Fabrication of silver nanoclusters with enhanced fluorescence triggered by ethanol solvent: a selective fluorescent probe for Cr3+ detection.

We present a facile method for the preparation of red-emitting and water-soluble silver nanoclusters (Ag NCs) using dihydrolipoic acid and sodium borohydride as the template and reducing agent. Ethanol solvent is demonstrated to endow Ag NCs with dramatically enhanced fluorescence; therefore, the Ag NCs are synthesized in ethanol/water solution (e/w-Ag NCs) instead of aqueous solution. Specific trivalent chromium (Cr3+) recognition capability of the e/w-Ag NCs can thus be obtained on the basis of its fluorescence quenching. The mechanisms for fluorescence enhancement and quenching of the e/w-Ag NCs triggered by ethanol and Cr3+, respectively, are investigated in detail. Next, a fluorescence method for detection of Cr3+ is established and its analytical performance is evaluated: the detection limit for Cr3+ is 0.71 µM and the linear range is from 2 to 40 µM. The fluorescent probe exhibits sufficient sensitivity and good selectivity toward Cr3+, illustrating that it has great promise for practical application in Cr3+ detection.

Facile method for iodide ion detection via the fluorescence decrease of dihydrolipoic acid/beta-cyclodextrin protected Ag nanoclusters.

In this work, novel photoluminescent Ag nanoclusters (Ag NCs) with red emission are synthesized and successfully used for detecting iodide ion (I-). The dihydrolipoic acid (DHLA) is used as the stabilizing agent and beta-cyclodextrin (ß-CD) is used as the auxiliary stabilizing agent. DHLA and ß-CD are combined with Ag atoms by the formation of AgS bonds and hydrophobic interaction, respectively. Functionalization of ß-CD endows good photoluminescent properties and solubility in water to the Ag NCs. The obtained DHLA and ß-CD-protected Ag NCs (DHLA/ß-CD-Ag NCs) are spherical and display a dispersed state. However, the DHLA/ß-CD-Ag NCs are aggregated in the presence of I-, accompanied by the decrease in their fluorescence intensity. Because the integrity of ß-CD cavities is retained on the surface of DHLA/ß-CD-Ag NCs, which preserves their capability for I- host-guest recognition, the DHLA/ß-CD-Ag NCs combine with I- through the formation of inclusion complexes. Based on this phenomenon, the prepared DHLA/ß-CD-Ag NCs can be designed as a novel fluorescent probe for I- detection. The limit of detection (LOD) is calculated as 0.06 µM, indicating that it is an ideal probe for I- detection in practical applications.

Fluorescence detection of melamine based on inhibiting Cu2+-induced disaggregation of red-emitting silver nanoclusters.

Herein, we report a facile method to synthesize red-emitting, water-soluble Ag nanoclusters (Ag NCs) employing lipoic acid as a stabilizing agent. The Ag NCs show aggregation-induced emission property and have good stability and optical properties. Cu2+ can disperse the aggregated Ag NCs, accompanied by the quenching of fluorescence. However, the formed Cu2+-melamine complex by the coordination chemistry between free copper ion and melamine is able to effectively avoid the quenching process of Cu2+ to the Ag NCs. Hence, the Ag NCs can be applied to design a novel fluorescent probe based on this property to detect melamine. In the determination of melamine, the as-prepared fluorescent Ag NCs exhibit favorable sensitivity and high selectivity. The limit of detection (LOD) down to 0.022 mg/L and good recoveries of real sample experiments were obtained. This fluorescent probe is proved to be convenient and rapid for detecting melamine, with potential application to trace melamine analysis in complicated samples.