Fiber-optic SERS sensor with optimized geometry: testing and optimization

A unique, geometry-optimized, surface-enhanced Raman scattering (SERS) fiber-optic sensor has been recently developed and built. Though this class of sensors can be very useful in many applications, their use is greatly hindered by the fact that their reusability can hardly be achieved because of the irreversible adsorption of the analyte molecules on the SERS-active substrate. Different substrates have been tested on our sensor with the purpose of increasing its reusability by means of cleaning procedures or good reproducibility in manufacturing the sensor, keeping, however, the same enhancement. We show that a partial reusability of the sensor is possible using SERS-active substrates prepared by a standard process of immobilization of silver nanoparticleswith 3-aminopropyltrimethoxysilane.We also show that a fairly good reproducibility can be achieved with a low-cost substrate realized in a short time by depositing a layer of polyvinyl alcohol (PVA) containing silver nanoparticles on the etched fiber tip.We prove as well that measurements are possible evenwith nanoparticles dispersed in the analyte solution instead of using a substrate directlymade on the sensor tip. Finally, we have successfully tested our sensorwith somemolecules cited in EFSA (European Food Safety Authority) and FDA (Food and Drug Administration) reports as molecules for which new detectionmethods are necessary.