Abstract
This paper presents eye-recognizable and repeatable biochemical flexible sensors using low angle-dependent stimuli-responsive photonic colloidal crystal hydrogel (PCCG) microbeads. Thanks to the stimuli-responsive PCCG microbeads exhibiting structural color, users can obtain sensing information without depending on the viewing angle and the mechanical deformation of the flexible sensor. Temperature-responsive PCCG microbeads and ethanol-responsive PCCG microbeads were fabricated from a pre-gel solution of N-isopropylacrylamide (NIPAM) and N-methylolacrylamide (NMAM) by using a centrifuge-based droplet shooting device (CDSD). As a proof-of-concept of thin and flexible biochemical sensors, temperature- and ethanol-sensing devices were demonstrated. By comparing the structural color of the stimuli-responsive PCCG microbeads and the color chart of the device, sensing information, including skin temperature of the human body and ethanol concentration in alcoholic beverages, was obtained successively. We expect that our device design using low angle-dependent stimuli-responsive PCCG microbeads would contribute to the development of user-friendly biochemical sensor devices for monitoring environmental and healthcare targets.
Highlights
This paper presents eye-recognizable and repeatable biochemical flexible sensors using low angledependent stimuli-responsive photonic colloidal crystal hydrogel (PCCG) microbeads
Owing to the stimuli-responsive PCCG microbeads in the flexible sheet, the angle dependency of our sensors can be suppressed because the ordered arrangement of spatially symmetric photonic colloidal crystals (PCC) such as microspheres or hemispherical domes does not change depending on the viewing angle[23,24,25,26]
As the peak wavelength obtained through spectroscopic measurement, λmax,meas, and the peak wavelength calculated using Eq (3), λmax,calc, are reasonably close, these results show that PNIPAM PCCG microbeads changed isotopically in volume while maintaining the lattice structure (S4)
Summary
This paper presents eye-recognizable and repeatable biochemical flexible sensors using low angledependent stimuli-responsive photonic colloidal crystal hydrogel (PCCG) microbeads. Thanks to the stimuli-responsive PCCG microbeads exhibiting structural color, users can obtain sensing information without depending on the viewing angle and the mechanical deformation of the flexible sensor. Sensors that respond to chemical and biological targets repeatedly for healthcare and environment sample monitoring have attracted growing interest For applying these stimuli-responsive hydrogels for biochemical sensors, it is necessary to convert the intensity of the stimulus to another type of information. We propose a stimuli-responsive PCCG-based eye-recognizable and repeatable biochemical flexible sensor with low angle dependency and high robustness against mechanical deformation by packaging stimuli-responsive PCCG microbeads as a sensing element (Fig. 1). We proposed the use of photonic crystal microbeads to practical eye-recognizable biochemical sensors to suppress the change in the structural color against the observation angle and the unexpected mechanical deformation. We integrated these stimuli-responsive PCCG microbeads with thin and flexible devices to demonstrate the measurement of the skin temperature of a human hand and the ethanol concentrations of alcoholic beverages
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