New insight into the electrochemical desorption of alkanethiol SAMs on gold

Abstract

A combination of Polarization Modulation Infrared Reflection Absorption Spectroscopy (PMIRRAS) under electrochemical control, Electrochemical Scanning Tunneling Microscopy (ECSTM) and Molecular Dynamics (MD) simulations has been used to shed light on the reductive desorption process of dodecanethiol (C12) and octadecanethiol (C18) SAMs on gold in aqueous electrolytes. Experimental PMIRRAS, ECSTM and MD simulations data for C12 desorption are consistent with formation of randomly distributed micellar aggregates stabilized by Na+ ions, coexisting with a lying-down phase of molecules. The analysis of pit and Au island coverage before and after desorption is consistent with the thiolate-Au adatoms models. On the other hand, PMIRRAS and MD data for C18 indicate that the desorbed alkanethiolates adopt a Na+ ion-stabilized bilayer of interdigitated alkanethiolates, with no evidence of lying down molecules. MD simulations also show that both the degree of order and tilt angle of the desorbed alkanethiolates change with the surface charge on the metal, going from bilayers to micelles. These results demonstrate the complexity of the alkanethiol desorption in the presence of water and the fact that chain length and counterions play a key role in a complex structure.

Accelerated Photo‐Induced Degradation of Benzidine‐p‐Aminothiophenolate Immobilized at Light‐Enhancing TiO2 Nanotube Electrodes

“…Moreover, it could potentially favor breaking of the Ti−S bonds and hence lead to (reductive) desorption of the dye as a competing side reaction. Such behavior has been observed for thiol‐bound compounds on metal electrodes . Importantly, an overall decreased photocatalytic degradation activity should be noted in this case.…”

“…Such behavior has been observed for thiol-bound compounds on metal electrodes. [22] Importantly,a no verall decreasedp hotocatalytic degradation activity should be noted in this case. Both are in fact observed in our experiments if we consider the rate constants derived at À0.4 V Ag/AgCl as ar ough estimation (convolutiono fd esorption and degradation)a nd comparet hem to those obtained at 0.4 V Ag/AgCl (Table 1).…”

Molecular recognition of 2,4,6-trinitrotoluene by 6-aminohexanethiol and surface-enhanced Raman scattering sensor

“…Further, the desorption potential of Au S bond in the case of AHT monolayer is higher by ∼0.1 V than that of the cysteamine monolayer. This can be attributed to the higher stability of Au S bond in the case of AHT monolayer due to increased van der Waals lateral integration upon increasing the hydrocarbon chain length of the alkyl thiol [31,48]. Thus, the higher stability of the AHT recognition molecule on the sensor surface is essential for the better shelf-life of the sensor.…”

“…The sharp desorption peak of AHT clearly depicts that AHT has formed a well packed monolayer on the pAu/AuNS surface [31]. This observation may provide indirect evidence that all the AHT molecules are oriented in the preferred trans conformation of alkanethiols on the surface [31,38,48]. To the contrary, the desorption LSV of cysteamine SAM from the pAu/AuNS surface shows two cathodic peaks at −0.91 V and −0.77 V. The presence of two desorption peaks of the cysteamine monolayer may be attributed in part to different Au S bond environments and different orientations of cysteamine on the pAu/AuS surface [35,36,49].…”

A regenerating ultrasensitive electrochemical impedance immunosensor for the detection of adenovirus

“…The long term stability of both approaches has been problematic (Cui and Martin, 2003;Cometto et al, 2012;Cooper and Legget, 1998;Lee et al, 2004;Nishida et al, 1996;Schoenfisch and Pemberton, 1998;Shadnam and Amirfazli, 2005;Yan et al, 2006), as is regeneration of the antibody. While electrochemical reductive desorption of self-assembled alkanethiols from gold electrodes is common (Pensa et al, 2012;Williams and Gorman, 2007;Mandler and Kraus-Ophir, 2011) and proven to be quite effective, studies pertaining to electrochemical removal of large proteins and pathogens covalently immobilized to self-assembled alkanethiols are infrequent. In this report, we show that electrochemical reductive desorption can also be used to develop a reproducible, repeatedly self-assembled, sensitive adenovirus immunosensor based on EIS.…”