The increasing load of pharmaceutical ingredients and wastes in riverine systems exacerbates threats to environmental as well as human health. An advanced plasmonic-based detection system has been designed to identify the aquatic presence of piperidine, a toxic molecule that serves as a building block in the pharmaceutical and food additive industries.

The plasmonic substrate of the sensor developed by researchers from Bar-Ilan University and the Weizmann Institute of Science in Israel comprises triangular cavities milled in a silver thin film and protected by a 5-nm layer of silicon dioxide. The beam of a focused ion microscope is controlled with a custom-built computer program to drill holes of different shapes and enhance the electrical field on the surface, leading to concentrated light in very small areas. The resulting amplification enables optical phenomena to be significantly increased and identify low concentrations of molecules previously undetectable with optical probes.

As reported in the journal Environmental Science: Nano, the plasmonic array detected piperidine both in water and ethanol solutions down to a concentration of 10⁻⁸ M. A mixture of two analytes in water was also successfully detected down to a concertation of 10⁻⁷ M.

With its confined and enhanced electromagnetic field, the plasmonic substrate offers an efficient alternative to other substrates currently used in surface enhanced Raman spectroscopy and offers scope for the use of cost-effective, portable Raman devices for environmental monitoring.