Polymerized Crystalline Colloidal Array Research Articles

Clinical Evaluation of a Photonic Crystal Sensor for Glucose Monitoring in Urine

AbstractSelf‐monitoring of blood glucose is not only an effective method to treat diabetes, but also a painful invasive process to patients. To develop a noninvasive technique, we evaluated the clinical performance of a polymerized crystalline colloidal array (PCCA) sensor for glucose monitoring in urine. A two‐dimensional crystalline colloidal array (CCA) was assembled using polystyrene particles and further embedded into 3‐acrylamidophenylboronic acid functionalized hydrogel. 101 urine samples were tested, and the glucose concentrations was calculated by the particle spacing of PCCA. All the urine samples were also analyzed by automated urine analyzers. Pearson correlation and linear regression analyses showed a linear relationship between the PCCA results with a range of 0.4‐53.3 mmol L−1 and the Cobas® 8000 references (r=0.914; [PCCA]=0.9281 [HK] + 2.0585 mmol L−1). Cohen's kappa (κ) statistic with 0.65 (sig < 0.05) showed the PCCA results had moderate agreement with references. Also, Bland‐Altman plot showed that AX‐4030 sensor's systematic error was higher than PCCA sensor (mean=7.4813 > 0.5271 mmol L−1). The PCCA urine glucose biosensor has the advantages of fast fabrication, low cost, easy operation and high sensitivity, which provides a promising technique for noninvasive point‐of‐care glucose monitoring.

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.

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.

Construction of near-infrared photonic crystal glucose-sensing materials for ratiometric sensing of glucose in tears

Noninvasive monitoring of glucose in tears is highly desirable in tight glucose control. The polymerized crystalline colloidal array (PCCA) that can be incorporated into contact lens represents one of the most promising materials for noninvasive monitoring of glucose in tears. However, low sensitivity and slow time response of the PCCA reported in previous arts has limited its clinical utility. This paper presents a new PCCA, denoted as NIR–PCCA, comprising a CCA of glucose-responsive sub-micrometered poly(styrene-co-acrylamide-co-3-acrylamidophenylboronic acid) microgels embedded within a slightly positive charged hydrogel matrix of poly(acrylamide-co-2-(dimethylamino)ethyl acrylate). This newly designed NIR–PCCA can reflect near-infrared (NIR) light, whose intensity (at 1722nm) would decrease evidently with increasing glucose concentration over the physiologically relevant range in tears. The lowest glucose concentration reliably detectable was as low as ca. 6.1μg/dL. The characteristic response time τsensing was 22.1±0.2s when adding glucose to 7.5mg/dL, and the higher the glucose concentration is, the faster the time response. Such a rationally designed NIR–PCCA is well suited for ratiometric NIR sensing of tear glucose under physiological conditions, thereby likely to bring this promising glucose-sensing material to the forefront of analytical devices for diabetes.

Mutual interaction between embedded microgel particles and the surrounding hydrogel matrix

Polymerized crystalline colloidal array (PCCA) films, i.e., a highly ordered crystalline colloidal array of poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-AAc)) microgel particles embedded in a polyacrylamide (PAAm) hydrogel matrix, were prepared. The interaction between the embedded thermosensitive microgel particles and the non-thermosensitive hydrogel matrix was studied, using the Bragg diffraction of the films as a tool. The intensity and position of the diffraction peak change with temperature, from which important information on the interaction between the microgel particles and the hydrogel matrix was deduced. Our results indicate that the non-thermosensitive, hydrophilic PAAm hydrogel matrix significantly influences the thermosensitive phase transition of the embedded P(NIPAM-AAc) microgel particles. Compared with the freely dispersed microgel particles in solution, only a small change in the volume phase transition temperature of the embedded microgel particles was observed; however, the phase transition becomes less sharp. More importantly, the extent of size change is reduced significantly. On the other hand, the temperature-induced swelling/deswelling of the embedded microgel particles induces a swelling/deswelling of the surrounding hydrogel matrix, revealing that the interaction between the two components is mutual. The temperature-induced swelling/deswelling of the microgel particles is fast; in contrast, the swelling/deswelling of the hydrogel matrix is much slower. The stiffness of the hydrogel matrix affects the interaction between the two components. As the hydrogel matrix becomes stiffer, its influence on the swelling of the microgel particles becomes more prominent. On the other hand, the influence of the microgel particles on the swelling of the hydrogel matrix becomes less prominent.

An imprinted crystalline colloidal array chemical-sensing material for detection of trace diethylstilbestrol

Based on a combination of the molecular imprinting technique and polymerized crystalline colloidal array, we have developed an imprinted crystalline colloidal array (ICCA) chemical-sensing material for the real-time and label-free detection of diethylstilbestrol (DES) in aqueous solution. This novel sensing material was prepared by a noncovalent and self-assembly approach using liquid monodispersed DES-imprinted colloidal spheres and was characterized by a three-dimensional (3D) ordered opal structure in which numerous nanocavities were derived from DES imprinting. Thus, the inherent high affinity of the nanocavities allowed ICCA to recognize DES with high specificity, and changes of the ordered periodic structure enabled ICCA to transfer the recognition events into readable optical signals (label-free). Owing to the special opal structure and without interference from the bulk hydrogel film, the ICCA enabled the rapid and sensitive detection of the target analyte. The understanding of the recognizing response has also been advanced by using molecular modeling software to compute rational interaction between the template molecules and the function monomers. After careful optimization of the assay conditions, the ICCA could decrease its diffraction intensity within just 7 min according to the DES concentration from 2 ng mL(-1) to 8.192 μg mL(-1), whereas there were no obvious diffraction intensity changes for the DES analogues. The adsorption results showed that the homogenous structure and large surface area of ICCA could improve its adsorption capacity. Therefore, such a sensing material with high selectivity, high sensitivity, high stability, and easy operation might offer an attractive alternative for establishing optical sensors for the rapid real-time monitoring of different residues in food and the environment.

Coupling of crystalline colloidal arrays with intrinsically conductive polymers: Reflection-type electrochromic devices

The attenuation of the reflected light from a polystyrene (PS) polymerized crystalline colloidal array (PCCA) is achieved through the electrochemical switching of the electrochromic material polyaniline-poly(2-acrylamido-2-methyl-1-propanesulfonicacid) (PANI-PAMPS). For this purpose, layered electrochromic devices (ECDs) were fabricated that employed a PS PCCA film, acting as both a reflecting substrate and polymeric electrolyte, and the conducting polymer PANI-PAMPS, which served as the electrochromic layer. The resulting ECDs exhibited the attenuation of reflectance peak at the stop band position of the PCCA with a 3% of reflectance contrast ratio.

Detection of bisphenol A using an opal photonic crystal sensor

A new opal photonic crystal sensor (OPCS) that allows the detection of label-free bisphenol A (BPA) is proposed in the current study. The concept of developing photonic-based sensors using combined photonic crystal technology and molecular imprinting techniques is introduced. First batches of the BPA-imprinted monodisperse PMMA spheres with a diameter of 220 (±5)nm were prepared based on the suspension polymerization, so numerous nanocavities derived from BPA imprinting were distributed in the PMMA spheres. The liquid monodisperse microspheres were made into a polymerized crystalline colloidal array (PCCA) opal photonic crystal sensor. The inherent high affinity of the nanocavities distributed in the sphere allows OPCS to recognize BPA specifically. The sensor is characterized by a 3D-ordered interconnected lattice structure. Between the monospheres, there are well-arranged pores allowing the target molecules to embed and transport. As a result, changes in diffraction intensity which are related to BPA concentrations can be observed with the sensor. The detection ranges of OPCS are at 1ng/ml–1μg/ml level. The new sensory system has high selectivity of the target molecules in their natural forms, is easy to use, and costs low. Overall, the proposed approach provides a versatile analytical system for the establishment of a new sensor for the detection of endocrine-disrupting chemicals.

Development of a new sensor material based on crystalline colloidal arrays embedded into polymer network

This study reports the development of a novel sensing material that reports on analyte concentrations via diffraction of visible light from polymerized crystalline colloidal arrays (PCCA). The PCCA contains periodic crystalline colloidal array (CCA) of spherical polystyrene colloids. This new method permanently locks the order of the CCA by embedding the CCA into a polymer network. These materials are mostly used in the development of novel materials which are basically called sensors for metal ions and all kinds of organic molecules. The polymer around the crystalline colloid can be functionalized with some recognition molecule, making these materials useful as optical sensors. We developed a sensor, utilizing crown ether, 2-aminomethyl-18-crown-6 (2A18C6) as the recognition agent, that detects K+ in the concentration range from 5 to 160 ppm.

Photonic crystal hydrogel material for the sensing of toxic mercury ions (Hg2+) in water

We report the development of a new photonic crystal hydrogel for the sensing of highly toxic mercury ion (Hg2+) in water. This new sensing material optically reports the Hg2+ concentration in watervia diffraction of visible light from polymerized crystalline colloidal array (PCCA). The PCCA consists of light diffracting crystalline colloidal array (CCA) of monodisperse, highly charged polystyrene particles, which are polymerized within the polyacrylamide hydrogel. The changes in hydrogel surroundings trigger the volume change of hydrogel, which alters the lattice spacing of CCA and hence shifts the diffraction wavelength of light. The ions responsive urease coupled PCCA (UPCCA) hydrolyzes the urea and produces the HCO3− and NH4+ ions inside the hydrogel. These ions induce the charge-screening of the polyacrylamide carboxylates by decreasing the electrostatic repulsion between carboxylates and the polyacrylamide backbone relaxes, causing the shrinkage of hydrogel. Hence the UPCCA exhibits the blue shift of the diffracted wavelength. Hg2+ being the principal inhibitor of the urease-urea hydrolysis perturbs urea hydrolysis by the UPCCA when UPCCA is exposed to Hg2+ along with urea and hence suppresses the production of ions. This intervenes the shrinkage of hydrogel and does not allow the hydrogel to shrink as it shrinks in absence of Hg2+. Therefore the PCCA net blue shift decreases in the presence of Hg2+ along with urea compared to only urea. The extent of this hydrogel volume change is a function of Hg2+ concentrations. This UPCCA photonic crystal sensor detects ultra low (1 ppb) concentration of Hg2+ in water, exhibits reversibility and displays very high selectivity towards Hg2+. The uncompetitive inhibition nature of the urease enzyme, when it is covalently attached in the polymer hydrogel backbone, is the driving force for the very high selectivity and reversibility of the UPCCA sensor.

Defect Generation Surrounding Nanoparticles in a Cross-Linked Hydrogel Network

A detailed understanding of polymer-nanoparticle interactions is a key element in demystifying the reinforcement mechanism for nanocomposites. To decouple the effects of the polymer-nanoparticle interactions from the particle distribution, we utilized polymerized crystalline colloidal arrays based on a thermosensitive hydrogel, poly(N-isopropylacrylamide) (pNIPAAm). First, the hydrogel network structure in the vicinity of the nanoparticles was investigated by the deswelling behavior of particle-filled hydrogels. The addition of nanoparticles led to an increased rate of deswelling when the particle-filled hydrogel was heated beyond the lower critical solution temperature (32 degrees C). To interpret this observation, we have suggested that the polymer network has a significant increase in defects (e.g., dangling chain ends) in the vicinity of the nanoparticles. The apparent percolation threshold associated with the interaction of the nanoparticles was about 20 times smaller than the theoretical percolation threshold of spherical particles. As a consequence, we have determined the thickness of this defect zone to be about 85 nm. This is much larger than the size of the unperturbed linear pNIPAAm chains, suggesting that the polymers that play a role in the adsorption are not constrained segments of polymers bound between cross-link junctions but relatively free chains. This finding enabled us to emulate the adsorption behavior of pNIPAAm hydrogels on the particles by simply adding linear pNIPAAm chains to the particle suspensions. We then prepared silica and polystyrene suspensions with free pNIPAAm chains at a concentration much lower than the overlap concentration c*. A rheological study was conducted to determine the adsorption thickness of linear polymer chains on both silica and polystyrene nanoparticles. No significant adsorption was observed on silica, whereas the resultant thickness of the polymer was 8 nm on polystyrene.

Polymerized Crystalline Colloidal Array Incorporated with Silver Nanoparticles

An intelligent polymerized crystalline colloidal array (PCCA) with relatively broader band gap was prepared. The PCCA was prepared by embedding monodisperse crosslinked spherical polystyrene colloids, which self-assemble into crystalline colloidal arrays (CCA) and diffract light in the UV-Vis region, into the 250 microm thick polyacrylamide hydrogel film partly crosslinked by disulfide. The groups of thiol were attached to the matrix of the PCCA via the cleavage of the disulfide in the aqueous solution of dithiothreitol (DTT). Upon applying the Ag+ solution to the PCCA with thiol groups, the Ag+ will be attached to the polyacrylamide chain. After the in-situ reduction of the Ag+ with NaBH4, the silver nanoparticles with the diameter of approximately 10 nm were incorporated into the PCCA. Because of the relatively lower refractive index of the silver nanoparticles within the visible spectrum, the average refractive index of the PCCA was reduced and the refractive index contrast between the polystyrene particles and the matrix was increased, which resulted in the blue shift of the photonic band gap and the relatively broader band gap.

Photonic crystal borax competitive binding carbohydrate sensing motif

We developed a photonic crystal sensing method for diol containing species such as carbohydrates based on a poly(vinyl alcohol) (PVA) hydrogel containing an embedded crystalline colloidal array (CCA). The polymerized CCA (PCCA) diffracts visible light. We show that in the presence of borax the diffraction wavelength shifts as the concentration of glucose changes. The diffraction shifts result from the competitive binding of glucose to borate, which reduces the concentration of borate bound to the PVA diols.

PREPARATION AND CHARACTERISTICS OF POLYMERIZED CRYSTALLINE COLLOIDAL ARRAYS BASED ON INTERACTIONS BETWEEN BIOTIN AND AVIDIN

Monodisperse,highly charged polystyrene colloidal particles with an average diameter of 170 nm were prepared by emulsifier-free emulsion polymerization.These particles spontaneously self-assemble into crystalline colloidal arrays(CCAs)in low ionic strength aqueous solutions due to long-range electrostatic repulsions among the particles.These CCAs diffract light,meeting the Bragg condition in the ultraviolet,visible and near-infrared spectral regions.CCAs were embedded into a polyacrylamide hydrogel to form polymerized crystalline colloidal arrays(PCCA)by adding acrylamide,N,N-methylenebisacrylamide and 2,2-diethoxyacetophene into the liquid CCAs,and then photopolymerizing the mixture of monomers to make a thin PCCA film.Modified PCCAs containing —NH_2 groups were prepared via Mannich reaction with ethylenediamine.Hydrogel modified with ethyleneamide underwent a volume phase transition in response to the change in ionic strength of the solution.The biotinylation of the PCCA was achieved by chemical conjugation of the polymer gel with biotin after appropriate chemical modification of the gel.The interaction of the biotinylated PCCA with avidin led to a shrinkage in volume of the system caused by increased cross-linking in the hydrogels due to the binding between biotin and avidin.This volume change of the hydrogels altered the periodicity of the CCAs,resulting in a blue shift in the diffraction spectra.When excess biotin hydrazide was added,it was able to displace avidin bound to the biotinylated PCCA by the formation of a stronger complex with avidin.The disassociation of avidin from the PCCA led to the re-swelling of the hydrogels,corresponding to an increase in the interparticle distance in the PCCA and thus a red shift in the diffraction spectra.Our results demonstrated the response of a model sensor system made of biotinylated PCCA to the binding of an interacting protein,avidin.This may provide a basis for the sensing of protein molecules by functionalized PCCA systems.

Cholesterol oxidase functionalization of a polymerized crystalline colloidal array

A cholesterol-responsive polymerized crystalline colloidal array (PCCA) is fabricated by covalently attaching the amine groups of cholesterol oxidase (ChOx) to an epoxide-functionalized PCCA. Approximately 0.6 mM of ChOx is immobilized on a PCCA, with the bound enzyme retaining about 85% of its initial activity, compared to the unbound enzyme. Kinetic studies reveal that the stability and activity of the free and bound enzyme are significantly improved upon binding to the PCCA, with the bound enzyme retaining 62% of its initial activity after 20 days, compared to no residual activity for the free enzyme. Furthermore, the bound enzyme exhibits a better tolerance to pH and temperature changes, as well as to repeated use. Upon exposure to 5.0 mM cholesterol, we observe diffraction peak wavelength shifts of as much as 63 nm, demonstrating potential application as an optical cholesterol sensor.

Poly(vinyl alcohol) Rehydratable Photonic Crystal Sensor Materials.

We developed a new photonic crystal hydrogel material based on the biocompatible polymer poly (vinyl alcohol) (PVA), which can be reversibly dehydrated and rehydrated, without the use of additional fillers, while retaining the diffraction and swelling properties of polymerized crystalline colloidal arrays (PCCA). This chemically modified PVA hydrogel photonic crystal efficiently diffracts light from the embedded crystalline colloidal array. This diffraction optically reports on volume changes occurring in the hydrogel by shifts in the wavelength of the diffracted light. We fabricated a pH sensor, which demonstrates a 350 nm wavelength shift between pH values of 3.3 and 8.5. We have also fabricated a Pb(+2) sensor, in which pendant crown ether groups bind lead ions. Immobilization of the ions within the hydrogel increases the osmotic pressure due to the formation of a Donnan potential, swelling the hydrogel and shifting the observed diffraction in proportion to the concentration of bound ions. The sensing responses of rehydrated PVA pH and Pb(+2) sensors were similar to that before drying. This reversibility of rehydration enables storage of these hydrogel photonic crystal sensors in the dry state, which makes them much more useful for commercial applications.

Progress in developing polymerized crystalline colloidal array sensors for point-of-care detection of myocardial ischemia

The difficulty of rapid, definitive diagnosis of myocardial ischemia leads to unnecessary hospital admissions and treatment delays. Previously, decreased metal binding affinity in human serum was investigated as a marker for myocardial ischemia. Polymerized Crystalline Colloidal Array (PCCA) sensors for Ni2+ may be useful in developing a point-of-care test to determine metal binding affinity in plasma and to help rule out myocardial ischemia. PCCA sensors for Ni2+, with 5-amino-8-hydroxyquinoline as a chelating agent, were tested in aqueous solutions and diluted human plasma. The peak wavelength diffracted by the sensors was monitored by reflectance spectrometry and correlated with Ni2+ concentration. The PCCA sensors show a linear response to aqueous Ni2+ concentrations between 0.2 and 1.0 mmol L(-1), and can detect changes in free Ni2+ concentration of <60 micromol L(-1). The sensors respond at physiologic pH and can be reversibly dehydrated. The PCCA sensors developed here can report on free Ni2+ concentration in the presence of human plasma. These sensors can be used to detect a decrease in the Ni2+ affinity of plasma proteins, which may indicate recent myocardial ischemia. PCCA sensors offer a practical approach to rapid, point-of-care detection of a proposed biochemical signature of myocardial ischemia.

Photonic crystal sensor for organophosphate nerve agents utilizing the organophosphorus hydrolase enzyme

We developed an intelligent polymerized crystalline colloidal array (IPCCA) photonic crystal sensing material which reversibly senses the organophosphate compound methyl paraoxon at micromolar concentrations in aqueous solutions. A periodic array of colloidal particles is embedded in a poly-2-hydroxyethylacrylate hydrogel. The particle lattice spacing is such that the array Bragg-diffracts visible light. We utilize a bimodular sensing approach in which the enzyme organophosphorus hydrolase (OPH) catalyzes the hydrolysis of methyl paraoxon at basic pH, producing p-nitrophenolate, dimethylphosphate, and two protons. The protons lower the pH and create a steady-state pH gradient. Protonation of the phenolates attached to the hydrogel makes the free energy of mixing of the hydrogel less favorable, which causes the hydrogel to shrink. The IPCCA's lattice constant decreases, which blueshifts the diffracted light. The magnitude of the steady-state diffraction blueshift is proportional to the concentration of methyl paraoxon. The current detection limit is 0.2 micromol methyl paraoxon per liter.

Preparation and thermo-responsive light diffraction behaviors of soft polymerized crystalline colloidal arrays.

We report the formation and light diffraction behavior of polymerized crystalline colloidal arrays (PCCA) based on lightly cross-linked thermosensitive particles of poly(,-diethylacrylamide---ethylacrylamide--2-hydroxyethyl methacrylate) in both thermosensitive and non-thermosensitive matrices. The formation process of the crystalline colloidal arrays (CCA) and the temperature-dependent light diffraction behavior of PCCAs are investigated and rationalized by the use of Flory's polymer solution and rubber elasticity theories. The light diffraction behaviors of the PCCAs studied were found to display one and two temperature transitions in non-thermosensitive and thermosensitive matrices, respectively. The effects of ionic strength and pH on PCCA films have also been investigated.

Fast Responsive Crystalline Colloidal Array Photonic Crystal Glucose Sensors

We developed new photonic crystal polymerized crystalline colloidal array (PCCA) glucose sensing materials, which operate on the basis of formation of cross-links in the hydrogel. These materials are composed of hydrogels that embed an array of approximately 100-nm-diameter monodisperse polystyrene colloids that Bragg diffract light in the visible spectral region. The hydrogels change volume as the glucose concentration varies. This changes the lattice spacing, which changes the wavelength of the diffracted light. In contrast to our previous glucose sensing photonic crystal materials, we no longer require Na+ chelating agents. These photonic crystal materials are being designed for use in glucose sensing contact lens for people with diabetes mellitus. We describe methods to speed up the response kinetics of these PCCA sensing materials. Rapid-response kinetics is achieved by controlling the elasticity and the hydrophilic-hydrophobic balance of the hydrogel system. A more hydrophobic hydrogel composition is obtained by copolymerizing n-hexylacrylate into an acrylamide-bisacrylamide hydrogel. The response rate significantly increases to where it fully responds within 90 s to the average glucose concentrations found in blood (5 mM) and within 300 s to the average glucose concentrations found in tear fluid (0.15 mM). We find unusual temperature-dependent kinetics, which derive from glucose mutarotation in solution. It is shown that alpha-d-glucose is the glucose anomer binding to the boronic acid derivative. Care must be taken in any glucose determination to ensure that the glucose mutarotation equilibrium has been established. We have demonstrated that the sensor is responsive to approximately 0.15 mM glucose concentrations in artificial tear fluid solution.