The Application Of Quantum Dots Based Optical Sensor In Biomedical Analytical Field

Quantum dots （QDs）, also named semiconductor nanocrystals, have been a newclass of fluorescent probes in recent years. Compared with conventional organicfluorescent dyes, QDs have gained increasing attention in many fields based on theirunique optical properties. Water-soluble QDs have shown special advantages andbright prospects for their application in bio-labeling, fluoroimmunoassay, cell imagingand DNA sequencing techniques. In order to expand the application of QDs inbiomedical analytical field, three optical biosensors were constructed based onwater-soluble CdTe QDs in the present work. Satisfied results were got when theywere applied to the specific detection of medicine, bioactive molecules andpathogenic DNA of malignant tumors.Chapter1is a brief review of development of QDs in recent decades, includingthe basic properties of QDs, the main prepared methods and their application inbiomedical analytical field. The design proposal and significance of this work are alsopresent in the end of this chapter.In chapter2, a novel optical biosensor for a common cold medicine （amantadinehydrochloride, AD） determination had been constructed successfully based on thefluorescence resonance energy transfer （FRET） between water-soluble β-cyclodextrin（β-CD）-functionalized CdTe QDs and Rhodamine B （RB）. In this chapter, CdTe QDsand β-CD were covalent linked with3-aminophenyl boronic acid （APBA） as a bridge.RB could enter the cavity of β-CD by hydrophobic interaction and the process ofFRET between QDs （donor） and RB （acceptor） occurred, which resulted in thedecreasing of fluorescent intensity of QDs. However, when AD replaced RB in thecavity based on its larger hydrophobic association constant with β-CD, the process ofFRET was switched off and the fluorescent intensity of QDs recovered. Theincreasing extent of fluorescent intensity of QDs was in proportion to theconcentration of AD in the range of1×10^-5-1.6×10^-4mol/L with a detection limit 8.82×10^-6mol/L. We also obtained a satisfied result using this spectrophotometricmethod for the determination of AD in pharmaceutical formulation. Furthermore,β-CD-functionalized CdTe QDs with AD in the cavity were incubated with targetHepG2cells. Green fluorescence of QDs in the cytoplasm of cells with greatmorphology was also observed. It could act as a visible biomarker for AD in cancercells fluorescence imaging, which presents a potential application in biomedical field.In chapter3, reverse microemulsion method was used for the synthesis ofsilica-coated QDs fluorescent microbeads and a simple nanosensor was fabricated todetect two bioactive molecules—dopamine （DA） and glutathione （GSH）—inphysiologically concentrations. Oxidized-dopamine could quench thephotoluminescence （PL） of modified QDs by an electron transfer process and GSHcould recover the PL of QDs as a strong reducing agent. The range of DA and GSHdetection were0.0005-0.1mmol/L and0.1-10mmol/L, respectively. The detectionlimits of them were2.41×10^-4mmol/L and6.37×10^-2mmol/L, respectively. Themethod was applied to the determination of dopamine and GSH and their recovery inhuman serum sample with satisfied results.In chapter4, a kind of novel QDs-based multiplex DNA sensor was firstlydeveloped for the simultaneous detection of two susceptive mutations DNA(DNA_BRAFand DNA_BRCA) based on “nano-on-micro” fluoroimmunoassay technique.Some capture DNA on the surface of amino-modified silica microbeads （AMSM）could hybridize with target DNA and only those unreacted capture DNA couldhybridize with excess QDs-labeled probe DNA. The more targets DNA added, thefewer unreacted capture DNA on the surface of AMSM appeared and the lowersignals emitted. So the PL intensity of green and red QDs on the surface of AMSMwere inversely proportional to the concentration of target DNABRAFand targetDNABRCAin the range of0.5-25nmol/L and1-25nmol/L, respectively. The detectionlimits were0.26nmol/L and0.57nmol/L, respectively. Mutant DNA sequences wereused for investigate the selectivity of this hybridization system with satisfied results. The sensor has great potential to expand its application to the early diagnosis ofcancer such as breast cancer, ovarian cancer and papillary thyroid carcinoma.