Quantitative E. coli Enzyme Detection in Reporter Hydrogel-Coated Paper Using a Smartphone Camera.

Kawaljit Kaur,Mareike Müller,Sergey I Druzhinin,Winny Chelangat,Nancy Wangechi Karuri,Holger Schönherr

doi:10.3390/bios11010025

Kawaljit Kaur, Mareike Müller + Show 4 more

Open Access

https://doi.org/10.3390/bios11010025

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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.

Highlights

Pathogenic bacteria are a major worldwide concern, e.g., in the areas of food and water safety as well as healthcare
Format chitosan-based auself-reporting hydrogels were successfully adapted this paper carrier-based to tonomously self-reporting hydrogels were successfully adapted to this paper carridetect and quantify concentrations of bacterial enzymes
We conclude that the heterogeneous β-Gus catalyzed hydrolysis of the chromogenic substrate chitosan-g-X-Gluc can be quantitatively described within the Michaelis enzymatic reaction scheme

Summary

Introduction

Pathogenic bacteria are a major worldwide concern, e.g., in the areas of food and water safety as well as healthcare. Independent of the local setting and level of development, any shortage or even lack of robust, reliable and affordable tests for rapid detection of pathogenic bacteria leads to a possible elevated transmission risk of pathogens, which may subsequently lead to life-threatening illnesses. This is true for some highly developed countries, where the screening of patients regarding colonialization with antimicrobial resistant bacteria is still not carried out routinely due to cost and resource issues. Bacterial contaminations in food and drinking water pose serious threats to the well-being of people in less-developed countries. For people living in regions that have no access to necessary technical and economic resources, microbiological water lab tests in approved laboratories are often practically out of reach

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