Photoprocessible Hydrogel Microsensor for Local Environment Measurement on a Microfluidic Chip

On-chip environment measurement is an important technique for control ambient conditions of cells and monitoring cell activities. However, integration of many sensors in the chip has difficulties such as position and interconnection of sensors. We developed hydrogel microsensors made of photocrosslinkable resin impregnating with indicators for on-chip measurement. This sensor can be used for both area measurement and 3-D sensing by shaping the hydrogel by UV ray patterning. This sensor requires no interconnections since environmental information is detected as optical information such as brightness and color. The YCrCb color space was suitable than the HSV color space in terms of the linearity of the color calibration (H: hue, S: saturation, V: values (brightness). Y : brightness, Cr: color difference of red, Cb: color difference of blue). In this paper, we demonstrated measurement of pH distribution in the microchannel using a color indicator and measurement of oxygen consumption of brown fat cell (BFC) using a fluorescent oxygen indicator. On pH measurement, we used YCrCb color space because Cr and Cb represented monotone variation and robust against brightness fluctuation. The hydrogel was patterned by photolithography into the stripe shape and modified with the indicator. Color change was detected by a color charge-coupled device (CCD). On oxygen measurement, we formed the hydrogel impregnating with the fluorescent indicator into microsphere. Fluorescence change was detected by the spectrophotometer. We succeeded in measuring local pH distribution and oxygen consumption of BFC inside the microfluidic chip.