Fluorescence quenching amplification in silica nanosensors for Au3+

Development of a reusable fluorescent nanosensor based on rhodamine B immobilized in Stöber silica for copper ion detection

This work has the goal of developing and evaluating a reusable fluorescent nanosensor for detection of Cu(ii) ion in aqueous solution, based on the immobilization of rhodamine B in silica nanoparticles prepared according to a modified Stöber method. In order to do this, a standard ammonium hydroxide ethanolic solution was mixed to ethanol under constant stirring, followed by the addition of tetraethoxysilane (TEOS). To immobilize the fluorescent reagent in the silica nanoparticles, rhodamine B ethanolic solution was added to the reacting mixture at different times (2; 3; 4 and 5 h) after starting the synthesis (which always lasts 7 h). The nanosensor obtained with the addition of rhodamine B after 5 h of synthesis showed the best sensitivity, measured as the fluorescence quenching, which was proportional to Cu(ii) ion. The nanosensor was selective to Cu(ii) ions and showed a linear range from 2.0 to 12.0 μmol L^-1, detection limit of 0.40 μmol L^-1, quantification limit of 1.3 μmol L^-1, response time of 50 s, being possible to be reused 3 times. The nanosensor was applied to the determination of Cu(ii) in sugar cane spirit and the results obtained did not show significant differences from those obtained by atomic absorption spectrometry at a confidence level of 95%.

Calix[4]arene Based Highly Efficient Fluorescent Sensor for Au(3+) and I(.)

This approach disclose the selective fluorogenic ion sensing ability of 5,11,17,23-tetratertbutyl-25,27-bis((2hydroxynaphthylimino)1,2-ethylenediaminecarbonylmethoxy)-26,28 dihydroxycalix[4]arene (C4NSB). Binding property of receptor probed by using selected various cations and anions with conferring of results that demonstrates 'turn-off' fluorescence response and significantly high chromogenic selectivity toward Au(3+) and I(-). Furthermore, selective nature of receptor was investigated in the presence of different co-existing competing ions. The limit of detection (LOD) for Au(3+) and I(-) was determined as 1.5 × 10(-5) and 4.5 × 10(-6) M respectively. Receptor C4NSB form (1:1) stoichiometric complex with both ions and their binding constants were calculated as 8.0 × 10(2) for Au(3+) and 15.6 × 10(2) M(-1) for I(-). Complexes were also characterized through FT-IR spectroscopy.

Nitrogen and sulfur codoped graphene quantum dots as a new fluorescent probe for Au3+ ions in aqueous media

The N and S codoped GQDs can be used as a promising label free fluorescent probe for the sensitive and selective detection of Au³⁺ in aqueous media, which provides a new application of the functionalized GQDs to the detection of metal ions.