Application Of Quantum Dot Fluorescence Sensor Based On Graphite

In recent years, new nanomaterials attracted wide attention. Nanomaterials have superior physical and chemical properties. Biosensors have good selectivity and sensitivity, and can sensitively detect performance in complex environments. After the combination new nanomaterials with biosensor, which give a lot of signal conversion technology.Nowadays, fluorescent biosensors are one of the most rapid development biosensors. With the development of analysis techniques, there is an urgent requirement to improve the selectivity and sensitivity of fluorescence biosensor to satisfy the demands. Among them,sensitivity is one of the important parameters of the biosensor. There are two main strategies used to improve the sensitivity of biosensors: using new nanomaterials to achieve signal amplification, and the other is the use of high quencher efficiency to achieve lower background signal.Based on the reported literatures about new nanomaterials, the specific contents are summarized as follows:（1） We report a fluorescent turn-on nanoprobe for ultrasensitive detection of prostate specific antigen（PSA） based on graphene oxide quantum dots@silver（GQDs@Ag） core-shell nanocrystals. The success of this work relies on the assembly of quantities of GQDs in one GQDs@Ag probe, which makes the ratio of probe to target significantly increased and thus enables the fluorescent signal enhancement. In particular, when the silver shell was removed via oxidative etching using hydrogen peroxide（H2O₂）, the incorporated GQDs could be readily released and the whole process caused little change to their fluorescence. We tested the probe for the ultrasensitive detection of PSA based on the sandwich protocol of immunosensors. In particular, magnetic beads（MBs） were employed to immobilize anti-PSA antibody（Ab₁） and acted as a separable capture probe, while GQDs@Ag was used as immunosensing probe by linking antibody（Ab₂）. The developed immunosensor showed a good linear relationship between the fluorescence intensity and the concentration of PSA in the range from 1 pg/mL to 20 ng/mL with a detection limit of 0.3 pg/mL. The immunosensor used for the analysis of clinical serum samples exhibited satisfactory results, which demonstrated its potential for practical diagnostic applications. This method provided a possible solution to the application of GQDs in immunosensing and could be potentially extended to be used in other similar systems.（2） We describe a highly sensitive nanoparticle–based fluorescence resonance energy transfer（FRET） probe developed without using molecularfluorophores as donors and acceptors.The success of this work relies on the strategy that DNA scission was designed to occur to the probe when target presented, which enabled the fluorescence signal “turn-on” of graphene quantum dots（GQDs） and thus quantitative analysis. In particular, amino-modified SiO₂ NPs were initially coated by GQDs to form highlyemitting SiO₂/GQDs, followed by conjunction with DNA functionalized gold nanoparticles（AuNPs–DNA） to form SiO₂/GQDs–DNA–Au NPs composite. Owing to the FRET interactionsbetween the GQDs and AuNPs, the fluorescence of GQDs was effectively quenched by Au NPs. When bleomycin（BLM）, a model analyte, was mixed with the probe, the fluorescence signal of GQDs would be restored due to the removal of AuNPs from the SiO₂/GQDs surface by DNA scission treatment with BLM in the presence of Fe（II）. The current FRET probe shows a good linearrelationship between the fluorescence intensity and the concentration of BLM inthe range from 0.5 nM to 1 μM with a detection limit of 0.2 nM. The probe also shows satisfactory results for the analysis of clinical serum samples. This method providesversatility to the application of GQDs in FRET biosensing and could be potentially extended to other similar systemsby replacing the linker between the GQDs and AuNPs.（3） A green approach was developed for the preparation of fluorescent carbon dots（CDs）by using sterculia lychnophora seeds as precursors. The preparation of CDs was performed by simple hydrothermal treatment. The quantum yield of as-prepared CDs was 6.9% by using quinine sulfate as the reference. A sensitive turn-on fluorescent sensor based on single-layer MnO₂ nanosheet-quenched fluorescent CDs has been developed for rapid and selective sensing of alkaline phosphatase（ALP）. Taking advantage of the strong interactions between MnO₂ nanosheet and CDs, the fluorescence of CDs was effectively quenched. The introduction of ALP,however, could catalyze the hydrolysis of AAP to give AA and MnO₂ nanosheets was decomposed into Mn2+ by AA, resulting a remarkable increase of fluorescent signal. These optimized designs together allow a high sensitivity for ALP, with a detection limit of 0.4 U/L observed. It has also been used for detection of ALP in human serum with satisfactory results,demonstrating its potential applications in clinical diagnosis.