An Optofluidic Surface Enhanced Raman Spectroscopy Microsystem for Sensitive Detection of Chemical and Biological molecules

Abstract

As the human population grows, there is an increasing demand for early detection of a variety of analytes in different fields. This demand mainly includes early and sensitive detection of pathogens, disease biomarkers, pesticides, food contaminants, and explosives. To address this, lab-on-a-chip (LOC) technology has emerged as a tool to improve portability, automation and sensitivity of sensors by taking advantage of integrated laboratory functions on a miniaturized chip. It is agreed that LOC has the potential to make various sensing modules practical for real- world applications. In this work, we have developed a highly sensitive, portable, and automated optofluidic surface enhanced Raman spectroscopy (SERS) microsystem for chemical and biological detection. SERS is a powerful molecular identification technique that combines laser spectroscopy with optical properties of metal nanoparticles. Optofluidic SERS is defined as the synergistic use of microfluidic functions to improve the performance of SERS. By leveraging microfluidic functions, the optofluidic SERS microsystem mixes and concentrates the sample and nanoparticles resulting in an improved performance as compared to conventional open microfluidic SERS systems. The device requires low sample volume and has multiplexed detection capabilities. Moreover, it is suitable for on-site detection of analytes in the field because of its improved automation and portability due to the integrated fiber optics. The final device consists of two regions of packed silica beads inside microchannels for biomolecular interaction as well as sample concentration for SERS measurements. Additionally, an on-chip micromixer and fiber optics are integrated into the device. Optical fibers aligned to the detection zone make the biosensor alignment-free, which greatly improves automation. Practical applications for the detection of real-world analytes (e.g., pesticides, fungicides, food contaminants, and DNA sequences) are demonstrated utilizing our optofluidic SERS microsystem. Detection of biological samples could be extended to proteins and proteolytic enzymes through displacement assays. Consequently, the integration of microfluidic functions, including a microporous reaction zone, a nanoparticle concentration zone, and a micromixer, combined with the use of integrated fiber optics and portable spectrometers, make our microsystem suitable for on-site detection of analytes at trace levels.