Rapid Bacteria Detection Methods Based On Colorimetric Assay

Bacterial contamination in drinking water can cause enteritis,dysentery,and other diseases,seriously threatening the survival and development of human beings.Effective detection of bacteria in drinking water plays an important role in monitoring its safety and hygiene.In addition,it can reduce the threat of waterborne bacterial infections.In this paper,a colorimetric detection method based on 4-MPBA-AuNPs was proposed to rapidly evaluate the total amount of bacteria in drinking water.The principle of this method is that 4-MPBA molecules can specifically identify carbohydrate molecules on the surface of bacteria and form covalent bonds through esterification,thus 4-MPBA-AuNPs are fixed on the surface of bacteria.Adding NaCl to 4-MPBA-AuNPs solution without bacteria can cause aggregation of 4-MPBA-AuNPs and the4-MPBA-AuNPs solution turns from red to blue.While in the presence of bacteria,the addition of NaCl solution does not cause 4-MPBA-AuNPs aggregation,and the color of the solution remains red.The color of4-MPBA-AuNPs solution indicates the concentration of bacteria in the sample.By detecting 5 different strains of bacteria,we proved this method to be a broad-spectrum bacteria detection strategy.The entire analysis process of the colorimetric bacteria detection method only needs two steps of sample adding operations,and visual detection results can be obtained within 20 minutes.This colorimetric reaction design is innovative through adjusting the space between 4-MPBA-AuNPs for broad-spectrum bacteria amount detection.In addition to the total amount of bacteria,bacterial viability is another issue closely related to its hazard for human health.In order to monitor bacterial viability in drinking water,a colorimetric detection strategy based on GOD/HRP bienzyme catalysis system was proposed.The principle of this method is that GOD catalyzes the oxidation of glucose to produce gluconic acid and hydrogen peroxide.Hydrogen peroxide and the chromogenic substrates(TBHBA and 4-APP)are catalyzed by HRP to form red quinone compounds,resulting in a deep red solution.Live bacteria can consume the glucose in the system,thus inhibiting the GOD-catalyzed reaction.Insufficient hydrogen peroxide further inhibits the HRP-catalyzed colorimetric reaction,so the solution is colorless or light red.The color change of the solution is related to the activity of bacteria in the sample.The color response can be qualitatively observed by the naked eye.The mixed bacteria sample detection shows that there is no mutual interference between different bacteria strains.To my knowledge,this is the first to utilize the glucose metabolism of live bacteria to design a bienzyme catalysis colorimetric reaction for bacterial viability evaluation.The two methods proposed in this paper are simple,reliable,and cost-effective,providing a feasible solution for rapid detection of total bacterial and bacterial activity in drinking water in resource-limited areas.The color response could be easily observed by the naked eye.Smartphones could be used as an endpoint reader to capture images for accurate determination of viability via RGB analysis.This is distinctly different from traditional colorimetric assay which relies on microplate reader,spectrophotometer,or other instruments to obtain absorbance.