An Aggregation-Induced Phosphorescence-Active “Turn-Off” Nanosensor Based on Ferric-Specific Quenching of Luminescent and Water-Soluble Au(I)–Cysteine Nanocomplexes

Schiff base fluorescent sensor with aggregation induced emission characteristics for the sensitive and specific Fe3+ detection

An aggregation induced emission based compound ((E)-4-((2-hydroxy-5-methoxybenzylidene)amino)benzoic acid) was synthesized through facile Schiff base condensation and characterized by various spectral techniques. The as-prepared compound represented a typical aggregation induced emission behavior in aqueous solution and exploited as a turn-off fluorescent sensor for Fe3+ detection in THF-H2O system (3:7, v/v) with high sensitivity and selectivity. The mechanism of the fluorescence quenching was intensively studied, which was attributed to both dynamic quenching and inner filter effect. The fluorescence probe displayed a highly broad dynamic response range (0.5-500 μM) for selective detection of Fe3+ with a limit of detection of 0.079 μM. The proposed method was successfully employed for detection and quantification of Fe3+ in human urine samples and proved to have potential for practical applications in biological field.

Alginic acid-functionalized silver nanoparticles: A rapid monitoring tool for detecting the technology-critical element tellurium

The increasing global demand for tellurium, driven by its critical role in alloys, photovoltaic devices, and electronics, has raised concerns about its environmental pollution and neurotoxicity. In response, the potential of alginic acid (AA), a renewable, low-cost, and sustainable biopolymer, was explored for the biosynthesis of ultra-small silver nanoparticles (AgNPs) and their application in the detection of tellurium (Te(IV)). The effect of key synthesis parameters on desired physicochemical properties and yield of AgNPs was established to ensure high specificity and sensitivity towards Te(IV). The purified AgNPs with AA surface ligands were utilized to demonstrate a ratiometric absorbance sensor that exhibits excellent linearity and nanomolar-level affinity. This approach achieved a high correlation coefficient of ∼ 0.982, with a low detection limit of about 22 nM. Further investigations into the effect of pH, ionic strength, and organic molecules were conducted to elucidate detection performance and molecular understanding. The detection mechanism relies on the coordination between Te(IV) ions and the carboxylate groups of AA, which initiates aggregation-induced plasmon coupling in adjacent AgNPs. The capability of this analytical method to monitor Te(IV) in real-world water samples features its rapidity, user-friendliness, and suitability for point-of-care monitoring, making it a promising alternative to more complex techniques.

Nanocomposite Materials Based on Polylactide and Gold Complex Compounds for Absorbed Dose Diagnostics in BNCT

In this study, approaches to the synthesis of complex compound of gold with cysteine [AuCys]n for measuring absorbed dose in boron neutron capture therapy (BNCT) were developed. The dependence of the complex particle size on pH were established. Nanocomposite materials based on polylactide containing [AuCys]n particles with an average size of about 20 nm were obtained using the crazing mechanism. The structure of obtained materials was studied by electron microscopy. The release kinetics of [AuCys]n from polymer matrix were investigated. Release of [AuCys]n from the volume of the polymeric matrix had a delayed start-this process began only after 24 h and was characterized by an effective rate constant of 1 μg/h from a 20 mg composite sample. At the same time, in vitro studies showed that the concentration of 6.25 μg/mL was reliably safe and did not reduce the survival of U251 and SW-620 cells.

Zirconium-Directed Supramolecular Self-Assembly of Coenzyme A@GNCs with Enhanced Phosphorescence for Developing Ultrasensitive Tracer Probe of Dipicolinic Acid, a Biomarker of Bacterial Spores

Luminescent gold nanoclusters (GNCs) are a class of attractive quantum-sized nanomaterials bridging the gap between organogold complexes and gold nanocrystals. They typically have a core-shell structure consisting of a Au(I)-organoligand shell-encapsulated few-atom Au(0) core. Their luminescent properties are greatly affected by their Au(I)-organoligand shell, which also supports the aggregation-induced emission (AIE) effect. However, so far, the luminescent Au nanoclusters encapsulated with the organoligands containing phosphoryl moiety have rarely been reported, not to mention their AIE. In this study, coenzyme A (CoA), an adenosine diphosphate (ADP) analogue that is composed of a bulky 5-phosphoribonucleotide adenosine moiety connected to a long branch of vitamin B5 (pantetheine) via a diphosphate ester linkage and ubiquitous in all living organisms, has been used to synthesize phosphorescent GNCs for the first time. Interestingly, the synthesized phosphorescent CoA@GNCs could be further induced to generate AIE via the PO32- and Zr4+ interactions, and the observed AIE was found to be highly specific to Zr4+ ions. In addition, the enhanced phosphorescent emission could be quickly turned down by dipicolinic acid (DPA), a universal and specific component and also a biomarker of bacterial spores. Therefore, a Zr4+-CoA@GNCs-based DPA biosensor for quick, facile, and highly sensitive detection of possible spore contamination has been developed, showing a linear concentration range from 0.5 to 20 μM with a limit of detection of 10 nM. This study has demonstrated a promising future for various organic molecules containing phosphoryl moiety for the preparation of AIE-active metal nanoclusters.

Aggregation-induced emission (AIE)-Based nanocomposites for intracellular biological process monitoring and photodynamic therapy

As a non-invasive visualization technique, photoluminescence imaging (PLI) has found its huge value in many biological applications associated with intracellular process monitoring and early and accurate diagnosis of diseases. PLI can also be combined with therapeutics to build imaging-guided theragnostic platforms for achieving early and precise treatment of diseases. Photodynamic therapy (PDT) as a quintessential phototheranostics technology has gained great benefits from the combination with PLI. Recently, aggregation-induced emission (AIE)-active materials have emerged as one of the most promising bioimaging and phototheranostic agents. Most of AIEgens, however, need to be chemically engineered to form versatile nanocomposites with improved their photophysical property, photochemical activity, biocompatibility, etc. In this review, we focus on three categories of AIE-active nanocomposites and highlight their application progresses in the intracellular biological process monitoring and PLI-guided PDT. We hope this review can guide further development of AIE-active nanocomposites and promote their practical applications for monitoring intracellular biological processes and imaging-guided PDT.

Using bimetallic Au/Cu nanoplatelets for construction of facile and label-free inner filter effect-based photoluminescence sensing platform for sarcosine detection

Herein, we report a facile and label-free method for sensitive and specific determination of prostate cancer biomarker sarcosine via using photoluminescent bimetallic Au/Cu nanoplatelets (AuCu NPs) to construct an inner filter effect (IFE)-based photoluminescence (PL) sensing platform. The AuCu NPs were formed by the cysteine-induced co-reduction reaction, which displayed bright PL with an emission peak at 560 nm. Meanwhile, the Cu(I) doping caused a maximum 25-fold enhancement of quantum yield (QY), compared with the native Au(I) complexes, i.e., from 0.85 to 21.5%. By integrating the AuCu NPs with p-phenylenediamine (PPD) oxidation reaction, an IFE-based sensor for sarcosine detection was constructed. In this method, sarcosine is oxidized under the catalysis of sarcosine oxidase (SOx) to yield H₂O₂. The latter further oxidizes PPD to form 2,5-diamino-N,N'-bis(p-aminophenyl)-l,4-benzoquinone di-imine (PPDox) in the presence of horseradish peroxidase (HRP). The UV-vis absorption spectrum of the PPDox can overlap well with the excitation and emission spectra of the AuCu NPs, resulting in the efficient quenching of the AuCu NPs via the IFE effect. Therefore, this IFE-based AuCu NPs/SOx/PPD/HRP sensing platform can be used for highly sensitive and specific sensing of sarcosine. The sensing platform showed two linear regions of the PL intensity of the AuCu NPs versus the concentration of sarcosine in the range of 0.5-5 μM and 5-100 μM with a detection limit (LOD) of 0.12 μM (S/N = 3). Furthermore, this IFE-based sensing platform could be developed into a paper-based biosensor for simple, instrument-free, and visual detection of sarcosine.

An optical sensing system with ratiometric and turn-off dual-mode of CDs@MnO2 nanosheets for the determination of H2O2 and glucose based on a combination of first-order scattering, fluorescence, and second-order scattering

The optical sensor with ratiometric and turn-off dual modes is constructed to detect H₂O₂ and glucose based on blue fluorescent carbon dots (CDs) and MnO₂ nanosheets with great ability of fluorescence quenching and scattering. Employing CDs@MnO₂ nanosheets nanocomposite as the probe, H₂O₂ is detected by simultaneously collecting first-order scattering (FOS, 353.5 nm), fluorescence (440 nm), and second-order scattering (SOS, 710 nm) under the excitation of 350 nm. H₂O₂ with strong oxidation property can etch the lamellar structure of MnO₂ nanosheets into nano-fragments, which made the fluorescence of CDs in the system recover and the scattering intensity (FOS and SOS) of the system decrease significantly. Therefore, the optical sensor combined FOS and fluorescence signals in ratiometric mode, and SOS signal in turn-off mode to realize sensitive determination of H₂O₂. The linear ranges of ratiometric mode and turn-off mode for H₂O₂ detection were 0.2-40 and 0.2-15 μM, respectively. And the limits of detection (LODs) of two modes were 73 and 104 nM, respectively. Furthermore, the sensor was also successfully applied to the detection of glucose which can react to produce H₂O₂. Satisfactorily, the LODs of this sensor for glucose detection were 95 and 113 nM for ratiometric mode and turn-off mode, respectively. This work not only provides a new method for the accurate detection of H₂O₂ and glucose, but also extends a new idea for the study of the combination of scattering and fluorescence.

Strongly phosphorescent and water-soluble gold(I)-silver(I)-cysteine nanoplatelets via versatile small biomolecule cysteine-assisted synthesis for intracellular hypochlorite detection

In biological systems, abnormal levels of hypochlorite (ClO^-) could result in cell dysfunctions. Herein, we report a facile, one-step and green approach based on the versatile small biomolecule cysteine both serving as reducing agent and ligand for synthesizing the strongly photoluminencent and water-soluble Au(I)-Ag(I)-cysteine complexes nanoplatelets (Au(I)-Ag(I)-Cys nanoplatelets) for intracellular hypochlorite detection. Multiple spectroscopic and microscopical tools have been used to characterize the resultant Au(I)-Ag(I)-Cys nanoplatelets. It was found that with the cysteine-assisted synthesis approach, the Ag(I) doping to the Au(I) complexes could form the supramolecular organometallic nanoplatelets. Inside, the Au(I)-Ag(I) metallophilic interactions showing an Au to Ag charge transfer property were formed, thereby enhancing the photoluminescence (PL) intensity via the charge transfer from the bioligand's S to the metal-metal center. The quantum yield (QY) was measured to show a maximum 16-fold enhancement (i.e., from 0.85 to 13.8%). Interestingly, in the presence of ClO^-, the metal-thiolate ligand structure of the as-synthesized Au(I)-Ag(I)-Cys nanoplatelets could be oxidatively damaged, causing the PL quenching, thereby producing the effect of biorecognition towards ClO^- anions. The ClO^--induced PL quenching produced two linear regions at ClO^- concentrations of 0.01-5.0 μM and 5.0-1000 μM with a limit of detection (LOD) of 8.0 nM (S/N = 3). The ClO^--induced PL quenching was specific over the other typical reactive oxygen species (ROS) and the potential interfering substances in biological samples. In addition, the Au(I)-Ag(I)-Cys nanoplatelets had good biocompatibility. Thus, they could be further developed as a biosensor for detecting endogenous ClO^- anions in living cells.

Seeking brightness from nature: Sustainable AIE macromolecule with clustering-triggered emission of xanthan gum and its multiple applications

Unconventional biomacromolecule luminescent agents have attracted widespread attention due to the potential applications in diverse fields. In order to explore new luminescent agents and gain a comprehensive understanding of their emission mechanism, the emission behavior of xanthan gum was investigated. Xanthan gum shown obvious aggregation-induced emission (AIE) characteristics in concentration solution. Moreover, xanthan gum has shown potential values in intracellular imaging and can be used as a biosensor for detecting Fe³⁺ and Cu²⁺ in human serum.

Photoluminescence of Tilapia skin collagen: Aggregation-induced emission with clustering triggered emission mechanism and its multiple applications

There is an urgent need for natural sources of aggregation-induced emission (AIE) materials which have good water solubility, biocompatibility, and can be produced in large quantities. Here, Tilapia skin collagen (Tsc) is a very abundant protein in nature, with solid-phase and solution-state fluorescence emission effect and its multiple applications was explored. Due to Tsc was in high concentration or aggregation state which shown AIE property. This obvious emission can be account for clustering-triggered emission (CTE) mechanism. The photoluminescence property of Tsc not only provide a deeper understanding of the emission characteristics of proteins, but also has important guiding significance for further elucidating the basis of fluorescence properties.

Phosphorescent MoS2 quantum dots as a temperature sensor and security ink

Currently, few phosphorescent materials (PMs) possess a long phosphorescence lasting time and have potential for application in chemical sensors. Herein, we disclose that the incorporation of few-layer molybdenum disulfide quantum dots (FL-MoS₂ QDs) into poly(vinyl alcohol) (PVA) matrices leads to the emission of bright green phosphorescence with a long lasting time of 3.0 s and a phosphorescence quantum yield of 20%. This enhanced phosphorescence originates from the formation of O-H⋯S hydrogen bonding networks between the rich sulfur sites of the FL-MoS₂ QDs and the hydroxyl groups of the PVA molecules, which not only rigidifies the vibration modes of the FL-MoS₂ QDs but also provides an oxygen barrier. Further investigations reveal that the FL-MoS₂ QD/PVA composites exhibit a longer phosphorescence lasting time than N,S-doped carbon dots, few layer tungsten disulfide quantum dots, Rhodamine 6G, and Rhodamine B in PVA matrices. Since heat efficiently induced the removal of water moisture from PVA matrices, the FL-MoS₂ QD/PVA composites could be implemented for phosphorescence turn-on and naked-eye detection of temperature variations ranging from 30 to 70 °C. By contrast, the carbon dot/PVA composites were incapable of sensing environmental temperature due to their weak hydrogen bonding with the hydroxyl groups of PVA matrices. Additionally, this study reveals the potential of the FL-MoS₂ QD/PVA composites as an advanced security ink for anti-counterfeiting and encryption applications. The given results could open a new direction for potential application of two-dimensional quantum dots in phosphorescence-based sensors and security inks.

Fluorescence Emission Behaviors of the L-Cysteine/Au(I) Complex in a Cyclodextrin-Based Metal-Organic Framework

Aggregation-induced emission (AIE) molecules are nonemissive in dilute solution but emit intensely upon aggregation in complete contrast to aggregation-caused quenching (ACQ) molecules. The emission of ACQ molecules, such as fluorescein, that have been encapsulated into the hydrophilic nanopores in a cyclodextrin-based metal-organic framework (CD-MOF) was reported to be enhanced due to the disappearance of concentration quenching and the restriction of thermal motion. However, the contribution of the restriction of thermal motion in CD-MOF could not be elucidated. In this study, an AIE-active L-cysteine/Au(I) (L-Cys/Au(I)) complex was synthesized and introduced into the nanopores of CD-MOF via a co-crystallization method. We determined the amount and chemical composition of the L-Cys/Au(I) complex in CD-MOF. The fluorescence intensity of the L-Cys/Au(I)@CD-MOF composite was investigated. The L-Cys/Au(I) complex that was synthesized from Au(III) chloride and L-cysteine was found to be a linear oligomer consisting of Cys5Au4. For the L-Cys/Au(I)@CD-MOF composite with a L-Cys/Au(I) complex of 0.45 per hydrophilic nanopore, the total fluorescence intensity of the isolated L-Cys/Au(I) complex in CD-MOF exceeded that of the L-Cys/Au(I) complex in the solid-state due to the restriction of the thermal motion without the aggregation of the complex.

Fluorescent linear polyurea based on toluene diisocyanate: Easy preparation, broad emission and potential applications

In contrast to conventional fluorescent polymers featured by large conjugation structures, a new class of fluorescent polymers without above conjugations are gaining constant interest owing to their significant academic importance and promising applications in diverse fields. These unconventional fluorescent polymers are in general composed of heteroatoms (e.g. N, O, P, and S) under different forms. Here we report our recent study on polyurea, prepared by a very simple one step precipitation polymerization of toluene diisocyanate in a binary solvent of water-acetone. This polyurea, basically consisting of phenyl ring and urea group, shows fluorescent emission in a broad concentration range, from very low (10-5 mg/mL) to its solubility limit (50 mg/mL), and in a wide range of emission wavelength from UV to visible regions of up to 500 nm under varied excitation wavelength. The emission behaviors were fully studied under different concentrations and excitations. It was concluded that the emission in UV region was intrinsic due to the conjugation between the phenyl and the adjacent urea unit; while the emission in visible region, strongly excitation dependent, was caused by the cluster formation of the molecular chains, in accordance with the cluster-triggered-emission (CTE) mechanism. The formation of the cluster was tested through dynamic light scattering, FTIR and UV absorbance. Tested in presence of different metal ions, Fe3+ demonstrated a quenching effect with high selectivity. Based on this study, different paper-based sensors were designed to detect Fe3+, H2O2 in bioanalysis and for data encryption. This work provides a simple way to prepare a polyurea, a novel type of unconventional fluorescent polymer, with high emission performance distinct from its known analogues.