pencil graphite electrodes (PGEs) were prepared and their affinities to bovine serum albumin were investigated. Preparation of the PGEs was performed using cyclic voltammetry (CV) and passive adsorption techniques. Improved electrochemical results were obtained with the PGEs prepared by CV technique compared to the PGEs prepared by passive adsorption technique. In order to obtain more sensitive results number of scans used in CV technique and the effect of concentration of CB were studied. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS) were used for the characterization of modified electrodes. The modified PGEs were then used for the electrochemical monitoring of affinity interaction between CB and bovine serum albumin. The effect of BSA concentration and interfering species (tryptophan, glucose and immunoglobulin G) on the response of the electrode were examined. The aim of this study was to prepare an easy, fast, stable and cheap modified electrode for the investigation of the well-known affinity of CB to serum albumin. The electrochemistry can provide alternative routes for dye-protein interaction instead of using classical time-consuming methods., (Copyright © 2013. Published by Elsevier B.V.)

Single-walled carbon nanotubes (SWCNT)-poly(vinylferrocenium) (PVF(+)) modified pencil graphite electrodes (PGEs) were developed in our study for the electrochemical monitoring of a sequence-selective DNA hybridization event. Firstly, SWCNT-PVF(+) modified PGE, PVF(+) modified PGE and unmodified PGE were characterized using scanning electron microscopy (SEM). The electrochemical behavior of these electrodes was then investigated using electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The SWCNT-PVF(+) modified PGEs were optimized for improved DNA sensing ability by measuring the guanine oxidation signal. In order to obtain the full coverage immobilization of the DNA probe following the optimum working conditions, the effect of amino-linked, thiol-linked and, bare oligonucleotides (ODNs), and the concentration of the DNA probe on the response of the modified electrode were examined. After optimization studies, the sequence-selective DNA hybridization was evaluated in the case of hybridization between an amino-linked probe and its complementary (target), a noncomplementary (NC) sequence, calf thymus double stranded DNA (dsDNA), and target/mismatch (MM) mixtures in the ratio of 1:1. SWCNT-PVF(+) modified PGEs presented very effective discrimination of DNA hybridization owing to their superior selectivity and sensitivity., (Copyright © 2011 Elsevier B.V. All rights reserved.)

A single walled carbon nanotube-chitosan (SWCNT-chitosan) modified disposable pencil graphite electrode (PGE) was used in this study for the electrochemical detection of Vitamin B(12). Electrochemical behaviors of SWCNT-chitosan PGE and chitosan modified PGE were compared by using cyclic voltammetry (CV), square-wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques. SWCNT-chitosan modified electrode was also used for the quantification of Vitamin B(12) in pharmaceutical products. The results show that this electrode system is suitable for sensitive Vitamin B(12) analysis giving good recovery results. The surface morphologies of the SWCNT-chitosan PGE, chitosan modified PGE and unmodified PGE were characterized by using scanning electron microscopy (SEM)., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The electrochemical preparation of nanostructured polymeric network consisted of poly(o-phenylenediamine)-multi-walled carbon nanotube (PoPD-MWCNT) on a disposable and commonly used pencil graphite electrode (PGE) was demonstrated. The obtained PoPD-MWCNT/PGE electrode was prepared via one-step electropolymerization using cyclic voltammetry (CV) and characterized by CV and electrochemical impedance spectroscopy (EIS). Surfaces topographies of the electrodes were investigated with scanning electron microscopy (SEM) in order to differentiate electrode modifications. The modified electrode highly improved the electrochemical properties of the PoPD/PGE and PGE. The fabrication process of the modified electrode was reproducible with a relative standard deviation of 3.8% (n = 3). Afterwards, sensitive detection of mitomycin C was performed based on the interaction of double-stranded DNA (dsDNA) immobilized on PoPD-MWCNT/PGE with mitomycin C. Thus, a detailed investigation of the interaction of dsDNA immobilized PoPD-MWCNT/PGEs with mitomycin C were also evaluated at various interaction intervals from 0 to 30 min in an efficient process. This promising electrode provided a linear concentration range for mitomycin C from 0.5 mg L−1 to 25 mg L−1 with a low limit of detection, 0.012 mg L−1, and a limit of quantification, 0.039 mg L−1, based on the guanine oxidation peaks using differential pulse voltammetry (DPV) (n = 3). The recoveries were also determined in spiked serum and satisfactory results emphasized the use of the electrode for clinical applications. [ABSTRACT FROM AUTHOR]

Abstract: A single walled carbon nanotube–chitosan (SWCNT–chitosan) modified disposable pencil graphite electrode (PGE) was used in this study for the electrochemical detection of Vitamin B12. Electrochemical behaviors of SWCNT–chitosan PGE and chitosan modified PGE were compared by using cyclic voltammetry (CV), square-wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques. SWCNT–chitosan modified electrode was also used for the quantification of Vitamin B12 in pharmaceutical products. The results show that this electrode system is suitable for sensitive Vitamin B12 analysis giving good recovery results. The surface morphologies of the SWCNT–chitosan PGE, chitosan modified PGE and unmodified PGE were characterized by using scanning electron microscopy (SEM). [Copyright &y& Elsevier]

Abstract: In this work, preparation and characterization of single-walled carbon nanotube–chitosan (SWNT–chitosan) modified disposable pencil graphite electrode (PGE) was carried out. Firstly, commercial single-walled carbon nanotube was purified and characterized using thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDX) for this purpose. Purified SWNT was mixed with chitosan polymer for preparing their composite. Then, PGE was modified with this composite. The characterization of the modified electrode was carried out using atomic force microscopy (AFM). The electrochemical behaviour of the obtained electrode was investigated and compared with the electrochemical behaviour of chitosan modified and unmodified PGEs using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and alternative current (AC) impedance spectroscopy. In order to obtain more sensitive electrochemical signals, the effect of SWNT concentration was studied. This modified electrode also showed electrocatalytic effect for hydrogen evolution. [ABSTRACT FROM AUTHOR]

Abstract: In this study, SnO2 nanoparticles (SNPs)-poly(vinylferrocenium) (PVF+) modified single-use graphite electrodes were developed for electrochemical monitoring of DNA hybridization. The surfaces of polymer modified and polymer–SNP modified pencil graphite electrodes (PGEs) were firstly characterized by using SEM analysis. The electrochemical behaviours of these electrodes were also investigated using the differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) techniques. The polymer–SNP modified PGEs were then tested for the electrochemical sensing of DNA based on the changes at the guanine oxidation signals. Experimental parameters, such as; different modifications in DNA oligonucleotides, DNA probe concentrations were examined to obtain more sensitive and selective electrochemical signals for nucleic acid hybridization. After optimization studies, DNA hybridization was investigated in the case of complementary of hepatitis B virus (HBV) probe, mismatch (MM), and noncomplementary (NC) sequences. [ABSTRACT FROM AUTHOR]

Abstract: Poly(vinylferrocenium) (PVF+) modified electrode was developed in this study for the electrochemical sensing of DNA based on the oxidation signals of polymer, adenine and guanine. Experimental parameters, such as; polymeric film thickness, DNA immobilization time and DNA concentration were examined in order to obtain more sensitive and selective electrochemical signals. After optimization studies, DNA hybridization was investigated. [Copyright &y& Elsevier]

[Display omitted] • MoS 2 /Chitosan/GOx-Gelatin surfaces were fabricated for the first time. • Morphological characterization supported the electrochemical results. • Robost and reproducible surfaces were obtained. • Glucose determination was accomplished in a sensitive and selective way. • Improved analytical performance was obtained compared to the GOx-Gelatin/PGE. Graphene-like new generation of two dimensional (2D) nanomaterials, in particular the family of transition metal dichalcogenides (TMDCs) have been attracting a wide range of research interest. Among the family of TMDCs, molybdenum disulfide (MoS 2) has been the most used one for biosensor applications. In this work, we detail the preparation of MoS 2 /chitosan composite modified pencil graphite electrode (MoS 2 /Chitosan/PGE) and its use as glucose biosensor after the modified electrode were immobilized with glucose oxidase (GOx)-gelatin (MoS 2 /Chitosan/GOx-Gelatin/PGE). This electrode was compared with the unmodified electrode in terms of electrochemical performance. Superior electrochemical responses were achieved including good electroactivity and sensitive glucose biosensing. For the MoS 2 /Chitosan/GOx-Gelatin modified PGE, a linear glucose concentration range was obtained from 10 μM to 800 μM with the equation of y = 0.0008x + 0.0547 (R2 = 0.9992) and a limit of detection (LOD) value of 3.18 µM. The relative standard deviation (RSD%) was calculated as 3.77% at 200 μM glucose (n = 5). The biosensor was tested in the presence of dopamine and ascorbic acid and our results presented the high selectivity of this novel MoS 2 /Chitosan/GOx-Gelatin modified PGE as a glucose biosensor. [ABSTRACT FROM AUTHOR]

Highlights: [•] Diphenylalanine based peptide nanostructures were prepared in various solvents. [•] Electrochemical behaviors of modified pencil graphite electrodes are investigated. [•] Electrode surfaces were modified for 30min by immobilizing peptide nanotubes. [•] Square Wave voltammetric analyses showed linearity over the range of 0.2–9.50μM. [ABSTRACT FROM AUTHOR]