Silver nanocluster-based colorimetric/fluorimetric dual-mode sensor for the detection of bromide and sulfite in waters and wastewaters

In this work, the development of a fluorimetric/colorimetric dual-mode nanosensor for the determination of sulfite and fluorimetric determination of bromide involving silver nanoclusters (AgNCs) is reported. SO2 and Br2 were found to significantly modify the optical properties of AgNCs. Particularly, both volatiles weakened the fluorescence of AgNCs, whereas a color change from nearly colorless to yellowish/brown occurred upon exposure of AgNCs to SO2. Accordingly, three smartphone-based optical assays were devised for sulfite and bromide determination, involving in situ volatile generation and enrichment/trapping of the selectively formed volatiles by AgNCs confined in a droplet and exposed to the headspace above the sample. A hydrophobized cellulose substrate acting as drop holder enabled integrating both the enrichment and the subsequent smartphone-based optical detection in a straightforward manner. Smartphone-based digitization of the enriched AgNCs microdrops and subsequent image processing using a smartphone and its integrated App, respectively, were used for quantitative purposes. Under optimal conditions, limits of detection (LODs) of 1.1 μM and 1.5 μM were achieved for the fluorimetric determination of sulfite and bromide, respectively, whereas sulfite was alternatively determined by colorimetric readout, yielding a LOD of 37.0 μM. The repeatability, expressed as relative standard deviation, was found to be in the range of 5.1–5.9 % in all cases (N = 8). The applicability of the method was demonstrated in aqueous samples of increasing complexity, with recoveries in the range 91–109 %. In addition, the responsiveness of AgNCs to SO2 and Br2 rendered them suitable for the monitoring of bromide and sulfite in increasingly relevant advanced reduction processes such as the UV/sulfite system, as demonstrated in this work.Agencia Estatal de Investigación | Ref. PID2022-136337OB-I00Universidade de Vigo/CISU

Droplet-based luminescent sensor supported onto hydrophobic cellulose substrate for assessing fish freshness following smartphone readout

In this work, two sensitive droplet-based luminescent assays with smartphone readout for the determination of trimethylamine nitrogen (TMA-N) and total volatile basic nitrogen (TVB-N) are reported. Both assays exploit the luminescence quenching of copper nanoclusters (CuNCs) produced when exposed to volatile nitrogen bases. In addition, hydrophobic-based cellulose substrates demonstrated their suitability as holders for both in-drop volatile enrichment and subsequent smartphone-based digitization of the enriched colloidal solution of CuNCs. Under optimal conditions, enrichment factors of 181 and 153 were obtained with the reported assays for TMA-N and TVB-N, respectively, leading to methodological LODs of 0.11 mg/100 g and 0.27 mg/100 g for TMA-N and TVB-N, respectively. The repeatability, expressed as RSD, was 5.2% and 5.6% for TMA-N and TVB-N, respectively (N = 8). The reported luminescent assays were successfully applied to the analysis of fish samples, showing statistically comparable results to those obtained with the reference methods of analysis.Agencia Estatal de Investigación | Ref. RTI2018-093697-B-I00Universidade de Vigo/CISU