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23 February 2010 In vitro testing of a protease-sensitive contrast agent for optoacoustic imaging
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We have designed a protease-sensitive imaging probe for optoacoustic imaging whose absorption spectrum changes upon cleavage by a protease of interest. The probe comprises an active site, a derivative of chlorophyll or natural photosynthetic bacteriochlorophyll that absorbs in the near infrared, conjugated to a peptide backbone specific to the protease being imaged. The uncleaved molecules tend to aggregate in dimers and trimers causing a change in the absorption spectrum relative to that of the monomer. Upon cleavage, the probe molecules de-aggregate giving rise to a spectrum characteristic of monomers. We show using photospectrometry that the two forms of the probe have markedly different absorption spectra, which could allow for in vivo optoacoustic identification using a multiwavelength imaging strategy. Optoacoustic measurements using a narrow-band dye laser find spectral peaks in the two forms of the probe at the expected location. The optoacoustic signal from the uncleaved probe is found to be considerably weaker than that of the cleaved probe, perhaps due to poor optical-acoustic coupling in the aggregated molecules. However, ultimately, it is detection of the cleaved probe that is of the greatest import since it reports on the protease activity of interest. PUBLISHERS NOTE 9/1/2010: The figure numbers are corrected. If you downloaded the incorrect version of Paper 75641T and no longer have access to download the correct paper, please contact for assistance.
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Anthony H. Green, James R. Norris, Jing Wang, Zhixing Xie, Hao F. Zhang, and Patrick J. La Riviere "In vitro testing of a protease-sensitive contrast agent for optoacoustic imaging", Proc. SPIE 7564, Photons Plus Ultrasound: Imaging and Sensing 2010, 75641T (23 February 2010);

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