Innovative Silicon Nanowires based Platforms for Bio-sensing

Silicon is the leading material for microelectronics and the realization of innovative sensing devices based on Si is of great interest for commercial applications. Si Nanowires (Si NWs) due to the high surface-to-volume ratio and their remarkable physical properties have attracted a huge interest of the research community as novel nanostructured platform for the realization of innovative sensing devices characterized by high performances and low realization costs [1-3]. We present how high aspect ratio Si NW arrays synthesized by a fast, low-cost and Si industrially compatible approach, can be used as multi-platform for the development of optical sensors for label-free detection of C-reactive protein (CRP) and beta amyloid (A?) oligomers, both biomolecules of crucial biomedical interest. CRP is related to a wide variety of clinical pathologies mainly ascribed to cardiovascular risk and its concentration in body fluids can range over 3 orders of magnitude, moving from blood serum to saliva. Hence a sensor with a tunable limit of detection is needed, in particular for non-invasive applications with saliva. So, in our first approach, exploiting the Si NWs ability to emit visible photoluminescence at room temperature due to quantum confinement effect [3], we demonstrate the realization of an optical biosensor working in a broad and "easily to change" concentration dynamic range, capable of high specific detection of C-Reactive protein down to fM concentration [4]. A? oligomers are precursors of amyloid fibrils and responsible of cellular processes causing the impairment of the cognitive functions in Alzheimer's and Parkinson's diseases [5]. Their formation take place 10 to 20 years before the disease symptoms became evident, so the detection of this species at low concentration (tens of pM) in the cerebrospinal fluids play a crucial role for early diagnosis of these pathologies. To this aim, in the second approach, Si NWs are used as tridimensional platform and are decorated with noble-metal nanoparticles produced by Pulsed Laser deposition (PLD) [6]. We show how the resulting substrate, exploiting a huge surface-to-volume ratio and the plasmonic properties of the metal nanoparticles, can be used for Surface Enhanced Raman Spectroscopy based detection of A? oligomers. References: [1] B. Fazio et al., Light: Science & Applications, 5, e16062 (2016) [2] B. Fazio et al., Nature Phot, 11:170-177 (2017) [3] M.J. Lo Faro et al., Sci. Rep., 5: 16753 (2016) [4] A. Irrera et al., ACS Photonics, just accepted, 10.1021/acsphotonics.7b00983 (2017) [5] F. Chiti et al., Annu Rev. Biochem, 86:27-68 (2017) [6] C. D'Andrea et al., Nanotechnology, 27:375603 (2016).