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Randomly oriented nanowires as sensors for surface- enhanced Raman spectroscopy

Nanostructured materials plated with metallic layer is a unique category within material science which explores numerous phenomena such as localized surface plasmon resonance (LSPR). Free metal electrons oscillations resonating with the visible excitation photons give strongly enhanced electric field in the nanostructure vicinity. This phenomenon is strongly utilized for ultrasensitive, fingerprint selective, fast analysis and an economical technique known as SERS i.e. surface-enhanced Raman spectroscopy. This paper is predominantly focused on fabrication and optimisation of the SERS substrates consisting of randomly oriented nanowires. The fabrication methodology includes fabrication of Si or ZnO nanowires on a wafer or optical fibre substrates utilizing 'Vapour- liquid-solid (VLS)' method within 'low-pressure chemical vapour deposition (LPCVD)' reactor or 'Chemical vapour deposition (CVD)'. SERS substrates’ optimization includes nano- structuring, and Ag metal plating by sputtering. The particularity of these specific silicon nanowires (SiNWs) is in their flexibility i.e. a possibility to shrink in bundles upon liquid immersion offering additional SERS signal enhancement. The morphological characteristics and the influence of sputtering are described by the fractal dimension and lacunar analysis. Finally, SERS substrates were characterized utilizing 4-mercaptophenylboronic acid (4-MPBA) as the test molecule. The laboratory substrates compared with the commercially available substrates showed excellent characteristics.

flexible hot spots ; horizontal silicon nanowires ; 4-mercaptophenylboronic acid ; surface-enhanced Raman spectroscopy (SERS) ; vapour–liquid–solid

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