Fluorescence lifetime measurements of boronate derivatives to determine glucose concentration

Novel fluorescence lifetime measurements of molecules based on boronate chemistry were performed. These molecules are the basis of a continuous, minimally invasive, glucose sensor using fluorescence lifetime measurements. This sensor, if coupled with an automated insulin delivery device, would allow for the constant monitoring and control of glucose levels in a person with diabetes. The proposed sensor includes a fluorescent molecule that changes its fluorescence properties upon binding selectively and reversibly to glucose. One such molecule investigated here is N-methyl-N-(9-methylene anthryl)-2-methylenephenylboronic acid (AB). The fluorescence intensity of AB was shown to change in response to changing glucose concentrations. (James, 1994) James proposed that when glucose binds to AB the fluorescence intensity increases due to an enhancement of the N→B dative bond which prevents photoinduced electron transfer (PET). The dative bond between the boron and the amine can prevent PET by binding the amine lone pair of electrons in interactions with the boron, prohibiting PET from quenching the fluorescence of anthracene.;Results of this research show the average fluorescence lifetime of AB also changes with glucose concentration. It is proposed that fluorescence is due to two components: (1) AB with an enhanced N→B interaction, and no PET, and (2) AB with a weak N→B interaction, resulting in fluorescence quenching by PET. Lifetime measurements of AB as a function of both the pH of the solvent and glucose concentration in the solution were made to characterize this two component system and investigate the interaction between the N and B atoms. Measurements of molecules similar to AB were also performed in order to isolate behavior of specific AB constituents. These molecules were 9-(Methylaminomethyl)-anthracene (MAMA), and N-benzyl-N-methyl-N-methyl anthracene (AB-B). Fluorescence lifetime measurements confirmed the two components of AB with lifetime values of approximately 11 nsec without PET and 3 nsec with PET. Electron transfer rates of AB were measured to be on the order of 108 sec-1. Analysis of AB as a glucose sensor showed it has the potential for measuring glucose concentrations in solution with less than 5% error.;Two novel glucose sensing molecules, Chloro-oxazone boronate (COB) and Napthyl-imide boronate (NIB), were synthesized. Both molecules have a N→B dative bond similar to AB, but with longer wavelength fluorophores. They displayed an increase in fluorescence with glucose concentration, however, more work needs to be done before fluorescence lifetime measurements of COB and NIB can be used to measure physiological glucose concentrations.