Rapid and sensitive naked eye detection of faecal pigments using their enhanced solid-state green fluorescence on a zinc acetate substrate

Abstract

The identification of trace faecal pigments in real-time and on-site detection remains a challenge for water quality monitoring. Herein, a simple, low-cost and rapid fluorescence-based analytical method has been developed in a solid matrix for faecal pigments like stercobilin and urobilin detection. This was made possible due to significant enhancement of green solid-state fluorescence (520 nm) by zinc(II) complexation with faecal pigments embedded in the surface of zinc acetate crystals. It enables naked-eye detection of these pigments even at a 10 μM level when excited with 365 nm blue-UV. It was demonstrated that easily available white cellulose paper strips or TLC silica plates coated with zinc acetate can be used as substrates. A photophysical study of solid-state faecal pigments–zinc(II) complexes suggests that green fluorescence enhancement results from the complexation, which can be attributed to the substantial decrease of the non-radiative decay rate (k_nr) as well as more efficient use of excitation light. The observation of reduced interference of humic acid fluorescence makes faecal pigment detection more efficient by this proposed method.