Photonic Crystal Hydrogel Research Articles

Direct laser writing photonic crystal hydrogel sensors for in-situ sensing in microfluidic device

Photonic crystal hydrogels (PCHs) are promising materials for in-situ sensing demands in cell incubation systems such as microfluidic devices. However, the lack of ability to precisely construct and settle PCH sensors limits their future development. In this paper, we developed a versatile and highly controllable strategy to fabricate PCH sensing systems via direct laser writing (DLW) technology. We show that, PCH microsensors with precise geometries and diverse compositions could be exactly generated at desired positions using two-photon lithography (TPL). With such smart sensors, in-situ and spatiotemporal monitor of environmental parameters in liquid microdomains could easily be achieved using a microscope. This is demonstrated by generating PCH sensors for in-situ pH and metal ion strength analysis in microfluidic devices.

Molecularly imprinted 2D photonic crystal hydrogel sensor for sodium dichloroisocyanurate.

Sodium dichloroisocyanurate (SDIC) is an efficient, safe and convenient halogen disinfectant that is widely used for hospital, tableware and swimming pool disinfection. In order to ensure its effective use and safety, especially in clinical settings, effective identification methods are necessary. The effective chlorine content is one of the quality standards for chlorine-containing disinfectants, but its complex experimental operation as well as poor specificity and portability limit its application. In contrast, testing based on molecularly imprinted photonic crystal sensors provides excellent performance. Therefore, it is of great significance to establish a new and simple SDIC recognition method. We prepared a novel molecularly imprinted two-dimensional (2D) photonic crystal hydrogel (MIPH) for sensitive and label-free recognition of SDIC. The response performance of the resultant MIPH sensor was determined by monitoring particle spacing changes in the polystyrene (PS) 2D photonic crystals embedded in the hydrogel. Particle spacing changes were recorded by measuring changes in the diameter of the Debye diffraction ring of the MIPH sensor. As the concentration of SDIC in solution increased from 1 × 10-2 to 1.0 mmol L-1, the diameter of the Debye diffraction ring increased by 6 mm, and the corresponding photonic crystal particle spacing decreased by 56 nm. The particle spacing changes in the MIPH sensor showed a linear relationship with the SDIC concentration in the range of 1 × 10-2-1.0 mmol L-1, and the limit of detection (S/N = 3) was found to be 3 × 10-3 mmol L-1. The constructed hydrogel sensor was successfully used to detect SDIC in sodium dichloroisocyanurate disinfectant powder, demonstrating recoveries of 96-100% and RSD of 7.2-7.6%. Our molecularly imprinted SDIC photonic crystal hydrogel provides a universal strategy for designing sensors for other clinical disinfectants.

A phenylboronic acid-based smart photonic crystal hydrogel sensor for colorimetric detection of glucose

A phenylboronic acid-based smart photonic crystal hydrogel (PNAPB) sensor with good recyclability was reported for the sensitive and colorimetric detection of glucose.

Visualizing and quantifying dynamic cellular forces with photonic crystal hydrogels.

Cellular forces play a crucial role in numerous biological processes, including tissue development, morphogenesis, and disease progression. However, existing methods for detecting cellular forces, such as traction force microscopy and atomic force microscopy, often face limitations in terms of high throughput, real-time monitoring, and applicability to complex biological systems. In this study, we utilized a novel Photonic Crystal Cellular Force Microscopy (PCCFM) system to visualize and quantify dynamic cellular forces. This system consists of a conventional optical microscope and a photonic crystal substrate formed by the periodic arrangement of silica nanoparticles within polyacrylamide hydrogels. Taking MDCK cells and BMSCs as examples, we found that PCCFM can capture dynamic cellular forces with high spatial and temporal resolution during the cell adhesion, spread, proliferation, and osteogenic differentiation. The application of this technique revealed distinct force patterns in different cellular stages, offering insights into the interplay between cellular forces and morphological changes. By investigating the migration of cells from MDCK cyst fragments, we could gain significant insights into tumour cell migration behaviours. The real-time, high-throughput analysis of cellular biomechanics from the PCCFM system offers valuable information on the mechanisms of tumour metastasis, potentially guiding therapeutic development and improving disease treatment strategies.

Applications of inverse opal photonic crystal hydrogels in the preparation of acid-base color-changing materials.

Hydrogels are three-dimensional (3D) crosslinked network hydrophilic polymers that have structures similar to that of biological protein tissue and can quickly absorb a large amount of water. Opal photonic crystals (OPCs) are a kind of photonic band gap material formed by the periodic arrangement of 3D media, and inverse opal photonic crystals (IOPCs) are their inverse structure. Inverse opal photonic crystal hydrogels (IOPCHs) can produce corresponding visual color responses to a change in acid or alkali in an external humid environment, which has wide applications in chemical sensing, anti-counterfeiting, medical detection, intelligent display, and other fields, and the field has developed rapidly in recent years. In this paper, the research progress on fast acid-base response IOPCHs (pH-IOPCHs) is comprehensively described from the perspective of material synthesis. The technical bottleneck of enhancing the performance of acid-base-responsive IOPCHs and the current practical application limitations are summarized, and the development prospects of acid-base-responsive IOPCHs are described. These comprehensive analyses are expected to provide new ideas for solving problems in the preparation and application of pH-IOPCHs.

Imaging cellular forces with photonic crystals

Current techniques for visualizing and quantifying cellular forces have limitations in live cell imaging, throughput, and multi-scale analysis, which impede progress in cell force research and its practical applications. We developed a photonic crystal cellular force microscopy (PCCFM) to image vertical cell forces over a wide field of view (1.3 mm ⨯ 1.0 mm, a 10 ⨯ objective image) at high speed (about 20 frames per second) without references. The photonic crystal hydrogel substrate (PCS) converts micro-nano deformations into perceivable color changes, enabling in situ visualization and quantification of tiny vertical cell forces with high throughput. It enabled long-term, cross-scale monitoring from subcellular focal adhesions to tissue-level cell sheets and aggregates.

Study on the Preparation and Application of Flexible Photonic Crystal Hydrogel Sensors

With the development of deformation structured color materials and sensor signal analysis, the combination of photonic crystals with optical structure characteristics and highly sensitive hydrogels in the environment can stimulate response under conditions of mechanical deformation, temperature, humidity, pH, etc. Optical-based hydrogel sensors avoid these disadvantages of conventional sensors, such as non-destructive measurements, high-speed transmission, almost interference-free, telemetry remote control, and many other advantages. This paper introduces the optical properties of photonic crystals and the synthesis of hydrogel polymers, and describes the working principle of photonic crystal hydrogel sensors. There is no systematic generalization of the direction of flexible sensors, so this paper summarizes the progress in the direction of physical, chemical, and biological sensors, and reviews the related research applications, and discusses the potential future directions and development challenges.

Direct Laser Writing Photonic Crystal Hydrogels with a Supramolecular Sacrificial Scaffold.

Photonic crystal hydrogels (PCHs), with smart stimulus-responsive abilities, have been widely exploited as colorimetric sensors for years. However, the current fabrication technologies are mostly applicable to produce PCHs with simple geometries at the sub-millimeter scale, limiting the introduction of structural design into PCH sensors as well as the accompanied advanced applications. This paper reports the microfabrication of three-dimensional (3D) PCHs with the help of supramolecular agarose PCH as a sacrificial scaffold by two-photon lithography (TPL). The supramolecular PCHs, formulated with SiO2 colloidal nanoparticles and agarose aqueous solutions, show bright structural color and are degradable upon short-time dimethyl sulfoxide treatment. Leveraging the supramolecular PCH as a sacrificial scaffold, PCHs with precise 3D geometries can be fabricated in an economical and efficient way. This work demonstrates the application of such a strategy in the creation of structural-designed PCH mechanical microsensors that have not been explored before.

New modes of converting chemical information with colloidal photonic crystal sensing units

Photonic crystal is a kind of device which can convert a chemical signal into an optical signal and is commonly used in sensing and detection. The maximum reflection wavelength representing the photonic band gap has been the most common converting mode in analytical usage which however discard too much valuable chemical information. In this work, we established two additional modes for mining chemical information more deeply in time and space as the sensing information to distinguish analytes. They are respectively based on dynamic analysis of the spectrum shift and the distinction of the RGB partition block value information of optical image. The molecular imprinting sensing mechanism worked well on three organophosphorus compounds to the detection limit of 10−4 M. The principle component analysis of above data did present a good discrimination of organophosphorus analytes from interfering counter anions to a low detection limit of 10−6 M. To make the detection more convenient and to achieve real-time on-site detection, we have designed the portable photonic crystal signal acquisition kit. Together with the mobile terminal, the kit connects the optical image collected on site, the algorithm working on the cloud and the input/output interactive interface of users in detection. The methods were constructed on an example made of a three-dimensional molecularly imprinted photonic crystal hydrogels sensing unit targeting on organo-phosphides.

Carbon dots-based fluorescent molecularly imprinted photonic crystal hydrogel strip: Portable and efficient strategy for selective detection of tetracycline in foods of animal origin

Rapid, portable, and sensitive detection of tetracycline (TC) is crucial for the environment and human health. In this study, we developed carbon dots (CDs)-based fluorescent molecularly imprinted photonic crystal hydrogel (FMIPH) strips for TC detection in animal-derived foods. CDs emit fluorescent signals, and molecularly imprinted polymers provide specific recognition sites for TC. Inverse opal photonic crystals afford stable 3D macroporous mass transfer channels that considerably reduce binding time between TC and the strips. The portable FMIPH strip exhibited a linear fluorescence response to TC in the concentration range of 0.1–50 μg mL−1, with a detection limit of 0.067 μg mL−1. Good recoveries of TC (93.86–112.59%) were observed in TC-spiked commercially available pork, eggs, and milk. A combination of FMIPH strips with a portable fluorescent reading device could achieve sensitive, on-site, and real-time detection of TC in animal-derived foods.

Application of Optical Hydrogels in Environmental Sensing

The ever‐increasing complexity of environmental pollutants urgently warrants the development of new detection technologies. Sensors based on the optical properties of hydrogels enabling fast and easy in situ detection are attracting increasing attention. In this paper, the data from 138 papers about different optical hydrogels (OHs) are extracted for statistical analysis. The detection performance and potential of various types of OHs in different environmental pollutant detection scenarios were evaluated and compared to those obtained using the standard detection method. Based on this analysis, the target recognition and sensing mechanisms of two main types of OHs are reviewed and discussed: photonic crystal hydrogels (PCHs) and fluorescent hydrogels (FHs). For PCHs, the environmental stimulus response, target receptors, inverse opal structures, and molecular imprinting techniques related to PCHs are reviewed and summarized. Furthermore, the different types of fluorophores (i.e., compound probes, biomacromolecules, quantum dots, and luminescent microbes) of FHs are discussed. Finally, the potential academic research directions to address the challenges of applying and developing OHs in environmental sensing are proposed, including the fusion of various OHs, introduction of the latest technologies in various fields to the construction of OHs, and development of multifunctional sensor arrays.

Self-regulating bioinspired supramolecular photonic hydrogels based on chemical reaction networks for monitoring activities of enzymes and biofuels

Inspired by the way many living organisms utilize chemical/biological reactions to regulate their skin and respond to stimuli in the external environment, we have developed a self-regulating hydrogel design by incorporating chemical reaction networks (CRNs) into biomimetic photonic crystal hydrogels. In this hydrogel system, we used host–guest supramolecular non-covalent bonds between beta-cyclodextrin (β-CD) and ferrocene (Fc) as partial crosslinkers and designed a CRN involving enzyme-fuel couples of horseradish peroxidase (HRP)/H2O2 and glucose oxidase (GOD)/d-glucose, by which the responsive hydrogel was transformed into a glucose-driven self-regulating hydrogel. Due to the biomimetic structural color in the hydrogel, the progress of the chemical reaction was accompanied by a change in the color of the hydrogel. Based on this principle, the designed supramolecular photonic hydrogel (SPH) can not only achieve naked-eye detection of H2O2 and glucose concentrations with the assistance of a smartphone but also monitor the reactions of HRP and GOD enzymes and determine their activity parameters. The sensitivity and stability of the sensor have been proven. In addition, due to the reversibility of the chemical reaction network, the sensor can be reused, thus having the potential to serve as a low-cost point-of-care sensor. The SPH was ultimately used to detect glucose in human plasma and H2O2 in liver tumor tissue. The results are comparable with commercial assay kits. By redesigning the chemical reaction network in the hydrogel, it is expected to be used for detecting other enzymes or fuels.

Molecularly imprinted two‐dimensional photonic crystal hydrogel sensor for the detection of gatifloxacin

AbstractUsing polystyrene two‐dimensional photonic crystal as template, gatifloxacin (GTFX) as imprinting molecule, methanol as solvent, acrylic acid as functional monomer, ethylene glycol dimethyl acrylate as crosslinking agent and 2,2‐diethyloxyacetophenone as initiator, after UV initiation polymerization the GTFX molecularly imprinted two‐dimensional photonic crystal hydrogel (GTFX‐MIPCH) sensor was prepared. The response performance of the hydrogel was investigated by measuring the diameter change of the Debye ring. The experimental results showed that the prepared GTFX‐MIPCH has a sensitive response to GTFX. When the concentration of GTFX increases from 0 to 1 × 10−4 mol L−1, the diameter of the Debye ring decreases by 8.50 mm, the corresponding particle spacing increases by 29.1 nm, and the color of the sensor changes from purple to orange. Also there was a linear relationship between the change of particle spacing (Δd) and the logarithm of GTFX concentration (lg c) in the range 10−12–10−6 mol L−1. It is noteworthy that the limit of detection of GTFX‐MIPCH is as low as 10−14 mol L−1. In addition, in a solution of GTFX analogues enrofloxacin, levofloxacin, ciprofloxacin and norfloxacin, the change of particle spacing of the GTFX‐MIPCH sensor is 13.3, 11.6, 11.1 and 10.3 nm respectively, indicating that GTFX‐MIPCH has good specific recognition ability for GTFX. Moreover, GTFX‐MIPCH shows good reusability and can also be used for the detection of GTFX in water samples. This GTFX‐MIPCH can achieve a visual detection effect on GTFX through the Debye ring and color change. © 2023 Society of Industrial Chemistry.

Multiplex Identification of Post‐Translational Modifications at Point‐of‐Care by Deep Learning‐Assisted Hydrogel Sensors

AbstractMultiplex detection of protein post‐translational modifications (PTMs), especially at point‐of‐care, is of great significance in cancer diagnosis. Herein, we report a machine learning‐assisted photonic crystal hydrogel (PCH) sensor for multiplex detection of PTMs. With closely‐related PCH sensors microfabricated on a single chip, our design achieved not only rapid screening of PTMs at specific protein sites by using only naked eyes/cellphone, but also the feasibility of real‐time monitoring of phosphorylation reactions. By taking advantage of multiplex sensor chips and a neural network algorithm, accurate prediction of PTMs by both their types and concentrations was enabled. This approach was ultimately used to detect and differentiate up/down regulation of different phosphorylation sites within the same protein in live mammalian cells. Our developed method thus holds potential for POC identification of various PTMs in early‐stage diagnosis of protein‐related diseases.

Multiplex Identification of Post-Translational Modifications at Point-of-Care by Deep Learning-Assisted Hydrogel Sensors.

Multiplex detection of protein post-translational modifications (PTMs), especially at point-of-care, is of great significance in cancer diagnosis. Herein, we report a machine learning-assisted photonic crystal hydrogel (PCH) sensor for multiplex detection of PTMs. With closely-related PCH sensors microfabricated on a single chip, our design achieved not only rapid screening of PTMs at specific protein sites by using only naked eyes/cellphone, but also the feasibility of real-time monitoring of phosphorylation reactions. By taking advantage of multiplex sensor chips and a neural network algorithm, accurate prediction of PTMs by both their types and concentrations was enabled. This approach was ultimately used to detect and differentiate up/down regulation of different phosphorylation sites within the same protein in live mammalian cells. Our developed method thus holds potential for POC identification of various PTMs in early-stage diagnosis of protein-related diseases.

Portable Comestible-Liquid Quality Test Enabled by Stretchable and Reusable Ion-Detection Photonic Papers.

Currently, there have been widespread investigation conducted into responsive photonic crystal hydrogels (RPCHs) characterized by high selectivity and sensitivity for colorimetric indicators and physical/chemical sensors. In spite of this, it remains challenging to use RPCHs for sensing due to their limited mechanical property and molding capability. In the present study, a double-network structure is proposed to design highly stretchable, sensitive, and reusable ion-detection photonic papers (IDPPs) for assessing the quality of visual and portable comestible liquids (e.g., soy sauce). It is constructed by integrating polyacrylamide and poly-methacryloxyethyl trimethyl ammonium chloride with highly ordered polystyrene microspheres. The double-network structure improves the mechanical properties of IDPPs with their elongation at break increasing from 110 to 1600%. Meanwhile, the optical properties of photonic crystals are retained. The IDPPs achieve a fast ion response by applying control on the swelling behavior of the hydration radius of the counter ions through ion exchange. Given a certain concentration range (0.01-0.10 M), chloride ions can be detected fast (3-30 s) by exchanging ions with a small hydration radius through an IDPP, which is clearly observable. Due to the improvement of mechanical properties and the reversible exchange of ions derived from IDPPs, their reusability is significantly enhanced (>30 times). Characterized by a simple operation, high durability, and excellent sustainability, these IDPPs are promising for practical application in food security and human health assessment.

Creatinine Imprinted Photonic Crystals Hydrogel Sensor

There is a demand for simple, selective, and efficient assays for the determination of clinically important metabolites such as creatinine for healthcare. Creatinine is the by-product of muscle energy metabolism and is excreted by the kidneys. To measure creatinine in the human serum, a creatinine imprinted photonic crystal hydrogel (CIPC hydrogel) for naked-eye detection is developed. CIPC hydrogel utilizes polystyrene-based two-dimensional (2D) photonic crystal colloidal arrays (PCs-array) embedded in the polyacrylamide hydrogel containing methacrylic acid which imprinted the creatinine template. The nanocavities in the hydrogel produced after the removal of the template bind to and recognize creatinine in the serum samples. The binding is selective and specific for creatinine. The binding is observed as shrinkage of the hydrogel volume and a decrease in the particle spacing which is monitored through changes in the Debye diffraction ring diameter and a visible blue-green to blue color shift. The binding event and the mechanism are investigated by molecular dockings. The CIPC sensor demonstrates a limit of detection (LOD) of 2.45 ± 1.6 µM, a linear detection range (25–500 µM), and recovery from 85.6 % to 99.9 % in the serum samples. CIPC hydrogel is available for the rapid and quantitative onsite detection of creatinine in the human serum sample.

Numerical Analysis of Structural Color for Photonic Crystal Hydrogel

Photonic crystal has become a powerful technique for regulating electromagnetic waves due to its excellent features, such as structure designability and dynamic adjustability; in addition, it has great application value. In this paper, we visualize colors on the Ostwald color model and analyze the color differences of each group of color patches via the minimum color difference model. The manipulation law of particle size, temperature, and humidity on the color change of photonic crystal hydrogel is verified by these color analyses.

A K+-sensitive photonic crystal hydrogel sensor for efficient visual monitoring of hyperkalemia/hypokalemia.

Potassium ions (K+) play crucial roles in many biological processes. Abnormal K+ levels in the body are usually associated with physiological disorders or diseases, and thus, developing K+-sensitive sensors/devices is of great importance for disease diagnosis and health monitoring. Herein, we report a K+-sensitive photonic crystal hydrogel (PCH) sensor with bright structural colors for efficient monitoring of serum potassium. This PCH sensor consists of a poly(acrylamide-co-N-isopropylacrylamide-co-benzo-15-crown-5-acrylamide) (PANBC) smart hydrogel with embedded Fe3O4 colloidal photonic crystals (CPCs), which could strongly diffract visible light and endow the hydrogel with brilliant structural colors. The rich 15-crown-5 (15C5) units appended on the polymer backbone could selectively bind K+ ions to form stable 2 : 1 [15C5]2/K+ supramolecular complexes. These bis-bidentate complexes served as physical crosslinkers to crosslink the hydrogel and contracted its volume, and thus reduced the lattice spacing of Fe3O4 CPCs and blue-shifted the light diffraction, and finally reported on the K+ concentrations by a color change of the PCH. Our fabricated PCH sensor possessed high K+ selectivity and pH- and thermo-sensitive response performances to K+. Most interestingly, the K+-responding PANBC PCH sensor could be conveniently regenerated via simple alternate flushing with hot/cold water due to the excellent thermosensitivity of the introduced PNIPAM moieties into the hydrogel. Such a PCH sensor provides a simple, low-cost and efficient strategy for visualized monitoring of hyperkalemia/hypokalemia, which will significantly promote the development of biosensors.

Precisely sensing hydrofluoric acid by photonic crystal hydrogels

It is a great challenge to detect hydrofluoric acid (HF) with high precision, good selectivity, and visual readouts characteristics. Herein, a new photonic crystal (PC) hydrogel HF sensor based on the “selective etching-induced swelling” mechanism has been developed. This HF sensor consisting of silica/water/hydroxyethyl acrylate and non-closely packed structures was fabricated through simple non-close-assembling, photopolymerization, and water swelling processes. Silica slightly etched by HF induces the swelling of PC hydrogel, leading to the variation of reflection wavelength and structural colors, thereby realizing visually and spectrally sensing HF (0–10 mM). The unique structure and compositions of PC hydrogel are the keys to the high sensing precision, outstanding selectivity, and low detection limit (0.1 mM). Furthermore, the sensor possesses tailorable, portable, easy-to-operation, and low-cost (<0.01 $/sensor) advantages. This work provides an efficient and convenient tool for sensing and recognizing HF in the aqueous solution for practical applications and upgrades the basic understanding of the photonic sensing mechanism.