This work illustrates the feasibility of an optoacoustic imaging probe in vitro testing. The imaging probe was based on the red shift in the absorption observed in the reaction centers of photosynthetic units. The chlorophyll a and bacteriochlorophyll a molecules which are at the center of this phenomenon were coupled with peptide sequences specific to target enzymes. The design process progressed through four iterations before a working molecular structure was found. The final design targeted matrix metalloproteinase-2 using the sequence HO-HRALMGLPGG-NH 2. A derivative of chlorophyll a was attached at the amine and was observed to aggregate when placed in a buffered solution. The addition of the enzyme cleaved the sequence, causing an absorption shift from 725nm to 665nm. In order to get the aggregation to occur, it was necessary that the peptide sequence contained a hydrophobic-hydrophilic gradient with the hydrophobic portion closest to the chlorophyll.;This absorption shift was further recognized by optoacoustics tomography. An inconsistency in the intensities implies that the aggregation is causing a change in the Gruneisen parameter. The aggregated form has a lower optoacoustic yield than the monomer form.
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