A simple approach for the discrimination of surfactants based on the control of squaraine aggregation

Physicochemical properties and interactions of perfluoroalkyl substances (PFAS) - Challenges and opportunities in sensing and remediation

Per- and polyfluoroalkyl substances (PFAS) is a class of persistent organic pollutants that presents health and environmental risks. PFAS are ubiquitously present in the environment, but current remediation technologies are ineffective in degrading them into innocuous chemicals, especially high energy degradation processes often generate toxic short chain intermediates. Therefore, the best remediation strategy is to first detect the source of pollution, followed by capturing and mineralising or recycling of the compounds. The main objective of this article is to summarise the unique physicochemical properties and to critically review the intermolecular and intramolecular physicochemical interactions of PFAS, and how these interactions can become obstacles; and at the same time, how they can be applied to the PFAS sensing, capturing, and recycling process. The physicochemical interactions of PFAS chemicals are being reviewed in this paper includes, (1) fluorophilic interactions, (2) hydrophobic interactions, (3) electrostatic interactions and cation bridging, (4) ionic exchange and (5) hydrogen bond. Moreover, all the different influential factors to these interactions have also been reported. Finally, properties of these interactions are compared against one another, and the recommendations for future designs of affinity materials for PFAS have been given.

π-Electronic ion pairs: building blocks for supramolecular nanoarchitectonics viaiπ-iπ interactions

The pairing of charged π-electronic systems and their ordered arrangement have been achieved by iπ-iπ interactions that are derived from synergetically worked electrostatic and dispersion forces. Charged π-electronic systems that provide ion pairs as building blocks for assemblies have been prepared by diverse strategies for introducing charge in the core π-electronic systems. One method to prepare charged π-electronic systems is the use of covalent bonding that makes π-electronic ions and valence-mismatched metal complexes as well as protonated and deprotonated states. Noncovalent ion complexation is another method used to create π-electronic ions, particularly for anion binding, producing negatively charged π-electronic systems. Charged π-electronic systems afford various ion pairs, consisting of both cationic and anionic π-systems, depending on their combinations. Geometries and electronic states of the constituents in π-electronic ion pairs affect the photophysical properties and assembling modes. Recent progress in π-electronic ion pairs has revealed intriguing characteristics, including the transformation into radical pairs through electron transfer and the magnetic properties influenced by the countercations. Furthermore, the assembly states exhibit diversity as observed in crystals and soft materials including liquid-crystal mesophases. While the chemistry of ion pairs (salts) is well-established, the field of π-electronic ion pairs is relatively new; however, it holds great promise for future applications in novel materials and devices.

Electrochemical sensing platform based on Zeolite/Graphite/Dimethylglyoxime nanocomposite for highly selective and ultrasensitive determination of nickel

In this work, the fabrication and analytical application of a novel, unique, mercury-free, and user-friendly voltammetric sensor of Ni(II) based on glassy carbon electrode (GCE) modified with zeolite(MOR)/graphite(G)/dimethylglyoxime(DMG) composite (MOR/G/DMG-GCE) and the voltammetric procedure for highly selective, ultra-trace determination of nickel ions were reported for the first time. Deposition of a thin layer of the chemically active MOR/G/DMG nanocomposite enables the selective and effective accumulation of Ni(II) ions in the form of the DMG-Ni(II) complex. In 0.1 mol L^-1 ammonia buffer (pH 9.0), the MOR/G/DMG-GCE exhibited linear response in the Ni(II) ions concentration range of 0.86 - 19.61 µg L^-1 and 0.57 - 15.75 µg L^-1, for the accumulation time of 30 s and 60 s, respectively. For 60 s of accumulation time, the limit of detection (S/N = 3) was 0.18 µg L^-1 (3.04 nM), and sensitivity of 0.202 µA L µg^-1 was achieved. The developed protocol was validated by the analysis of wastewater certified reference materials. Its practical usefulness was confirmed by the determination of nickel released from metallic jewelry submerged in artificial sweat and stainless steel pot during water boiling. The obtained results were verified by electrothermal atomic absorption spectroscopy as a reference method.

Charge-Segregated Stacking Structure with Anisotropic Electric Conductivity in NIR-Absorbing and Emitting Positively Charged π-Electronic Systems

Squarylium-based π-electronic cation with an augmented dipole was synthesized by methylation of zwitterionic squarylium. The cation formed various ion pairs in combination with anions, and the ion pairs exhibited distinct photophysical properties in the dispersed state, ascribed to the formation of J- and H-aggregates. The ion pairs provided solid-state assemblies based on cation stacking. It is noteworthy that complete segregation of cations and anions was observed in a pseudo-polymorph of the ion pair with pentacyanocyclopentadienide as a π-electronic anion. In the crystalline state, the ion pairs exhibited photophysical properties and electric conductivity derived from cation stacking. In particular, the charge-segregated ion-pairing assembly induces an electric conductive pathway along the stacking axis. The charge-segregated mode and fascinating properties were derived from the reduced electrostatic repulsion between adjacent π-electronic cations via dipole-dipole interactions.

Construction of Red Fluorescent Dual Targeting Mechanically Interlocked Molecules for Live Cancer Cell Specific Lysosomal Staining and Multicolor Cellular Imaging

We have designed and synthesized red fluorescent mechanically interlocked molecules with dual targeting functionality for live cancer cell specific active targeting followed by selective internalization and imaging of malignant lysosomes along with real-time tracking, 3D, and multicolor cellular imaging applications.

Management of fluorescent organic/inorganic nanohybrids for biomedical applications in the NIR-II region

Biomedical fluorescence imaging in the second near-infrared (NIR-II, 100-1700 nm) window provides great potential for visualizing physiological and pathological processes, owing to the reduced tissue absorption, scattering, and autofluorescence. Various types of NIR-II probes have been reported in the past decade. Among them, NIR-II organic/inorganic nanohybrids have attracted widespread attention due to their unique properties by integrating the advantages of both organic and inorganic species. Versatile organic/inorganic nanohybrids provide the possibility of realizing a combination of functions, controllable size, and multiple optical features. This tutorial review summarizes the reported organic and inorganic species in nanohybrids, and their biomedical applications in NIR-II fluorescence and lifetime imaging. Finally, the challenges and outlook of organic/inorganic nanohybrids in biomedical applications are discussed.

Near-infrared probes for luminescence lifetime imaging

Biomedical luminescence imaging in the near-infrared (NIR, 700-1700 nm) region has shown great potential in visualizing biological processes and pathological conditions at cellular and animal levels, owing to the reduced tissue absorption and scattering compared to light in the visible (400-700 nm) region. To overcome the background interference and signal attenuation during intensity-based luminescence imaging, lifetime imaging has demonstrated a reliable imaging modality complementary to intensity measurement. Several selective or environment-responsive probes have been successfully developed for luminescence lifetime imaging and multiplex detection. This review summarizes recent advances in the application of luminescence lifetime imaging at cellular and animal levels in NIR-I and NIR-II regions. Finally, the challenges and further directions of luminescence lifetime imaging are also discussed.

Activatable fluorescence sensors for in vivo bio-detection in the second near-infrared window

Fluorescence imaging in the second near-infrared (NIR-II, 1000–1700 nm) window has exhibited advantages of high optical resolution at deeper penetration (ca. 5–20 mm) in bio-tissues owing to the reduced photon scattering, absorption and tissue autofluorescence. However, the non-responsive and “always on” sensors lack the ability of selective imaging of lesion areas, leading to the low signal-to-background ratio (SBR) and poor sensitivity during bio-detection. In contrast, activatable sensors show signal variation in fluorescence intensity, spectral wavelength and fluorescence lifetime after responding to the micro-environment stimuli, leading to the high detection sensitivity and reliability in bio-sensing. This minireview summarizes the design and detection ability of recently reported NIR-II activatable sensors. Furthermore, the challenges, opportunities and prospects of NIR-II activatable bio-sensing are also discussed.

Fluorescence imaging in the second near-infrared (NIR-II, 1000–1700 nm) window has exhibited advantages of high optical resolution at deeper penetration (ca. 5–20 mm) in bio-tissues owing to the reduced photon scattering and tissue autofluorescence.

Molecular Fluorophores for Deep-Tissue Bioimaging

Fluorescence imaging has made tremendous inroads toward understanding the complexity of biological systems, but in vivo deep-tissue imaging remains a great challenge due to the optical opacity of biological tissue. Recent improvements in laser and detector manufacturing have allowed the expansion of nonlinear and linear fluorescence imaging to the underexplored "tissue-transparent" second near-infrared (NIR-II; 1000-1700 nm) window, opening up new opportunities for optical access deep inside opaque tissue. Molecular fluorophores have historically played a major role in fluorescence bioimaging. It is increasingly important to design new molecular fluorophores to fully unlock the potential of NIR-II imaging techniques. In this outlook, we give an overview of the novel molecular fluorophores developed for deep-tissue bioimaging in the past five years and discuss their pros and cons in applications. Guidelines for designing new molecular fluorophores with the desirable properties are also provided.

Synthesis of the cationic fluorescent probes for the detection of anionic surfactants by electrostatic self-assembly

Anionic surfactants were widespread used in car cleaning agents, household detergents, agricultural and industrial processes, and considered as a major source of environmental pollutant. Therefore, it is necessary to develop a fast, simple, highly selective and sensitive probe for the detection of anionic surfactants. Here, we synthesized two aggregation induced emission (AIE)-active molecules 4,4',4″,4‴-(ethene-1,1,2,2-tetrayltetrakis(benzene-4,1-diyl))tetrakis (1-(4-bromobenzyl)pyridin-1-ium) bromide (TPE-Br) and 4,4',4″,4‴-(ethene-1,1,2,2-trayltetrakis(benzene-4,1-diyl))tetrakis(1-methylpyridin-1-ium)iodide (TPE-I), which were then applied as fluorescence probes for detecting sodium dodecyl sulfate (SDS) with high selectivity and sensitivity. In the presence of SDS, a multi-fold fluorescence emission intensity enhancement was observed in both two probes (TPE-Br and TPE-I) due to the electrostatic self-assembly of AIE molecular. The limits of detection are 71.5 and 120 nM for TPE-Br and TPE-I, respectively. This study may provide a new strategy for environmental monitoring by AIE-based fluorescent probe.

Self-assembling nanoprobes that display two-dimensional fluorescent signals for identification of surfactants and bacteria

The imidazolium-pyrene self-assembling nanoprobes can rapidly discriminate four types of surfactants.

A BODIPY-carbazole hybrid as a fluorescent probe: the design, synthesis, and discrimination of surfactants and the determination of the CMC values

A novel fluorescent probe (BDP-Zn²⁺) was developed to efficiently discriminate four kinds of surfactants and determine the CMC values.

Dual Sensing Performance of 1,2-Squaraine for the Colorimetric Detection of Fe3+ and Hg2+ Ions

A simple 1,2-squaraine based chemosensor material (SQ) has been reported to show dual sensing performance for colorimetric detection of Fe³⁺ and Hg²⁺ ions. Compared to common instrumental analysis, this method could provide fast and direct detection though colorimetric changes by the naked eye. The sensor has shown excellent selectivity over the other metal ions by tuning different solvent environments. The detection limit for Fe³⁺ could reach to 0.538 μM, which was lower than that in the environmental agency guideline (U.S. Environmental Protection Agency, U.S. EPA) in drinking water. And for Hg²⁺ detection, the limit was calculated as 1.689 μM in our case. A 1:1 binding mode between SQ⁻Fe³⁺ and SQ⁻Hg²⁺ ion were evidenced by Job's plot measurement and IR analysis. The proposed different binding mechanisms were also supported by Density Function Theory (DFT) calculation. All these findings provide a unique material and a simple, facile, and low cost colorimetric method for dual metal ions analysis and have shown preliminary analytical applications in industrial water sample analysis.

Specific colorimetric detection of Fe3+ ions in aqueous solution by squaraine-based chemosensor

A new squaraine based chemosensor TSQ was developed for colorimetric detection of Fe3+ ions. A thymine moiety in TSQ was constructed to act as an ion acceptor. The sensor displayed an instant colorimetric response specific to Fe3+ over the other metal ions in 20% AcOH-H2O solution. The limit of detection was much lower than that of the environmental protection agency guideline (5.37 μM) in drinking water. A 1 : 1 binding between TSQ and Fe3+ ion was evidenced by Job's plot measurement, ESI-MS and Fourier transform infrared (IR) measurements. Moreover, the proposed sensing mechanism of the receptor towards Fe3+ was strongly supported by DFT calculation. Finally, the sensor has proven to be suitable in real sample applications.

Point-of-Care Identification of Bacteria Using Protein-Encapsulated Gold Nanoclusters

The rapid, simple, and reliable identification of the most prevalent pathogens is essential for clinical diagnostics, biology, and food safety. Herein, four protein-encapsulated gold nanoclusters (protein-AuNCs) are designed and prepared as a sensor array for rapid identification of bacteria. The discrimination of six kinds of bacteria, including two kinds of drug-resistant bacteria, is successfully realized by the as-fabricated sensor array. The strategy presented here shows the advantages of easy synthesis and convenient to use. Furthermore, 100% classification accuracy is achieved by the sensor array consisting of two protein-AuNCs probes, demonstrating the design with sufficient diagnostic capacity. Taken together, the developed sensor array holds great promise for facile diagnosis of bacterial infection in resource-limited settings.

An Efficient 1064 nm NIR-II Excitation Fluorescent Molecular Dye for Deep-Tissue High-Resolution Dynamic Bioimaging

A small-molecule fluorophore FD-1080 with both excitation and emission in the NIR-II region has been successfully synthesized for in vivo imaging. A heptamethine structure is designed to shift the absorption and emission into NIR-II region. Sulphonic and cyclohexene groups are introduced to enhance its water solubility and stability. The quantum yield of FD-1080 is 0.31 %, and can be increased to 5.94 % after combining with fetal bovine serum (FBS). Significantly, 1064 nm NIR-II excitation was demonstrated with the high tissue penetration depth and superior imaging resolution compared to previously reported NIR excitation from 650 nm to 980 nm. FD-1080 is not only capable of realizing non-invasive high-resolution deep-tissue hindlimb vasculature and brain vessel bioimaging, but also quantifying the respiratory rate based on the dynamic imaging of respiratory craniocaudal motion of the liver for the awake and anaesthetized mouse.

The environmental-sensitivity of a fluorescent ZTRS–Cd(ii) complex was applied to discriminate different types of surfactants and determine their CMC values

One probe to distinguish four types of surfactants based on Cd(ii) binding modes between imidic acid and amide tautomeric forms.

Light up detection of heparin based on aggregation-induced emission and synergistic counter ion displacement

An easily accessible fluorescent light up probe HPQ-TBP-I is developed for sensitive and selective detection of heparin based on a synergistic strategy of aggregation-induced emission (AIE) and displacement of the fluorescence quencher iodide ion.