On-site detection platform for total microbial activity assessment in environmental solid samples

Abstract

Variations in soil enzymatic activity constitute sensitive early indicators of environmental perturbations, highlighting the need for portable, reliable, and user-friendly methodologies capable of quantifying such changes on site. The fluorescein diacetate (FDA) hydrolysis assay is widely employed to estimate total microbial activity associated with hydrolytic enzymes, including proteases, lipases, and esterases. In the present work, we report the development of a portable analytical platform to perform the FDA hydrolysis assay directly on solid samples in the field. The proposed system substitutes conventional laboratory instrumentation with a compact acrylic chip and a smartphone. Image capture, data processing, and result display are managed by a smartphone app. The performance of the portable FDA assay was validated against the standard laboratory procedure, exhibiting excellent correlation and analytical accuracy. The platform was subsequently applied to diverse case studies: assessing soil fertility in horticultural and agricultural systems, characterizing various vermicompost samples as organic amendments, and monitoring a bioremediation process in pesticide-contaminated soils. In all applications, the portable system yielded results consistent with those obtained with the laboratory methodology. This novel platform represents a valuable tool for the acquisition of real-time, on-site biochemical data from solid environmental matrices, thereby facilitating rapid and informed decision-making in environmental management and soil health assessment.