Construction Of Novel Functionalized Silver Nanoclusters And Its Applications In Biosensing

With the development of science and technology,nanotechnology has gradually been applied to various scientific fields.The rise of nanotechnology has offered a new avenue for the development of scientific research,which plays an important role in biological and diagnostic applications.The nanobiosensing technology,a combination of nanotechnology and biotechnology,hold great potential for the research of life sciences.Nanomaterials are often used as the most important part of nanotechnology,have unique optical,catalytic,and electronic properties that play an important role in biosensing platforms.As a special nanomaterial,silver nanoclusters?AgNCs?have important application in catalysis,medicine,and biosensing fields due to its excellent optical properties,good biocompatibility,easy surface modification and low toxicity.The unique optical properties of AgNCs make it a useful fluorescent probe for the detection of heavy metal ions,small biomolecules and nucleic acids as well as bioimaging.Usually,the AgNCs that are prepared directly in aqueous media possess high surface energy,which are prone to agglomeration,resulting in the low fluorescence or even no fluorescence of as-prepared AgNCs.However,if a template is added to control the growth of AgNCs,it may be easy to prepare AgNCs with excellent performance.Herein,using hyperbranched polyethyleneimine?hPEI?as a template,we have reported a simple method to synthesize novel silver nanoclusters with uniform size and high fluorescence.The presence of hPEI on the surface of as-prepared AgNCs?hPEI-AgNCs?is beneficial to the functionalization of biomolecules.On the one hand,the large positive charges of hPEI-AgNCs make it easy to bind to negatively charged molecules.On the other hand,owing to the large amount of primary amines and imines in hPEI itself,as-prepared hPEI-AgNCs exhibit strong electron donating ability,making it easy to interact with electron-deficient molecules.Therefore,the quantitative detection of hyaluronidase?HAase?and2,4,6-trinitrotoluene?TNT?can be achieved by using these special properties of hPEI-AgNCs.In Chapter 2,we used hPEI as template to one-step synthesize functional hPEI-AgNCs with high fluorescence and large amount of positive charges,which can easily interact with negatively charged hyaluronic acid?HA?.When the HA is added,based on the electrostatic interaction of positive and negative charges,the fluorescence of hPEI-AgNCs was effectively quenched via aggregation-induced fluorescence quenching?AIQ?.However,upon incubation HAase with the mixture of hPEI-AgNCs and HA,HAase can degrade HA into small fragments,which reduce the aggregation effect of hPEI-AgNCs and the fluorescence of hPEI-AgNCs is recovered,with an enhanced fluorescence signal directly correlated with the activity of HAase.The developed sensing strategy is demonstrated to enable simple and sensitive detection of HAase with a detection limit of 0.4 mg mL^-1.More importantly,it has been successfully used for detecting HAase activity in human serum samples.In Chapter 3,we combined hPEI-AgNCs with paper based microfluidic analytical devices??PADs?to achieve quantitative detection of TNT.In this method,hPEI can specifically bind to electron-deficient TNT through donor-receptor interaction to form Meissenheimer complex.The absorption spectra of the Meissenheimer complex overlap with the fluorescence emission peak of hPEI-AgNCs.The hPEI-AgNCs are prone to fluorescence resonance energy transfer?FRET?to quench the fluorescence.And this binding process may also initiate aggregation of hPEI-AgNCs and quench the fluorescence of hPEI-AgNCs by the AIQ effect.hPEI-AgNCs can detect sensitively 10 nM TNT in aqueous solution.In addition,hPEI-AgNCs integrate with?PADs were developed as point-of-care testing platform for visual TNT quality monitoring.with ultraviolet irradiation,the fluorescence change of hPEI-AgNCs for TNT can be easily observed by naked-eyes or recorded by a common CCD camera without complicated instruments.Using Image J software,a linear correlation for TNT was obtained in the range of 2 ng to 50 0 ng with a detection limit estimated to be 2 ng.?PADs are easy to store and transport,and can be used as a good detection platform for high-throughput sample analysis without cross-contamination.This add-and-read manner on paper-based platform is expected to apply to other targets by virtue of altering probes.