Gold Nanoparticles with Self-Assembled Cysteine Monolayer Coupled to Nitrate Reductase in Polypyrrole Matrix Enhanced Nitrate Biosensor

Abstract

We have developed here a novel, highly sensitive and selective nitrate (NO −3 ) biosensor by covalent immobilization of nitrate reductase (NaR) in self-assembled monolayer (SAM) of cysteine on gold nanoparticles (GNP)-polypyrrole (PPy) modified platinum electrode. Incorporation of GNP in highly microporous PPy matrix was confirmed by morphological scanning electron microscope (SEM) images. The electrochemical behavior of the NaR modified electrode exhibited the characteristic reversible redox peaks at the potential, −0.76 and −0.62 V versus Ag/AgCl. Further, the GNP-PPy nanocomposite enhanced the current response by 2-fold perhaps by enhancing the immobilization of NaR and also direct electron transfer between the deeply buried active site and the electrode surface. The common biological interferences like ascorbic acid, uric acid were not interfering with the NO − 3 measurement at low concentration levels. This biosensor showed a wide linear range of response over the concentration of NO − 3 from 1 M to 1 mM, with higher sensitivity of 84.5 nA M −1 and a detection limit of 0.5 M. Moreover, the NO − 3 level present in the nitrate-rich beetroot juice and the NO − 3 release from the lipopolysaccharide treated human breast cancer cells were estimated.

Label-Free Electrochemical Immunoassay for C-Reactive Protein

“…Earlier reports that were published on label-free CRP measurements [ 13 , 17 , 18 ] are limited in sensitivity, and do not encompass a clinically relevant range. Subsequently, to promote the sensitivity and the stability of the electrodes, nanomaterials, such as carbon nanotubes, gold nanoparticles (AuNPs), quantum dots, graphene, and metal oxide nanoparticles have been in the focus of interest [ 19 , 20 , 21 , 22 , 23 , 24 ]. In this context, Zhu et al reported the AuNPs amplified label-free electrochemical immunosensor for CRP [ 25 ].…”

A miniaturized electrochemical assay for homocysteine using screen-printed electrodes with cytochrome c anchored gold nanoparticles

“…Despite its good selectivity and low detection limits, it requires extensive, time-consuming sample preparation and derivatization steps prior to sample analysis. [18][19][20][21] Hence, there is growing interest in the development of direct and indirect electrochemical methods for the determination of HcySH. chemiluminescence, 14 fluorescence, 15 and UV-Vis detection protocols, 16,17 which are also employed for clinical HcySH assays, involve expensive reagents and instrumentation systems.…”

“…To overcome these limitations, electrochemical biosensor techniques have recently been considered as an alternative for the measurement of clinically important biomarkers owing to the obvious practical advantages of operation simplicity (less labor-intensive), low costs of fabrication, and suitability for real time detection. [18][19][20][21] Hence, there is growing interest in the development of direct and indirect electrochemical methods for the determination of HcySH. Initially, the ability of specific chemicalsfor instance aminothiadiazole, nitrogen doped graphene nanosheets and cobalt phthalocyanine modified electrodeswas investigated for the direct oxidation of HcySH.…”

Enzymatic Biosensors

“…Therefore,Madasamy et al (2013) 21 Schematic illustration of the electrochemical reduction of NO 3 À by NaR during the measurement of NO 3 À . The measurement of NO 3 À concentration in beetroot supplement provides supporting information to prove its natural remedy effect.…”