High-Performance and Multifunctional Colorimetric Humidity Sensors Based on Mesoporous Photonic Crystals and Nanogels

Abstract

Colorimetric sensors, as a key branch of the application of photonic crystals (PCs), brings enthusiasm to scientists to do research. Here, simple mesoporous and structurally colored one-dimensional photonic crystals (1DPCs) constructed by alternating assembly of poly­(acrylamide-N,N′-methylene bis­(acrylamide)) (P­(AM-MBA)) nanogels and TiO2 nanoparticles are reported as high-performance colorimetric humidity sensors. The sensors with bright colors display rapid response to relative humidity (RH) change and reach sensing balance in 0.5 s. By varying RH from 47.0% to 89.3%, stopband of a sensor changes from 426 to 668 nm, almost spanning the whole visible range. Meanwhile, visual sensing of RH possesses good reversibility and repeatability. Moreover, the sensors with delicate patterns are facilely fabricated by partial UV photodegradation of the polymer layers with nano TiO2 as catalyst. The delicate patterns and backgrounds show different colors and change color simultaneously and quickly by varying the ambient humidity. Accurate QR code pattern is also realized on the PC sensor; it is found successful reading of the data is only achieved by increasing RH to realize high color contrast between the code and background. Given their excellent properties, the porous hybrid PCs are promising as high-performance humidity sensors with potential display, decoration, information-storage, and encryption functions.

Ultrasensitive Dual‐Mode Humidity Detection Using a Plasmonic‐Photonic Hybrid Waveguide

“…Here, PPHS-based dualmode RH detection offers a unique tool for isolating the individual contribution of RI variation and volume expansion in the www.advopticalmat.de process of moisture absorption, which cannot be distinguished by conventional single-mode detections. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Figure 4a,b indicates a pure thickness-induced effect and pure RI-induced effect on 4th-order WG and SPP modes by FDTD simulations. Clearly, for a PPHS with a thick PVA film (h > 850 nm), SPP mode is independent of the thickness of PVA film (Figure 4a, top) and thus completely determined by the RI of PVA (Figure 4b, top).…”

“…For optical sensing, two effects, permittivity variation and volume expansion, can be easily detected by tracking the resonant wavelength or light intensity in the process of absorption moisture. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] For example, integrated with moisture-sensitive coating, several photonic architectures such as plasmonic structure, [8][9][10][11][12][13][14][15] photonic crystal cavity, [16][17][18][19][20] Fabry-Pérot (FP) cavity, [21] fiber Bragg's grating, [22][23][24] and long periodicity grating [25,26] have been explored as humidity sensors. For this type of humidity sensor, refractive index (RI) variation and volume expansion are considered to be concurrent and play counteracting roles in tailoring the resonant wavelength of optical modes.…”

A reversible and fast-responsive humidity sensor based on a lead-free Cs2TeCl6 double perovskite

“…The response (t res ) and recovery time (t rec ) are defined as the time needed to attain 90% of DI(I À I 0 ), where I 0 is the initial current, which in the present case is taken as the value at 5% RH, and I is the current measured at different RH levels. 25 Hence, the humidity sensor exhibits an ultra-fast response and recovery time of 13.8 and 1.39 s, respectively, which are mainly due to the planar structure, where the water molecules can be easily volatilized during the desorption process. 26 In addition, the bond between the Cs 2 TeCl 6 thin film surface and water molecules is relatively weaker than that on the metal oxide ceramics humidity sensor since the hydrogen bond H-Cl is weaker than H-O.…”

Recent Advances in Sensing Applications of Molecularly Imprinted Photonic Crystals

“…Inspired by the discoloration of natural PhCs, this ordered materials are used in colorimetric sensors, which can directly convert external stimuli into visible color changes with a low-cost and simple operation (Lai et al, 2012 ; Frascella et al, 2013 ). At present, PhCs sensors have been applied to the detection of humidity (Kou et al, 2018 ; Di Palma et al, 2019 ), organic solvents (Yu et al, 2020 ), antibiotics (Hou et al, 2015 ), and so on (Wu et al, 2019 ; Qiu et al, 2020 ; Rizvi et al, 2020 ).…”