Highly Sensitive Diffraction Grating of Hydrogels as Sensors for Carbon Dioxide Detection

Abstract

A diffraction grating of a stimulus-responsive hydrogel was fabricated for the detection of CO2 with a low detection limit. The hydrogel consisted of dimethylaminopropyl methacrylamide (DMAPMA), methyl methacrylate, and 2-hydroxyethyl methacrylate. The sensing gratings were fabricated through soft-lithographic duplication of photoinduced surface-relief-gratings on azo molecular glass films on the hydrogel surfaces. The detection of an analyte was achieved by the reaction of tertiary amino groups of DMAPMA in the hydrogel with CO2 in water and swelling of hydrogel gratings to cause the variation of the optical-diffraction efficiency (DE). The relationship between DE and CO2 concentration, controlled by the gas-injection rate and volume, was systematically investigated. The performance of continuous detection of CO2 was also evaluated. The sensing device showed high sensitivity, reliable readability, and excellent repeatability for CO2 detection. The CO2-sensing performance of the hydrogel grating was proved to be almost unaffected by relative humidity variations of the environment in a wide range.

Reflective leaky waveguide gratings (LWGs) with internal referencing for sensing

“…Hydrogel gratings have been used to sense a wide variety of analytes including microorganisms, 1 proteins, [2][3][4][5] glucose, 6 pH, 7,8 metal ions, 9,10 and volatiles. 11,12 In comparison to other label-free optical sensors, [13][14][15] hydrogel gratings can provide more effective referencing because sensor and reference regions are closely spaced. Equally, hydrogel gratings are internally referenced, which means they comprise inherent features allowing analyte binding to be separated from common-mode effects such as interferents in sample solutions.…”

Hydrogel gratings with patterned analyte responsive dyes for spectroscopic sensing

“…Previous work on hydrogel gratings has only produced low aspect ratio structures (<1), because all previous methods at some stage require free-standing hydrogel strips which do not have the required rigidity to be self-supporting at high aspect ratios. 17 In this work, high aspect (∼23) ratio patterns were produced by photodeprotection of amines in a hydrogel of acrylamide and copolymer. Subsequently, the patterned free amines were reacted with an analyte responsive dye to form a grating.…”

Hydrogel-based holographic sensors and biosensors: past, present, and future

“…1c). As previously mentioned, this technique was first introduced by Wang, who created masters by the ablation of azopolymers films through soft-lithography [41,[63][64][65][66][67]. Both period and depth depend on the angle between the interfering laser beams and the energy and irradiation time, respectively.…”

“…The final step to fabricate surface relief hydrogel-based diffraction gratings is to mold the hydrogel onto PDMS. This process can be carried out by adding monomer solution to the surface of the PDMS grating [68] or by stamping PDMS onto the solution [41,[63][64][65][66][67]. Whatever the chosen technique, the hydrogel should be moldable and easily detachable from PDMS.…”

“…The sensor responded within a wide concentration range and reached limits of detection of 2 ppm in very short times. Besides, the sensor was reversible by simply introducing an inert gas into the sample cell to desorb CO 2 [67].…”