Ultra-thin CoAl layered double hydroxide nanosheets for the construction of highly sensitive and selective QCM humidity sensor

To achieve real-time monitoring of humidity in various applications,we prepared facile and ultra-thin CoAl layered double hydroxide(CoAl LDH)nanosheets to engineer quartz crystal microbalances(QCM).The characteristics of CoAl LDH were investigated by transmission electron microscopy(TEM),X-ray diffraction(XRD),X-ray photoelectric spectroscopy(XPS),Brunauer–Emmett–Telle(BET),atomic force microscopy(AFM)and zeta potential.Due to their large specific surface area and abundant hydroxyl groups,CoAl LDH nanosheets exhibit good humidity sensing performance.In a range of 11.3%and 97.6%relative humidity(RH),the sensor behaved an ultrahigh sensitivity(127.8 Hz/%RH),fast response(9.1 s)and recovery time(3.1 s),low hysteresis(3.1%RH),good linearity(R^(2)=0.9993),stability and selectivity.Besides,the sensor can recover the initial response frequency after being wetted by deionized water,revealing superior self-recovery ability under high humidity.Based on in-situ Fourier transform infrared spectroscopy(FT-IR),the adsorption mechanism of CoAl LDH toward water molecules was explored.The QCM sensor can distinguish different respiratory states of people and wetting degree of fingers,as well as monitor the humidity in vegetable packaging,suggesting excellent properties and a promising application in humidity sensing.

Functional poly(carboxybetaine methacrylate)coated paper sensor for high efficient and multiple detection of nutrients in fruit

Rapid and simultaneous in situ detection of multi-components is extremely crucial for the real-time monitoring of nutrients in fruits.Herein,a facile and user-friendly poly(carboxybetaine methacrylate)-coated paper-based microfluidic device(pCBMA-μPAD)has been exploited to synchronously identify and semi-quantify vitamin C.glucose,sucro se and fructose in fruits.The pCBMA was successfully grafted from the surface of paper sensor using a co nvenient and robust method,which was confirmed by Fourier transform infrared spectroscopy(FT-IR)and X-ray photoelectron spectrometry(XPS).The superior hydrophilicity and ultra-low fouling of pCBMA endowed the pCBMA-μPAD with remarkably rapid response(3 min),high sensitivity,good linear relationship and low detection limit(LOD)(vitamin C:y=33.809+5.175 x,R^2=0.993,LOD=0.179 mmol/L;glucose:y=-0.113+30.0661 g(x),R^2=0.988,LOD=0.095 mmol/L;sucrose:y--5.334+34.858 lg(x),R^2=0.996,LOD=0.097 mmol/L;fructose:y=4.996+23.325 lg(x),R^2=0.994,LOD=0.140 mmol/L).Furthermore,satisfactory results were yielded in the detection of these nutrients in 9 fruits,which were much agreed well with those obtained by spectrophotometry.Such a portable and versatile pCBMA-μPAD will pro foundly shape the future of food analysis,especially for the assessment of food quality and nutrition in the process of agricultural production and marketing.