Imprinted Photonic Hydrogels for the Size- and Shell-Selective Recognition of Nanoparticles

Greenificated Molecularly Imprinted Materials for Advanced Applications

Molecular imprinting technology (MIT) produces artificial binding sites with precise complementarity to substrates and thereby is capable of exquisite molecular recognition. Over five decades of evolution, it is predicted that the resulting host imprinted materials will overtake natural receptors for research and application purposes, but in practice, this has not yet been realized due to the unsustainability of their life cycles (i.e., precursors, creation, use, recycling, and end-of-life). To address this issue, greenificated molecularly imprinted polymers (GMIPs) are a new class of plastic antibodies that have approached sustainability by following one or more of the greenification principles, while also demonstrating more far-reaching applications compared to their natural counterparts. In this review, the most recent developments in the delicate design and advanced application of GMIPs in six fast-growing and emerging fields are surveyed, namely biomedicine/therapy, catalysis, energy harvesting/storage, nanoparticle detection, gas sensing/adsorption, and environmental remediation. In addition, their distinct features are highlighted, and the optimal means to utilize these features for attaining incredibly far-reaching applications are discussed. Importantly, the obscure technical challenges of the greenificated MIT are revealed, and conceivable solutions are offered. Lastly, several perspectives on future research directions are proposed.

Microfluidics-Assisted Fabrication of Dual Stopband Photonic Microcapsules and Their Applications for Anticounterfeiting

The assembly of two different kinds of colloidal particle-based photonic structures into an individual micro-object can achieve multifunctionality. In this study, core–shell photonic microcapsules with dual structural colors and photonic stop bands were prepared through a standard microfluidic technique. Photocurable resin suspension of silica nanoparticles and an aqueous suspension of nanogels were used as shell and core parts of microcapsules, respectively. The structural colors of shells and cores can be tuned by adjusting the concentrations of silica nanoparticles and soft nanogels in their corresponding suspensions. The individual microcapsules possess two distinct stop bands when the two suspensions are combined appropriately. Remarkably, the color information of the core part cannot be directly viewed at a macroscopic level (such as visual inspection) but can be detected at a microscopic scale (such as optical microscopy observation). The color information hidden enables the capability for information encryption and has potentially critical applications in anti-counterfeiting, display, and other fields.

Technical Challenges of Molecular-Imprinting-Based Optical Sensors for Environmental Pollutants

Combating environmental pollution constantly requires new affinity tools to selectively recognize and sensitively detect them. Molecularly imprinted polymers (MIPs) are plastic antibodies that have exhibited great potential as recognition units in optical sensing platforms to monitor wide varieties of environmental pollutants, including ionic species, organic compounds, gases, and even manufactured nanoparticles. The construction, sensing strategies, and applications of molecular-imprinting-based optical sensors (MI-OSs) have been discussed in recent reviews, thus we deliberately set them aside. This Perspective elaborates on unanswered questions and main approaches being taken to address the challenges of MI-OS technologies, which have been less considered until now. Specifically, we highlight obscure technical aspects of MI-OS fabrication and validation that impact their practical applications and importantly offer conceivable solutions to related problems to bridge the research gap.

Molecular Imprints Frozen by Strong Intermolecular Interactions in Place of Cross-Linking

A new way to freeze molecular imprints in a polymer material is reported. So far, molecular imprinted polymers (MIP) involve copolymerization of a functional monomer and large amounts of cross-linking agent, which keeps the template shape memory in rigid molecular imprints. MIP materials are prepared herein without cross-linking agent. Stiff chains of polyaniline grafted on a solid support as a brush-like material achieve the necessary rigidity. Differential adsorption to imprinted and non-imprinted materials provides evidence of molecular imprints. A correct adsorption isotherm for mobile adsorbed layers (Volmer isotherm) is introduced instead of the popular but inadequate Langmuir isotherm. Non-selective adsorption is entropic, whereas adsorption to molecular imprints has an enthalpic contribution coming from specific interactions. Fast adsorption kinetics are a definite benefit with regards to applications such as chromatographic separations and chemical sensors.

Osmosis manipulable morphology and photonic property of microcapsules with colloidal nano-in-micro structure

Full visible spectrum photonic droplets and consequent microcapsules with nano-in-micro structure were prepared through microfluidic technique. Photo-curable resin and suspension of monodispersed soft nanogels were used as shell and core of the microcapsules, respectively. Upon UV irradiation, the droplets can be subsequently transformed into photonic microcapsules with an ultrathin polymeric shell. The shell thickness of the photonic microcapsules was found to be approximately 700 nm. Due to the ultrathin shell and soft core, the photonic microcapsules with nano-in-micro structure display dramatic changes both in shapes and photonic property under the impact of osmosis effect or temperature stimulus. Typically, the shell and core parts of nano-in-micro structure could respectively undergo a size expansion/even rupture and a size decrease/buckling under hypotonic and hypertonic condition. Correspondingly, the peak value of the reflection spectra of the microcapsules showed a redshift and blue shift, respectively. The mechanism to the structure and optical properties variation involves the osmotic pressure induced the volume-fraction change of the nanogel-based photonic dispersion and the shell buckling of the core/shell microcapsules.

Controllable Structural Colored Screen for Real-Time Display via Near-Infrared Light

Patterned colloidal crystals with stimuli-responsive materials provide sensitive and versatile means for investigating the varying ambiance of heat, light, electricity, magnetism, and stress. However, it remains a challenge to integrate stimuli-responsive materials with colloidal crystals by a simple and efficient method, thus restricting them from being used in general applications. Inspired from chameleons, we present a facile yet high-quality approach for the fabrication of the assembly of colloidal nanoparticles based on the hydrophilic-modified thermosensitive films. Various kinds of integral thermosensitive structural colored (TSSC) films are simply prepared in a high-quality screen on a large scale, with low cost, angle independence, and excellent flexibility. Simply turning on the near-infrared (NIR) laser brings heat to the irradiated region to increase the temperature. Integration of the multi-colored photonic bandgap (PBG) of the thermal-sensitive colloidal crystal and flexible anti-counterfeit labels into the NIR light exciting screens can change the intensity of PBG obviously. This advanced technology not only provides an efficient strategy for the preparation of colloidal crystal but also demonstrates a highly thermosensitive structural colored screen that has great prospect for information storage, anticounterfeiting, and real-time display materials.

Visual test for the presence of the illegal additive ethyl anthranilate by using a photonic crystal test strip

A test strip has been developed for the rapid detection of the illegal additive ethyl anthranilate (EA) in wine. The detection scheme is based on a combination of photonic crystal based detection and molecular imprinting based recognition. The resulting molecularly imprinted photonic crystal (MIPC) undergoes a gradual color change from green to yellow to red upon binding of EA. A semi-quantitative colorimetric card can be used to estimate the content of EA, either visually or by making use of an optical fiber spectrometer. A linear relationship was found between the Bragg diffraction peak shift and the concentration of EA in the range from 0.1 mM to 10 mM. The detection limit is 10 μM. The test has been successfully used to screening for the presence of EA in grape wine. The test strip is selective, and can be re-used after re-activation. Graphical abstract Schematic representation of the fabrication and application of the molecularly imprinted photonic crystal (MIPC) based test trip. The resulting MIPC undergoes a gradual color change from green to yellow to red upon binding of the illegal wine additive ethyl anthranilate (EA).

Deposition of CdTe quantum dots on microfluidic paper chips for rapid fluorescence detection of pesticide 2,4-D

Rapid detection of pesticides in fruits is an ongoing challenge. The objective of the present study was to develop novel fluorescent microfluidic paper chips for specific recognition and sensitive detection of the pesticide 2,4-D through the electron-transfer-induced fluorescence quenching mechanism. CdTe quantum dots (QDs) were deposited onto cellulose paper (base material) to yield imprinted paper chips (paper@QDs@MIPs). This method allows the transferability of the molecularly imprinted fluorescence sensor from the liquid phase to the solid phase (paper base) for rapid and portable analysis. The resultant imprinted paper chips were effectively characterized, and they exhibited ideal ordered spatial network structure, chemical stability, and fluorescence property. The paper@QDs@MIPs showed that 2,4-D binding significantly reduced the fluorescence intensity within less than 18 min, and it achieved satisfactory linearity in the range of 0.83-100 μM and high detectability of 90 nM. The recognition specificity for 2,4-D relative to its analogues was shown, and the imprinting factor was 2.13. In addition, the recoveries of the spiked bean sprouts at three concentration levels ranged within 94.2-107.0%, with a relative standard deviation of less than 5.9%. Collectively, the device provided an effective platform for rapid recognition, convenience, and detection of trace food pollutants in complex matrices, thereby ensuring food safety and further promoting surface imprinting studies.

Flory-Huggins Photonic Sensors for the Optical Assessment of Molecular Diffusion Coefficients in Polymers

The lack of cost-effective systems for the assessment of air pollutants is a concern for health and safety in urban and industrial areas. The use of polymer thin films as label-free colorimetric sensors featuring specific interactions with pollutants would then represent a paradigm shift in environmental monitoring and packaging technologies, allowing to assess air quality, formation of byproducts in closed environment, and the barrier properties of the polymers. To this end, all-polymer distributed Bragg reflectors represent a promising approach toward a reliable and cost-effective transduction of chemical stimuli and effective colorimetric label-free selective detectors. We show selectivity attained by specific interactions between the polymer and analytes. Such interactions drive the analyte intercalation through the polymer structure and its kinetics, converting it in a dynamic optical response which is at the basis of the Flory-Huggins photonic sensors. The multivariate analyses of the response kinetics also allow distinguishing binary mixtures. Additionally, we demonstrate that such optical responses can be used to esteem the diffusion coefficients of small molecules within polymer media via simple UV-vis spectroscopy retrieving data comparable to those obtained with state-of-the-art gravimetric procedures. Last, we assess the figures of merit of the sensors in terms of lower detection limit, sensitivity, and reversibility, demonstrating that such devices can pave the way to an innovative, simple, and low-cost detection method integrable to in situ assessment of barrier polymers used for the encapsulation of optoelectronic devices, food packaging, and goods storage in general.