Silver-coated ZnO disordered nanostructures as low-cost and label-free Raman biosensing platform for fast detection of complex organic profiles

The need of cheap and easy to use biosensors for rapid diagnostics is a crucial challenge in medicine: indeed, devices must offer multiple properties such as fast response, high sensitivity, reduced need of sample processing, etc. In this respect, optical biosensors remain a promising class of biodevices. Here we present an extensive investigation of the surface properties of silver-coated zinc oxide disordered nanostructures as efficient biosensing platform to detect complex organic profiles via Raman spectroscopy. In particular, we combine low temperature and large area manufacturing techniques to offer a low-cost tool for rapid detection of untreated organic samples like human blood avoiding the usage of expensive manufacturing methods to grow ordered nanostructures and providing safer materials respect the implementation of metal nanoparticles thus opening the possibility to adopt these devices also in vivo. After an accurate study using rhodamine, comparing Raman response for as deposited and lasered surfaces, different metal layers (gold vs silver) and different metal thicknesses (from 25 to 150 nm), we successfully validate the performance of the silver-coated lasered platform on untreated human blood obtaining high resolved response and identifying several organic signatures attributable to hypoxanthine, glucose and lipoprotein.