pH and ionic strength responsive photonic polymers fabricated by using colloidal crystal templating

In this paper, monodispersed silica particles were synthesized using tetraethoxysiliane hydrolyzing in ethanol by a Stöber–Fink–Bobn method and then self-assembled on cleaning glass slides to form silica colloidal crystals. After photopolymerization of methacrylic acid mixing with ethylene glycol dimethylacrylate and hydrofluoric acid etching, the pH-responsive polymers were obtained with highly 3D-ordered macroporous structures templated by silica colloidal crystals. These polymers films can swell or deswell in response to external stimuli, causing a change of Bragg diffraction to read pH or ionic strength of various solutions by optical signals or electrochemical signals. As an application, they can be used as chemical sensors to detect pH or ionic strength variation of environment.     

All-fibre one-way filter based on both-end-filled photonic liquid crystal fibres

We propose an all-fibre one-way filter based on photonic crystal fibres (PCFs) with both ends of the air holes filled with liquid crystals. According to the resonant condition of the antiresonant reflecting optical wave-guide (ARROW) model, the transmission characteristics of the proposed photonic liquid crystal fibres (PLCFs) are directional. The transmission spectra can be tuned by changing the incident direction of the input light and the length of the empty PCF section. The shorter the length of the PLCFs, the more peaks in the transmission spectra. The all-fibre both-end-filled PLCFs can be applied to the design of one-way multiband filters.     

Photoswitching properties of photonic band gap material containing azo-polymer liquid crystal

A photochemically tunable photonic crystal was prepared by infiltration of the polymer liquid crystal (LC) having azo-chromophores in a SiO₂ inverse opal structure. The SiO₂ inverse opal film infiltrated with the polymer LC reflected a light corresponding to the periodicity as well as the refractive indices of the inverse opal structure. Linearly polarized light irradiation caused the shift of the reflection band to longer wavelength more than 15 nm. This is caused by the formation of uniaxially anisotropic molecular orientation of the polymer LC. The switched state was stable under interior light, and reversible switching of the reflection band can be achieved by the linearly and circularly polarized light irradiation. This photoswitching property will be suitable not only for various optical materials, but also for introduction of defects in the photonic crystals.     

Electro-optical properties of photo-aligned photonic ferroelectric liquid crystal fibres

Electro-optical and spectral studies of isotropic photonic crystal fibre (PCF) infiltrated with photo-aligned ferroelectric liquid crystal (FLC) under influence of external electric field are described. Desired alignment of FLC molecules is provided by generation of photo-aligning surface on the inner side of PCF structure. Propagation of light spectrum, as well as light attenuation have been investigated in details. Moreover, the electro-optical response times were measured and analysed.     

Progress toward the development of a point-of-care photonic crystal ammonia sensor

We have developed an ammonia-sensitive material by coupling the Berthelot reaction to our polymerized crystalline colloidal array (PCCA) technology. The material consists of a periodic array of highly charged colloidal particles (110 nm diameter) embedded in a poly(hydroxyethyl acrylate) hydrogel. The particles have a lattice spacing such that they Bragg-diffract visible light. In the Berthelot reaction, ammonia, hypochlorite, and phenol react to produce the dye molecule indophenol blue in an aqueous solution. We use this reaction in our sensor by covalently attaching 3-aminophenol to the hydrogel backbone, which forms cross-links through the Berthelot mechanism. Ammonia reacts with hypochlorite, forming monochloramine, which then reacts with a pendant aminophenol to form a benzoquinone chlorimine. The benzoquinone chlorimine reacts with another pendant aminophenol to form a cross-link. The creation of new cross-links causes the hydrogel to shrink, which reduces the lattice spacing of the embedded colloidal array. This volume change results in a blue-shift in the diffracted light proportional to the concentration of NH₃ in the sample. We demonstrate that the NH₃ photonic crystal sensing material is capable of quantitative determination of concentrations in the physiological range (50–350 μmol NH₃ L⁻¹) in human blood serum.     

Fluorescence enhancement for the complex PAMAM-BSA in the presence of photonic crystal heterostructures

The paper presents the optical characterization of the multilayer film composed of styrene (ST)-poly(ethylene glycol) methyl ether methacrylate (PEGMA 1100)-gold nanoparticles (Au)-poly(amidoamine) PAMAM (G4)-bovine serum albumin (BSA). The addition of the last layer composed of BSA resulted in an unusual optical behaviour, i.e. increase of the fluorescence emission intensity, respectively the intensity of the UV-vis reflection, compared with the ST-PEGMA 1100-Au-G4 film. The explanation could be attributed to the presence of photonic crystal heterostructures. The multilayer film has been characterized by optical microscopy, AFM, UV-vis, and fluorescence.     

Temperature-controllable beam splitter and optical filter based on filling liquid crystal into both ends of photonic crystal fibres

We first presented an optical device of integrated beam splitter and filter based on the photonic crystal fibres (PCFs) with both ends of the air-holes filled with liquid crystal (LCs). All of the air-holes of one end of PCFs were filled with LCs and for the other end two air-holes near the solid core were selectively filled with LCs. As a beam splitter, when the two-filled-holes end was heated, the light power partly transmitted steadily from the central solid core into the two holes filled with LCs after the clearing point. As a filter, when the two-filled-holes end was heated, a peak near 760 nm of transmission spectrum got weak and another peak near 608 nm was maintained. While heating the full-filled end, the peak near 760 nm got strong and the peak near 608 nm got extremely weak. So this optical device could be applied to beam splitter and filter.     

The fabrication of polymer dispersed liquid crystal based on SiO2 photonic crystal template

The conductance of polymer matrix is an important factor for the property of the polymer dispersed liquid crystal (PDLC). The nanographites are dispersed into the polymer matrix for optimising the dielectric conductive property. The synthesised nanoparticles SiO₂ was used as photonic crystal (PC) to work as a template for fabricating PDLC films. A mixture of pre-polymer and liquid crystals (LCs) was infiltrated into the void of the PC and polymerised under ultraviolet light. The void of the PC made uniform the dispersion of the liquid crystals in the films. The optical property of the PDLC films was optimised by doped nanographites and negative charge SiO₂ template. The effect of negative charge SiO₂ and nanographites on the threshold voltage and driving voltage was researched. The morphology of the PDLC films was studied by the FTIR image. The dispersed LCs droplets were uniformly affected by the addition of the nanographites. The LCs droplets dispersed in the polymer were located in the void of the SiO₂ photonic crystal.     

A nonionic surfactant-decorated liquid crystal sensor for sensitive and selective detection of proteins

Proteins are responsible for most biochemical events in human body. It is essential to develop sensitive and selective methods for the detection of proteins. In this study, liquid crystal (LC)-based sensor for highly selective and sensitive detection of lysozyme, concanavalin A (Con A), and bovine serum albumin (BSA) was constructed by utilizing the LC interface decorated with a nonionic surfactant, dodecyl β-d-glucopyranoside. A change of the LC optical images from bright to dark appearance was observed after transferring dodecyl β-d-glucopyranoside onto the aqueous/LC interface due to the formation of stable self-assembled surfactant monolayer, regardless of pH and ion concentrations studied in a wide range. The optical images turned back from dark to bright appearance after addition of lysozyme, Con A and BSA, respectively. Noteworthy is that these proteins can be further distinguished by adding enzyme inhibitors and controlling incubation temperature of the protein solutions based on three different interaction mechanisms between proteins and dodecyl β-d-glucopyranoside, viz. enzymatic hydrolysis, specific saccharide binding, and physical absorption. The LC-based sensor decorated with dodecyl β-d-glucopyranoside shows high sensitivity for protein detection. The limit of detection (LOD) for lysozyme, Con A and BSA reaches around 0.1 μg/mL, 0.01 μg/mL and 0.001 μg/mL, respectively. These results might provide new insights into increasing selectivity and sensitivity of LC-based sensors for the detection of proteins.     

Au nanoparticles based ultra-fast “Turn-On” fluorescent sensor for detection of biothiols and its application in living cell imaging

Au or other metal nanostructures have the ability to strongly quench the fluorescence of fluorophores.This feature has made AuNP-conjugates attractive for the construction of platforms for various bioanalytes to overcome the limitations of small molecule fluorophores(poor solubility,long reaction time).In this paper,an ultrafast "Turn-On" fluo rescent sensor for biothiols was constructed.The sensor is based on the fluorescent resonance energy transfer(FRET) effect between the fluorophore(PN) and AuNPs,which effectively quenches the fluorescence of the fluorophore.In the presence of thiols,PN is displaced and released from AuNP surfaces,and thus,the fluorescence is rapidly restored.The sensor features appreciable water solubility and ultrafast response time(a few seconds for Cys).In addition,it exhibits high selectivity and a detection limit as low as 12 nmol/L for Hcy.Moreover,the sensor presents good biocompatibility and has been successfully applied for imaging biothiols in living cells.