Abstract:
There is a growing demand for rapid and sensitive detection approaches for pathogenic
bacteria that can be applied by non-specialists in non-laboratory field settings. Here, the detection of
the typical E. coli enzyme β-glucuronidase using a chitosan-based sensing hydrogel-coated paper
sensor and the detailed analysis of the reaction kinetics, as detected by a smartphone camera, is
reported. The chromogenic reporter unit affords an intense blue color in a two-step reaction, which
was analyzed using a modified Michaelis–Menten approach. This generalizable approach can be used
to determine the limit of detection and comprises an invaluable tool to characterize the performance
of lab-in-a-phone type approaches. For the particular system analyzed, the ratio of reaction rate and
equilibrium constants of the enzyme–substrate complex are 0.3 and 0.9 pM−1h
−1
for β-glucuronidase
in phosphate buffered saline and lysogeny broth, respectively. The minimal degree of substrate
conversion for detection of the indigo pigment formed during the reaction is 0.15, while the minimal
time required for detection in this particular system is ~2 h at an enzyme concentration of 100 nM.
Therefore, this approach is applicable for quantitative lab-in-a-phone based point of care detection
systems that are based on enzymatic substrate conversion via bacterial enzymes
