Herein, we designed a noncommutative logic gate (INHIBIT gate) by utilizing citrate-capped AuNPs as a signal transducer and S2− and TU as mechanical activators and devised a colorimetric sensor for inexpensive, label-free, rapid, sensitive and selective determination of S2−. Under the optimum conditions, 4 μM S2− could induce a significant color change which can be directly recognized by naked eyes. The calibration curve for the absorbance ratios of A680/A520 against S2− concentration was linear in the range from 2 to 9 μM and the RSD was 1.3% for the determination of 4 μM S2− (n = 6). Moreover, this logic gate was successfully applied for sensing S2− in various practical samples, implying its wide applications in food, environment, and biological system.
A new colorimetric and fluorogenic probe ( RN 3 ) based on rhodamine-B has been successfully designed and synthesized. It displays a selective response to Hg 2+ in the aqueous buffer solution over the other competing metals. Upon addition of Hg 2+ , the solution of RN 3 exhibits a ‘naked eye’ observable color change from colorless to red and an intensive fluorescence with about 105-fold enhancement. The changes in the color and fluorescence are ascribed to the ring-opening of spirolactam in rhodamine fluorophore, which is induced by a binding of the constructed receptor to Hg 2+ with the association and dissociation constants of 0.22 × 10 5 M −1 and 25.2 μM, respectively. The Job's plot experiment determines a 1:1 binding stoichiometry between RN 3 and Hg 2+ . The resultant “turn-on” fluorescence in buffer solution, allows the application of a method to determine Hg 2+ levels in the range of 4.0–15.0 μM, with the limit of detection (LOD) calculated at 60.7 nM (3σ/slope). In addition, the fluorescence ‘turn-off’ and color ‘fading-out’ happen to the mixture of RN 3 -Hg 2+ by further addition of I − or S 2− . The reversible switching cycles of fluorescence intensity upon alternate additions of Hg 2+ and S 2− demonstrate that RN 3 can perform as an INHIBIT logic gate. Furthermore, the potential of RN 3 as a fluorescent probe has been demonstrated for cellular imaging .
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