"Green" Synthesis Of Visible To Near-infrared Emission Semiconductor Quantum Dots And Their Application For Detection Of HBsAg

Semiconductor quantum dots have shown great potential applications in light-emitting diodes (LEDs), biomedical diagnosis, and solar cells because of their high photostability, size-tunable emission with narrow full width at half maximum (FWHM), and broad excitation range. A range of recent research efforts have focused on various strategies to synthesize CdSe, CdTe and CdxHg1-xTe quantum dots because their emission color can be easily tuned from visible to Near-Infrared region. But, there are still some shortages limiting the applications of these quantum dots:1) CdSe, CdTe and CdxHg1-xTe quantum dots have high content of Cd2+ and Hg2+ ions which is essentially toxic. Under in vivo conditions, released Cd2+and Hg2+ ions tightly bind to large plasma proteins and can not be efficiently cleared out of the body. In the application of quantum dot-based devices, quantum dots containing Cd and Hg may pollute the environment.2) Previous methods for synthesizing these quantum dots were involved using alkylphosphine (such as trioctylphosphine (TOP) and tributylphosphine (TBP)). It is well known that alkylphosphine and organometallic salts are hazardous, unstable, and expensive materials and generally glove box is requested in the operation.3) CdTe and CdxHg1-xTe quantum dots have poor stability if they are used as Near-Infrared fluorescent probes. So, it is urgent to synthesize non-toxic, stable and low-cost quantum dots with visible to Near-Infrared emitting spectra in a "phosphine free" system.We have synthesized several types of quantum dots in organic solvents by overcoming all the above mentioned shortages. The main results and conclusions are as follows:(1) High quality and low-toxic ZnSe and ZnSe/ZnS core-shell quantum dots have been synthesized when Se-ODE complex (dissolving Se or SeO2 in ODE) was chosen as the phosphine-free selenium precursor. The photoluminescence (PL) full width at half-maximum (FWHM) was well controlled between 14 and 17 nm and the PL quantum yields (QYs) of ZnSe/ZnS quantum dots can reach 70%. Cu2- or Mn2+ doped ZnSe/ZnS quantum dots were also synthesized by simply modifying this phosphine-free method. The emission range has been extended to 480 and 610 nm with the use of Cu2+ and Mn2+ dopants compared with the emission coverage of ZnSe at around 400 nm.(2) We have developed a new method for the synthesis of different-sized CdTe quantum dots by using Te (or TeO2) with trioctylphosphine oxide as Te precursor and low-cost paraffin as solvent. Different shapes of CdTe nanocryatals can be obtained by simply adjusting the injection and/or growth temperatures. Flower, spherical, tetrapod and dendrimer shaped CdTe quantum dots were prepared when the temperature was increased from" 220 to 350℃. The PL emission of CdTe quantum dots covers a wide range from 510 to 730 nm and the quantum dots' QYs can reach 70%. Their PL FWHM was well controlled between 28 and 35 nm. Compared with the method using phosphine tellurium precursors, the quality of the as-prepared CdTe quantum dots reached the same high level, but the total cost can be saved as high as 50%.(3) As core, different-sized CdTe quantum dots were also used to synthesize CdTe/CdSe and CdTe/CdS core-shell type-Ⅱquantum dots. Due to the special band gap alignment of type-Ⅱcore-shell structure, holes and electrons can be separated and delocalized into core materials and shell materials, and this facilitates the wide range tunability of band gap of core-shell system by choosing suitable materials. The separation of holes and electrons slows down the speed of carrier recombination, which can effectively prolong the PL lifetime of such materials. The small crystal lattice mismatch between CdTe and CdSe (or CdS) can enhance the stability of their core-shell structures and the epitaxial growth strategy to fabricate such system also helps the delocalization of carriers. Non-mercury based Near-infrared quantum dots can be prepared using such type-Ⅱstructures and the emission stability and practicability of such materials is supposed to be much better than Hg-based nanomaterials.(4) High quality water-soluble Mn:ZnSe/ZnS and ZnSe/CdSe/ZnS quantum dots were prepared by a phase transfer method, in which amphiphilic oligomers was used as surface coating agents. The as-prepared aqueous quantum dots were high fluorescent and extremely stable. A biocompatible test has been carried out and such prepared water-soluble quantum dots were used to target hepatitis cells and found that the oligomer-functionalized quantum dots were excellent fluorescence labels for detecting the Human Hepatitis B Surface Antigen. The sensitivity of antigen detection can reach 0.05 ng/mL.