Novel Fluorescent Sensors Based On Nanomaterials

Due to the rapid development of related discipline and new technology, fluorescence analysis has been got a great promotion in sensitivity, selectivity and accuracy. It also has excellent application in virous fields. Owing to their desirable optical propertiy, nanomaterials are good candidates for the design of novel and sensitive fluorescence sensor.In this paper, the application of nanomaterials(quantum dots, gold nanocluster) in the detection of biomolecules such as glucose, thrombin, alkaline phosphatase and mouse Ig G was studied. Quantum dots, as a developed and widely used fluorescent nanomaterial, with the advantages of good photostability, narrow emission spectra, strong photoluminescence, have gained great attention and played important roles in virous fields. Gold nanocluster is a kind of novel nanomaterials after quantum dots, which has smaller size(<2 nm). The gold nanocluster is highly attractive for biosensing application because it contains many advantages, such as ultrasmall size, good biocompatibility, water solubility, large Stokes shift, low toxicity, high quantum yield, facile synthesis and so on.In this thesis, we took quantum dots(Cd S and Cd Te quantum dots) and gold nanocluster as our research objects, the major contents are as follows:1. A novel sensor for glucose based on the fluorescence quenching of quantum dotsA novel and sensitive assembled quantum dots(QDs)-bienzyme(glucose oxidase(GOD) and horseradish peroxidise(HRP)) hybrid system was designed for the direct determination of glucose. Using o-phenylenediamine(OPD) or 3,3’-diaminobenzidine(DAB) as substrate of HRP, whose corresponding oxidation product(ox OPD or ox DAB) effectively quenched the fluorescence of thioglycollic acid(TGA)-capped Cd S QDs. The fluorescence quenching of the Cd S QDs was proportional to the concentration of glucose and a detection limit of 0.1 mol/L(or 20 nmol/L) was achieved under the optimum conditions when using OPD(or DAB) as the substrate of HRP. The sensing system was also applied to the determination of glucose in human serum with satisfactory results without any need for complicated sample pretreatments。2. A sensitive thrombin fluorescence sensor based on the photoinduced electron transfer combing mimicking enzyme signal amplificationA novel and highly sensitive aptasensor was developed to detect thrombin on the basis of photoinduced electron transfer(PET) induced fluorescence quenching of Cd Te quantum dots(QDs) amplified by the enzyme mimetics. The above generated G-quadruplex/hemin and a Pt NPs/G-quadruplex/hemin complex as a secondary aptamer for thrombin were enzyme mimetics, which could catalyze the oxidation of hydroquinone(HQ) to 2-hydroxy-p-benzoquinone(HPB) using H2O2 as an oxidant. The large quantities of HPB produced were found to be also efficient fluorescence quenchers for Cd Te QDs through PET. In addition, The recognition of thrombin by the immobilized primary aptamer generated G-quadruplex/hemin in situ, which could effectively quench the fluorescence of Cd Te QDs due to PET. Based on the fluorescence quenching of Cd Te QDs by the dual PET processes, a highly sensitive and selective detection protocol for thrombin was achieved. Under optimized conditions, a linear response for thrombin was achieved in the range of 0.05 pmol/L to 10 nmol/L with a detection limit of 0.015 pmol/L. Such an innovative aptasensor provides a promising platform for sensitive and selective biological detection.3. A novel “turn-on” fluorescence probe for the sensitive detection of alkaline phosphatase and immunoassay based on gold nanoclusterFor the BSA-Au NCs,a combination of Au-S bond with the scaffold BSA acted as a stabilizer and protector for the structure and fluorescence of Au NCs. The fluorescence of Au NCs was first quenched by KMn O4 due to the oxidation of the Au0 and BSA which further broke the Au-S bond. Subsequently, the addition of ascorbic acid(AA) restored the fluorescence by the reduction of Au3+ and BSA which reformed the Au-S bond. Ascorbic acid-2-phosphate(AAP), a substrate of alkaline phosphatase(ALP), could be hydrolyzed by ALP to give AA, using this hydrolysis, a novel turn-on fluorescent probe was developed for the sensitive detection of ALP. The detection limit was as low as 0.003 U/L. In addition, this testing protocol was expanded to mouse Ig G immunoassay detection with the detection limit of 1.5 pg/m L. The present approach paved the way to develop convenient, sensitive, and selective metal NCs-based fluorescent turn-on sensors/probes for the promising applications in biosensing.