Electrochemical Immunosensors with PQQ-Decorated Carbon Nanotubes as Signal Labels for Electrocatalytic Oxidation of Tris(2-carboxyethyl)phosphine

Abstract

Nanocatalysts are a promising alternative to natural enzymes as the signal labels of electrochemical biosensors. However, the surface modification of nanocatalysts and sensor electrodes with recognition elements and blockers may form a barrier to direct electron transfer, thus limiting the application of nanocatalysts in electrochemical immunoassays. Electron mediators can accelerate the electron transfer between nanocatalysts and electrodes. Nevertheless, it is hard to simultaneously achieve fast electron exchange between nanocatalysts and redox mediators as well as substrates. This work presents a scheme for the design of electrochemical immunosensors with nanocatalysts as signal labels, in which pyrroloquinoline quinone (PQQ) is the redox-active center of the nanocatalyst. PQQ was decorated on the surface of carbon nanotubes to catalyze the electrochemical oxidation of tris(2-carboxyethyl)phosphine (TCEP) with ferrocenylmethanol (FcM) as the electron mediator. With prostate-specific antigen (PSA) as the model analyte, the detection limit of the sandwich-type immunosensor was found to be 5 pg/mL. The keys to success for this scheme are the slow chemical reaction between TCEP and ferricinum ions, and the high turnover frequency between ferricinum ions, PQQ. and TCEP. This work should be valuable for designing of novel nanolabels and nanocatalytic schemes for electrochemical biosensors.

Electro-oxidation of amino-functionalized multiwalled carbon nanotubes

“…Amino-functionalized MWCNTs (MWCNTs-NH 2 ) have aroused considerable interest since the amino groups attached to the CNTs allows a diversity of further chemical functionalization as well as showing valuable properties in themselves 15 notably as absorbents for metal ions, 16,17 acting as supports for the preparation of electrocatalysts 18,19 and facilitating the fabrication of (bio) sensors. 20,21 The formation of MWCNTs-NH 2 have been realized by different approaches.…”

Optical Bioassays Based on the Signal Amplification of Redox Cycling

“…Under the optimized conditions, the method exhibited a linear range of 0.02-4 μM and a LOD of 14.8 nM. PQQ-modified nanomaterials have been exploited as redox mediators for the catalytic oxidation of TCEP and thiols [53][54][55][56]. For this consideration, Xia et al reported the colorimetric immunoassay of prostate specific antigen (PSA) based on PQQ-initiated redox cycling between Fe 3+ -ferrozine and TCEP [57].…”