Tailored surface-enhanced raman substrates for sensitive, economical, and reusable contaminant detection

Abstract

Raman spectroscopy is an effective characterization technique for the detection of a wide range of analytes due to its potential to provide figure-print spectra of a variety of molecules by detecting the inelastic scattering of incident photons with very low signal-to-noise ratio. Structured plasmonic substrates which enhance the weak Raman signal is a solution to increase Raman signal via reducing noise, which is known as surface-enhanced Raman spectroscopy (SERS). From the past few decades, researchers have fabricated many of SERS substrates that show good enhancement factor, are highly sensitive towards trace level detection, and are also stable for months. But what about other parameters like flexibility, reusability, and degradation? Based on the literature reports, very few studies are based on the substrate’s homogeneity and reproducibility, although there are rare reports available on the substrate’s reusability. Majority of the literature has focused on the fabrication of SERS substrates based on solid substrates. These substrates are advantageous for various sensing applications. However, with these substrates, the molecules can be detected easily from the planar or flat objects, whereas on non-planar objects such as banana, mango, etc., the detection is quite complex. Hence, non-destructive such as on-field: pathogens, fertilizer, and trace chemical detection is difficult. Therefore, a flexible SERS substrate that can adjust on any kind of surface to detect the molecules is in great demand. In the current work, both solid as well as flexible SERS substrates have been fabricated by the facile and reproducible method. The solid substrate has been prepared by a cost-effective dealloying method for a varied time-period to determine which dealloying time shows the highest enhancement in the signal. The final networked structure of Nanoporous gold (NP-Au) shows excellent SERS activity. On the other hand, the flexible substrate has been prepared by replicating the pattern of red rose petals by using a polymer to make the patterned substrate. The nanocasting approach has been used to create the inverted texture of rose, and then the textured substrate is made SERS active by the deposition of pre-synthesized Au NPs via a self assembly approach. After fabrication, the effectiveness of both substrates has been tested by detecting the Raman active molecule such as R6G (organic contaminant) and further, from a real-world application point of view, these substrates have also been used for the detection of urea (fertilizer). The highlighted point about the substrates is that these are reusable by applying a simple washing method and show good sensing capability by detecting urea molecules in the nanomolar range.