ИСТИНА

Quantum dots (QD) are colloidal nanocrystals with unique optical properties determining their applications in industry, biotechnology, medicine, pharmacology, etc. A large number of papers have been published on QD hydrophilization without sacrificing brightness and stability of QD solutions. There are two major ways for the transfer of hydrophobic QD into aqueous solutions: ligand exchange and coating with amphiphilic polymers. The second method has a number of advantages: as a rule, the fluorescence intensity and photostabitity are higher and the pH and ionic strength windows are wider. We use a low-cost and available copolymer/oligomer acrylic acid/methylacrylic acid/methylmethacrylate (AA/MAA/MMA) for the hydrophilization of CdSe/CdZnS/ZnS QD by adding it to the oleic-acid-stabilized QD in toluene. Upon removal of the organic solvent, the QD residue is dissolved in pure water. As a result, an aqueous solution of QD is obtained without any substantial decrease in the quantum yield. Such buffers as acetate, TRIS, hydrocarbonate and borate quench the fluorescence by 20–30% while phosphate has no effect on the intensity of fluorescence. The addition of the second (cationic) polymer (polyallylamine (PAA) or polydiallyldimethylammonium (PDADMA)) eliminates the quenching effect of the buffer, thus enhancing the fluorescence intensity of QD by 15–20% in solution and up to 30% on silica support. Besides, PAA and PDADMA improve the temporal stability of dilute aqueous QD solutions from days to weeks. All other studied cationic polymers (polyethylenimine, polyhexamethylene guanidine and chitosan) just quench the fluorescence of the AA/MAA/MMA-coated QD by 10–20%. Also, we deposited QD from toluene onto TLC plates with subsequent layer-by-layer deposition of copolymer/oligomer AA/MAA/MMA and cationic polymers from organic solutions and aqueous ethanol. Quenching of the modified QD by various antimicrobial agents has been studied. The strongest quenchers are tetracycline, fluoroquinolones and sulfanilamides (61–97% quenching by 10 µM in solution). Important is the concentration of AA/MAA/MMA copolymer, as its excess suppresses the quenching effect of the analyte (the tolerable molar ratio of copolymer unit to Cd2+ ion on silica equals 2.5). The studied systems can be used in the development of chemical sensors. The authors thank the Russian Foundation for Basic Research for the financial support (grant No 13-03-00441-a).