Fabrication of silver-decorated zinc oxide nanowire sensor in microchannels for surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) performed in microfluidic channels offers multiple benefits to the sensitive and reliable detection of dilute analytes while utilizing the advantages of microfluidics, including small samples, high throughput, and portability. Physical deposition of metallic nanoparticles by techniques, such as electron beam deposition, results in dense populations of nanoparticles and hotspots between nanoparticles for sensitive detection. However, not only do physically deposited SERS-active surfaces necessitate additional steps during device fabrication, but also surface fabrication is itself complicated by the constraints imposed by the microfluidic channel. Our work demonstrates a robust approach to the physical fabrication of an SERS-active substrates inside a poly(dimethylsiloxane) (PDMS) microfluidic channel. Direct growth of zinc oxide nanowires inside the PDMS channel and e-beam deposition of silver to coat the nanowires was performed before bonding PDMS to glass. This process enables label-free SERS sensing of micromolar crystal violet and melamine with minimal spectral interference from the PDMS-based channel.