Real time in vivo imaging and measurement of serine protease activity in the mouse hippocampus using a dedicated complementary metal-oxide semiconductor imaging device.

The aim of the present study is to demonstrate the application of complementary metal-oxide semiconductor (CMOS) imaging technology for studying the mouse brain. By using a dedicated CMOS image sensor, we have successfully imaged and measured brain serine protease activity in vivo, in real-time, and for an extended period of time. We have developed a biofluorescence imaging device by packaging the CMOS image sensor which enabled on-chip imaging configuration. In this configuration, no optics are required whereby an excitation filter is applied onto the sensor to replace the filter cube block found in conventional fluorescence microscopes. The fully packaged device measures 350 microm thick x 2.7 mm wide, consists of an array of 176 x 144 pixels, and is small enough for measurement inside a single hemisphere of the mouse brain, while still providing sufficient imaging resolution. In the experiment, intraperitoneally injected kainic acid induced upregulation of serine protease activity in the brain. These events were captured in real time by imaging and measuring the fluorescence from a fluorogenic substrate that detected this activity. The entire device, which weighs less than 1% of the body weight of the mouse, holds promise for studying freely moving animals.

Functional verification of pulse frequency modulation-based image sensor for retinal prosthesis by in vitro electrophysiological experiments using frog retina.

The functioning of a 16 x 16 pixel pulse frequency modulation (PFM) image sensor for retinal prosthesis is verified through in vitro electrophysiological experiments using detached frog retinas. This image sensor is a prototype for demonstrating the application to in vitro electrophysiological experiments. Each pixel of the image sensor consists of a pulse generator (PFM photosensor), a stimulus circuit, and a stimulus electrode (Al bonding pad). The image sensor is fabricated using standard 0.6 microm CMOS technology. For in vitro electrophysiological experiments, a Pt/Au stacked electrode is formed on the Al bonding pad of each pixel and the entire sensor is fixed in epoxy resin. The PFM image sensor is confirmed experimentally to provide electrical stimulus to the retinal cells in a detached frog retina.

A new neural imaging approach using a CMOS imaging device.

We have developed and demonstrated the use of a dedicated CMOS device for in vivo functional imaging of the mouse brain. In order to achieve this, a 176 x 144 pixel array image sensor is designed, fabricated and specially packaged using a novel process. By using on-chip fluorescence imaging configuration, we have successfully imaged deep inside the hippocampus of the mouse brain. Functional imaging is verified by using a fluorogenic substrate that detects the presence of serine protease in the brain. Introduction of kainic acid induces the expression of the serine protease. The protease reacts with the substrate which then fluorescence. By imaging and measuring the fluorescence signal, we have successfully measured the brain protease activity and accurately determined its reaction onset. This method represents a novel approach for neural imaging.

A CMOS optical/potential image sensor with 7.5μm pixel size for on-chip neural and DNA spot sensing.

An optical/potential CMOS image sensor was designed and fabricated for bioimaging applications. The image sensor is capable to simultaneously sense an optical image and an on-chip potential image. Target applications of the sensor are on-chip (optical + potential) neural imaging and on-chip DNA microarray sensing. The sensor has a QCIF (176 × 144) pixel array with alternatively aligned optical/potential sensing pixels. The pixel size is 7.5 μm × 7.5 μm. The potential resolution is confirmed to be better than 10 mV. An on-chip fluorescence imaging of a mouse's hippocampus was performed to demonstrate that fluorescence imaging is possible with on-chip configuration.

Flexible and extendible neural stimulation/recording device based on cooperative multi-chip CMOS LSI architecture.

An LSI-based cooperative multi-chip neural stimulation/recording device is proposed and fabricated. The proposed multi-chip device consists of small (600 microm x 600 microm in the present design) intelligent neural stimulation/recording chips (unit chip). The unit chip has a neural stimulation/recording electrode array and individual control circuit. It can work with other unit chips cooperatively. One can configure any number of the unit chips as the multi-chip neural stimulation/recording device. Compared to conventional single-chip architecture, the proposed multi-chip architecture has advantages in thinness, mechanical strength and flexibility, and extendibility. That makes the multi-chip neural stimulation/ recording device more suitable for in vivo applications than conventional single-chip devices. Packaging technology for cooperative multi-chip device is also discussed. We developed a thin, flexible packaging technique for the multi-chip neural stimulation/recording device and LSI-compatible Pt/Au stacked biocompatible bump electrode.