An ultrasensitive method of real time pH monitoring with complementary metal oxide semiconductor image sensor

• A new approach on quantifying various pH solutions with a CMOS image sensor.
• pH indicator blended hydrogel film was fabricated for pH analysis.
• A distinct RGB color change analyzed by CMOS image sensor.
• Chromaticity diagram and Euclidean distance represent the RGB color space.
• The CMOS image sensor based pH measurement produces sensitive pH detection.

CMOS sensors are becoming a powerful tool in the biological and chemical field. In this work, we introduce a new approach on quantifying various pH solutions with a CMOS image sensor. The CMOS image sensor based pH measurement produces high-accuracy analysis, making it a truly portable and user friendly system. pH indicator blended hydrogel matrix was fabricated as a thin film to the accurate color development. A distinct color change of red, green and blue (RGB) develops in the hydrogel film by applying various pH solutions (pH 1–14). The semi-quantitative pH evolution was acquired by visual read out. Further, CMOS image sensor absorbs the RGB color intensity of the film and hue value converted into digital numbers with the aid of an analog-to-digital converter (ADC) to determine the pH ranges of solutions. Chromaticity diagram and Euclidean distance represent the RGB color space and differentiation of pH ranges, respectively. This technique is applicable to sense the various toxic chemicals and chemical vapors by situ sensing. Ultimately, the entire approach can be integrated into smartphone and operable with the user friendly manner.

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