Vertically Aligned Silicon Nanowire Array Decorated by Ag or Au Nanoparticles as SERS Substrate for Bio-molecular Detection S. Chakraborti 1 & R. N. Basu 1 & S. K. Panda 1,2 Received: 29 January 2017 /Accepted: 9 May 2017 # Springer Science+Business Media New York 2017 Abstract This review article summerises preparation tech- niques of vertically aligned silicon nanowire (Si NW) arrays through metal-assisted chemical etching (MacEtch) process and plasmonic nanoparticles (Ag and Au) with the perspective of the fabrication of surface-enhanced Raman scattering (SERS)-active substrates which are highly efficient for bio- molecular detection. At first, basic methods and mechanisms for SERS have been introduced and size and shape effects of the nanoparticles (NPs) on plasmonic vibration have been discussed. Comparative discussions on optical and plasmonic characteristics of Ag and Au NPs have also been presented in this section. Potential techniques for the synthesis of Ag and Au NPs with different sizes and shapes have been reported in the following section. Basic processes and mechanism for the fabrication of vertically aligned Si NW arrays on Si by MacEtch of Si wafer have been discussed. Template-assisted fabrication techniques for the vertically aligned Si NW arrays with controlled diameter and number density have also been reported. Finally, multifarious ways for the fabrication of SERS-active substrates by assembling noble metal NPs onto the NW surface have been discussed and their performance for bio-molecular detection has also been reported. Keywords Noble metal nanoparticles . Silicon nanowire array . Metal-assisted chemical etching . Surface-enhanced Raman scattering (SERS) . Electromagnetic hotspot . Bio-molecular detector Introduction Incidence of electromagnetic beam on metal/dielectric inter- face excites coherant oscillations of free electrons at the boundary which are often recognized as surface plasmons (SPs). The resonance (surface plasmon resonance) condition is established when the frequency of electromagnetic beam matches with the natural frequency of the free electron oscil- lation. Understanding of surface plasmon resonance (SPR) provides a design concept that guides the development of complex material structures with optimal optical properties. SPs are now being investigated for various application- oriented purposes which include photonics, magneto-optics, sensing of biological and chemical species, medical diagnosis, and environmental monitoring [1–5]. SPs, however, strongly depends on the size, shape, and environment of the surround- ing metal body, enabling emerging research field like surface plasmon-based photonics or plasmonics. In case of low di- mensional metal structures like quantum dots, nanoparticles (NPs), and nanorods, localized surface plasmon (LSP) excita- tion originates which can induce a strong enhancement of electromagnetic field in the near field region, leading to wide applications of plasmonic devices. It is widely recognized that Raman signal can be enhanced by a factor of 10 6 to 10 8 using noble metal nanostructured substrates, termed as surface-enhanced Raman scattering, a LSP-based powerful analytical tool which has attracted great interest for the detection of wide range of adsorbate molecules because of its ultrahigh sensitivity down to the single-molecule * R. N. Basu rnbasu@cgcri.res.in * S. K. Panda sovan.panda@gmail.com 1 Fuel Cell and Battery Division, CSIR—Central Glass and Ceramic Research Institute, Kolkata 700032, India 2 Department of Electronics, Bidhan Chandra College, Rishra, Hooghly, West Bengal 712248, India Plasmonics DOI 10.1007/s11468-017-0605-2