Synthesis Of Functionalized Mn-doped ZnS Quantum Dots For Biosensing And Cell Imaging

Photoluminescence spectrometry is the technique of choice for biosensing andcell imaging owing to the apparent advantages of fluorescent probes over othermethods in virtue of sensitivity and convenience. Quantum dots （QDs） offer uniqueadvantages over organic dyes such as great photostability, high photoluminescenceefficiency, size-dependent emission wavelengths, broad excitation and sharp emissionprofiles, thus QDs have been widely explored for biosensing and cell imaging. Themain contents are summarized as follows:（1） Ultrasonic and microwave irradiation-assisted synthesis of PEI-capped Mn-dopedZnS QDs for selective detection of guanosine5’-triphosphate （GTP） wasinvestigated. Compared with fluorescent tags for biomolecules, Mn-doped ZnSQDs have many advantages, such as bright photoluminescence, broad ultraviolet,narrow emission, and high photostability. Application of ultrasonic andmicrowave technique for the synthesis of QDs is gaining importance. Theultrasonic and microwave technique gives several beneficial advantages such asrapid synthesis, formation of uniform crystals, homogeneous nucleation, facilemorphology control, energy efficiency and so on. Under the optimal conditions,the PEI-capped Mn-doped ZnS QDs gives excellent selectivity andreproducibility, and low detection limit （3s;0.6μM）. The developedphosphorescence probe favors biolobical applications since the interference fromscattering light and autofluorescence is effecitively eliminated.（2） Ultrasonic assisted synthesis of adenosine triphosphate （ATP）-capped Mn-dopedMn-doped ZnS QDs for rapid, selective and sensitive detection of arginine andmethylated arginine based on the supramolecular Mg²⁺-ATP-arginine ternarysystem was investigated. The ultrasonic approach was used for the synthesis ofATP-capped QDs because of its rapid, simple, low cost, and efficient merits. Thechoice of ATP as capping ligand in synthesis of functional QDs provided apowerful means of rationally controlling Mn-doped ZnS QDs properties. ATP could render Mn-doped ZnS QDs stable against aggregation and water soluble,and tetain the nucleotides structure needed to specially bind to its target. Thespecific binding of ATP-capped Mn-doped ZnS QDs in the presence of Mg²⁺gave excellent selectivity and reproducibility （1.7%relative standard deviationfor11replicate detections of10μM arginine） and low detection limit （3s;0.23μM） of arginine.（3） Silica-coated S2--enriched Mn-doped ZnS quantum dots （SiO2-S-Mn-ZnS QDs）was developed for imaging intracellular Zn2+ions. Detection of intracellular Zn2+has gained great attention because of its biological significances. Here we showthe fabrication of SiO2-S-Mn-ZnS QDs by enriching S2-with a silica shell on thesurface of Mn-doped ZnS QDs via a sol-gel process for imaging intracellularZn2+ions. Mn-doped ZnS QDs were chosen because of excellentphotoluminescence properties and a nontoxic nature. The prepared probe offershigh sensitivity and selectivity for Zn2+at physiological pH by taking advantageof the surface defects of the SiO2-S-Mn-ZnS QDs. The developed probe gave agood linearity for the calibration plot （the recovered photoluminescence intensityof the SiO2-S-Mn-ZnS QDs against the concentration of Zn2+from0.3to15μM）,excellent reproducibility （1.2%relative standard deviation for11replicatemeasurements of Zn2+at3μM）, and low detection limit （3s;80nM Zn2+）. TheSiO2-S-Mn-ZnS QDs showed negligible cytotoxicity, good sensitivity, andselectivity for Zn2+in a photoluminescence turn-on mode, being a promisingprobe for photoluminescence imaging of intracellular Zn2+.