Detection of Zn2+ ion on a reusable fluorescent mesoporous silica beads in aqueous medium

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%.

Novel Amino-pillar[5]arene as a Fluorescent Probe for Highly Selective Detection of Au3+ Ions

A novel fluorescent probe, amino-pillar[5]arene (APA), was prepared via a green, effective, and convenient synthetic method, which was characterized by nuclear magnetic resonance (NMR), infrared (IR), and high-resolution mass spectrometry. The fluorescence sensing behavior of the APA probe toward 22 metal ions in aqueous solutions were studied by fluorescence spectroscopy. The results showed that APA could be used as a selective fluorescent probe for the specificity detection of Au3+ ions. Moreover, the detection characteristics were investigated by fluorescence spectral titration, pH effect, fluorescence competitive experiments, Job's plot analysis, 1H NMR, and IR. The results indicated that detection of Au3+ ions by the APA probe could be achieved in the range of pH 1-13.5 and that other coexisting metal ions did not cause any marked interference. The titration analysis results indicated that the fluorescence intensity decreased as the concentration of Au3+ ions increased, with an excellent correlation (R 2 = 0.9942). The detection limit was as low as 7.59 × 10-8 mol·L-1, and the binding ratio of the APA probe with Au3+ ions was 2:1. Therefore, the APA probe has potential applications for detecting Au3+ ions in the environment and in living organisms.

Fluorescence switching method for cascade detection of salicylaldehyde and zinc(II) ion using protein protected gold nanoclusters

A new fluorescence switching sensor for cascade detection of salicylaldehyde (SA) and Zinc(II) ion was developed based on bovine serum albumin protected gold nanoclusters (BSA-AuNCs). In the detection, SA interacted with amino groups of BSA-AuNCs, inducing simultaneous formation of fluorescent Schiff base and fluorescence quenching of AuNCs. Zn(II) could further strongly coordinate with the Schiff base ligands, leading to blue-shift and increase of the fluorescence from Schiff base-metal coordination complexes and simultaneous recovery of fluorescence from AuNCs. The new fluorescence switching sensor for Zn(2+) detection has advantages of simplicity, rapidity, naked-eye detection, high sensitivity and selectivity. The linear range of the method for Zn(2+) detection is from 0.1 μM to 100 μM with the limit of detection (LOD) of 29.28 nM. In practical samples, the recoveries of the samples ranged from 99.63% to 100.58%.