Abstract
Herein, we report a combined strategy encompassing electrochemical and X-ray photoelectron spectroscopy (XPS) experiments to investigate self-assembled monolayer (SAM) conformational reorganization onto an electrode surface due to the application of an electrical field. In particular, 3-mercaptopriopionic acid SAM (3MPA SAM) modified gold electrodes are activated with a 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysulfosuccinimide (NHSS) (EDC-NHSS) mixture by shortening the activation time, from 2 h to 15/20 min, labelled as Protocol-A, -B and -C, respectively. This step, later followed by a deactivation process with ethanolamine (EA), plays a key role in the reaction yields (formation of N-(2-hydroxyethyl)-3-mercaptopropanamide, NMPA) but also in the conformational rearrangement observed during the application of the electrical field. This study aims at explaining the high performance (i.e., single-molecule detection at a large electrode interface) of bioelectronic devices, where the 3MPA-based SAM structure is pivotal in achieving extremely high sensing performance levels due to its interchain interaction. Cyclic voltammetry (CV) experiments performed in K4Fe(CN)6:K3Fe(CN)6 for 3MPA SAMs that are activated/deactivated show similar trends of anodic peak current (IA) over time, mainly related to the presence of interchain hydrogen bonds, driving the conformational rearrangements (tightening of SAMs structure) while applying an electrical field. In addition, XPS analysis allows correlation of the deactivation yield with electrochemical data (conformational rearrangements), identifying the best protocol in terms of high reaction yield, mainly related to the shorter reaction time, and not triggering any side reactions. Finally, Protocol-C’s SAM surface coverage, determined by CV in H2SO4 and differential pulse voltammetry (DPV) in NaOH, was 1.29 * 1013 molecules cm−2, being similar to the bioreceptor surface coverage in single-molecule detection at a large electrode interface.
Highlights
IntroductionThe chemical modification of surfaces represents a key step in the development of (bio)sensors [1–8]
This article is an open access articleThe chemical modification of surfaces represents a key step in the development ofsensors [1–8]
The optimization of self-assembled monolayer (SAM) layers growth protocols is crucial for device development [24–26], with interchain interactions largely affecting their performance [13,27,28]
Summary
The chemical modification of surfaces represents a key step in the development of (bio)sensors [1–8]. In this regard, interchain interactions (e.g., Van der Waals interactions, hydrogen bonds, etc.) play a key role in the control of growth kinetics and SAM conformational rearrangements [9–12]. For thiol-based SAMs, the formation of the typical comb-like structure proceeds via a two-step process, where high-energy interchain interactions like distributed under the terms and conditions of the Creative Commons. Nanomaterials 2022, 12, 867 hydrophobic forces [13–17], dipole-dipole interactions [18], and hydrogen bonds [10,11,19], can lead to complex SAM reorganisation within the densely packed monolayer [9,11,20–23]. The optimization of SAM layers growth protocols is crucial for device development [24–26], with interchain interactions largely affecting their performance [13,27,28]. Afterwards, the blocking/deactivation was performed by reacting the latter with ethanolamine (EA), generating
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