The Research Of Fluorescent Biosensing System For Biomacromolecules Based On Near Infrared Silver Sulfide Quantum Dots

Fluorometry is extremely attractive due to its easy operation,high sensitivity,noninvasive and real-time monitoring in biosystem.Fluorescent quantum dots?QDs?,with higher photostability than traditional organic dyes,and thus they have wider applicability.In recent years,with the development of QDs and their applications in the biomedical field,there is increased demand for developing quantum dots with better performance.Near-infrared silver sulfide quantum dots?NIR Ag₂S QDs?with a narrow band gap,the emission wavelength can be tuned from the near-infrared region?NIR?to the second near-infrared region?NIR-II?.They have high fluorescence intensity and quantum yield.In addition,NIR Ag₂S QDs are free of toxic heavy metal elements and have low biotoxicity,which considered to be a kind of fluorescent materials with good biocompatibility.Therefore,the development of bioanalytical sensing systems based on NIR Ag₂S QDs is a very interesting research work.In this paper,NIR Ag₂S QDs were synthesized,and biosensing systems were constructed based on their fluorescence properties,which successfully realized the sensing and imaging of biomacromolecules cytochrome c and alkaline phosphatase.The details are as follows:Chapter 1 OverviewIn this chapter,the development of quantum dots?QDs?and near infrared quantum dots?NIR QDs?are briefly introduced.The synthesis,functional modification and biological applications of NIR Ag₂S QDs are highlighted.Finally,we summarized the works and discussed the significance of our research.Chapter 2 Fluorometric assay for cytochrome c based on near infrared Ag₂S quantum dotsIn this chapter,the 3-mercaptopropionic acid-stabilized Ag₂S QDs were synthesized by hydrothermal synthesis in a one-pot method.The fluorescence emission wavelength of as-synthesized Ag₂S QDs is around 790 nm,and the properties was characterized by TEM,XRD,FTIR,XPS and so on.It was found that the products of cytochrome c?Cyt c?hydrolyzed by trypsin can catalyze H₂O₂ to release?OH.The?OH oxidized caffeic acid to yield quinones,which can quench the fluorescence of Ag₂S QDs by electron transfer mechanism.Therefore,we designed a cascade reaction based on Cyt c triggering,which led to the fluorescence quenching of Ag₂S QDs,and achieved sensitive detection of Cyt c.The fluorescence sensing assay has a linear response range of 2.0 to 150 nM for Cyt c with a detection limit as low as 1.7 nM,which is suitable for the detection of Cyt c at the cellular level.Chapter 3 A ratiometric fluorescent assay for the detection of alkaline phosphatase based on near infrared Ag₂S quantum dots and calceinThere are carboxyl ligands on the surface of 3-mercaptopropionic acid-stabilized NIR Ag₂S QDs,which can bind to Ce³⁺and resulted the enhance fluorescence of Ag₂S QDs.While the fluorescence of calcein is quenching by complexing Ce³⁺with its own carboxyl groups.The p-nitrophenyl phosphate?pNPP?is hydrolyzed to produce PO₄^3-by alkaline phosphatase?ALP?,and PO₄^3-can bind to Ce³⁺with higher affinity than Ag₂S QDs and calcein.Therefore,the NIR fluorescence from Ag₂S QDs is reduced while the fluorescence from calcein is recovered.Based on this discovery,we constructed a ratiometric fluorescent assay for the detection of ALP based on NIR QDs-Ag₂S and calcein.Charaterazed with TEM,Zeta potential,DLS and fluorescence lifetime,it was confirmed that Ce³⁺enhanced the fluorescence of NIR Ag₂S QDs by the mechanism of aggregation-induced enhancement?AIE?and the fluorescence quenching of calcein results from the static quenching mechanism.The linear response of the sensing system to ALP ranged from 2 to 100 mU/mL with a detection limit of 1.28mU/mL and the assay was successfully used for ALP detection in serum,ALP inhibitor screening and imaging of endogenous ALP in HeLa cells.