En optisk sensor för att minska beroendet av biocider i kemisk industri

Purpose and goal

All three aims for stage 1 were fulfilled. Enumeration of bacteria in colloidal silica by fluorescence spectroscopy was demonstrated, and components were identified for a custom online sensor. Further research needs are to determine the limitations of the method for different types of industrial fluids, maximize fluorescence sensitivity by increasing signal response and/or reducing background interferences, and ensure that detection limits meet the hygiene requirements of the industrial process.

Expected results and effects

Using the developed fluorescence method, it was possible to accurately quantify bacteria in an opaque fluid (50% colloidal silica) with a linear response down to 1 000 000 cells per mL. Confocal microscopy gave comparable results while cultivation methods were unreliable or even unusable for certain types of bacteria. The results indicate that the fluorescence spectroscopy is a promising basis for an optical sensor in process industry, but that the method requires development and optimization to improve the sensitivity and detection limit.

Planned approach and implementation

The detection method “front-face fluorescence” enabled the analysis of opaque samples. A fluorescence fingerprint was characterized that was representative for several species of bacteria. The microbial fingerprints were isolated mathematically from other substances and from scattered light. The method was calibrated against bacterial cell counts determined by confocal microscopy, and the linear response, sensitivity and detection limit were determined by the analysis of samples with gradually decreasing concentrations of bacteria cells.