Biosensors Based On Quantum Dots

Quantum dots (QDs) have been received abroad attention and research because of its unique optical, photochemical and electrochemical properties, and they have been used as biological probes and photoelectric materials. Although quantum dots have many advantages, there are also some inevitable shortcomings for single quantum dots. For example, the stronger self quenching, more sensitive to heat and chemical interference, and easy to reunite over time, all these above limit the application of QDs. So we need to improve the disadvantages of quantum dots to be better used in the field of electrochemical and photochemical. Functionalized quantum dots not only increased the biocompatibility of the QDs, but also expanded the scope of its application in biological detection. This paper has studied three biosensors of nano-composite materials which based on the quantum dots. After represented the prepared materials with a series of characterized methods, we also tested the biosensors using the electrochemical technology and the electrochemical luminescence technology.The main work contents as follows:1. Electrochemical Biosensor for Ni2+ Detection Based on a DNAzyme-CdSe nanocomposite. The detection and speciation analysis of metal-ion is very important for environmental monitoring. A novel electrochemical biosensor for Nickel (Ⅱ) detection based on a DNAzyme-CdSe nanocomposite was developed. We firstly hybridized with capture probe (DNA1) and sequentially with DNA (DNA2) on the gold electrode. Then CdSe QDs were incorporated the specific recognition of DNA2 by covalent assem-bling. Upon addition of nickel ion into the above system, the substrate strand of the immobilized DNAzyme was catalytically cleaved by target Ni2+, resulting in disassociation of the shorter DNA frag-ments containing CdSe QDs. The remaining CdSe QDs on the electrode surface detected by differential pulse anodic stripping voltammetry (DPASV). Under optimal conditions, the as-prepared sensor ex-hibited high sensitivity and fast response to Ni2+ with the linear range from 20 nM to 0.2 mM and alow detection limit of 6.67 nM. The prepared biosensor also shows good stability and good reproducibility and high selectivity toward target Ni2+ against other metal ions because of highly specific Ni2+-dependent DNAzyme. Thus, our strategy has a good potential in the environment surveys.2. Multifunctional Reduced Graphene Oxide (RGO)/Fe3O4/CdSe Nanocomposite for Electrochemiluminescence Immunosensor. A novel multifunctional reduced graphene oxide (RGO)/Fe3O4/PDDA/CdSe nanocomposite has beensuccessfully prepared and used as probe for an electrochemiluminescence (ECL) immunosensor of human interleukin-6 (IL-6). The prepared RGO/Fe3O4/PDDA/CdSe nanocomposite was characterized bytransmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-vis) absorption spectroscopy, anda vibrating sample magnetometer (VSM). This nanocomposite shows magnetism, ECL properties, and good biocompatibility. Furthermore, the RGO/Fe3O4/PDDA/CdSe nanomaterial was applied to develop anultrasensitive ECL immunosensor for detection of IL-6. The ECL intensity decreased linearly with the IL-6concentrations in the range 0.002 to 20 ng/mL. Furthermore, the developed ECL immunosensor with highsensitivity, stability and excellent reproducibility can be used for detection of real samples, which make itpossible to be used in clinical detection.3. A Facile in situ Synthesis of Metal-Organic Framework-CdSe Nanocomposites for Ultrasensitive Electrochemiluminescence Detection of Carcinoembryonic Antigen. A novel highly electrochemiluminescence (ECL) metal-organic frameworks (MOFs) have been successfully synthesized by combining CdSe quantum dots (QDs) and MIL-101 in one step by facile hydrothermal method. The as-prepared MOFs-CdSe nanocompositescombine a high ECL activity and sensing selectivity derived from CdSe and the highly selectiveadsorption and efficient accumulation performance of MOFs. The selective accumulation effectof MOFs can greatly amplify the sensing signal and specificity of the ECL probe. The resultingnanocomposites were applied to develop an ultrasensitive ECL immunosensor for detection ofcarcinoembryonic antigen (CEA). This ECL immunosensor has a sensitive response to CEA in alinear range of 10-12 mg/mL to 10-4 mg/mL with a detection limit of 0.33 fg/mL. The developed ECL immunosensor shows high sensitivity, good stability, specificity, and excellent reproducibility, and can be used for detection of real samples, which providing potential application in clinical detection.