Affordable plasmonic biosensing: democratizing SERS with scalable, field-compatible substrate fabrication.

Efficient and accurate plasmonic biosensing in the field remains a challenge. Despite its potential to revolutionize point-of-care (PoC) diagnostics through unparalleled sensitivity and precise molecular fingerprinting, adoption of traditional surface-enhanced Raman spectroscopy (SERS) has not proven feasible in the field. High production costs, complex fabrication, specialized equipment, and persistent issues with stability and reproducibility impede development for PoC use. Addressing these challenges, this study innovates a democratized and cost-effective fabrication kit that enables the SERS substrate production using commonly available materials and straightforward electrochemistry without compromising on sensitivity and reproducibility. Importantly, this method leverages commercially available bottled water and simple battery-powered fabrication, eliminating reliance on a power grid and enabling local production of biosensors in resource-restricted regions. The cost of producing the fabrication kit is $39.54 with raw materials purchased at bulk retail prices, while the cost of consumables for fabricating each test is just 1.33¢. We demonstrate the efficacy of these substrates in two critical applications: the rapid detection of bacteria and pesticides. We detect trace levels of pesticides such as Thiram and Thiabendazole down to 0.1 ppm using a digital SERS approach. We also demonstrated the identification of bacteria isolated from culture, namely Escherichia coli and Bacillus subtilis. We envision that this label-free, high-sensitivity substrate, when paired with portable Raman spectrometers, could open doors for a new era of field-deployable biosensing, paving the way for its adoption for a plethora of applications, from public health to food testing.