Cascade Structured Plasmonic Liquid Crystal Biosensor for the Rapid Detection of Harmful Bacteria Dispersed in Potable Water

Pathogenic microorganisms contaminating potable water are a serious water quality concern because they have severe consequences for human and environmental health. Managing water contamination requires the availability of fast and highly sensitive point-of-use detection systems responsive to a wide concentration range. In the present work, this goal is achieved by realizing a cascade-structured biosensor that exploits innovative stimuli-responsive materials such as gold nanorods (AuNRs) and photosensitive nematic liquid crystals (NLCs). The cascade structure is fabricated by interfacing a glass substrate in a back-to-front arrangement, hosting an array of bioactivated AuNRs and an NLC cell. The AuNRs array integrates microfluidic channels, allowing direct water sampling and the analysis of reduced water volumes with high sensitivity. The biosensor combines in the same device two independent optical transducers: a bioactive AuNRs array (plasmonic biosensor), sensitive to refractive index alterations, and an NLC cell that detects the presence of pathogens by responding to light intensity variations. The plasmonic biosensor performs exceptionally well for very low concentrations of bacteria. In contrast, the NLC biosensor works for high-concentration bacteria, thus providing a cascade-like detection system able to detect bacteria in a wide concentration range from 10 to 10⁹ CFU mL⁻¹.