Fig. 3

Representative bacterial whole cell biosensors (BWCBs). A Design and in vitro and in situ evaluation of Ingestible Micro-Bio-Electronic Device (IMBED) to detect gastrointestinal bleeding. Reprinted with permission from [16] B Selective colonization of bacteria in cancerous tissue harnessed for detecting liver metastases. The probiotic E. coli Nissle 1917 was engineered to express β-galactosidase enzyme LacZ to metabolize systemically injected LuGal into luciferin, detectable in urine. Reprinted with permission from [10]. C Design of a Vibrio cholerae detection system in E. coli. The quorum sensing proteins CqsS, LuxU and LuxO from V. cholera were combined with a genetic inverter (CRISPR) for tight control of GFP expression upon detecting V. cholera. At high cell density, CAI-1 dephosphorylate CqsS which dephosphorylate LuxO. Dephosphorylated LuxO cannot activate Qrr4 promoter and subsequently gRNA is not expressed. In the absence of gRNA, GFP is expressed. Reprinted with permission from [18]. D Detection of bacteria-based urinary tract infections (UTIs) using cellphone-based UTI bioluminescence extinction technology (CUBET). Reprinted with permission from [20]. E Architecture and functional composition of transcriptor-based digital amplifying genetic switches. The clinical sensor promoter drives integrase expression; integrase inverts a transcriptor module that controls the flow of RNA polymerase (RNA pol) along the DNA. Two transcriptors that respond to different signals can be composed in a series to produce an AND gate. A/D, analog to digital. Reprinted with permission from [9]. F Protein biomarker test for point-of-care medical diagnostics. Engineered E. coli cells with surface-displayed nanobodies are mixed with a biological sample. If the sample contains the protein biomarker indicative of a diseased state, cross-linking between bacterial cells and biomarker molecules occurs, leading to cell agglutination and change of the test sample's appearance. Reprinted with permission from [19]