Dynamic Monitoring Of The Interaction Of (-)-epigallocatechin Gallate With Human Saliva By Quartz Crystal Microbalance With Disspation And Fluorescence Quenching

Objective: The aim of this paper is to monitor the dynamic process of the biofilm formation of whole saliva (WS), parotid saliva (PS), and submandibular gland/sublingual gland saliva (SMSLS) in the hydroxyapatite (HA) surface by quartz crystal microbalance with dissipation (QCM-D) in real time and in situ, to monitor the process of adsorption and desorption of EGCG on WS and PS which were immobilized on the surface of gold quartz crystal chip by self-assembled monolayer, to monitor the effect of EGCG quenching the fluorescence of WS PS. Methods: WS, PS, and SMSLS which were collected by stimulating method. The shift of frequency and dissipation, the salivary boifilm thickness, mass, shear elastic modulus, and shear viscosity of WS, PS, and SMSLS adsorbing onto the hydroxyapatite surfaces and EGCG adssorbing onto the WS biofilm and the PS biofilm have been studied. According to the correlation coefficient of Langmuir and Fruendlich adsorption model, to decide which is fit to describe the adsorption of EGCG on WS and PS biofim. The adsorption kinetic constants of Langmuir and Fruendlich adsorption model, K, Mm, Kf, and 1/n, were calculated. The interaction between salivary proteins and EGCG was studied by Fluorescence Quenching. The static quenching constant KS, the apparent static quenching constant K, the apparent static quenching binding constant KA, the apparent static quenching binding constant KLB and the binding sites n were calculated. Result: When the adsorption of salivary protein reached saturation, the order of thickness and mass of the salivary biofilm is SMSLS>WS>PS (p<0.05). In contrast, the order of the shear elastic modulus and shear viscosity of the salivary biofilm is PS>WS>SMSLS (p<0.05). When EGCG adsorbed on the PS biofilm, loose EGCG adlayer was formated, the shear elastic modulus and shear viscosity of the EGCG-PS boifilm decreased. But the WS biofilm contained much more water; EGCG adlayer induced the loss of some amount of water made the EGCG-WS biofilm more rigid, so he shear elastic modulus and shear viscosity increased. The Langmuir isotherm and Freundlich isotherm both are fit to describe the adsorption isotherm of EGCG onto the WS biofilm and PS biofilm. The WS biofilm has more capacity and affinity to EGCG than the PS biofilm. EGCG has similar sensitivity to the fluorescence group of WS and PS. The WS and PS's fluorescence were quenched by EGCG in the way of static quenching, the reaction didi not cause change of protein conformation. One protein molecular has one EGCG bond site. Conclusion: The significant difference about the adsorption and biofilm formation properties of the different saliva on HA was caused by their different components. The affinity and adsorption capacity of adsorbing EGCG onto the WS and PS biofilm are different. Saliva protein molecules are in combination with EGCG form compound so that the saliva protein fluorescence quenching in solution.