The Development of a Multi-Modal Raman and Fluorescence Spectroscopic Platform for Point-of-Care Applications

Abstract

The development of optical biosensors has enabled sensitive and specific detection of target analytes associated with diseases. Fluorescence is a commonly used optical modality for biosensing applications due to its high efficiency and the availability of labels to tag target analytes. Another sensitive optical modality is its spectroscopy which can enable specific detection of a target analyte based on its chemical composition. The inherently weak Raman scattering signals can be enhanced using metallic nanostructures through surface-enhanced Raman scattering (SERS). Many sensing probes and detection schemes have been developed for fluorescence, SERS, and dual fluorescence and SERS-based techniques. Spectroscopy-based instrumentation is required for Raman signal readout, however, fluorescence-based techniques can be readout through spectroscopy- or intensity-based approaches. The development of compact optical readout platforms has the potential to impact diagnostic and sensing needs at the point of care (POC). POC platforms can be used for chronic disease biomarker detection for applications such as cardiovascular disease (CVD). CVD has a disproportionate burden on low-income communities and POC technologies can aid in providing earlier biomarker detection.

In this work, a multi-modal Raman and fluorescence spectroscopic platform was developed for POC applications. The developed spectroscopic platform was miniaturized from a portable, benchtop form factor to a handheld device by utilizing innovative optical designs and grating manufacturing techniques. The portable system utilized separate excitation and collection arms to minimize signal crosstalk and improve detection sensitivity. The Raman arm used a spectroscopy-based detection method, and the fluorescence arm was intensity-based. The first handheld design utilized two separate detection arms, but both were spectroscopy-based methods. The final handheld design utilized a single spectrometer bench to separate both optical signals and measure their intensities using a single detector. A compound grating was designed and manufactured with an industry collaborator, Wasatch Photonics, to enable the separation of the Raman and fluorescence signals onto different regions of interest of the same detector area. Lastly, commercial Raman spectrometers were used to measure the assay response of a paper-fluidic platform for CVD biomarker sensing to determine the potential clinical utility at the POC.