Silole-Infiltrated Photonic Crystal Films as Effective Fluorescence Sensor for Fe3+and Hg2+

Recent advances in AIEgen-based chemosensors for small molecule detection, with a focus on ion sensing

Since the aggregation-based emission (AIE) phenomenon emerged in 2001, numerous chemical designs have been built around the AIE concept, displaying its utility for diverse applications, including optics, electronics, energy, and biosciences. The present review critically evaluates the broad applicability of AIEgen-based chemical models towards sensing small analytes and the structural design strategies adjusting the mode of action reported since the last decade. Various AIEgen models have been discussed, providing qualitative and quantitative estimation of cationic metal ions and anionic species, as well as biomolecular, cellular, and organelle-specific probes. A systematic overview of the reported structural design and the underlying working mode will pave the way for designing and developing the next generation of AIEgens for specific applications.

Photoelectric Multi-Signal Output Sensor Based on Two-Dimensional Covalent Organic Polymer Film Modified by Novel Aggregation-Induced Emission Probes

Optical sensors, especially fluorescence sensors, have been widely used because of their advantages in sensing, such as the high sensitivity, good selectivity, no radiation source, and easy operation. Here, we report an example of fluorescence sensing based on two-dimensional (2D) covalent organic polymers and highlight that the material can achieve a fast response and multi-signal output. This 2DPTPAK+TAPB-based sensor can quickly detect aromatic hydrocarbons and Fe3+ by the fluorescence signal or electrical resistance signal.

Bio-inspired structural colors and their applications

Structural colors, generated by the interaction of interference, diffraction, and scattering between incident light and periodic nanostructured surfaces with features of the same scale with incident visible light wavelengths, have recently attracted intense interest in a wide range of research fields, due to their advantages such as various brilliant colors, long-term stability and environmental friendliness, low energy consumption, and mysterious biological functions. Tremendous effort has been made to design structural colors and considerable progress has been achieved in the past few decades. However, there are still significant challenges and obstacles, such as durability, portability, compatibility, recyclability, mass production of structural-color materials, etc., that need to be solved by rational structural design and novel manufacturing strategies. In this review, we summarize the recent progress of bio-inspired structural colors and their applications. First, we introduce several typical natural structural colors displayed by living organisms from fundamental optical phenomena, including interference, diffraction grating, scattering, photonic crystals effects, the combination of different phenomena, etc. Subsequently, we review recent progress in bio-inspired artificial structural colors generated from advanced micro/nanoscale manufacturing strategies to relevant biomimetic approaches, including self-assembly, template methods, phase conversion, magnetron sputtering, atomic layer deposition, etc. Besides, we also present the current and potential applications of structural colors in various fields, such as displays, anti-counterfeiting, wearable electronics, stealth, printing, etc. Finally, we discuss the challenges and future development directions of structural colors, aiming to push forward the research and applications of structural-color materials.

The diversity of the coordination bond generated a POSS-based fluorescent probe for the reversible detection of Cu(II), Fe(III) and amino acids

In recent years, it has been found that Cu²⁺, Fe³⁺, and amino acids play an irreplaceable and subtle role in organisms and have attracted the considerable attention of many researchers. Therefore, it is vital to design visual indicators to reveal the relationships between metal ions and amino acids. However, there have been few reports on this vigorous subject. Fortunately, based on the different coordination effects between metal ions and boron groups, we have designed an accessible fluorescent probe (PSI-A). Borane was introduced as an ion-sensitive group to form a novel POSS-based fluorescent probe, which achieves fascinating performance, in situ dynamic multiple detection, excellent photostability, and enervative biological toxicity. PSI-A exhibited predominant selectivity and sensitivity to Cu²⁺/amino acids and Fe³⁺/amino acids sequence reactions in HepG2 cells and zebrafish. The fluorescence of PSI-A was quenched by Cu²⁺, which can be recovered by adding Asp, Ser, Arg, Ace or Trp. Additionally, the fluorescence of PSI-A quenched by Fe³⁺ can be restored after adding Asp. PSI-A is available to monitor Cu²⁺/amino acids and Fe³⁺/amino acids sequence reactions and can be repeated for at least three consecutive cycles without a fatigued performance. Therefore, this multifunctional fluorescent probe may have prospective application potentials in the biological field.

Bis-BODIPY linked-triazole based on catechol core for selective dual detection of Ag+ and Hg2

Herein, we introduced a new chemosensor, bis-BODIPY linked-triazole based on catechol (BODIPY-OO) prepared by bridging two units of BODIPY fluorophore/triazole binding group with a catechol unit. A solution of this compound displayed 4- and 2-fold enhancements in fluorescence intensity after adding a mole equivalent amount of Ag⁺ and Hg²⁺ ions in methanol media, respectively. ¹H NMR titrations of BODIPY-OO with Ag⁺ and Hg²⁺ suggested that the triazole was involved in the recognition process. BODIPY-OO showed high sensitivity toward Ag⁺ and Hg²⁺ over other metal ions with detection limits of 0.45 μM and 1 μM, respectively. It can also distinguish Hg²⁺ from Ag⁺ by addition of an EDTA. This compound can therefore be employed as practical fluorescent probe for monitoring the presence of Ag⁺ and Hg²⁺ ions.

BODIPY–triazole–catechol combination serves as a “turn-on” fluorescent probe for dual detection and differentiation of Hg²⁺ and Ag⁺ ions.

Light-Emitting Multifunctional Maleic Acid-co-2-(N-(hydroxymethyl)acrylamido)succinic Acid-co-N-(hydroxymethyl)acrylamide for Fe(III) Sensing, Removal, and Cell Imaging

The intrinsically fluorescent highly hydrophilic multifunctional aliphatic terpolymer, maleic acid (MA)-co-2-(N-(hydroxymethyl)acrylamido)succinic acid (NHASA)-co-N-(hydroxymethyl)acrylamide (NHMA), that is, 1, was designed and synthesized via C-C/N-C-coupled in situ allocation of a fluorophore monomer, that is, NHASA, composed of amido and carboxylic acid functionalities in the polymerization of two nonemissive MA and NHMA. The scalable and reusable intrinsically fluorescent biocompatible 1 was suitable for sensing and high-performance adsorptive exclusion of Fe(III), along with the imaging of Madin-Darby canine kidney cells. The structure of 1, in situ fluorophore monomer, aggregation-induced enhanced emission, cell-imaging ability, and superadsorption mechanism were studied via microstructural analyses using 1H/13C NMR, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, atomic absorption spectroscopy, ultraviolet-visible spectroscopy, thermogravimetric analysis, dynamic light scattering, high-resolution transmission electron microscopy, solid-state fluorescence, fluorescence lifetime, and fluorescence imaging, along with measuring kinetics, isotherms, and thermodynamic parameters. The location, electronic structures, and geometries of the fluorophore and absorption and emission properties of 1 were investigated using density functional theory and natural transition orbital analyses. The limit of detection and the maximum adsorption capacity were 2.45 × 10-7 M and 542.81 mg g-1, respectively.

Aggregation-tuned dual emission of silole derivatives: synthesis, crystal structure, and photophysical properties

Novel silole derivatives are highly emissive in the microcrystalline state and the dual emission can be tuned by the aggregation states.

Fluorescent Terpolymers via In Situ Allocation of Aliphatic Fluorophore Monomers: Fe(III) Sensor, High-Performance Removals, and Bioimaging

Herein, purely aliphatic intrinsically fluorescent terpolymers, i.e., 1 and 2, are synthesized through one-pot solution polymerization via N-H functionalized and multi C-C/C-N coupled in situ protrusion of fluorescent monomers using two nonemissive monomers. These scalable terpolymers are suitable for highly selective Fe(III) sensing, high-performance exclusion of Fe(III), logic function and the imaging of normal mammalian Madin-Darby canine kidney and human osteosarcoma cancer cell lines. The structures of terpolymers, in situ attachment of fluorescent monomers, clusteroluminescence, adsorption-mechanism, and cell-imaging abilities are understood via unadsorbed and/or adsorbed microstructural analyses using ¹ H/¹³ C NMR, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy, atomic absorption spectroscopy, thermogravimetric analysis, high-resolution transmission electron microscopy, dynamic light scattering, fluorescence imaging, and fluorescence lifetime. The geometries, electronic structures, location of fluorophores, and singlet-singlet absorption and emission of terpolymers are examined using density functional theory (DFT) and time-dependent DFT. For the precise identification of fluorophores, transition from occupied natural transition orbitals (NTOs) to unoccupied NTOs is computed. For 1/2, limit of detection (LOD) values and adsorption capacities are 6.0 × 10^-7 /8.0 × 10^-7 m and 147.82/120.56 mg g^-1 at pH_i = 7.0 and 303 K, respectively. The overall properties of 1 are more advantageous compared to 2 in sensing, cell imaging, and adsorptive exclusion of Fe(III).

A tetraphenylethylene-based covalent organic polymer for highly selective and sensitive detection of Fe3+ and as a white light emitting diode

A newly prepared tetraphenylethylene-based (TPE-based) covalent organic polymer (COP) named COP-1 exhibits high selectivity for sensing Fe3+ and the limit of detection (LOD) for Fe3+ is 0.42 μM, which is lower than the reported metal-free porous polymers. Furthermore, a WLED is fabricated and the CIE coordinates are (0.32, 0.33), very close to pure white light. The COP-1 shows potential applications in biosensors of Fe3+ and preparation of WLEDs.

Polysulfide microspheres with chemical modification for generation of interfaces with macroscopic colour variation and biomimetic superhydrophobicity

Both superwettability and structural colours have attracted considerable attention in recent years. In addition, the combination of structural colours and superwettability could endow materials with broader application prospects. The combination provides a new strategy to design novel functional materials, and there are many studies pertaining to these materials that have been reported in recent years. Herein, a polysulfide (PSF) superhydrophobic coating was synthesized successfully. The PSF superhydrophobic coating possesses excellent superhydrophobicity, oleophobicity for diesel and macroscopic structural colour variation when wetted. The colour is changed when the coating is wetted and it returns to its original colour after drying. In addition, the surface presents better reusability and thermostability which satisfies various daily needs. The PSF superhydrophobic coating can be considered as an excellent candidate for designing wetting responsive materials, and it has enormous application potential in the fields of detection, sensing, anti-counterfeiting and security. For the first time, we present a novel and low-cost strategy to fabricate materials with both superhydrophobicity and structural colour, offering significant insights into the practical application of these functional materials.

Ultrathin two-dimensional porous organic nanosheets with molecular rotors for chemical sensing

Molecular rotors have played an important role in recent materials chemistry. Although several studies on functional materials containing molecular rotors have been reported for fluorescence sensing, this concept has yet to be realized in two-dimensional (2D) materials. Here we report the preparation of all-carbon, π-conjugated 2D porous organic nanosheets, named NUS-24, which contain flexible tetraphenylethylene (TPE) units as the molecular rotors. NUS-24 nanosheets exhibit high stability, large lateral size, and ultrathin thickness (2-5 nm). The dynamic TPE rotors exposed on the surface of NUS-24 nanosheets can be restricted in the aggregated state with different water fractions, which is reminiscent of the aggregation-induced emission mechanism, thereby leading to the size-selective turn-on fluorescence by volatile organic compounds. Significantly, the ultrathin 2D nanosheets and its composite membranes show much higher sensitivity and selectivity toward Fe³⁺ ions and nitro-containing compounds sensing, suggesting their potential applications in explosive detection and environmental monitoring.

Self-Assembled Curved Macroporous Photonic Crystal-Based Surfactant Detectors

Surfactants are extensively used as detergents, dispersants, and emulsifiers. Thus, wastewater containing high-concentration surfactants discharged to the environment pose a serious threat to the ecosystem. Unfortunately, conventional detection methods for surfactants suffer from the use of sophisticated instruments and cannot perform detections for various surfactants by a single analysis. The article reports the development of simple and sensitive surfactant detection using doctor-blade-coated three-dimensional curved macroporous photonic crystals on a cylindrical rod. The photonic crystals exhibit different hydrophobicities at various angular positions after surface modification. The penetration of aqueous surfactant solutions in the interconnected macropores causes red-shift as well as reduction in amplitude in the optical stop bands, resulting in surfactant detection with visible readout. The correlation between the surface tension, as well as the solution-infiltrated angular position, and the concentration of aqueous surfactant solutions has also been investigated in this study.

Wettability with Aggregation-Induced Emission Luminogens

Aggregation-induced emission luminogens (AIEgens) have become an emerging field since the concept of AIE was proposed in 2001. Recently, AIEgens have attracted considerable attention due to their abnormal non-emissive fluorescent behavior in solution but strongly emissive behavior in the aggregate state. By utilizing the inherent hydrophobicity, AIEgens can be used to monitor the crystal formation and dewetting behavior in the self-assembly process. More importantly, some stimuli-responsive AIE-active surfaces have been successfully fabricated. In this perspective review, we outline the advances of surface wettability of AIEgens and its applications.

Biomimetic superwettable materials with structural colours

This review aims at offering a comprehension elaboration of the mechanism, recent biomimetic research and applications of biomimetic superwettable materials with structural colours. Futhermore, this review will provide significant insight into the design, fabrication and application of biomimetic superwettable materials with structural colours.

Optical nose based on porous silicon photonic crystal infiltrated with ionic liquids

A photonic-nose for the detection and discrimination of volatile organic compounds (VOCs) was constructed. Each sensing element on the photonic sensor array was formed by infiltrating a specific type of ionic liquid (IL) into the pore channel of a patterned porous silicon (PSi) chip. Upon exposure to VOC, the density of IL dramatically decreased due to the nano-confinement effect. As a result, the IL located in pore channel expanded its volume and protrude out of the pore channel, leading to the formation of microdroplets on the PSi surface. These VOC-stimulated microdroplets could scatter the light reflected from the PSi rugate filter, thereby producing an optical response to VOC. The intensity of the optical response produced by IL/PSi sensor mainly depends on the size and shape of microdroplets, which is related to the concentration of VOC and the physi-chemical propertied of ILs. For ethanol vapor, the optical response has linear relationship with its relative vapor pressure within 0-60%. The LOD of the IL/PSi sensor for ethanol detection is calculated to be 1.3 ppm. It takes around 30 s to reach a full optical response, while the time for recovery is less than 1 min. In addition, the sensor displayed good stability and reproducibility. Owing to the different molecular interaction between IL and VOC, the ILs/PSi sensor array can generate a unique cross-reactive "fingerprint" in response to a specific type of VOC analyte. With the assistance of image technologies and principle components analysis (PCA), rapid discrimination of VOC analyte could be achieved based on the pattern recognition of photonic sensor array. The technology established in this work allows monitoring in-door air pollution in a visualized way.

Luminescent films for chemo- and biosensing

Luminescent films have received great interest for chemo-/bio-sensing applications due to their distinct advantages over solution-based probes, such as good stability and portability, tunable shape and size, non-invasion, real-time detection, extensive suitability in gas/vapor sensing, and recycling. On the other hand, they can achieve selective and sensitive detection of chemical/biological species using special luminophores with a recognition moiety or the assembly of common luminophores and functional materials. Nowadays, the extensively used assembly techniques include drop-casting/spin-coating, Langmuir-Blodgett (LB), self-assembled monolayers (SAMs), layer-by-layer (LBL), and electrospinning. Therefore, this review summarizes the recent advances in luminescent films with these assembly techniques and their applications in chemo-/bio-sensing. We mainly focused on the discussion of the relationship between the sensing properties of the films and their architecture. Furthermore, we discussed some critical challenges existing in this field and possible solutions that have been or are being developed to overcome these challenges.

Luminescent photonic crystals with multi-functionality and tunability

We develop a general method to incorporate aggregation-induced emission luminogens into photonic crystals (PCs) and the resulting luminescent PCs display diverse structural colors in response to water stimulation.

The marriage of reflected light originating from photonic crystals (PCs) and emitted light would create miraculous phenomena. However, traditional luminophores cannot avoid the problem of aggregation-caused quenching. To solve this problem, we develop a general method to incorporate aggregation-induced emission luminogens (AIEgens) into PCs via physical absorption or chemical reaction. The resulting luminescent PCs display diverse structural colors in response to water stimulation, due to the swelling of the aqueous medium. Such a water-tunable photonic band gap red-shift has the ability to modulate the AIEgen emission, as well as narrowing its full width at half maximum (FWHM), which allows the luminescent PC to behave as a smart intramolecular filter that is capable of creating arbitrary light from only one material. In addition, the filter is believed to modulate the broad emission spectra of AIEgens arising from different conformations. Furthermore, the luminescent PC can respond to ethanol stimulation due to two factors: (a) swelling of the aqueous medium (external tuning); and (b) expansion of nanoparticles (internal tuning). By exploiting the synergy of the external-internal tuning, the emission wavelength and intensity can be finely changed. Both the water- and ethanol-tunable emission shift fit to a linear relationship, and thus the luminescent PC could be able to quantitatively detect humidity in the environment and alcohol in wine.

Aggregation-induced emission of siloles

Aggregation-induced emission (AIE) is a unique and significant photophysical phenomenon that differs greatly from the commonly acknowledged aggregation-caused emission quenching observed for many π-conjugated planar chromophores. The mechanistic decipherment of the AIE phenomenon is of high importance for the advance of new AIE systems and exploitation of their potential applications. Propeller-like 2,3,4,5-tetraphenylsiloles are archetypal AIE-active luminogens, and have been adopted as a core part in the design of numerous luminescent materials with diverse functionalities. In this review article, we elucidate the impacts of substituents on the AIE activity and shed light on the structure-property relationship of siloles, with the aim of promoting the judicious design of AIE-active functional materials in the future. Recent representative advances of new silole-based functional materials and their potential applications are reviewed as well.

Masking agent-free and channel-switch-mode simultaneous sensing of Fe(3+) and Hg(2+) using dual-excitation graphene quantum dots

A novel channel-switch-mode strategy for simultaneous sensing of Fe(3+) and Hg(2+) is developed with dual-excitation single-emission graphene quantum dots (GQDs). By utilizing the dual-channel fluorescence response performance of GQDs, this strategy achieved a facile, low-cost, masking agent-free, quantitative and selective dual-ion assay even in mixed ion samples and practical water samples.

An overview of the recent developments on Hg2+ recognition

Adverse influences of mercury on living organisms are well known. Despite efforts from various regulatory agencies, the build-up of Hg²⁺ concentration in the environment is of serious concern. This necessitates the search for new and efficient reagents for recognition and detection of Hg²⁺ in environmental samples.