Crystalline Colloidal Array Research Articles

A Gelated Colloidal Crystal Attached Lens for Noninvasive Continuous Monitoring of Tear Glucose.

Patients of diabetes mellitus urgently need noninvasive and continuous glucose monitoring in daily point-of-care. As the tear glucose concentration has a positive correlation with that in blood, the hydrogel colloidal crystal integrated into contact lens possesses promising potential for noninvasive monitoring of glucose in tears. This paper presents a new glucose-responsive sensor, which consists a crystalline colloidal array (CCA) embedded in hydrogel matrix, attached onto a rigid gas permeable (RGP) contact lens. This novel sensing lens is able to selectively diffract visible light, whose wavelength shifts between 567 and 468 nm according to the alternation of the glucose concentration between 0 and 50 mM and its visible color change between reddish yellow, green, and blue. The detection limit of responsive glucose concentration can be reduced to 0.05 mM. Its combination with a contact lens endows it with excellent biocompatibility and portability, which shows great possibility for it to push the development of glucose-detecting devices into new era.

Ultraviolet Raman Wide-Field Hyperspectral Imaging Spectrometer for Standoff Trace Explosive Detection.

We constructed the first deep ultraviolet (UV) Raman standoff wide-field imaging spectrometer. Our novel deep UV imaging spectrometer utilizes a photonic crystal to select Raman spectral regions for detection. The photonic crystal is composed of highly charged, monodisperse 35.5 ± 2.9 nm silica nanoparticles that self-assemble in solution to produce a face centered cubic crystalline colloidal array that Bragg diffracts a narrow ∼1.0 nm full width at half-maximum (FWHM) UV spectral region. We utilize this photonic crystal to select and image two different spectral regions containing resonance Raman bands of pentaerythritol tetranitrate (PETN) and NH4NO3 (AN). These two deep UV Raman spectral regions diffracted were selected by angle tuning the photonic crystal. We utilized this imaging spectrometer to measure 229 nm excited UV Raman images containing ∼10-1000 µg/cm2 samples of solid PETN and AN on aluminum surfaces at 2.3 m standoff distances. We estimate detection limits of ∼1 µg/cm2 for PETN and AN films under these experimental conditions.

A non-enzymatic urine glucose sensor with 2-D photonic crystal hydrogel.

A novel polymerized crystalline colloidal array (PCCA) sensing material for the detection of urine glucose was developed by embedding a two-dimensional (2-D) polystyrene crystalline colloidal array (CCA) in 3-acrylamidophenylboronic acid (3-APBA)-functionalized hydrogel. After adjusting the cross-linker concentration, this material showed significant sensitivity for glucose under lab conditions, the particle spacing of the PCCA changed from 917 to 824nm (93nm) within 3min as the glucose concentration increased from 0 to 10mM, and the structural color of the PCCA changed from red through orange, to green, and finally, to cyan. In further experiments, this material was used to semi-quantitatively detect glucose in 20 human urine (HU) samples. Compared with the traditional dry-chemistry method, which was applied widely in clinical diagnosis, the PCCA method was more accurate and cost-effective. Moreover, this method can efficiently avoid the errors induced by most of the urine-interfering elements like vitamin C and ketone body. With a homemade portable optical detector, this low-cost intelligent sensing material can provide a more convenient and efficient strategy for the urine glucose detection in clinical diagnosis and point-of-care monitoring.

A novel enrichment imprinted crystalline colloidal array for the ultratrace detection of chloramphenicol

A novel photonic crystal (PC) for the enrichment and detection of trace chloramphenicol (Cm) was constructed based on the combination of the imprinted crystalline colloidal array (ICCA) and the enrichment effect induced by wettability differences. The enrichment ICCA (E-ICCA) material had a highly ordered opal structure consisted of hydrophilic molecular imprinting polymer (MIP) spheres and the surrounding hydrophobic polydimethylsiloxane (PDMS) matrix, thus showing the desired structural color but also possessing the large hydrophilicity/hydrophobicity (HP) interaction area to enable efficient enrichment of the target Cm molecules from a highly dilute solution to the MIP sphere surface. The sensitive Cm recognition of MIP spheres finally caused the reduced reflection intensity and a red shift of the material due to changes of the periodic structure. Using this sensing platform, the highly sensitive detection of Cm (as low as 1.5×10−9M) with high selectivity was achieved without using label techniques and expensive detection instruments. Furthermore, the developed method successfully used to screen Cm in drinking water samples. Therefore, this approach is extensible to the construction of many sensor systems for the sensitive detection of drugs, diseases, and pollutions of food and the environment.

Highly sensitive multiresponsive photonic hydrogels based on a crosslinked Acrylamide- N-isopropylacrylamide (AM-NIPAM) co-polymer containing Fe3O4@C crystalline colloidal arrays

Multiresponsive photonic hydrogels (MRPHs) were prepared by magnetically controlled self-assembly of Fe3O4@C nanoparticles and these are sensitive to temperature, humidity, compression, tension and ethanol. This exhibits brilliant structural color thanks to the combination of AM and NIPAM monomers. Along with the increase of compression and tension on the MRPHs, the reflection peak of the samples blue shifts. When exposed MRPHs in environments with different humidity, its structure color red shifts as the humidity increases from 33% RH to 95% RH. Besides, the reflection peak redshift was observed when the MRPHs was immersed in absolute ethyl alcohol. This work may provide a new way to prepare smart photonic hydrogel with integrated functions of mechano-, humidity-, temperature- and solvent- responses.

Diffusion process of an ink drop in core–shell silica–titania pigment particles

Recording coatings have been successfully prepared by the core–shell structural silica–titanium dioxide particles, which were synthesized using sol–gel methods and fabricated as a close-packed colloidal crystalline array. The size of the nano-silica particles (50–100nm) was controlled via varying the concentration of ammonium hydroxide. The silica spheres coated with titania (core–shell structure) were prepared by a self-assembly coating deposition process. Transmission electron microscopy and scanning electron microscopy were used to analyze the microstructure of the core/shell composite particles. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to analyze the molecular structure of the composite particles and the formation of the chemical bonds (Ti–O and Ti–O–Si) on the shell surface. The prepared composite pigment particles were applied in recording materials. The diffusion process of the ink drop on the surface of the recording materials was studied by the edge detection method. We also investigated the role of the ink drop in the diffusion process of the different composite pigment particle.

A composite hydrogels-based photonic crystal multi-sensor

A facile route to prepare stimuli-sensitive poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) gelated crystalline colloidal array photonic crystal material was developed. PVA was physically gelated by utilizing an ethanol-assisted method, the resulting hydrogel/crystal composite film was then functionalized with PAA to form an interpenetrating hydrogel film. This sensor film is able to efficiently diffract the visible light and rapidly respond to various environmental stimuli such as solvent, pH and strain, and the accompanying structural color shift can be repeatedly changed and easily distinguished by naked eye.

Optically diffracting hydrogels for screening kinase activity in vitro and in cell lysate: impact of material and solution properties.

Optically diffracting films based on hydrogel-encapsulated crystalline colloidal arrays have considerable utility as sensors for detecting enzymaticphosphorylation and, thus, in screening small molecule modulators of kinases. In this work, we have investigated the impact of hydrogel properties, as well as the role of the ionic character of the surrounding environment, on the optical sensitivity of kinase responsive crystalline colloidal array-containing hydrogels. In agreement with a model of hydrogel swelling, the optical sensitivity of such materials increased as the shear modulus and the Flory-Huggins interaction parameter between polymer and solvent decreased. Additionally, elimination of extraneous charges in the polymer backbone by exploiting azide-alkyne click chemistry to functionalize the hydrogels with a peptide substrate for protein kinase A further enhanced the sensitivity of the optically diffracting films. Increasing peptide concentration and, in turn, immobilized charge within the hydrogel network was shown to increase the optical response over a range of ionic strength conditions. Ultimately, we showed that, by tuning the hydrogel and solution properties, as little as 0.1 U/μL protein kinase A could be detected in short reaction times (i.e., 2 h), which is comparable to conventional biochemical kinase assays. We further showed that this approach can be used to detect protein kinase A activity in lysate from HEK293 cells. The sensitivity of the resulting films, coupled with the advantages of photonic crystal based sensors (e.g., label free detection), makes this approach highly attractive for screening enzymatic phosphorylation.

Study on a Photonic Crystal Hydrogel Material for Chemical Sensing

There is intense interest in the applications of photonic crystal hydrogel materials for the detection of glucose, metal ions, organophosphates and so on. In this paper, monodisperse polystyrene spheres with diameters between 100 ~ 440 nm were synthesized by emulsion polymerization. Highly charged polystyrene spheres readily self-assembled into crystalline colloidal array because of electrostatic interactions. Photonic crystal hydrogel materials were formed by polymerization of acrylamide hydrogel around the crystalline colloidal arrays of polystyrene spheres. After chemical modification of hydrogel backbone with carboxyl groups, our photonic crystals hydrogel materials are demonstrated to be excellent in response to pH and ionic strength changes.

2-Allylhexafluoroisopropanol Treated Photonic Crystal Material for DMMP Detection

Some photonic crystal materials are developed as chemical detection materials. Varies of sensitive chemical group can be used for varies of chemical detection. In this paper, Polystyrene particles in 240 nm size were prepared firstly. The polystyrene particles were self-assembled into crystalline colloidal arrays. A kind of fluoride-bearing chemical, 2-Allylhexafluoroisopropanol, were induced to the Polystyrene crystalline colloidal arrays. Then the diffraction properties were test. After treated by 2-Allylhexafluoroisopropanol, the Polystyrene crystalline colloidal arrays get a change of diffraction in both the wavelength and the intensity. When exposed to saturated vapor of DMMP.

Preparation and upconversion emission modification of crystalline colloidal arrays and rare earth fluoride microcrystal composites.

In this paper, highly ordered crystalline colloidal arrays containing rare earth fluoride microcrystals were fabricated. The upconversion emission property of rare earth fluoride microcrystals in crystalline colloidal arrays was studied and modified. A significant suppression and enhancement of the upconversion emission from the rare earth fluorides can be observed in the regions of the photonic band gap and its band edge, respectively. The suppression or enhancement factor was shown to be related to the ordered degree of the crystalline colloidal arrays and is critical in the preparation of upconversion displays and low-threshold lasers.

Uniform core-shell photonic crystal microbeads as microcarriers for optical encoding.

We demonstrate a rapid and robust method to fabricate uniform core-shell photonic crystal (PC) microbeads by the microfluidic and centrifugation-redispersion technique. Colored crystalline colloidal arrays (CCAs) were first prepared through centrifugation-redispersion approach by self-assembly of polystyrene-poly(N-isopropylacrylamide) (PS-PNIPAm) core/shell nanoparticles (NPs). Different from the conventional NPs (e.g., charged PS or PNIPAm NPs), PS-PNIPAm NPs could easily self-assemble into well-ordered CCAs by only one purification step without laborious pretreatment (e.g., dialysis or ion exchange) or slow solvent-evaporation process. The CCAs is then encapsulated into a transparent polymer shell with functional groups (e.g., copolymer of ETPTA and butyl acrylate (BA)), triggering the formation of core-shell PC microbeads which can be used as optical encoding microcarriers. Importantly, this technique allows us to produce core-shell PC microbeads in a rapid and robust way, and the optical reflections of the PC microbeads appear highly stable to various external stimuli (e.g., temperature, pH value, and ionic strength) relying on the features of the CCAs core and protection of the polymer shell. Moreover, various probe biomolecules (e.g., proteins, antibodies, and so on) can be easily linked on the surface of the core-shell PC microbeads owing to the hydrophilic modification induced by the hydrolysis of BA on the microbead surface, enabling the multiplex biomolecular detection.

Photonic crystal kinase biosensor.

We have developed a novel biosensor for kinases that is based on a kinase-responsive polymer hydrogel, which enables label-free screening of kinase activity via changes in optical properties. The hydrogel is specifically designed to swell reversibly upon phosphorylation of a target peptide, triggering a change in optical diffraction from a crystalline colloidal array of particles impregnated into the hydrogel. Diffraction measurements, and charge staining, confirmed the responsive nature of the hydrogel. Moreover, the change in diffraction of the hydrogel upon treatment with kinase exhibited a time- and dose-dependent response. A theoretical model for ionic polymer networks describes the observed optical response well and can be used to quantify the extent of phosphorylation.

Fabrication of polymerized crystalline colloidal array thin film modified β-cyclodextrin polymer for paraoxon-ethyl and parathion-ethyl detection.

We have developed an optical chemical sensor for the detection of organophosphate (OP) compounds using a polymerized crystalline colloidal array (PCCA) thin film composed of a close-packed colloidal array of polystyrene particles. The PCCA thin film was modified with β-cyclodextrin (β-CD) polymer as a capping cavity for the selective detection of paraoxon-ethyl and parathion-ethyl chemical agents. The fabrication of the modified PCCA thin film was optimized and the structure was characterized using scanning electron microscopy (SEM). The arrangement of polystyrene particles in the PCCA follows a pattern of the fcc (111) planes with strong diffraction peak in the visible spectral region and pH dependence. The diffraction peak of the β-CD modified PCCA thin film showed a red shift according to the change of paraoxon-ethyl and parathion-ethyl concentrations at a fast response time (10 s) and high sensitivity with detection limits of 2.0 and 3.4 ppb, respectively. Furthermore, the proposed interaction mechanism of β-CD with paraoxon-ethyl and parathion-ethyl in the β-CD modified PCCA thin film were discussed.

Structural Color Manipulation Using Tunable Photonic Crystals with Enhanced Switching Reliability

tuning in the whole visible regime through large changes in the particle-particle separation originating from the electrophoretic movement of the charged particles while maintaining the ordered crystal structure under the external fields.[10] In spite of these merits, there is no report that considered these systems applicable for reversible switching for practical application. Although de-ionized water is the most suitable dispersion medium for producing high quality periodic crystalline structures with enhanced reflectance in these systems, the electrolysis of water molecules at the indium tin oxide (ITO) surface produces significant amounts of H+ and OH− ions as by-products at the cathode and anode, respectively. Therefore, the diffusion of those ions into colloidal arrays substantially limits the tuning stability and range because this phenomena induces decreased thickness of electrical double layer on the surface of the colloidal nanoparticles. To solve this problem, ITO surface was modified by various dielectric insulator passivation layers, including SiO2, SiN, polyimide, and parylene that can block electrochemical reactions at the electrodes (unpublished results). However, this methodology resulted in a substantial reduction of the color tuning range due to decreases in voltage applied to the colloidal dispersion because of the large amount of additional impedance introduced by the passivation layer. Considering the volume resistivity of these commonly used passivation materials (∼1016 Ω m), required thickness of the passivation layer should be at the sub-nm scale in order not to decrease the voltage applied significantly in colloidal dispersion. Preparation of such a thin and uniform film without any defected area is extremely difficult to achieve. Here we report our effort for achieving enhanced tuning stability of the colloidal photonic crystal composed of long-range ordered crystalline colloidal arrays through modifying the ITO electrode with ion exchange resins. The thin layer of over-coating on the ITO surface allowed increased number of cycles of stable color-tuning switching from red to green over 800 times, which is the best result ever reported for a tunable photo nic crystal whose Δλ can be manipulated more than 100 nm. Figure 1(a) depicts the device structure of a unit pixel and the concept of improving the stability of photonic structural color tuning through blocking ion diffusion from both electrodes by coating the electrode surface with a layer of ion-exchange resin. A colloidal dispersion composed of monodisperse 138 nm-diameter polystyrene (PS) nanoparticles dispersed in deionized water was injected between two electrodes. The strong negative charge of the nanoparticles and their thick electrical double layer induce the self-assembly of the long-range ordered colloids through electrostatic repulsion, which dominates the Structural Color Manipulation Using Tunable Photonic Crystals with Enhanced Switching Reliability

From Metastable Colloidal Crystalline Arrays to Fast Responsive Mechanochromic Photonic Gels: An Organic Gel for Deformation‐Based Display Panels

An efficient and straightforward method is developed to prepare a mechanochromic photonic gel by fixing the metastable SiO2 colloidal crystalline array (CCA) in the mixture of ethylene glycol (EG) and poly(ethylene glycol) methacrylate (PEGMA) through photopolymerization. Thanks to the recent fabrication of solvent‐wrapped, metastable CCA, a high volume fraction of EG (46%) is introduced to the photonic gel before particle assembly, but not by swelling after polymerization, which leads to a more deformable composite than most reported opal gels. Compared to traditional photonic gels, this opal gel not only has improved mechanochromic sensitivity to weak external force and extended color tuning range from red to blue (Δλ = 150 nm), but also possesses fast and reversible response in millisecond level (20–200 ms), repeatable reflection signals in cycling and fatigue tests, and good resolution in response to localized deformation, which renders it an ideal deformation‐based photonic display screen. A new trigger system is designed to solve the large deformation causing color fading in conventional mechanochromic gels and brilliant red, green, and blue (RGB) pixels can be conveniently manipulated by ‘pushing’ operations.

A molecularly imprinted colloidal array as a colorimetric sensor for label-free detection of p-nitrophenol

We report on the synthesis of a label-free p-nitrophenol (PNP) responsive crystalline colloidal array (CCA) based on the combination of a photonic crystal and the molecular imprinting technique.

Solvent Wrapped Metastable Colloidal Crystals: Highly Mutable Colloidal Assemblies Sensitive to Weak External Disturbance

Solvent wrapped "metastable" crystalline colloidal arrays (CCAs) have been prepared by supersaturation induced precipitation and self-assembly of monodisperse particles in polar/nonpolar organic solvents. These metastable CCAs possess ordered structures but with less stability comparing with traditionally fixed colloidal crystal systems. They are stabilized by the balance between long-range attraction and electrostatic repulsion of neighboring like-charged particles. Monitoring the reflection intensity during evaporation suggests that these crystals can exist for several hours at 90 °C and even longer at room temperature. Based on the evolution of particle volume fraction in whole suspension (φ(SiO2)), crystal phase (φ(crystal)), and liquid phase (φ(liquid)), the formation of metastable CCAs can be understood as a microscopic phase separation process, where the homogeneous dispersion will separate into a "crystal phase" with orderly stacked particles and a "liquid phase" with randomly dispersed particles. Further calculation of the volume fraction of crystal phase (V(crystal)/V(total)) and the ratio of particles in crystal phase (f(crystal)) shows that with the increase of designed Φ(SiO2), more particles precipitate to form colloidal crystals with larger sizes but the lattice spacing of the microcrystals remains constant. Unlike fixed or traditional responsive CCAs, these metastable CCAs can reversibly assemble and disassemble with great ease, because little energy is involved or required in this transformation. Therefore, they can sense weak external disturbances, including subtle motion and slight friction or shearing forces.

Continuous modification of upconversion luminescence of fluorescent dye in the crystalline colloidal arrays

The crystalline colloidal arrays with controllable photonic bandgaps were prepared by the change of volume fraction of the polystyrene microspheres. Upconversion emission property of fluorescent dye has investigated in crystalline colloidal array, and continuous modification of the upconversion emission of fluorescent dye was observed. A significant suppression of upconversion emission of dye in the range of the photonic bandgap as well as enhancement at the bandgap edge was obtained in the crystalline colloidal arrays. In addition, upconversion emission of dye was also enhanced when the excited light overlapped with the long or short bandgap edge of the crystalline colloidal arrays, which is due to slow photons effect near the edges of a photonic bandgap. The continuous modification and enhancement of upconversion emission may be important for the development of low-threshold upconversion lasers and displays.

Hydrogel-Based Glucose Sensors: Effects of Phenylboronic Acid Chemical Structure on Response

Phenylboronic acids (PBAs) are being considered for glucose sensing and controlled insulin release, because of their affinity for diol-containing molecules. The interaction of immobilized PBAs in a hydrogel matrix with glucose can lead to volumetric changes that have been used to monitor glucose concentration and release insulin. Although the interaction of PBAs with diol-containing molecules has been intensively studied, the response of PBA-modified hydrogels as a function of the specific PBA chemistry is not well understood. To understand the interaction of immobilized PBAs with glucose in hydrogel systems under physiological conditions, the glucose-dependent volumetric changes of a series of hydrogel sensors functionalized with different classes of PBAs were investigated. The volume change induced by PBA-glucose interactions is converted to the diffracted wavelength shift by a crystalline colloidal array embedded in the hydrogel matrix. The PBAs studied contain varying structural parameters such as the...