Design of a Low-Cost Surface-Enhanced Raman Spectroscopy (SERS) Substrate Using a Modified Seed-Mediated Gold Nanoparticle Growth within a Cellulose-Based Filter Membrane

Despite nearly one-third of American women contracting bacterial vaginosis (BV) in their lifetime, there remains no rapid detection platform for the infection. Most detection techniques used today exhibit low specificity, are invasive, or are slow due to the requirement of amplification techniques or overnight cultures. Herein, we describe a foundational protocol for the synthesis of a disposable nanoplasmonic substrate for capturing bacteria using cellulose-based filter membranes. The platform is used in conjunction with surface-enhanced Raman spectroscopy (SERS) to detect the biochemical composition of the captured bacteria. SERS can enhance a molecule’s intrinsic Raman signal by 104x or more, negating the need for overnight bacterial culture and more laborious amplification techniques. To be useful for biological detection, the substrate must enhance the Raman signal of target molecules while producing a low background noise from the cellulose paper and other contaminants. Herein, a modified seed-mediated gold nanoparticle growth protocol was established to generate the SERS substrate. Background signal reduction and target molecule signal enhancement were optimized by altering the concentration and size of gold nanoparticles grown throughout the fibers of the cellulose paper. The optimization steps included identifying the ideal cellulose paper soaking duration, reagent concentrations, and drying times to produce a SERS compatible substrate. Reflection measurements using a portable Ocean Optics spectrometer were used to indirectly determine the wavelength range of the plasmonic absorbance. SERS measurements were acquired using a benchtop Raman micro-spectroscopy system at 785 nm excitation. Malachite green isothiocyanate, a common Raman reporter molecule, was used to demonstrate the SERS signal enhancement capabilities of the substrate. The designed substrate was proven to generate a reproducible signal, thus establishing a protocol to create an effective, low-cost substrate optimally suited for small biomolecule detection. In the future, we hope to engineer the selective binding properties of the substrate to be specific to bacteria-associated BV infections.