Digital photocorrosion biosensing of Bacillus cereus group spores

Monitoring pathogenic bacteria in anthropogenic and natural water reservoirs remains a major challenge for health authorities, requiring the development of rapid, portable, low-labor, and cost-effective detection methods. Digital photocorrosion (DIP) using GaAs/AlGaAs biosensors has recently demonstrated promising results for detecting Legionella pneumophila and Escherichia coli , with increasing bacterial concentrations resulting in delayed biochip DIP rates. However, bacterial spores, such as those of the Bacillus cereus group, induced accelerated DIP rates, creating a significant challenge for the interpretation of spore biosensing responses. In this study, we investigated the mechanisms underlying the accelerated DIP rates induced by Bacillus thuringiensis subsp. kurstaki spores immobilized on biofunctionalized surfaces of GaAs-AlGaAs biochips. Fourier-transform infrared (FTIR) spectroscopy and conductivity measurements suggested that this distinctive behaviour is associated with activation-related modifications of the local ionic environment surrounding viable spores. Meanwhile, heat-killed spores and vegetative cells showed delayed DIP rates, indicating that the biosensor can distinguish viable spores from inactivated spores and vegetative cells. These findings provide new mechanistic insight into biological processes influencing DIP measurements and contribute to a more reliable interpretation of bacterial spore biosensing. The results are expected to support further optimization and validation of robust, field-deployable DIP biosensors for detecting bacterial spores in environmental samples.