Potential-Induced Structural Alterations in the Tethered Bilayer Lipid Membrane-Anchoring Monolayers Revealed by Electrochemical Surface-Enhanced Raman Spectroscopy

Abstract

Mixed self-assembled monolayers (SAMs) are widely used to anchor tethered lipid bilayer membranes (tBLMs) that mimic biological membranes and are useful platforms for fundamental studies and construction of biosensors. Electrode potential is an important variable in the construction of biosensors based on tBLMs and fundamental studies. In this work, potential-induced structural changes in mixed SAMs composed of lipid-like long-chain WC14 molecules and short surface backfiller 2-mercaptoethanol (ME-D4) was probed in situ by isotope-edited electrochemical surface-enhanced Raman spectroscopy (EC-SERS) coupled with first-principles calculations, reductive desorption voltammetry, and generalized two-dimensional correlation spectroscopy (2DCOS). We show that negative electrode polarization leads to the lengthening of Au–S and Au–O bonds and reorganization of molecules in the headgroup region. Calculations predicted the preferential formation of Au–O bonds of ME-D4 at more positive electrode potentials. Alkane chains of WC14 form potential-induced clusters at more negative electrode polarization in mixed monolayers, a phenomenon that is witnessed from all-trans vibrations of the C–C group at 1129 cm–1. The evidence of the formation of tBLM on mixed WC14/ME-D4 SAMs is documented by SERS. Specifically, the peak position of olefin group stretching vibration suggests a fluid-like structure of tBLM. This work provides vibrational spectroscopy evidence for the potential-induced formation of phase-segregation clusters of the hydrophobic thiols in mixed monolayers, a phenomenon that should be considered in preparation of tBLMs, construction of membrane-based biosensors, bioengineering developments, and studies of biomolecular processes using model membranes.

The Impact of an Anchoring Layer on the Formation of Tethered Bilayer Lipid Membranes on Silver Substrates

“…Specific for WC14, all-trans ν(C-C) T spectral mode at 1129 cm -1 was only observed for the WC14 monolayer composed from the 100% anchor concentration. This band was previously shown to be diagnostic of water and electric potential induced rearrangement of hydrophobic alkane chains into molecular surface clusters [13,21]. The clustering effect was linked with the formation of defected lipid tBLM membranes [5,13].…”

“…This band was previously shown to be diagnostic of water and electric potential induced rearrangement of hydrophobic alkane chains into molecular surface clusters [13,21]. The clustering effect was linked with the formation of defected lipid tBLM membranes [5,13].…”

“…rearrangement of hydrophobic alkane chains into molecular surface clusters [13,21]. The clustering effect was linked with the formation of defected lipid tBLM membranes [5,13].…”

“…The size of backfillers and density of long-chain anchors determine the physical properties of such submembrane reservoirs, which is essential for the lipid membrane functionality and protein incorporation [9][10][11]. Attachment of tBLMs to noble metals allows monitoring of the biologically relevant events with surface-sensitive techniques, including surface plasmon resonance spectroscopy (SPR), measurements with a quartz-crystal microbalance (QCM), surface-enhanced Raman scattering (SERS), and electrochemical techniques, such as electrochemical impedance spectroscopy (EIS) [12,13].…”

Formation of tethered bilayer lipid membranes on gold surface probed by in situ SEIRAS

“…The stability and functional properties of tBLM rely toughly on the composition and structure of anchoring SAM [11,[15][16][17][18][19]. However, the molecular level knowledge on the structure and formation of a mixed monolayer in a solution still remains scarce largely because of a limited number of available techniques providing molecular information from the electrode/solution interface.…”