New approaches to the synthesis of colloidal quantum dots on InP based biomarkers to create

    This work is aimed at getting non-toxic water-soluble quantum dots - dimensional semiconductor structures, which is a critical problem in modern biomedicine Russia and abroad for diagnosis and visualization of certain tissues or cancerous tumors in living organisms. Until recently as biomarkers investigated nanocrystals and heterostructures based on compounds A2B6, however, the use of such compounds in living organisms is severely limited by toxicity . Quantum dots based compounds A3B5, namely InP, is much less toxic than ionic compounds A2B6 through much President Grant MK- 4778.2013.3more strong covalent bond. Currently, the synthesis of InP quantum dots is quite complex and lengthy process , which uses expensive precursors , so the search and development of alternative relatively simple , easily reproducible and cost-effective methods for their synthesis is an urgent task . An important problem is a translated CT obtained in an aqueous solution , as their synthesis is carried out in nonpolar organic solvents. For this it is necessary to carry out the replacement of stabilizing shells . Furthermore, the obtained CT InP often characterized by extremely low quantum yield of luminescence sometimes not reaching 0.1 % , due to the large number of defects on the surface of the nanocrystals , and therefore an important task is to find ways to improve the luminescent properties .
    Colloidal quantum dots (QDs ), indium phosphide was synthesized by the original method in a special quartz reaction unit in an inert atmosphere of argon. As the stabilizer, a surface obtained nanocrystals used myristic acid (MA), trioctylphosphine and trioctylphosphine oxide mixture (TOP / TOPO), as well geptandikarbonovuyu acid and 6 - aminocaproic acid in the presence of myristic acid. As the source of phosphorus used phosphine gas . Synthesis temperature was varied , the composition of the reaction mixture , and the composition of the precipitant . Found that MA- samples are characterized by better crystallinity (for which there is more rings on the electron diffraction pattern ) . These samples were obtained at low temperatures in the micrographs resemble tetrapods or parts thereof , whereas the samples synthesized at high temperatures - almost spherical . Synthesis at low temperatures leads to production of nanoparticles of an average diameter of less than (2.5 and 4.5 at 200 nm , and 260ºC ) and a narrow size distribution. The particles are stabilized by TOP / TOPO, do not have any particular shape. All synthesized samples after separation from the reaction mixture had a very weak luminescence quantum yield (CV ) of less than 0.5% . Bifunctional organic acids used to obtain nanostructures with polar outer part of the stabilizing shell to provide CT solubility in water. In these experiments the cross-linking of the crystallites and their loss in the sediment , so in the future water-soluble QDs prepared by replacing conventional stabilizer (AI) for bipolar in the organic phase .
    To replace the membranes using standard samples CT InP, MA stabilized , since the latter is quite labile ligand , as well as samples of heterostructures InP / ZnSe with two monolayers Accrued zinc selenide and also stabilized myristic acid. Aliquots of raw CT was mixed with 5 - fold excess of mercaptoacetic 3- mercaptopropionate , and 6 - aminocaproic acid . If merkaptokislot as InP, and InP / ZnSe QDs immediately coagulated and precipitated , which means almost instant replacement myristic shell on bipolar mercapto- shell. Selected samples were dissolved in aqueous ammonia to pH 10-11 - alkaline environment needed to deprotonate the carboxyl groups of the bifunctional ligands. For samples InP discoloration and turbidity was observed due to irreversible degradation of - apparently merkaptostabilizatory weakly bound to the surface of pure nanokrstallov InP, or In-S bond on the surface is easily hydrolyzed such colloids . It should be noted that aqueous solutions heterostructures InP / ZnSe are stable , no degradation was observed during the months of storage . Study of the luminescence of the studied samples showed its complete lack of InP- aqueous solutions , which is a result of poor stabilization of surface defects merkaptokislotami . In experiments on membranes replacing 6 - aminocaproic acid sludge formation were observed, and the extraction into the aqueous phase also failed . It can be concluded that the replacement of the shell does not occur , apparently due to a rather strong binding of myristic acid core CT .
  To increase the quantum yield of the method used capacity ZnSe shells and ZnS, which leads to the compensation of surface defects nanocrystalline cores CT InP, such as dangling bonds . Investigation of luminescence spectra taken during experiments capacity ZnS shell at 220ºC samples shows a clear enhancement of the luminescence samples. In the process of building shell ZnS luminescence intensity increases gradually within an hour , and then ceases to change , while the quantum yield reaches 4.8 %.
    Capacity shell ZnSe performed in two ways : 1) the addition of a mixture of zinc and trioktilfosfidselenida myristate (TOPSe) to a solution of CT (molar ratio Zn / Se 1:1); 2) sequentially adding zinc myristate and TOPSe every 20 minutes. In the first method , the luminescence intensity increase markedly enhanced CT ( CT stock solution almost luminescent , KV ~ 0.1 %). Of luminescence spectra shows that the intensity of the luminescence increases with the passage of time , and HF reaches 5.5 % after 2 h after the onset of capacity , the maximum shifts to longer wavelengths from 629 to 636 nm , which indicates the increase in the average diameter of the samples by increasing the shell ZnSe. To investigate the effect of temperature dependence on building shell ZnSe was synthesized at 220 , 260 and 300C in the presence of excess zinc myristate and TOPSe ( their number is equivalent to getting 2 monolayers ZnSe). In all cases, the luminescence intensity increases greatly compared with the initial sample CT InP. It is found that excessive amounts of the reagents at the same time to an increase in synthesis resulted in a 1.5 fold luminescence (CV 8% ) as compared with the build-up of one monolayer ZnSe, which corresponds to a greater thickness of the shell ZnSe. By increasing the capacity of 1 to 2 hours , the luminescence intensity decreases slightly , but remained higher than that of the sample coated with a monolayer of ZnSe .
    In the second method, the luminescence capacity is greatly increased after the capacity of the first and second layer ZnSe. Subsequent increase led to a drop of the luminescence intensity . After building two monolayers ZnSe sample mean diameter increased from 3.7 nm to 4.2 nm. From EDX data that selenium is present in the sample and hence a small amount on the surface of RT is preferably zinc, which passivates the surface, which leads to an increase in luminescence intensity . Zinc selenide is formed on the surface of the sample in small amounts.