Digital enzyme linked immunosorbent assay (ELISA) is an ultra-sensitive technology for detecting biomarkers and
viruses etc. As a conventional ELISA technique, a target molecule is bonded to an antibody with an enzyme by antigen-antibody reaction. In this technology, a femto-liter droplet chamber array is used as reaction chambers. Due to its small
volume, the concentration of fluorescent product by single enzyme can be sufficient for detection by a fluorescent
microscopy. In this work, we demonstrate a miniaturized lensless imaging device for digital ELISA by using a custom
image sensor. The pixel array of the sensor is coated with a 20 μm-thick yellow filter to eliminate excitation light at 470
nm and covered by a fiber optic plate (FOP) to protect the sensor without resolution degradation. The droplet chamber
array formed on a 50μm-thick glass plate is directly placed on the FOP. In the digital ELISA, microbeads coated with
antibody are loaded into the droplet chamber array, and the ratio of the fluorescent to the non-fluorescent chambers with
the microbeads are observed. In the fluorescence imaging, the spatial resolution is degraded by the spreading through the
glass plate because the fluorescence is irradiated omnidirectionally. This degradation is compensated by image
processing and the resolution of ~35 μm was achieved. In the bright field imaging, the projected images of the beads
with collimated illumination are observed. By varying the incident angle and image composition, microbeads were
The structures in advanced complementary metal-oxide-semiconductor (CMOS) integrated circuit technology are in the range of deep-submicron. It allows designing and integrating nano-photonic structures for the visible to near infrared region on a chip. In this work, we designed and fabricated an image sensor with on-pixel metal wire grid polarizers by using a 65-nm standard CMOS technology. It is known that the extinction ratio of a metal wire grid polarizer is increased with decrease in the grid pitch. With the metal wire layers of the 65-nm technology, the grid pitch sufficiently smaller than the wavelengths of visible light can be realized. The extinction ratio of approximately 20 dB has been successfully achieved at a wavelength of 750 nm. In the CMOS technologies, it is usual to include multiple metal layers. This feature is also useful to increase the extinction ratio of polarizers. We designed dual layer polarizers. Each layer partially reflects incident light. Thus, the layers form a cavity and its transmission spectrum depends on the layer position. The extinction ratio of 19.2 dB at 780 nm was achieved with the grid pitch greater than the single layer polarizer. The high extinction ratio is obtained only red to near infrared region because the fine metal layers of deepsubmicron standard CMOS process is usually composed of Cu. Thus, it should be applied for measurement or observation where wide spectrum is not required such as optical rotation measurement of optically active materials or electro-optic imaging of RF/THz wave.
Green fluorescent materials such as Green Fluorescence Protein (GFP) and fluorescein are often used for observing
neural activities. Thus, it is important to observe the fluorescence in a freely moving state in order to understand neural
activities corresponding to behaviors. In this work, we developed an implantable CMOS imaging device for in-vivo
green fluorescence imaging with efficient excitation light rejection using a combination of absorption filters. An
interference filter is usually used for a fluorescence microscope in order to achieve high fluorescence imaging sensitivity.
However, in the case of the implantable device, interference filters are not suitable because their transmission spectra
depend on incident angle. To solve this problem we used two kinds of absorption filters that do not have angle
dependence. An absorption filter consisting of yellow dye (VARYFAST YELLOW 3150) was coated on the pixel array
of an image sensor. The rejection ratio of ideal excitation light (490 nm) against green fluorescence (510 nm) was
99.66%. However, the blue LED as an excitation light source has a broad emission spectrum and its intensity at 510 nm
is 2.2 x 10<sup>-2</sup> times the emission peak intensity. By coating LEDs with the emission absorption filters, the intensity of the
unwanted component of the excitation light was reduced to 1.4 x 10<sup>-4</sup>. Using the combination of absorption filters, we achieved excitation light transmittance of 10<sup>-5</sup> onto the image sensor. It is expected that high-sensitivity green
fluorescence imaging of neural activities in a freely moving mouse will be possible by using this technology.
We present a multi-chip electric stimulator for a retinal prosthesis. The stimulator consists of small silicon devices (unit chips) molded in a thin film. It has an advantage over the conventional devices in physical flexibility and extendibility. The smart unit chip (600 μm square, in this work) is an integrated circuit (IC) that includes digital serial interface circuits, analog switch circuits and on-chip stimulus electrodes. In contrast to conventional stimulators, the present stimulator can be driven with only four wires. The multi-chip configuration enables to make the stimulator flexible and durable to bending stress. The device can be bended to place the stimulation electrodes in good contact with retinal tissue. In this paper, we present the design of the stimulator device with 0.35-μm complementary metal-oxide semiconductor (CMOS) technology. We also report a thin, flexible packaging technique for the stimulator and preliminary experimental results of a sputtered iridium oxide (IrO<sub>x</sub>) film that can be used for chronic stimulation.
We report a low-voltage digital vision chip based on a pulse-frequency-modulation (PFM) photosensor using capacitive feedback reset and pulse-domain digital image processing to explore its feasibility of low power consumption and high dynamic range even at a low power-supply voltage. An example of the applications of the vision chip is retinal prosthesis, in which supplied power is limited. The pixel is composed of a PFM photosensor with a dynamic pulse memory, pulse gates, and a 1-bit digital image processor. The binary value stored at the dynamic pulse memory is read to the 1-bit digital image processor. The image processor executes spatial filtering by mutual operations between the pulses from the pixel and those from the four neighboring pixels. The weights in image processing are controlled by pulse gates. We fabricated a test chip in a standard 0.35-μm CMOS technology. Pixel size and pixel counts were 100 μm sq. and 32 x 32, respectively. In the experiments, four neighboring pixels were considered in image processing. The test chip successfully operated at low power supply voltage around 1.25 V. The frame rate was 26 kfps. Low-pass filtering, edge enhancement, and edge detection have been demonstrated. Relationships between power supply voltages and characteristics of the vision chip are investigated.
We have designed and fabricated a 176×144-pixels (QCIF) CMOS image sensor for on-chip bio-fluorescence imaging of the mouse brain. In our approach, a single CMOS image sensor chip without additional optics is used. This enables imaging at arbitrary depths into the brain; a clear advantage compared to existing optical microscopy methods. Packaging of the chip represents a challenge for in vivo imaging. We developed a novel packaging process whereby an excitation filter is applied onto the sensor. This eliminates the use of a filter cube found in conventional fluorescence microscopes. The fully packaged chip is about 350 μm thick. Using the device, we demonstrated in vitro on-chip fluorescence imaging of a 400 μm thick mouse brain slice detailing the hippocampus. The image obtained compares favorably to the image captured by conventional microscopes in terms of image resolution. In order to study imaging in vivo, we also developed a phantom media. In situ fluorophore measurement shows that detection through the turbid medium of up to 1 mm thickness is possible. We have successfully demonstrated imaging deep into the hippocampal region of the mouse brain where quantitative fluorometric measurements was made. This work is expected to lead to a promising new tool for imaging the brain in vivo.
We have fabricated a CMOS image sensor which can simultaneously capture optical and on-chip potential images. The target applications of the sensor are; 1) on-chip DNA (and other biomolecular) sensing
and 2) on-chip neural cell imaging. The sensor was fabricated using a 0.35μm 2-poly, 4-metals standard CMOS process. The sensor has a pixel array that consists of alternatively aligned optical sensing pixels (88×144) and potential sensing pixels (88×144). The total size of the array is QCIF (176×144). The size of the pixel is 7.5μm×7.5μm. The potential sensing pixel has a sensing electrode which capacitively couples with the measurement target on the sensor. It can be operated either in a wide-range (over 5V) mode or in a high-sensitivity (1.6mV/LSB) mode. Two-dimensional optical and potential imaging function was also demonstrated. Probes with gel tips were placed on the sensor surface and potential was applied. A potential spot with diameter smaller than 50μm was successfully observed in the dual imaging operation.
Image sensors with pulse modulation measurement scheme are fabricated for bioimaging and biosensing ap-plications. We designed pulse modulation photosensors, a 64×64-pixels image sensor for in vitro bioimaging, and a 176×144-pixels (QCIF) image sensor for in vivo bioimaging. We demonstrated the feasibility of the pulse modulation measurement scheme for biosensing applications. We obtained a dynamic range of 120dB and minimum sensing intensity level of 2nW/cm<sup>2</sup>. We also confirmed that 0.2% of intensity change is detectable at the minimum intensity region. An in vitro, on-chip imaging of a mouse hippocampus was successfully demonstrated. A sensor module for in vivo imaging is also developed.
We have developed a CMOS vision chip, an image sensor with pixel-level signal processing, to replace photoreceptor cells in the retina. In this paper, we describe a pixel-level signal processing, which is to control on the stimulus waveform and the amount of the electrical injection charge.
Our CMOS vision chip is an array of a pixel, which consists of a photo detector, a pulse shaper, and a current stimulus circuit. The photo detector circuit generates a pulse frequency modulated (PFM) pulse, which frequency is proportional to the intensity of the incoming light. The PFM photo detector is also modified to restrict the maximum frequency of PFM pulse signal for safety neural stimulation.
The PFM pulse signal should be converted into suitable waveform for efficient neural stimulation. We have employed a pulse shaper to generate one stimulus pulse from one PFM pulse. The pulse parameters (i.e., pulse duration, polarity, etc) of the output pulse signal are controlled by the external signal.
For the electrical neural stimulus, the stimulus intensity is given by the amount of the electrical injection charge. The amount of the injection charge should be enough to evoke a phosphene but should be low to avoid the damage of the retinal tissue caused by the excess charge injection. In our prototyped CMOS vision chip, the stimulus current amplitude is used to control the amount of charge. The 6-bit binary-weighted digital-to-analog converter (DAC) with 2μA resolution is used to control the stimulus current amplitude.
Inspired by biological information scheme, pulse frequency modulation (PFM) technique is robust for noise sources due to its digital encode of analog signals. In a viewpoint of image sensors, PFM is also useful for a wide dynamic range and has already been demonstrated over 60 dB. We have designed a pixel circuit of a CMOS image sensor using PFM for the next generation architecture of vision chips. The chip is fabricated using a standard 0.35 micrometers double poly, triple metal CMOS technology. The photodiode is a parasitic pn diode between p-well and n-diffusion with the size of 2 micrometers squares. The top of the photodiode is covered with third metal and 1 micrometers square hole is open for aperture. Feedback circuits consist of a Schmitt trigger and two inverters. We have demonstrated by introducing PFM the chip works well under the power supply voltage of 0.55V with 50 dB. Such a low voltage operation suggests deep sub-micron technologies, for example, 0.18 micrometers technologies could be applied to the sensor. The other important point in our chip is that the photodiode is very small in size of 2 micrometers by 2 micrometers with the aperture size of 1 micrometers by 1 micrometers . This enables us to realize an image sensor with a small fill factor, which is very useful for vision chips where functional circuits are integrated in each pixel.
This paper proposes and demonstrates a novel type of a vision chip that utilizes pulse trains for image processing. The chip is based on a pulse frequency modulation (PFM) technique, which is used in neurobiological systems. Two types of chips are designed; one is a pixel TEG (test element group) chip for testing availability of PFM for image acquisition using 0.35 micrometers triple-metal double-poly CMOS process and the other is for a vision chip with inhibitory interconnections using 1.2 micrometers double-metal double-poly CMOS process. The TEG chip works well in the power supply voltage of 0.7 V and has a dynamic range of 20 dB with a power consumption of less than 1 (mu) W. The operation of the mutual inhibition in the vision chip is confirmed by simulation. Also the comparison with the other pulse modulation technique, pulse width modulation is discussed.