Detection of microbial activity using a colorimetric reaction on paper-based analytical devices

MACAGNO, J.; BERLI, C.L.A.; SATUF, M.L.

Córdoba

Congreso; II Brazil Argentine Microfluidics Congress and V Congreso de Microfluídica Argentina; 2019

Microfluídica Argentina, UNC

A paper-based colorimetric assay was setup for the detection of enzymatic microbial activity in biobeds samples. Fluorescein diacetate (FDA) hydrolysis is widely accepted as an accurate and simple method for measuring total microbial activity in variety of environmental samples, including soils. Colourless fluorescein diacetate is hydrolysed by both free and membrane bound enzymes, releasing fluorescein, a coloured end-product that is normally measured by spectrophotometry. The goal of this work is to avoid the use of bulky equipment for the measurement step, so that the assay can be achieved out of the lab, at the points of need. In a first stage of development, the enzymatic reaction was carried out in the standard mode, and then the reaction products were transferred to a paper-based analytical device, which was particularly designed to exploit the reflected light. Images of the coloured substrate were capture by the cellphone camera and then processed to extract light intensity information. Calibration curves with fluorescein and tests with real soil samples were carried out. The programme ImageJ© was used to process the images, where the intensity of the RGB channels was investigated to optimized the detection. A satisfactory correlation between the results from the conventional method and those from the paper-based device was obtained. These preliminary results suggest that the proposed assay format possesses the capability for on-field detection of microbial activity. Next stage consists in the systematic integration of the reaction steps into the paper-based device, and a further exploitation of cellphone facilities for data recording, analysis, and networking.