A Chemical Free Approach For Increasing The Biochemical Surface Enhanced Raman Spectroscopy Sers Based Sensing Capabilities Of Colloidal Silver Nanoparticles PDF Download

The unique optoelectronic properties of silver nanoparticles (AgNPs) have led to their explosive use in a multitude of both research and industrial settings in recent years. Localized surface plasmon resonance (LSPR) exhibited by AgNPs has been exploited extensively as a nano-scale probe in a variety of spectroscopic detection modalities, particularly in surface-enhanced Raman spectroscopy (SERS). The SERS effect is highly dependent upon the LSPR interaction with optical laser frequencies, thus optimization of LSPR via specific control of AgNP dimensionality and composition of the surrounding medium is vital for increasing the efficacy of SERS-based nano-sensing. This work aimed to augment LSPR of AgNPs by applying the chemical free technique of tangential flow filtration (TFF) to a Creighton colloid of spherical AgNPs and specifically tailoring their size-distribution, concentration, and purity. First, a large batch of Creighton AgNPs (1-100 nm in diameter) were size-selected (20 nm and 12 nm in average diameter), concentrated, and purified via a three-step TFF procedure and characterized for effectiveness as SERS substrates in pre-resonance, resonance, and single-molecule resonance conditions for a Raman reporter, rhodamine 6G. The 20 nm AgNPs were found to have the highest surface enhancement factors (SEFs) in pre-resonance and single molecule resonance (SEFS of 2.1 x 10^6 and 2.5 x 10^10), while the 12 nm AgNPs yielded the highest SEFs in resonant conditions (2.0 x 10^6). The TFF procedure was then introduced to a diverse class of undergraduate and graduate students in an Experimental Nanomaterials and Nanoscience course to demonstrate the versatility of the proposed method for both gold nanoparticles and AgNPs, as well as the ease of applicability for use in different research disciplines and settings. Lastly, the 20 nm TFF-obtained AgNPs were employed for the sub-nanomolar biochemical detection of a potent apoptotic metabolite, chelerythrine (CET), in human lens epithelial cell extracts. The TFF-fractionated AgNP colloid allowed for quantification of CET content within several cell compartments via a reproducible calibration curve extending over five orders of magnitude (10^-5 to 10^-10 M in CET concentration). The results of these aims offer strong evidence that TFF can be 1) utilized to yield SERS substrates capable of extending detection limits and increasing spectral signals, 2) easily adapted for a variety of nanoparticle colloids as well as research and industrial settings, and 3) employed to obtain AgNPs that facilitate trace biochemical SERS-based detection even in extensive biological matrices.