Packaging sensing cells in spores for long-term preservation of sensors: A tool for biomedical and environmental analysis

Whole-cell sensing systems have successfully been employed for detection of various biologically and environmentally important analytes. A limitation to their use for on-field analysis is the paucity of preservation methods for long-term storage and transport. For that, we have previously developed spore-based genetically engineered whole-cell sensing systems that are able not only to maintain the activity of the sensing cells but also to preserve it for long periods of time in normal and extreme environmental conditions. Herein, we have employed these spore-based sensing systems for analysis of real samples, such as blood serum and freshwater. Spores were able to germinate in the presence of the sample matrix, and the minimum time required for the spores to germinate and generate vegetative sensing cells able to elicit a measurable response to target analytes resulted to be around 2 h. Of the two spore-based sensing systems selected to detect model analytes in real samples, one was able to detect arsenic concentrations as low as 1×10^-7 M in freshwater and serum samples, and the other one could sense down to 1×10^-6 M of zinc in serum. The analysis of human serum samples from healthy subjects for their zinc content proved the viability of spore-based sensing systems. The complete assays, including spore germination and analyte detection, were performed in 2.5 h or less for arsenic and zinc. Furthermore, the assay is inexpensive and simple to carry out and offers unique advantages for the incorporation of the spore-based sensing systems into portable analytical platforms, such as microfluidic devices, to be employed for on-site analysis.