Adenosine capped QDs based fluorescent sensor for detection of dopamine with high selectivity and sensitivity.

Facile detection of dopamine (DA) in biological samples for diagnostics remains a challenge. This paper reported an effective fluorescent sensor based on adenosine capped CdSe/ZnS quantum dots (A-QDs) for highly sensitive detection of DA in human urine samples. In this assay, adenosine serves as a capping ligand or stabilizer for QDs to render high-quality QDs dispersed in water, and as a receptor for DA to attach DA onto the surface of A-QDs. DA molecules can bind to A-QDs via non-covalent bonding, leading to the fluorescence quenching of A-QDs due to electron transfer. The A-QDs based fluorescence probe showed a limit of detection (LOD) of ca. 29.3 nM for DA detection. This facile method exhibited high selectivity and anti-interference in the presence of amino acid, ascorbic acid (AA), uric acid (UA) and glucide with 100-fold higher concentration in PBS solution. Furthermore, it was also successfully used in the detection of DA in the human urine samples with quantitative recoveries (94.80-103.40%).

Highly bright water-soluble silica coated quantum dots with excellent stability.

Silica coating via a Stöber method is an effective route to render luminescent quantum dots (QDs) with great biocompatibility, low toxicity and water-solubility for bioapplications. However, the bottleneck in this route is the access of highly luminescent, colloidally stable QD dispersion in alcoholic solution. Herein, we report a facile route based on the Stöber method for the synthesis of isolated silica coated QDs (QD@SiO2) with high emission efficiencies, tunable small size (less than 30 nm) and excellent stability. Prior to silica coating, the initial oil-soluble QDs were made dispersible in alcohol-water media by replacing the native hydrophobic ligands with adenosine 5'-monophosphate (AMP). Then, 3-mercaptopropyl-trimethoxysilane (MPS) was introduced to serve as silane nucleation primers. Finally, a silica shell with controllable thickness was obtained on the QD surface by hydrolysis/condensation of tetraethyl orthosilicate (TEOS). Remarkably, the resultant QD@SiO2 had nearly the same high luminescent efficiency (50-65%) as that of initial oil-soluble QDs and exhibited excellent long-term photo and colloidal stability in harsh environments (pH range of 3-13, saturated NaCl solution and thermal treatment at 100 °C). It was demonstrated that the cytotoxicity of the resultant QD@SiO2 was significantly diminished. Moreover, the QD@SiO2 conjugated with folic acid exhibits high specific binding toward receptor-positive Hela cells over receptor-negative A549 cells, indicating the potential of our obtained QD@SiO2 as robust biomarkers in cells due to their chemical processibility and low cytotoxicity.

A quantum dot-based "off-on" fluorescent probe for biological detection of zinc ions.

Since zinc ions play an important role in various physiological activities, developing a facile detection method for Zn(2+) is highly desirable. Owing to their superior optical properties, semiconductor quantum dots (QDs) have been developed as a promising alternative for organic fluorophores in fluorescence analysis. In this study, water soluble di-2-picolylamine-dithiolcarbamate (DPA-DTC)/proline-dithiolcarbamate (P-DTC) co-capped CdSe/ZnS QDs as a sensitive and selective "turn-on" fluorescence probe for Zn(2+) was reported. The probe was easily obtained via ligand exchange. The initial bright fluorescence of QDs was effectively quenched by DPA-DTC that acted as an effective hole trapper. Upon complexation with Zn(2+), the formation of Zn(2+)-DPA-DTC complex altered the energetic position of the HOMO for DPA-DTC, which rendered it unfavorable for the hole transfer. Thus the QDs PL was switched on. Under optimal conditions, a good linear relationship between the fluorescence response and Zn(2+) concentration could be obtained in the range from 0.9 to 16 µM. The limit of detection for Zn(2+) was found to be 0.7 µM. Furthermore, the present probe exhibited a high selectivity for Zn(2+) over other common metal ions and was successfully used in the detection of Zn(2+) in simulated biological fluids.