A Facile Method for Selective Deposition of Metal Nanoparticles into Nanohole Arrays for Recyclable Plasmonic Sensors

Plasmonic nano-arrays are extensively studied as ultrasensitive vapor sensors [1, 2]. Tunable processes for selective deposition of plasmonic nanoparticles in arrays of host nanoholes are desired for fabrication of next-generation plasmonic devices and sensors. Reported techniques [3, 4] for deposition of gold nanoparticles (AuNPs) into prepatterned nanoholes yield low filling density and are limited to holes created in polymeric substrates which are known to be labile and subject to swelling. We report a method for selective deposition of gold nanoparticles (AuNPs) into nanoholes fabricated in fused silica (FS). Arrays of nanoholes with variable hole size and density are created in the positive resist PMMA by e-beam lithography and transferred into fused silica using cyclic reactive ion etching. The nanoholes are filled with AuNPs using evaporative deposition followed by mechanical rubbing. This simple yet effective approach yields highly selective deposition of AuNPs in nanoholes as small as 150 nm. The effect of the chemical termination of the substrate, the concentration of the AuNPs suspension, and the size and the pitch distance of the nanoholes on the density of AuNPs in the holes was investigated. This approach is being extended to other plasmonic nanoparticles and a variety of substrates. We also demonstrate that the AuNPs can be etched away to reproduce the nanohole array in FS, which can be refilled with fresh nanoparticles. Hence, this method paves the way for recyclable plasmonic sensors that can be regenerated after exposure to analyte.<br/><br/>1. Jiang, J., et al., <i>Plasmonic nano-arrays for ultrasensitive bio-sensing.</i> Nanophotonics, 2018. <b>7</b>(9): p. 1517-1531.<br/>2. Wang, Q. and L. Wang, <i>Lab-on-fiber: plasmonic nano-arrays for sensing.</i> Nanoscale, 2020. <b>12</b>(14): p. 7485-7499.<br/>3. Morakinyo, M.K. and S.B. Rananavare. <i>Positional control over nanoparticle deposition into nanoholes</i>. in <i>11th IEEE International Conference on Nanotechnology</i>. 2011. IEEE.<br/>4. Morakinyo, M.K. and S.B. Rananavare, <i>Reducing the effects of shot noise using nanoparticles.</i> Journal of Materials Chemistry C, 2015. <b>3</b>(5): p. 955-959.