Detection of trace concentrations of small and big molecules through vibrational spectroscopy
Date
2024-08-01
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Abstract
In this thesis, we aim to detect analytes of varying sizes using surface-enhanced Raman spectroscopy (SERS) without the need for customizing the morphology of nanostructured substrate. Signal enhancement in SERS occurs near plasmonic nanoparticles within "hotspots" (<10 nm), which limits detection to molecules that can access these regions. We investigated two differently fabricated SERS-active substrates: pulsed laser deposited gold nanoparticles and electrochemically deposited silver nanoparticles, optimized for 633 nm and 532 nm Raman lasers, respectively. Characterization was performed using UV-Visible spectroscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. We analyzed zeatin, a small plant hormone (219 Da), and hemoglobin (Hb), a large protein (64,500 Da). Zeatin detection ranged from 1 mM to 1 nM, even in complex bacterial media, while Hb detection involved ligand-functionalized substrates targeting the heme group for specific oriented immobilization, detecting down to 10 nM. This study demonstrates the potential of SERS for sensitive and selective detection of diverse analytes, paving the way for advanced biosensing applications.