Sensors Based On Liquid Photonic Crystals

Liquid photonic crystals are ordered arrays of colloidal crystals surrounded by solvents,and also liquid self-assembled structures coexisting with colloidal saturated solutions.As a type of new intelligent material,liquid photonic crystals have many characteristics,such as rheology,metastability,reversible assembly and disassembly,and so on.Under weak stimuli,crystal structure can change sensitively,so the change can produce corresponding optical response after sensing physical or chemical stimuli.The above characteristics make liquid photonic crystals can be applied to various fields such as sensors,reflective display devices and so on,which have attracted continuous attention from researchers.Traditional photonic crystal sensors are mostly solid-state or gel responsive materials,which have some limitations in practical applications.Therefore,there are still some key problems that need to be solved urgently.For example,how to further improve the accuracy of sensor detection results?How to obtain reproducible measurement results under different environmental conditions?In order to solve the above problems,liquid photonic crystals were prepared by thermal volatilization induced precipitation,and on this basis,liquid photonic crystal detection reagent for reliable sensing of Cu²⁺in water and temperature sensor were constructed respectivelyIn the work of liquid photonic crystal detection reagent for reliable sensing of Cu²⁺,we used SiO₂ colloidal particles supersaturated in an ethanol solution containing propylene carbonate?PC?and salicylic acid?Sal?to prepare a new sensing material of"SiO₂/PC"liquid photonic crystal containing Sal?Sal-LPC?,which can be used to accurately detect the concentration of Cu²⁺in water.Compared with the traditional photonic crystal hydrogel sensor,the liquid PC reagent is directly composed of colloidal particles and reactive substances,and does not require a complicated synthesis and modification process.When the Sal-LPC reagent is mixed with the test sample,Cu²⁺promotes the release of H⁺in Sal and shrinks the photonic lattice.Besides,the detection reagent has a stronger response to Cu²⁺than other cations.Its sensitivity and measurement range can be optimized by the SiO₂ volume fraction and Sal dosage.We established a working curve between the blue shift of the Sal-LPC reflection peak and the concentration of Cu²⁺.The blueshift of the reflection peak after adding an unknown aqueous solution corresponds to the working curve to determine the concentration of Cu²⁺.More importantly,the optical response of Sal-LPC is almost unaffected by changes in synthesis,storage,or application.It can response the analyte quickly and quantitatively,ensuring the accuracy and repeatability of results in chemical analysis or environmental monitoring.In the work of temperature sensors based on liquid photonic crystals,we first constructed a liquid photonic crystal response reagent consisting of silica colloidal particles,propylene carbonate and glycerol.In this liquid colloidal crystal system,the viscosity of the solution will decrease as the temperature increases,which will increase the mutual repulsive force between the colloidal particles,increase the lattice spacing and improve the order of assembly,so that the structural color will change with temperature correspondingly.At the same time,based on the above working principle,we systematically studied the internal relationship between the reflection spectrum of the liquid photonic crystal and the ambient temperature,and established a working curve of temperature measurement.The unknown ambient temperature can be determined by measuring the reflection peak wavelength of the temperature detection reagent.The sensor can still maintain stable reflection wavelength and bright structural color after multiple detection cycles.Based on the above characteristics,the liquid photonic crystal temperature sensor provides an intuitive and convenient measurement solution for ambient temperature measurement.