Fast, highly sensitive and label free detection of small genetic sequence difference of DNA using novel Surface-Enhanced Raman Spectroscopy nanostructured sensor

Abstract

In this work we present a fast and label-free technique for biomolecules detection. The approach has been proved to be powerful to investigate small DNA mutation. Surface enhanced Raman spectroscopy (SERS) is an outstanding technique for DNA analyses by providing a specific fingerprint of chemical structure with a high sensitivity in a very short acquisition time. Homogeneous decoration of Silicon nanowires (SiNWs) by silver nanoparticles (Ag-NPs) was carried out using pulsed laser deposition (PLD) technique. SiNWs have been synthesized via metal-assisted chemical etching (MACE) method. We investigate in this work the effect of the Ag-NPs nanodecoration conditions through the variation of the laser ablation pulses number (NLAP). Thus, the Ag-NPs decorated SiNWs were used as sensors to detect organic and biomolecules by means of Surface Enhanced Raman Spectroscopy (SERS). By varying the NLAP, we were able to identify the optimal combination of Ag-NPs' size and surface coverage that yields the highest SERS signal. SEM images revealed well-ordered SiNWs (~2.4 μm-long and 30–60 nm diam.) with their uniform decoration by Ag-NP. High resolution-TEM analyses confirmed the effective decoration of the SiNWs by Ag-NPs of which average size is found to increase linearly from ~20 to 50 nm when the NLAP is increased from 500 to 10,000. The Ag-NPs/SiNWs matrix shows significantly higher (150 fold) Raman signal compared to their Ag-NPs-decorated-flat‑silicon counterparts. We found that SERS efficiency is sensitive to the nanoparticles size and reaches its maximum of (1.6 × 106) for the Ag-NPs having the optimal diameter of ~40 nm (obtained at NLP = 5000). The developed sensor proved to be highly sensitive to detect upto pico-molar concentrations of R6G. These Ag-NPs/SiNWs probes were demonstrated to have outstanding potential for label free detection of DNA samples with high sensitivity and reproducibility. It was found that the developed nanohybrid sensor is able to differentiate DNAs with very small genetic sequence difference.