Remote quantitative transport and imaging investigations of small fluorescent molecular probes in an interstitial tissue model
Houlne, Michael Patrick
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The diffusive transport characteristics of a unique class of small fluorescent molecular probes in an interstitial tissue model are investigated using micro-endoscopy. The probes employed in the present work are organo-metallic complexes of polyazamacrocycles chelated to Terbium. These particular molecules have large Stoke's shifts, making them amendable to tissue analysis. The delocalized electronic structure of the organic chelate absorbs ultra-violate light (~270 nm) and, after inter-molecular transfer, the lanthanide cation fluoresces in the visible region (550 nm). The diffusive transport properties of the probe molecules are related to their chemical structure, which governs their affinity toward the components of the interstitial model. The basic polyazamacrocyde is functionalized with three phosphate groups. Presently, methyl, ethyl, propyl and butyl alkyl chains are added to the phosphate groups on the polyazamacrocyde to modify the affinity of the probes toward the components of the interstitial model. The interstitial tissue model is constructed by preparing a Type I collagen gel in phosphate buffer solution. Known quantities of the probe are injected into the gel and the resulting diffusive transport of the probe is digitally imaged through a micro-endoscope as a function of time. Microendoscopy coupled with digital imaging allows remote, quantitative analysis of the transport process in near real time. Cross sectional analysis of the images yields the concentration profile of the probe as it diffuses through the gel. The concentration profile is fit to Fick's second law of diffusion to determine the diffusion coefficient for each of the probe molecules.