Plasma-Tailored Polydimethylsiloxane Substrates for Eventing of Single Molecules Using Wrinkle-Enhanced Raman Spectroscopy

Surface-enhanced Raman spectroscopy (SERS) technique is widely adapted for detecting and analyzing analytes of various concentrations with the capability of reaching the single molecule (SM) level. Especially, the SM-SERS technique flourishes in studies involving biomolecular sequences and for characterizing molecular reaction kinetics. However, the technique is limited by the need for a suitable SERS substrate for witnessing and analyzing multiple SM events. This work demonstrates a facile way of fabricating suitable SERS substrates, consisting of wrinkled polydimethylsiloxane (PDMS) grafted with gold nanoparticles for swift eventing of SM events. Maskless reactive ion etching (RIE) technique is adapted to create in situ crack-free wrinkles on PDMS with tunable fluoroxy- or oxy-skins, which opens up avenues in geometric and surface tunability. These wrinkles are created by utilizing the capability of maskless RIE to etch various patterns, including nanograss, onto polymer surfaces, optimizing the procedure as a single-recipe process. During the grafting of gold nanoparticles, these period-specific wrinkles can create strong coupling regions under optimal drying conditions, facilitating rapid SM eventing opportunity (49 observable SM events on a minimal 15 μm × 15 μm scan area) at ultralow concentrations (atto-molar), providing at least an order of magnitude improvement in SM eventing compared to the literature. The signal intensity enhancement factor of 7.5 × 10 7, arising from the wrinkled SERS substrate, proves satisfactory to observe SM events, rendering the substrates attractive for commercial low-analyte detection methods.