Aerosol Jet Printed Surface-Enhanced Raman Substrates: Application for High-Sensitivity Detection of Perfluoroalkyl Substances.

Printing technologies offer an attractive means for producing low-cost surface-enhanced Raman spectroscopy (SERS) substrates with high-throughput methods. The development of these substrates is especially important for field-deployable detection of environmental contaminants. Toward this end, we demonstrate SERS-based substrates fabricated through aerosol jet printing of silver nanoparticles and graphene inks on Kapton films. Our printed arrays exhibited measurable intensities for fluorescein and rhodamine dyes down to concentrations of 10 -7 M, with the highest SERS intensities obtained for four print passes of Ag nanoparticles. The substrates also exhibited an excellent shelf life, with little reduction in fluorescein intensities after 9 months of shelf storage. We also demonstrated the capability of our substrates to sense perfluoroalkyl substances (PFAS), the so-called forever chemicals that resist degradation due to their strong C-F bonds and persist in the environment. Interestingly, the addition of graphene to the Ag nanoparticles greatly enhanced the SERS intensity of the perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) molecules under basic conditions (pH ∼ 9) compared to that of fluorescein and rhodamine. We were able to successfully detect SERS spectra from nano- and picomolar (∼0.4 ppt) concentrations of PFOA and PFOS, respectively, demonstrating the viability of deploying our SERS sensors in the environment for the ultrasensitive detection of contaminants.