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This paper presents a CMOS image sensor with auto-switched mode readout architecture for high throughput and high dynamic range scientific imaging applications. The proposed readout circuit compares background illumination with a threshold level and automatically adjusts the pixel array to operate in either linear or logarithmic mode by feeding back a mode switching control signal. This novel readout architecture allows simultaneous linear-logarithmic operation of each pixel, resulting in direct readout of image sequence covering a dynamic range of 121 dB. A chip consisting of 16 times 16 8-T pixel array and the proposed readout circuit has been designed and fabricated using AMI 0.5 mum technology. The chip has been verified for imaging clusters of nano particles (CoFe2O4) illuminated using bright green LED. Experiment results confirm high dynamic range performance due to linear-logarithmic auto-switched mode operation.