Nanopatterned metal surfaces are widely used for surface-enhanced Raman spectroscopy (SERS). Effectiveness of the sensors depends on how well ligand and analyte molecules can diffuse into the regions of highest enhancement. In liquid phase sensing, this is often contingent upon the ability of the solvent to completely wet the nanostructures.The topic of surface wetting receives little to no attention in the SERS literature. Yet, wetting experiments on gold SERS nanodomes, used as a case study, resulted in a distinctly hydrophobic behavior, which is incompatible with aqueous sensing. Outside the field of SERS, the effort in surface wetting is usually aimed in the opposite direction, to further reduce surface wetting. Also, the approaches used in those works are typically incompatible with SERS devices.This thesis is dedicated to the subject of surface wetting in the context of SERS sensing. Four alternative techniques that can promote complete wetting on nanopatterns without sacrificing SERS efficiency are introduced and discussed in detail. They are: (1) addition of ethanol; (2) addition of surfactants; (3) mild oxygen plasma cleaning; and (4) hydrophilic monolayers. The first two methods modify the solvent, and the last two modify the sensor surface. The general theoretical principles of surface wetting, as well as specific principles for each technique are discussed and complemented by an experimental evaluation of their relative effectiveness in promoting hydrophilicity.Using some of the developed approaches to aqueous surface wetting, detection of short single-stranded homooligoadenosine in 1 uM solutions is demonstrated for the first time using SERS nanodomes. This is an important milestone on the path to development this substrate into a universal multiplexed sensing platform for disease diagnosis and prevention.
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Surface wetting methods compatible with solid SERS substrates
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