Recent Advances in AIEgens for Metal Ion Biosensing and Bioimaging

Chitosan based fluorescent probe with AIE property for detection of Fe3+ and bacteria

Fluorescent probe with aggregation-induced emission (AIE) property has been widely used because of the advantages of high sensitivity, good selectivity and non-destructive testing. The development of fluorescent probe with good biocompatibility, photostability and biodegradability is of great significance in biomedicine and environmental detection. Herein, a novel type of fluorophore CS-TPE for detection of Fe3+ and bacteria was prepared by the Schiff base reaction of chitosan (CS) and 4-(1,2,2-triphenylethenyl) benzaldehyde (TPE-CHO). The fluorescence response mechanism of CS-TPE system was investigated by various characterization techniques. CS-TPE had an obvious AIE behavior with strong blue-green emissions at 473 nm and reaches the highest photoluminescence (PL) emission in 90 % H2O/ethanol mixtures. CS-TPE fluorescent probe exhibited sensitive quenching response to Fe3+, which can be used as a biosensor for detecting the concentration of Fe3+ with short response time (5 min), low detection limit (0.998 μM) and wide detection range (10-300 μM). Meanwhile, CS-TPE exhibited good antibacterial performance for S. aureus and E. coli. It is expected to realize the real-time fluorescence monitoring of metal ion detection and antibacterial process.

Heavy metal ion sensing strategies using fluorophores for environmental remediation

The main aim of this review is to provide a holistic summary of the latest advances within the research area focusing on the detection of heavy metal ion pollution, particularly the sensing strategies. The review explores various heavy metal ion detection approaches, encompassing spectrometry, electrochemical methods, and optical techniques. Numerous initiatives have been undertaken in recent times in response to the increasing demand for fast, sensitive, and selective sensors. Notably, fluorescent sensors have acquired prominence owing to the numerous advantages such as good specificity, reversibility, and sensitivity. Further, this review also explores the advantages of various nanomaterials employed in sensing heavy metal ions. In this regard, exclusive emphasis is placed on fluorescent nanomaterials based on organic dyes, quantum dots, and fluorescent aptasensors for metal ion removal from aqueous systems, and to identify the fate of heavy metal ions in the natural environment.

Aggregation-Induced Emission Luminogen: Role in Biopsy for Precision Medicine

Biopsy, including tissue and liquid biopsy, offers comprehensive and real-time physiological and pathological information for disease detection, diagnosis, and monitoring. Fluorescent probes are frequently selected to obtain adequate information on pathological processes in a rapid and minimally invasive manner based on their advantages for biopsy. However, conventional fluorescent probes have been found to show aggregation-caused quenching (ACQ) properties, impeding greater progresses in this area. Since the discovery of aggregation-induced emission luminogen (AIEgen) have promoted rapid advancements in molecular bionanomaterials owing to their unique properties, including high quantum yield (QY) and signal-to-noise ratio (SNR), etc. This review seeks to present the latest advances in AIEgen-based biofluorescent probes for biopsy in real or artificial samples, and also the key properties of these AIE probes. This review is divided into: (i) tissue biopsy based on smart AIEgens, (ii) blood sample biopsy based on smart AIEgens, (iii) urine sample biopsy based on smart AIEgens, (iv) saliva sample biopsy based on smart AIEgens, (v) biopsy of other liquid samples based on smart AIEgens, and (vi) perspectives and conclusion. This review could provide additional guidance to motivate interest and bolster more innovative ideas for further exploring the applications of various smart AIEgens in precision medicine.

Multi-stimuli-responsive cyanostilbene derivatives: Their fluorescent and mechanochromic properties, and potential application in water sensing and anti-counterfeiting

In recent years, aggregation-induced emission luminogens (AIEgens) have witnessed numerous groundbreaking advances in fundamental theoretical research and functional applications. Notably, stimuli-responsive AIEgens have achieved remarkable results, demonstrating immense potential for application in various fields such as chemistry, materials science, biology, and medicine. Herein, two multi-stimuli-responsive cyanostilbene derivatives TPE-CNTPA and PH-CNTPA were synthesized by introducing tetraphenylethylene (TPE) and trifluoromethyl groups, respectively. Primarily, under the combined mechanism of aggregation-induced emission (AIE) and twisted intramolecular charge transfer (TICT), TPE-CNTPA and PH-CNTPA exhibit "on-off-on" fluorescent emission characteristics in solution. Secondly, under 365 nm ultraviolet light irradiation, the photo-induced isomerization of PH-CNTPA causes changes in photophysical property, demonstrating its responsiveness to ultraviolet light. In addition, TPE-CNTPA and PH-CNTPA exhibit high-contrast mechanochromic properties, providing broader possibilities for their potential applications in various fields. Moreover, owing to the unique fluorescence emission characteristics, TPE-CNTPA and PH-CNTP have enormous potential for application in the field of encryption anti-counterfeiting. Besides, PH-CNTPA can be utilized for the detection of trace water in single or mixed solvents, demonstrating outstanding sensitivity and anti-interference properties in different solvents. This research work reveals the potential in the fields of water sensing and anti-counterfeiting for these two multi-stimuli-responsive compounds.

The complexometric behavior of selected aroyl-S,N-ketene acetals shows that they are more than AIEgens

Using the established synthetic methods, aroyl-S,N-ketene acetals and subsequent bi- and multichromophores can be readily synthesized. Aside from pronounced AIE (aggregation induced emission) properties, these selected examples possess distinct complexometric behavior for various metals purely based on the underlying structural motifs. This affects the fluorescence properties of the materials which can be readily exploited for metal ion detection and for the formation of different metal-aroyl-S,N-ketene acetal complexes that were confirmed by Job plot analysis. In particular, gold(I), iron(III), and ruthenium (III) ions reveal complexation enhanced or quenched emission. For most dyes, weakly coodinating complexes were observed, only in case of a phenanthroline aroyl-S,N-ketene acetal multichromophore, measurements indicate the formation of a strongly coordinating complex. For this multichromophore, the complexation results in a loss of fluorescence intensity whereas for dimethylamino-aroyl-S,N-ketene acetals and bipyridine bichromophores, the observed quantum yield is nearly tripled upon complexation. Even if no stable complexes are formed, changes in absorption and emission properties allow for a simple ion detection.

Tetrakispyrazolylethene: Protonation-Induced Emission

Tetrakispyrazolylethene (1) was synthesized from pyrazole and hexachloroethane through a one-step substitution reaction. The increase of emission was detected both in solid and aqueous THF solution, compared with that in anhydrous THF. While the former originates from the crystal packing, the latter is attributed to the protonation-induced emission, independent of aggregation, based on the optical measurement under varying concentrations and particle-size distribution analysis.

Design of New Schiff Bases and Their Heavy Metal Ion Complexes for Environmental Applications: A Molecular Dynamics and Density Function Theory Study

Schiff bases (SBs) are important ligands in coordination chemistry due to their unique structural properties. Their ability to form complexes with metal ions has been exploited for the environmental detection of emerging water contaminants. In this work, we evaluated the complexation ability of three newly proposed SBs, 1-3, by complete conformational analysis, using a combination of Molecular Dynamics and Density Functional Theory studies, to understand their ability to coordinate toxic heavy metal (HMs) ions. From this study, it emerges that all the ligands present geometries that make them suitable to complex HMs through the N-imino moieties or, in the case of 3, with the support of the oxygen atoms of the ethylene diether chain. In particular, this ligand shows the most promising coordination behavior, particularly with Pb2+.

Molecularly Targeted Fluorescent Sensors for Visualizing and Tracking Cellular Senescence

Specific identification and monitoring of senescent cells are essential for the in-depth understanding and regulation of senescence-related life processes and diseases. Fluorescent sensors providing real-time and in situ information with spatiotemporal resolution are unparalleled tools and have contributed greatly to this field. This review focuses on the recent progress in fluorescent sensors for molecularly targeted imaging and real-time tracking of cellular senescence. The molecular design, sensing mechanisms, and biological activities of the sensors are discussed. The sensors are categorized by the types of markers and targeting ligands. Accordingly, their molecular recognition and fluorescent performance towards senescence biomarkers are summarized. Finally, the perspective and challenges in this field are discussed, which are expected to assist future design of next-generation sensors for monitoring cellular senescence.

Advancements in Biosensors Based on the Assembles of Small Organic Molecules and Peptides

Over the past few decades, molecular self-assembly has witnessed tremendous progress in a variety of biosensing and biomedical applications. In particular, self-assembled nanostructures of small organic molecules and peptides with intriguing characteristics (e.g., structure tailoring, facile processability, and excellent biocompatibility) have shown outstanding potential in the development of various biosensors. In this review, we introduced the unique properties of self-assembled nanostructures with small organic molecules and peptides for biosensing applications. We first discussed the applications of such nanostructures in electrochemical biosensors as electrode supports for enzymes and cells and as signal labels with a large number of electroactive units for signal amplification. Secondly, the utilization of fluorescent nanomaterials by self-assembled dyes or peptides was introduced. Thereinto, typical examples based on target-responsive aggregation-induced emission and decomposition-induced fluorescent enhancement were discussed. Finally, the applications of self-assembled nanomaterials in the colorimetric assays were summarized. We also briefly addressed the challenges and future prospects of biosensors based on self-assembled nanostructures.

Optical and quantitative detection of cobalt ion using graphitic carbon nitride-based chemosensor for hydrometallurgy of waste lithium-ion batteries

A hydrometallurgy is one of the most important techniques for recycling waste LIBs, where identifying the exact composition of the metal-leached solution is critical in controlling the metal extraction efficiency and the stoichiometry of the regenerated product. In this study, we report a simple and selective optical detection of high-concentrated Co²⁺ using a graphitic carbon nitride (g-CN)-based fluorescent chemosensor. g-CN is prepared by molten salt synthesis using dicyandiamide (DCDA) and LiI/KI. The mass ratio of LiI/KI to DCDA modifies the resulting g-CN (CNI) in terms of in-plane molecular distances of base sites including cyano functional groups (─CN) and fluorescent emission wavelength via nucleophilic substitution. The fluorescent sensing performance of CNIs is evaluated through photoluminescence (PL) emission spectroscopy in a broad Co²⁺ concentration range (10^-4-10⁰ M). The correlation between the surface exposure of hidden nitrogen pots (base sites) and PL intensity change is achieved where the linear relationship between the PL quenching and the logarithm of Co²⁺ concentration in the analyte solution is well established with the regression of 0.9959. This study will provide the design principle of the chemosensor suitable for the fast and accurate optical detection of Co²⁺ present in a broad concentration range for hydrometallurgy for the recycling of waste LIBs.

Stimuli-Responsive Electrospun Fluorescent Fibers Augmented with Aggregation-Induced Emission (AIE) for Smart Applications

This review addresses the latest advancements in the integration of aggregation-induced emission (AIE) materials with polymer electrospinning, to accomplish fine-scale electrospun fibers with tunable photophysical and photochemical properties. Micro- and nanoscale fibers augmented with AIE dyes (termed AIEgens) are bespoke composite systems that can overcome the limitation posed by aggregation-caused quenching, a critical deficiency of conventional luminescent materials. This review comprises three parts. First, the reader is exposed to the basic concepts of AIE and the fundamental mechanisms underpinning the restriction of intermolecular motions. This is followed by an introduction to electrospinning techniques pertinent to AIE-based fibers, and the core parameters for controlling fiber architecture and resultant properties. Second, exemplars are drawn from latest research to demonstrate how electrospun nanofibers and porous films incorporating modified AIEgens (especially tetraphenylethylene and triphenylamine derivatives) can yield enhanced photostability, photothermal properties, photoefficiency (quantum yield), and improved device sensitivity. Advanced applications are drawn from several promising sectors, encompassing optoelectronics, drug delivery and biology, chemosensors and mechanochromic sensors, and innovative photothermal devices, among others. Finally, the outstanding challenges together with potential opportunities in the nascent field of electrospun AIE-active fibers are presented, for stimulating frontier research and explorations in this exciting field.

Pyrene-Based AIE Active Materials for Bioimaging and Theranostics Applications

Aggregation-induced emission (AIE) is a unique research topic and property that can lead to a wide range of applications, including cellular imaging, theranostics, analyte quantitation and the specific detection of biologically important species. Towards the development of the AIE-active materials, many aromatic moieties composed of tetraphenylethylene, anthracene, pyrene, etc., have been developed. Among these aromatic moieties, pyrene is an aromatic hydrocarbon with a polycyclic flat structure containing four fused benzene rings to provide an unusual electron delocalization feature that is important in the AIE property. Numerous pyrene-based AIE-active materials have been reported with the AIE property towards sensing, imaging and theranostics applications. Most importantly, these AIE-active pyrene moieties exist as small molecules, Schiff bases, polymers, supramolecules, metal-organic frameworks, etc. This comprehensive review outlines utilizations of AIE-active pyrene-based materials on the imaging and theranostics studies. Moreover, the design and synthesis of these pyrene-based molecules are delivered with discussions on their future scopes.

Amphipolar, Amphiphilic 2,4-diarylpyrano[2,3-b]indoles as Turn-ON Luminophores in Acidic and Basic Media

A versatile amphiphilic pyrano[2,3-b]indole for halochromic turn-ON luminescence in acidic or basic media is accessed by an insertion-coupling-cycloisomerization and adjusting solubilizing and phenolic functionalities. While almost non-emissive in neutral solutions, treatment with acids or bases like trifluoroacetic acid (TFA) or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) reveals distinct luminescence at wavelengths of 540 nm or 630 nm in propan-2-ol, respectively. Turn-ON emission can be detected at pH values as mild as pH = 5.31 or 8.70. Quantum yields in propan-2-ol are substantial for protonated (Φf = 0.058) and deprotonated (Φf = 0.059) species. Photometrically, pKa1 of 3.5 and pKa2 of 10.5 were determined in propan-2-ol. With lipophilic polyether sidechains and hydrophilic protonation and deprotonation sites the molecule can be regarded as amphipolar, which results in good solubility properties for different organic solvents. In aqueous media, an organic co-solvent like propan-2-ol (35%) or tetrahydrofuran (25%) is needed, and the solution can be diluted with pure water without precipitation of the compound. At higher concentrations of water, a turbid solution is formed, which indicates the formation of micellar structures or clusters. With dynamic light scattering we could show that these clusters increase in size with increasing water content.

Activity-based NIR fluorescent probes based on the versatile hemicyanine scaffold: design strategy, biomedical applications, and outlook

The discovery of a near-infrared (NIR, 650-900 nm) fluorescent chromophore hemicyanine dye with high structural tailorability is of great significance in the field of detection, bioimaging, and medical therapeutic applications. It exhibits many outstanding advantages including absorption and emission in the NIR region, tunable spectral properties, high photostability as well as a large Stokes shift. These properties are superior to those of conventional fluorogens, such as coumarin, fluorescein, naphthalimides, rhodamine, and cyanine. Researchers have made remarkable progress in developing activity-based multifunctional fluorescent probes based on hemicyanine skeletons for monitoring vital biomolecules in living systems through the output of fluorescence/photoacoustic signals, and integration of diagnosis and treatment of diseases using chemotherapy or photothermal/photodynamic therapy or combination therapy. These achievements prompted researchers to develop more smart fluorescent probes using a hemicyanine fluorogen as a template. In this review, we begin by describing the brief history of the discovery of hemicyanine dyes, synthetic approaches, and design strategies for activity-based functional fluorescent probes. Then, many selected hemicyanine-based probes that can detect ions, small biomolecules, overexpressed enzymes and diagnostic reagents for diseases are systematically highlighted. Finally, potential drawbacks and the outlook for future investigation and clinical medicine transformation of hemicyanine-based activatable functional probes are also discussed.

The Multifarious Applications of Copper Nanoclusters in Biosensing and Bioimaging and Their Translational Role in Early Disease Detection

Nanoclusters possess an ultrasmall size, amongst other favorable attributes, such as a high fluorescence and long-term colloidal stability, and consequently, they carry several advantages when applied in biological systems for use in diagnosis and therapy. Particularly, the early diagnosis of diseases may be facilitated by the right combination of bioimaging modalities and suitable probes. Amongst several metallic nanoclusters, copper nanoclusters (Cu NCs) present advantages over gold or silver NCs, owing to their several advantages, such as high yield, raw abundance, low cost, and presence as an important trace element in biological systems. Additionally, their usage in diagnostics and therapeutic modalities is emerging. As a result, the fluorescent properties of Cu NCs are exploited for use in optical imaging technology, which is the most commonly used research tool in the field of biomedicine. Optical imaging technology presents a myriad of advantages over other bioimaging technologies, which are discussed in this review, and has a promising future, particularly in early cancer diagnosis and imaging-guided treatment. Furthermore, we have consolidated, to the best of our knowledge, the recent trends and applications of copper nanoclusters (Cu NCs), a class of metal nanoclusters that have been gaining much traction as ideal bioimaging probes, in this review. The potential modes in which the Cu NCs are used for bioimaging purposes (e.g., as a fluorescence, magnetic resonance imaging (MRI), two-photon imaging probe) are firstly delineated, followed by their applications as biosensors and bioimaging probes, with a focus on disease detection.

Aggregation induced emission molecules for detection of nucleic acids

Aggregation-induced emission (AIE) is an ingenious concept in the field of luminescent molecules. AIE is the energy released in an excited state that in turn is converted into light irrespective of being in either liquid phase or solid phase. Aggregation or crystallization of AIE molecules impedes the free movement of molecules and it resultantly becomes highly fluorescent. It is currently being used for several applications including sensing, diagnostic, protein, DNA or RNA detection, cells and cell organelles imaging. AIEs are highly sensitive and specific for binding with target molecules. In this chapter, we underline different AIE molecules for detection of nucleic acids.

Zinc (II) and AIEgens: The "Clip Approach" for a Novel Fluorophore Family. A Review

Aggregation-induced emission (AIE) compounds display a photophysical phenomenon in which the aggregate state exhibits stronger emission than the isolated units. The common term of "AIEgens" was coined to describe compounds undergoing the AIE effect. Due to the recent interest in AIEgens, the search for novel hybrid organic-inorganic compounds with unique luminescence properties in the aggregate phase is a relevant goal. In this perspective, the abundant, inexpensive, and nontoxic d10 zinc cation offers unique opportunities for building AIE active fluorophores, sensing probes, and bioimaging tools. Considering the novelty of the topic, relevant examples collected in the last 5 years (2016-2021) through scientific production can be considered fully representative of the state-of-the-art. Starting from the simple phenomenological approach and considering different typological and chemical units and structures, we focused on zinc-based AIEgens offering synthetic novelty, research completeness, and relevant applications. A special section was devoted to Zn(II)-based AIEgens for living cell imaging as the novel technological frontier in biology and medicine.

Development of novel GnRH and Tat48-60 based luminescent probes with enhanced cellular uptake and bioimaging profile

There is a clear need to develop photostable chromophores for bioimaging with respect to the classically utilized green fluorescent dye fluorescein. Along these lines, we utilized a phosphorescent carboxy-substituted ruthenium(ii) polypyridyl [Ru(bipy)2(mcb)]2+ (bipy = 2,2'-bipyridyl and mcb = 4-carboxy-4'-methyl-2,2'-bipyridyl) complex. We developed two luminescent peptide conjugates of the cell-penetrating peptide Tat48-60 consisting of either [Ru(bipy)2(mcb)]2+ or 5(6)-carboxyfluorescein (5(6)-FAM) tethered on the Lys50 of the peptide through amide bond. We confirmed the efficient cellular uptake of both bioconjugates in HeLa cells by confocal microscopy and flow cytometry and proved that the ruthenium-based chromophore possesses enhanced photostability compared to a 5(6)-FAM-based peptide, after continuous laser scanning. Furthermore, we designed and developed a luminescent agent with high photostability, based on the ruthenium core, that could be selectively localized in cancer cells overexpressing the GnRH receptor (GnRH-R). To achieve this, we took advantage of the tumor-homing character of d-Lys6-GnRH which selectively recognizes the GnRH-R. The [Ru(bipy)2(mcb)]2+-d-Lys6-GnRH peptide conjugate was synthesized, and its cellular uptake was evaluated through flow cytometric analysis and live-cell imaging in HeLa and T24 bladder cancer cells as negative and positive controls of GnRH-R, respectively. Besides the selective targeting that the specific conjugate could offer, we also recorded high internalization levels in T24 bladder cancer cells. The ruthenium(ii) polypyridyl peptide-based conjugates we developed is an intriguing approach that offers targeted cell imaging in the Near Infrared region, and simultaneously paves the way for further advancements in the dynamic studies on cellular imaging.

A multicolor and ratiometric fluorescent sensing platform for metal ions based on arene-metal-ion contact

Despite continuous and active development of fluorescent metal-ion probes, their molecular design for ratiometric detection is restricted by the limited choice of available sensing mechanisms. Here we present a multicolor and ratiometric fluorescent sensing platform for metal ions based on the interaction between the metal ion and the aromatic ring of a fluorophore (arene-metal-ion, AM, coordination). Our molecular design provided the probes possessing a 1,9-bis(2'-pyridyl)-2,5,8-triazanonane as a flexible metal ion binding unit attached to a tricyclic fluorophore. This architecture allows to sense various metal ions, such as Zn(II), Cu(II), Cd(II), Ag(I), and Hg(II) with emission red-shifts. We showed that this probe design is applicable to a series of tricyclic fluorophores, which allow ratiometric detection of the metal ions from the blue to the near-infrared wavelengths. X-ray crystallography and theoretical calculations indicate that the coordinated metal ion has van der Waals contact with the fluorophore, perturbing the dye's electronic structure and ring conformation to induce the emission red-shift. A set of the probes was useful for the differential sensing of eight metal ions in a one-pot single titration via principal component analysis. We also demonstrate that a xanthene fluorophore is applicable to the ratiometric imaging of metal ions under live-cell conditions.

A quinoline-based fluorescent chemosensor for palladium ion (Pd2+)-selective detection in aqueous solution

Quinoline-based fluorescent chemosensors have been extensively developed for various metal cations, but it was still rare for Pd²⁺-selective detection. In this work, a novel quinoline-benzimidazole conjugate containing one carboxylic acid group (QBM) was designed, and the QBM displayed highly selective fluorescence quenching response towards Pd²⁺ over other metal cations in aqueous solution. The fluorescence titration revealed a good linear relationship between the fluorescence intensity and the Pd²⁺ concentration in the range of 0.5-10 μmol L^-1, with the detection limit of 0.26 μmol L^-1 (S/N = 3). Fluorescence detection of Pd²⁺ in practical water sample was also successfully achieved.

The preparation of novel triphenylamine-based AIE-effect fluorescent probe for selectively detecting mercury(ii) ion in aqueous solution

A novel triphenylamine-based TPA-ME exhibits good AIE fluorescence in a DMF/Water system and excellent probe property for detecting Hg²⁺ in solution.

Tetraphenylethylene AIEgen bearing thiophenylbipyridine receptor for selective detection of copper(ii) ion

A new tetraphenylethylene (TPE) AIEgen appended with a thiophenylbipyridine moiety exhibits sensitivity and selectivity towards copper ions via a PET “turn on–turn off” mechanism.

Selective ratiometric red-emission detection of In3+ in aqueous solutions and in live cells using a fluorescent peptidyl probe and metal chelating agent

Indium has been regarded as one of the most rarely used metal ions; however, the consumption of indium has increased intensively due to its increasing use in electrodes of liquid crystal displays (LCDs). In recent years, warnings have been issued about the toxicity of indium to aquatic ecosystems and humans. Thus, the development of efficient and selective detection methods for In³⁺ in aquatic environments as well as in live cells is highly required. However, the selective and sensitive detection of In³⁺ in the presence of trivalent metal ions and other metal ions is highly challenging. In the present study, we synthesized a fluorescent probe (1) for In³⁺ and Al³⁺ based on an unnatural peptide receptor and an aggregation-induced emission fluorophore and developed a selective fluorescent detection method for In³⁺ in aqueous solutions and live cells using the probe and a metal chelating agent. 1 recognized In³⁺ and Al³⁺ selectively among 19 metal ions in aqueous solutions depending on pH by the enhancement of the red emission at 600 nm and decrease in the green emission at 530 nm. 1 sensitively detected In³⁺ and Al³⁺ by ratiometric response in a wide pH range (3.5-7.4), and the ratiometric response was complete within 20 seconds in an aqueous buffered solution at pH 5.0. Interestingly, the addition of EDTA to the complex of 1 with In³⁺ or Al³⁺ did not induce the Al³⁺-free spectrum but instead induced the In³⁺-free spectrum; thus, In³⁺ and Al³⁺ could be easily differentiated. The detection limit of 1 for In³⁺ ions was 211 nM (R² = 0.981) in purely aqueous solutions. The fluorescence ratiometric detection method using 1 could quantify low concentrations of In³⁺ in ground water and tap water. Fluorescence cell image studies revealed that the probe was cell-permeable, and low concentrations of In³⁺ inside the cells could be recognized by the enhancement of the red emission at 600 nm. The binding mode study via NMR, IR, and CD spectroscopy revealed how the peptide receptor of 1 interacted with In³⁺ and resulted in the enhancement of the red emission in an aqueous solution.

A ratiometric fluorescence sensor based on enzymatically activatable micellization of TPE derivatives for quantitative detection of alkaline phosphatase activity in serum

A novel ratiometric fluorescence assay via enzymatically activatable micellization in aqueous solution was devised for quantitative detection of alkaline phosphatase (ALP) activity. We demonstrated that the dephosphorylation of the water-soluble, phosphate-functionalized, fluorophore monomer P-TPE-TG, induced by an enzymatic reaction of ALP, leads to micelle formation in aqueous solution because its water-soluble functionality is reduced. The dephosphorylation-induced micellization of P-TPE-TG exhibited a ratiometric sensing response for various ALP concentrations (10–200 mU mL⁻¹) and provided a suitable sensing platform for naked eye detection with increased fluorescence quantum yield (Φ = 3.2%), even compared to a typical TPE-based sensor (Φ = 1.0%), where ALP can be sensed with a detection limit of 0.034 mU mL⁻¹. In addition, P-TPE-TG displayed excellent sensing performance at concentrations from 0 to 50 mU mL⁻¹ in diluted human serum (10%), which offers the capability to exploit ratiometric responses for bioactive substances under practical conditions.

A novel ratiometric fluorescence assay via enzymatically activatable micellization in aqueous solution was devised for quantitative detection of alkaline phosphatase (ALP) activity.