Active Control of Silver Nanostructure Aggregates for Ultrahigh Sensitive SERS Detection of Organic Molecules: Single Molecule Approach

Abstract

P-type and n-type of Porous Silicon (PSi) substrates have been prepared by electrochemical and photo-electrochemical etching processes, respectively. Unique morphological features of Psi were employed to synthesis efficient and low cost Surface-Enhanced Raman Scattering (SERS) active substances by incorporating different forms of silver nanoparticles AgNPs. Ion reduction process of silver ions by three types of PSi samples was used to develop AgNPs, Ag cluster, and Ag loop aggregates-based active SERS substrates for efficient detection of Cy3 dyes molecules. The performances of the active SERS substrates were studied extensively through analysis of scanning electron microscopy and Raman spectra. The results show that the detection process of Cy3 dyes molecules was increased with increasing the density of hot spot's regions. The developed AgNPs aggregate/p-PSi substrate with the smallest inter-particle gap size exhibits the strongest SERS enhancement and produced the best reproducibility as compared with the other two substrates. The amplified Raman efficiencies for AgNPs aggregate/p-PSi, Ag cluster aggregate/n-PSi, and Ag loop aggregate/n2-PSi substrates were calculated to be 1010, 106, and 103, respectively. The experimental results show that the AgNPs aggregate/p-PSi SERS substrate exhibited significant enhancement factor of 1.07 × 1013 for 10-14 M dye concentration using single molecule detection technique