A low noise current readout architecture for fluorescence detection in living subjects

Optical molecular imaging is emerging as a powerful preclinical research tool for investigating and quantifying molecular events in living subjects, with applications including earlier detection of disease, therapeutic monitoring and understanding fundamental biology [1]. For example, imaging the fluorescent molecular probe RGD-Cy5.5, which specifically binds to molecules (α_vβ₃ integrin receptors) that regulate new blood vessel growth in tumors, can be used to quantify this growth [2]. Capturing the fluorescent signal in living subjects with an implanted biosensor would enable continuous monitoring of tumors in freely moving subjects. Continuous monitoring in the setting of cancer would give valuable information on tumor progression, both in assessing drug efficacy and detecting recurrent tumor growth after treatment. Presently, fluorescence imaging in living subjects is performed with bulky instrumentation that does not permit continuous monitoring of freely moving subjects over long time periods. In order to make a fluorescence-detection system implantable, and portable, a laser excitation source, a photodetector and a readout circuit for measuring and digitizing photocurrents are integrated in a single package, and continuous fluorescence detection is demonstrated in live animals.