On-Chip In vivo Functional Imaging of the Mouse Brain Using a CMOS Image Sensor

We have developed a new method for in vivo functional imaging of the mouse brain using a dedicated CMOS image sensor chip. The image sensor has 176times144-pixels with pixel size of 7.5times7.5 mum ². A novel packaging process is developed to enable on-chip fluorescence imaging. The sensor chip is attached to a flexible polyimide substrate and sealed in epoxy. A thin-film resist is spin-coated directly onto the image sensor chip for excitation light filtering. By applying multiple coating, a transmittance below -44 dB is achieved. Also, the device has a selectivity of more than 80% for the fluorescence emission of 7-amino-4-methylcoumarin (AMC). The entire packaged device is about 350 mum thick, hence minimizing injury during invasive imaging inside the brain. In vivo functional imaging is performed by using a synthetic fluorogenic substrate which detects the presence of two serine proteases species in the brain. The introduction of kainic acid induces the expression of these protease species, which then reacts with the substrate to release the AMC fluorophore. Imaging of the AMC fluorescence allows the serine protease activity to be measured in real-time. We have successfully measured the protease activity and accurately determined its reaction onset