Sensors for detection of calcium associated with bacterial endospore suspensions Original Research Article

We describe a method of detecting bacterial endospores via quantitation of calcium uniquely associated with spore suspensions. The sensor is created by combining a fluorescent calcium-sensitive indicator, calcein, in a viscous membrane on planar, silica glass coupons. The sensor coupon is affixed to the distal end of an optical fiber, which provides excitation light and collects the fluorescence emission. Aqueous micro-droplets of bacterial spores are added to the sensor and the resulting increase in fluorescence intensity is monitored. This assay effectively exploits the high concentration of calcium ion found in the spore core and expressed on the surface, and fluorescence spectroscopy, as an indirect method to detect and quantify spore concentration. This sensor technology is applicable to near real-time detection of calcium in bacterial spore suspensions without interference from light scattering or other ambient biological materials such as bacteria, pollen, viruses, and fungal spores.