(683a) Noninvasive, Optical, Continuous, Real-Time Molecular Sensing and Kinetic Modeling Using a Novel, near-Infrared, Implantable, Microfabricated VCSEL Based-Biosensor

Molecular imaging employing optical imaging instrumentation is a widespread, robust technique for in vivo imaging in preclinical models. Nevertheless, current limitations of optical imaging instrumentation include bulky, expensive equipment, the requirements for anesthetized, immobilized subjects, limitations to deep tissue imaging and temporal resolution, and the inability to perform long term (days) continuous imaging in one field of view. To complement whole body imaging approaches, we have recently developed a novel microfabricated, implantable biosensor, consisting of a Vertical Cavity Surface Emitting Laser (VCSEL), photodetector and optical filter optimized for Cy5.5 (675 excitation, 5 nm bandwidth) excitation and emission (O’Sullivan, Parashurama et al. Optics Express 2010). Here we utilize the same miniature biosensor, housing two detectors with one as a reference, to perform continuous molecular sensing of an established molecular probe pair, cRGD-Cy5.5 (n=6) and cRAD-Cy5.5 (n=3) in U87 tumors in nude mice. After injection, continuous sensing was achieved for every 5 seconds per detector as long as six hours, and major sources of noise were replicated with a reference detector. Peak activity was measured between 700-1000s after injection for both RAD and RGD. With background subtraction, the signal to background ratio for cRGD at 30 min, 1 h, 1.5h, and 2h was 1.69 ± 0.37,  1.73  ± 0.28,  1.75 ± 0.37, and 1.83 ± 0.42, respectively (N=6). On the other hand, the signal to background ratio of  cRAD at 30 min, 1 h, 1.5h, and 2h was 0.68 ± 0.20, 0.77 ± 0.20, 0.84 ± 0.27, 0.91 ± 0.27,  respectively (N=3), and the differences between were statistically significant (30 min (P<0.001), 1h (P<0.001), 1.5h (P<0.002), 2h (P<0.010) and correlated well with CCD camera data.  We then analyzed continuous data by performing 4 parameter curve fitting of normalized, continuous data for individual mice, comparing control sites to tumor sites. Our results quantitatively demonstrate that in certain subgroups of mice, loss of signal (probe) from tumor occurs at a different rate then loss of signal (probe) from control site. We conclude that our biosensor works in a comparable fashion to CCD camera, can be used to continuously sense dynamics of molecular probe in a disease model, can reveal individual difference between mice, and can be adapted for both as a new enabling tool in noninvasive sensing and minimally invasive sensing, in both preclinical models and potentially clinical settings.