Electron Permeable Self-Assembled Monolayers of Dithiolated Aromatic Scaffolds on Gold for Biosensor Applications

Abstract

Self-assembled monolayers (SAMs) of thiolated compounds are formed by the spontaneous chemisorption of thiolate groups on metal surfaces. In biosensors, they are most commonly used to covalently immobilize a biorecognition molecule onto the surface of the transducer, thus offering the possibility of controlling the orientation, distribution, and spacing of the sensing element while reducing nonspecific interactions. In this paper, self-assembled monolayers of dithiolated derivatives of 3,5-dihydroxybenzyl alcohol containing carboxyl and hydroxyl end groups have been prepared on gold surfaces and characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Impedance measurements revealed that SAM formation is essentially completed after 3-5 h of exposure by observing the successive blocking of the faradic response of ferricyanide anion due to the adsorption of the dithiol molecules. The surface coverage of these molecules, estimated by reductive desorption experiments, was in the range of (1.1-2.8) x 10-10 mol/cm2. To demonstrate the potential of the dithiol SAM, a model system for detection of a tumor marker, prostate-specific antigen (PSA), was developed. The carboxyl groups of the SAM were succinimide-activated, and an anti-PSA antibody was covalently immobilized via amide bonds. The modified SAM was used for the label-free detection of prostate-specific antigen using EIS with a detection limit of 9 ng/mL. The results described here demonstrate that this kind of dithiol-modified SAM can be used as supports in electrochemical biosensors and the results are explained in terms of the structural features of these dithiols.

Acetylcholinesterase biosensor based on self-assembled monolayer-modified gold-screen printed electrodes for organophosphorus insecticide detection

“…SAMs were usually prepared using the affinity of thiols such as alkanethiols for some metal surfaces, particularly gold. In this case, the main advantage consists in the immobilization of the enzyme close to the electrode surface with a high degree of control over the molecular architecture of the recognition interface [17,18]. Few papers in literature report the assembling of a AChE-SAM biosensor.…”

Suppression of Non-specific Adsorption Using Densified Tri(ethylene glycol) alkanethiols: Monolayer Characteristics Evaluated by Electrochemical Measurements

“…[5][6][7][8][9] The mechanism that prevents non-specific protein adsorption on PEG (OEG) layers has also been studied by using spectroscopic measurements (infrared spectroscopy, X-ray photoelectron spectroscopy) and other methods, including an electric charge technique and measurements of hydrophilicity, hydrophobicity and bulkiness of terminating groups. [10][11][12][13][14] The hydrophilicity and flexiblity of PEG (OEG) structures are largely responsible for its repellency. Although the larger OEG units are more effective in preventing non-specific adsorption (R-(CH2)11SH; R, ethylene glycol units), the di(ethylene glycol) unit is known to be the shortest unit capable of repelling protein adsorption.…”

Investigation of Ph-Assisted Human Serum Albumin (HSA)-Cobalt (Co)Binding Using Nanomechanical Deflection and Circular Dichroism

“…This ligand binds to the gold surface strongly forming PEG-islands [43] and provides improved flexibility to biomolecules. We have chosen PEG based crosslinking ligand to provide required sensitivity to HSA molecules as this crosslinking ligand prevents non-specific interactions, and provides more spatial orientation to HSA due dithiolate anchoring terminal towards gold face [43,44]. The characterization of the surface with SAM (PEG 12 -CL) was achieved using FTIR and fluorescence spectroscopy.…”