PlQC based highly sensitive and reproducible novel SERS active substrate for biomolecule detection with high specificity

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for biomolecule sensing. When combined with a broadband plasmonic structure, label-free, highly sensitive detection of specific molecules is possible. It is non-invasive, sensitive, fast, and can be used for in-situ analysis, unlike enzyme-linked immunosorbent assay, fluorescence immunoassay, and radioimmunoassay. However, one of the challenges is to have an active SERS substrate that is uniform, sensitive, and specific to molecules of interest. In this work, we report plasmonic quasicrystal (PlQC) as a highly sensitive (enhancement factor approximate to 1014), uniform, reproducible, and stable (concerning time and ambient conditions) SERS active substrate. Herein, we present the label-free sensing of standard cotinine (up to 1 ng/mL), the ideal biomarker for nicotine exposure due to its long lifetime compared to nicotine. In addition, up to 1 nanogram level of cotinine has also been detected in synthetic urine and saliva employing PlQC as a SERS-active substrate. Our results on the principal component analysis of Rhodamine 6G and Cotinine demonstrate that broadband, dispersionless PlQC is suitable for label-free detection of single biomolecules.