‘Off–on’ switchable fluorescent probe for prompt and cost-efficient detection of bacteria

The rapid and straightforward detection of bacteria in food and human samples is becoming important, particularly in view of the development of point-of-care devices and lab-on-a-chip tools for prevention and treatment of bacterial infections. In the present work, we present the design of a cost-efficient, switchable, fluoresce-based probe for the rapid detection of glucosidase-producing bacteria. The probe was prepared by functionalising streptavidin-coated magnetic particles with a switchable substrate capable of indicating the presence of the metabolic enzyme glucosidase (Glu-C-MPs). Under normal conditions the probe is 'off' but is switched 'on' in the presence of glucosidase-producing bacteria, leading to a measurable increase in fluorescence, indicating the presence of bacteria in the sample. The selectivity of the probe was firstly evaluated using enzymatic experiments, showing that it can detect both alpha- and beta-glucosidase. Subsequently, we tested the efficacy of the probe in detecting bacteria using microorganisms that tend to infect the urinary tract, inducing over-active bladder (OAB) in women. The probe successfully detected the presence of E. coli, K. pneumoniae and P. aeruginosa at low concentrations (75 CFU), within 60 minutes and with a good signal-to-noise ratio. 3 hours were required to observe an increase in fluorescence in the presence of Enterococcus and S. aureus, indicating that these microorganisms produce lower amounts of the detected enzyme. Glu-C-MPs are a promising tool for the prompt, easy and cost-efficient detection of microorganisms, demonstrating a high selectivity and sensitivity for glucosidase-producing bacteria. Thanks to the simple readout and the low-cost instrumentation required for the analysis, the proposed approach could pave the way for the development of affordable point-of-care devices.