A classical “on–off–on” fluorescence detection system was constructed based on FRET to detect three different types of pollutants.

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In this paper, silver nanoparticles (AgNPs) were successfully green-synthesized for the first time using Hedysarum polysaccharide (HPS) as a reducing agent, stabilizer, and modifier (HPS-AgNP). Thiamazole could induce the aggregation of HPS-AgNPs in the residue on a cellulose membrane. A syringe paper-based analytical device was creatively established to ensure the tightness, stability, and good repeatability of the test. The color information remaining on the cellulose membrane was converted into gray values using ImageJ software. Hence, the linear regression curve for thiamazole was established as y = 1 + 0.179x with a detection limit (LOD) of 24.6 nM in the relatively wide range of 0.1~10 μM. This syringe paper-based analytical device was successfully applied to the biological samples.

Three types of pollutants investigated are commonly used and pose a great threat to both environment and human health. This article was aimed at the representative three kinds of pollutants, mainly to explore a fast, simple, sensitive, visible naked eye detection method. The colorimetric detection by gold nanoparticles (AuNPs) was first tried. The cross-linking reaction occurred owing to the strong forces between targets and AuNPs, leading to the aggregation and color change. However, large-scaled aggregation was easily formed and settled which failed to realize accurate quantification. Thus, AuNPs were considered to be used in fluorescence detection as reaction bridge. The introduction of AuNPs could effectively quench the fluorescence of Rhodamine B based on the fluorescence resonance energy transfer (FRET). Since three types of pollutants had great affinity with AuNPs, Rhodamine B dissociated from the solution, causing the recovery of red fluorescence. The fluorescent responses toward three targets were established, resulting in the good linearity in a wide range with low detection limits. The selectivity was well investigated among the same types of interferences. This simple, fast and sensitive fluorescence detection system was first used for simultaneously detecting three types of pollutants and finally successfully applied to real samples.