Researchers at Ghent University have detected protease using surface-enhanced Raman spectroscopy (SERS) performed with a tiny waveguide. The work moves toward real-time, label-free, lab-on-a-chip protease monitoring, which could offer a high-throughput approach to screen for new drugs that inhibit proteases involved in disease. Proteases, which break down the peptide bonds that hold proteins together, play an important role as drug targets due to their functionality in diseases such as cancer, Alzheimer’s disease, and arthritis. “We hope that our interdisciplinary approach can one day enable fast and efficient discovery of new drugs for a variety of protease-linked diseases, thus improving lives of millions of patients around the world,” said Nina Turk of the imec research center at Ghent University. In SERS, a metal surface with nanoscale roughness enhances weak signals produced when light interacts with a sample. Due to its high sensitivity, the technique can detect analytes in extremely small volumes. Though SERS has been used for sensitive and selective detection of proteases, this has only been demonstrated using a large Raman microscopy setup. Nanoplamsonic slot waveguides, meanwhile, have emerged as a method to efficiently excite and collect SERS signals. These waveguides consist of two rails that form a small gap through which light can be guided. Coating the inside of the gap with gold nanostructures can be used to produce the SERS effect. Because of their small size, waveguides can be incorporated into lab-on-a-chip devices, allowing simultaneous measurement of many analytes for high-throughput drug discovery. To see if these nanoplasmonic slot waveguides would be useful for SERS detection of proteases, the researchers fabricated a waveguide and designed an experiment for detecting the trypsin protease. They created a specific peptide substrate for trypsin that binds to the gold nanostructure. When the trypsin peptide cleaves to the substrate, part of the substrate diffuses away, creating a detectable reduction in intensity for the SERS spectrum. The experiment revealed a 70% decrease in SERS intensity after 1 hr of trypsin incubation, showing that nanoplasmonic slot waveguides could be used to detect trypsin. The researchers are now working to expand their platform so it can detect the activity of two or more proteases simultaneously. The work was a collaboration of Ghent University-imec and the Flemish Institute for Biotechnology, under the supervision of Roel Baets and Kris Gevaert. The research was presented at the OSA Frontiers in Optics and Laser Science APS/DLS (FiO + LS) conference Sept. 14-17.