Investigation Of New Nanoassembly For Enzyme Activity Detection And Tumor Imaging

Enzyme is a kind of biological active macromolecules that could catalyze various metabolic reactions in organism.Recent studies have shown that in the process of tumor cell growth and migration,the abnormal expression of gene of tumor cells result in changes of enzymatic properties and functions.Hence,monitoring and detecting the biological behavior of the enzymes is of great importance for early diagnosis and treatment of the tumor.Nanobiosensors,which combined nanomaterials with biosensors,have provided numerous brand-new ways for enzyme activity detection and bioimaging.It not only improves the analytical capability such as analytical speed and precision,but also helps bioimaging of the tumor cells and tumor tissues.Meanwhile,nanobiosensors hold an increasingly important position in the field of clinical diagnosis and other areas.In this thesis,two important tumor-related markers were selected as the model targets.Combined with self-assembly techniques and fluorescence imaging techniques,we use a novel two-dimensional nanomaterials(graphite carbon nitride nanosheets)to develop a simple,responsive,highly sensitive,highly selective nanobiosensor method for hyaluronidase activity and fluorescence imaging,and we also use peptide self-assembly techniques to develop a biocompatible,highly sensitive,highly selective nanosensor for cathepsin-B activity detection and fluorescence activatable imaging.Hyaluronidase(HAase)is an important cellular glycosidase that can effectively degrade hyaluronic acid(HA)and is a potential biomarker for clinical diagnosis.Overexpression of HAase can lead to a variety of serious diseases,even cancer.In chapter 2,we use hyaluronic acid functionalized gold nanoparticles(HA-AuNPs)and graphite carbon nitride nanosheets(g-C3N4)to establish a new nanoassembly for HAase detection and activatable imaging in living cells.The nanoassembly could easily be prepared through electrostatic adsorption and hydrophobic interaction between HA-AuNPs and g-C3N4,and those fluorescence quietly weak due to fluorescence resonance energy transfer(FRET).When adding HAase,the degradation of the HA by HAase makes the disintegration of the nanoassembly,then release of the g-C3N4 nanosheets from the nanoassembly,resulting in the recovery of fluorescent signals.Simultaneously,the nanoassembly could specifically enter the tumor cells through HA receptor-mediated endocytosis.The overexpression of HAase in tumor cells act effectively on the nanoassembly,resulting in high-intensity fluorescent signal for activatable fluorescence imaging.Cathepsin-B(Cat-B)is one of important markers in many tumor cells.In chapter 3,we designed peptide sequences that could spontaneously assemble into polypeptide nanoparticles for Cat-B activity detection and highly sensitive tumor cells imaging.The amphiphilic peptide sequences embrace matrix metalloproteinases-2(MMP-2)-responsive peptides hydrophilic areas,and a hydrophobic areas,which contains fluorescent labeled donor-acceptor pair Cat B-responsive peptide and pH-responsive peptide sequences.Under the physiological condition,the amphiphilic peptide is easily self-assembled to form nanopaticles.The nanopaticles is corresponding responsed by MMP-2 and the lower pH value of tumor cells along with Cat-B,and its fluorescent signal is finally activated to realize highly sensitive,selective bioimaging.