Raman spectroscopy is a powerful, ultrasensitive analytical technique that is finding increased use in environmental monitoring and detection of biomolecules. This technique is advantageous as it requires no sample preparation, it is non-destructive, and enables quick identification of molecular structure(s) by vibrational “fingerprint”. Unfortunately, only 1 in 10¹⁵ incident photons is inelastically Raman scattered, which severely limits the sensitivity of Raman measurements. Gold and silver surfaces have been shown to enhance Raman scattering of surface adsorbed molecules. This technique is called surface-enhanced Raman scattering (SERS), and enhancement factors ranging from 10³ to 10¹⁵ have been reported. Such enormous enhancements can improve the sensitivities of Raman-based methods.

Micro- and nano-plastic contaminants are of increasing environmental concern that require new analytical techniques to detect of particles less than 1mm. In this report, SERS has been used to detect micro-plastics such as small as 1 mm polystyrene microspheres. We are currently working on a new class of SERS-based plasmonic filters to enable the detection of particles less than 1 mm, which has proven challenging thus far in field of environmental plastic detection. The goal of this research project is to demonstrate the effectiveness of a novel SERS-based plasmonic filter for detecting submicron environmental plastic contaminants. These films are prepared by depositing preformed silver or gold colloidal nanoparticles onto commercial polycarbonate membranes with etched pores. After metal particle deposition, solutions containing microplastic particles can be filtered using the plasmonic SERS filters. Plastic particles greater than the pore size are deposited onto the SERS filter. The filter is then analyzed using a scanning confocal Raman microscope.

Quinten Hardy

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