Low Light CMOS Contact Imager with an Integrated Poly-Acrylic Emission Filter for Fluorescence Detection

This study presents the fabrication of a low cost poly-acrylic acid (PAA) based emission filter integrated with a low light CMOS contact imager for fluorescence detection. The process involves the use of PAA as an adhesive for the emission filter. The poly-acrylic solution was chosen due its optical transparent properties, adhesive properties, miscibility with polar protic solvents and most importantly its bio-compatibility with a biological environment. The emission filter, also known as an absorption filter, involves dissolving an absorbing specimen in a polar protic solvent and mixing it with the PAA to uniformly bond the absorbing specimen and harden the filter. The PAA is optically transparent in solid form and therefore does not contribute to the absorbance of light in the visible spectrum. Many combinations of absorbing specimen and polar protic solvents can be derived, yielding different filter characteristics in different parts of the spectrum. We report a specific combination as a first example of implementation of our technology. The filter reported has excitation in the green spectrum and emission in the red spectrum, utilizing the increased quantum efficiency of the photo sensitive sensor array. The thickness of the filter (20 μm) was chosen by calculating the desired SNR using Beer-Lambert’s law for liquids, Quantum Yield of the fluorophore and the Quantum Efficiency of the sensor array. The filters promising characteristics make it suitable for low light fluorescence detection. The filter was integrated with a fully functional low noise, low light CMOS contact imager and experimental results using fluorescence polystyrene micro-spheres are presented

Dual Extension CMOS Imager and Peripherals for Biomedical Applications

A dual extension CMOS imager, also known as a High and Low Light Imager (HALLI), and peripherals for biomedical applications is presented in this thesis. The HALLI utilizes a single column parallel partitioned pixel amplifier with variable topology for the detection of both high and low light levels in the same frame. For fluorescence detection the fabrication of a low cost poly-acrylic acid (PAA) based emission filter integrated with the CMOS contact imager is introduced. An additional peripheral proposed in this research is a rail-to-rail differential difference amplifier which can be integrated as part of the imager architecture and will allow for high resolution analog-to-digital conversion using a newly developed expanding technique. The HALLI and peripherals are key components towards achieving a lab-on-a-chip device for biomedical applications