# Ethanol-Assisted Alkanethiol Self-Assembled Monolayer Disruption by Mobile Siloxane Oligomers for Precise Galvanic Replacement Positioning

## TL;DR

This paper introduces a method using siloxane oligomers and ethanol to disrupt alkanethiol monolayers on gold surfaces, enabling precise metal replacement and fluorescence-based bioimaging.

## Contribution

A novel ethanol-mediated approach for controlled disruption of self-assembled monolayers using mobile siloxane oligomers is introduced.

## Key findings

- Ethanol enables controllable diffusion and disruption of alkanethiol monolayers on gold surfaces.
- Disrupted regions allow selective galvanic replacement and enhanced fluorescence emission.
- The method supports ratiometric bioimaging with multiple internal standards.

## Abstract

Siloxane oligomers
with low molecular weights often exist in elastomeric
polymers, e.g., polydimethylsiloxane, and can be troublesome chemical
species when utilizing polymers due to their hard-to-control behavior
and unpredictable mobility. For instance, the presence of these species
can contaminate surfaces and affect molecular integrity when these
polymers are applied in developing functional substrates. In this
study, on the contrary, we provide an unconventional approach whereby
siloxane oligomers originating from a polymerized matrix are transported
to alkanethiol self-assembled monolayer (SAM)-functionalized Au through
the mediation of ethanol pre-entrapped in the elastomer. Relying on
the interface mobile environment provided by ethanol, siloxane oligomers
controllably diffuse, transfer, and disrupt a preformed alkanethiol
monolayer on Au during conformal contact sealing, which in turn promotes
the detachment of Au-thiolates from the surface. Spectroscopic analyses,
including sum frequency generation vibrational spectroscopy and X-ray
photoelectron spectroscopy, confirm the disruption of SAMs and the
detachment of Au-thiolates. Several key parameters, including conformal
contact sealing duration, molecule backbone chain length, and terminal
group functionality, are critical in this SAM disruption phenomenon.
The produced disordered SAM environment enables the penetration of
ions when placed in solutions and supports underlying metal oxidation
for precise feature transfer. Furthermore, selective galvanic replacements
between different metals can be triggered at SAM-disrupted regions
to produce bimetallic substrates. These bimetallic interfaces selectively
enhance fluorophore-dependent fluorescence emission by interparticle
electric field promotion. By combining multiple spatial SAM disruption
operations on the same substrate, the produced fluorescent assay,
built with manifold internal standards, offers a reliable platform,
supporting ratiometric treatments for further bioimaging analysis
and detection.