Highly sensitive and stable SERS sensing on superhydrophobic ladder-like nanostructures

Abstract

A new type of plasmonically active Laser-Induced Periodic Surface Structures (LIPSS) is fabricated on the stainless-steel surface. In particular, these LIPSS appear as ladder-like periodic patterns whose periodicity can also be controllable at a nanoscale. Here we demonstrated the ability to use these structured surfaces for sensitive SERS (Surface Enhance Raman Spectroscopy) signal measurements. Also, these nanostructured substrates exhibit hydrophobic nature with a contact angle of ∼147 ± 2. The hydrophobic nature of the surface confines the test samples to a small area without spreading, which increases the sensitivity of SERS signals by several folds. These SERS measurements are demonstrated using standard methylene blue (MB) dye with a 532 nm Raman excitation wavelength. Structural uniformity over a large area allows it to qualify as a reliable SERS platform. The random signal measurement across a large sample showed only a 7 % relative standard deviation. The lowest detectable concentration between 10 fM to 100 fM, with an enhancement factor of 2 × 109 for 10 fM, is demonstrated by drop casting the silver nano particles on the substrate. The substrate provides excellent thermal stability to the analyte due to better heat conduction, which reduces laser exposure-induced photodegradation of samples. Also, the lowest detectable concentration of picric acid is 10 µM. The demonstrated SERS active substrates can be used ubiquitously for all sensing applications with great sensitivity, greater repeatability, and increased photodegradation threshold energy. They get better with aging after fabrication and can be scaled to industrial productions.