Photonic Crystal Enhanced SERS Detection of Analytes Separated by Ultrathin Layer Chromatography Using a Diatom Frustule Monolayer
Joseph A. Kraai, Alan X. Wang, Gregory L. Rorrer
Abstract
Abstract Diatoms are single‐celled algae that biologically fabricate nanostructured silica shells with ordered pore arrays called frustules that resemble a 2D photonic crystal. A monolayer of Pinnularia frustules isolated from cell culture is deposited on a glass substrate and then conformally coated with silver nanoparticles (AgNPs) to serve as a nanostructured thin film for ultrathin layer chromatography (UTLC). Malachite green and Nile red are resolved in toluene mobile phase and the separated analytes are profiled micro‐Raman spectroscopy, where plasmonic AgNPs provide surface‐enhanced Raman scattering (SERS). The AgNP‐diatom frustule monolayer improves SERS detection of malachite green by an average factor of 1.8 ± 0.1 over the plasmonic AgNP layer on glass. Analysis of hot spots on the AgNP‐diatom frustule monolayer reveals that nearly 20% of the SERS active area intensifies the SERS signal at least tenfold over the SERS signal for AgNP on glass. Diatom‐SERS enhancement is attributed to guided‐mode resonances of the Raman laser source, which in turn further enhances the localized surface plasmonic resonance from AgNPs. Overall, the AgNP‐diatom frustule monolayer thin film is a new functional material that uniquely enables separation of analytes by UTLC, quantitative SERS detection of separated analytes, and photonic enhancement of the SERS signals.