Dual Function Surface-Enhanced Raman Active Extractor for the Detection of Environmental Contaminants

Abstract

Surface-enhanced Raman spectroscopy (SERS) has lagged behind other analytical techniques utilized in routine chemical analyses despite the information-rich spectra produced. This can be attributed in part to the difficulties in finding effective substrates that provide high sensitivity and highly reproducible SERS responses. Herein, we have developed a silver-coated polypropylene filter (AgPPF) as a highly sensitive and promising SERS substrate for the detection of environmentally significant chemicals, including selected pharmaceuticals, personal care products, and possible endocrine disruptors. The present approach involves preconcentration studies of selected environmental compounds with 3M's High Performance Extraction Disc Cartridges (HPEDCs) and characterization of the same HPEDC filters as a SERS substrate. The polypropylene microfiber prefilter that encloses the empore extraction medium is modified by physical vapor deposition with silver and used as the SERS substrate. The HPEDC itself is used to concentrate analytes into a desired concentration range, achieving maximum sensitivity. Surface roughness and nanoscale structure of silver films on the microfiber were characterized by atomic force microscopy (AFM). The mass thickness of the silver and volume were optimized for the highest SERS signal using rhodamine 6G as a model compound. A novel component of our HPEDC studies involves the hyphenation of the concentration protocol and SERS. The hyphenation of sample concentration and SERS allows more sensitive surface-enhanced detection. Mitoxanthrone dihydrochloride, crystal violet dye, 4-aminobenzoic acid, and rhodamine 6G were employed to study the sensitive SERS detection and were observed as low as 5 × 10⁻⁸ M to 1 × 10⁻¹⁰ M without any preconcentration step. Additionally, SERS signatures of some flavonoids, targeted as possible Endocrine Disrupting Chemicals by the US Environmental Protection Agency, such as Apigenin and Daidzein, are reported along with their sensitive detection down to ng/mL for the first time with preconcentration.