Development of promising surface enhanced Raman scattering substrate: Freckled SiO 2 @Au nanocomposites Parul Khurana a , Sheenam Thatai a , Jyoti Boken b , Surendra Prasad c, ⁎, Dinesh Kumar a, ⁎⁎ a Department of Chemistry, Banasthali University, Banasthali 304022, India b Department of Physics, Banasthali University, Banasthali 304022, India c School of Biological and Chemical Sciences, Faculty of Science, Technology and Environment, The University of the South Pacific, Private Mail Bag, Suva, Fiji abstract article info Article history: Received 21 January 2015 Received in revised form 21 March 2015 Accepted 21 March 2015 Available online 28 March 2015 Keywords: Surface enhanced Raman scattering Freckled shell SiO 2 @Au nanocomposite Crystal violet analyte molecule Core–shell nanocomposite Surface plasmon resonance This paper describes SiO 2 @Au core–shell nanocomposites (NCs) as an excellent surface enhanced Raman scatter- ing (SERS) substrate in this emerging field. The network of monodispersed silica (SiO 2 ) core of ~ 430 and 880 nm sizes with varying shell thickness from 12–50 nm was synthesized. The synthesized freckled SiO 2 @Au NCs provide much better surface consistency and in tune generate a huge SERS signals enhancement. The study confirmed that the appropriate shell thickness and core size are responsible for the dramatic enhancement of the SERS signal intensities of the analyte crystal violet (CV) molecule by an order of 10 12 –10 9 . The SiO 2 @Au core–shell NCs with 880 nm core and 30 nm shell thickness showed the maximum enhancement in SERS signals of order 10 12 using CV analyte molecule while the NCs with diameter 430 nm and 20 nm shell thickness produced the maximum enhancement of 10 9 corresponding to 1620 and 1618 cm -1 peaks respectively at the excitation wavelength of 532 nm. The advantage of choosing freckled SiO 2 @Au core–shell NCs instead of nanoparticles (NPs) is that the core being dielectric provides additional electric field to Au nanoshell. Thus it generates more domains on the surface, is responsible for the enhancement of SERS signals and has been shown to be excellent substrate for SERS sensing applications. The results showed that the SiO 2 @Au core–shell NCs with 880 nm core and 30 nm shell thickness act as an excellent substrate for SERS sensing. © 2015 Published by Elsevier B.V. 1. Introduction The surface enhanced Raman scattering (SERS) is an advancement of Raman scattering which overcome some of the limitations of normal Raman scattering [1]. The SERS provides many fold enhancement in Raman signal intensity, which is sufficient for single molecule detection [2]. Due to its usefulness in various fields such as trace analysis, bio diag- nosis, in vivo study, etc. the SERS has been receiving renewed interest in recent years [3,4]. It has become an important spectroscopic tool owing to its single molecule detection ability, capability of providing structural information for analytes of interest, minimal sample preparation and ease of operation [3,5]. However, there is lack of consistent techniques for controlling the properties of local fields at the metal surface which has been a major experimental limitation regarding quantification and understanding of SERS [3,6]. Thus, there is need for further development of sensitive SERS substrate that can be stored for a long period with possible promise of the enhancement of Raman signals. The most commonly used SERS active substrates are Ag and Au colloids but the stability of colloidal solutions and reproducibility of aggregation are the two major problems. Although metal electrode substrates are more stable than colloids, they are less sensitive [7].A new way to overcome these limitations is to produce a core–shell nano- scale material consisting of ‘dielectric core’ and ‘metallic shell’ which exhibits plasmon resonance that can be tuned from near UV to near IR [8]. Attracted by the unique optoelectronic and physicochemical properties, the gold nanoparticles (Au NPs) and core–shell gold nanocomposites (NCs) have widely been used which act as promising SERS substrate [9–11] where the tunability of the plasmon band in core–shell NCs has led to tremendous potential in chemical and biomedical fields [10]. The SERS activity depends not only on the nature of the metals but also on their shape [12], size [9,12,13] and thickness of shell and inter- particle coupling of NPs [12,14]. An ever-expanding technique in nanoscience has provided great opportunities to fabricate a wide variety of nanostructures with controllable size and shape [4,8,11]. Such concentric tunable geometry has been designed for more effective enhancement of Raman signals [6,8]. Accordingly, it is of great interest to extend the SERS substrate from inexact surfaces and disordered structures to well-defined and ordered nanostructures to gain the highest SERS activity [15]. Therefore, for the first time we have Microchemical Journal 122 (2015) 45–49 ⁎ Corresponding author. Tel.: +679 3232416. ⁎⁎ Corresponding author. Tel.:+91 9928108023. E-mail addresses: prasad_su@usp.ac.fj (S. Prasad), dschoudhary2002@yahoo.com (D. Kumar). http://dx.doi.org/10.1016/j.microc.2015.03.014 0026-265X/© 2015 Published by Elsevier B.V. Contents lists available at ScienceDirect Microchemical Journal journal homepage: www.elsevier.com/locate/microc