In Situ Self Assembly of Thiolated ortho‐Quinone Capped Electrocatalysts for Bioanalytical Applications

Abstract

Thiolated o-quinone-capped electrocatalysts modeled on the naturally occurring o-quinone cofactor pyrroloquinoline quinone (PQQ) were designed and synthesized for the development of biosensor devices. The o-quinonecapped electrocatalysts self assembled on gold electrodes through a thiolated phenyleneethynylene linkage to form a monolayer less than 2 nm in thickness. Cyclic voltammetric measurements demonstrated reversible electrochemical properties between the quinone and hydroquinone forms of the head group. In an amperometric sensing mode, the modified electrodes reproducibly detected ethanethiol at micromolar levels demonstrating their robust electrocatalytic activity toward thiols. Their redox cycling and electrocatalytic properties show promise for detection of biologically important thiols and other nucleophiles. Redox-cycling quinones play important roles in biological signaling, metabolic pathways, gene expression, and disease prevention [1]. Their widespread incorporation in biological processes results from the efficiency of the quinone electron-transfer and their reactivity to nucleophiles. The redox active o-quinone moiety exhibits an efficient, pH-dependent reversible electron transfer between its oxidized and reduced forms, which makes o-quinones attractive electrocatalysts for molecular devices and sensors [2]. However, one drawback is the binding of reactive nucleophiles by Michael type addition. Although this property can be exploited to develop biosensing devices to detect biomarkers and infectious agents through binding of DNA, proteins and other biomolecules containing nucleophilic groups [3][4][5], it compromises their integrity as redox-cycling electrocatalysts for biosensor applications.Two recent examples of sensors based on naturally occurring o-quinone redox cofactors utilize tryptophan tryptophylquinone (TTQ) [6] and pyrroloquinoline quinone (PQQ) [7][8][9][10]. In both cases the o-quinone moiety serves as an efficient electron shuttle without deactivation of the electrocatalyst. This unique combination of properties is attributed to the substituted o-quinone ring found in PQQ and TTQ that impedes 1,4-addition of nucleophiles.Interestingly, PQQ catalyzes non-enzymatic reactions such as the oxidation of thiols to disulfides [11,12], which we have utilized to develop sensitive and selective thiol detection strategies with PQQ entrapped in a polypyrrole conducting polymer membrane [7][8][9][10].As part of an effort to harness the electrocatalytic properties of the natural o-quinone cofactors, we have initiated research to synthesize o-quinone analogues with exceptional redox cycling capabilities similar to PQQ [13]. One challenge with this approach is maintaining electrocatalyst levels in the sensing membrane for extended time periods. In order to improve sensor stability and also enhance the versatility for thiol detection, we have designed and synthesized second generation o-quinone electrocatalysts, where the o-quinone is anchored to the electrode via a thiol-terminated electric...

New self-assembled layers composed with gold nanoparticles, cysteamine and dihydrolipoic acid deposited on bare gold template for highly sensitive and selective simultaneous sensing of dopamine in the presence of interfering ascorbic and uric acids

“…1a) demonstrates that with the formation of adsorbate, the S-H bonds are broken and the S atoms are directly bonded with the Au surface atoms. This result is consistent with the previously reported proton abstraction from alkanethiols adsorbed on Au [52][53][54][55].…”

Gold Surface Functionalization with S‐containing Organic Compounds and Gold Nanoparticles for Ethylene Glycol Electrooxidation

“…From a comparison of the transmission FT‐IR spectrum of the liquid 3‐mercaptoprpionic acid with the infrared reflection spectrum of this acid adsorbed at Au surface, presented earlier in literature 35, it is evident that the S atoms are directly bonded with Au surface atoms, as in the case previously reported for some organic compounds with the thiol atoms adsorbed on Au substrate 39–42. The basic strategy for the preparation of modified electrodes used in the present paper may be illustrated by Scheme :…”

Amperometric Detection of Histamine with a Pyrroloquinoline‐Quinone Modified Electrode

“…The PQQ based electrodes were also successfully utilized to detect thiocholine for the real-time monitoring of acetylcholinesterase activity in the presence of the known neurotoxin carbofuran [21]. In addition our recent studies have focused on exploring new electrocatalysts including novel thiolated oquinone-capped molecular wires that form self-assembled electrocatalytic layers on gold electrodes [22,23].…”