Fluorescence Response Research Articles

Role of Oxygen Defects in Eliciting a Divergent Fluorescence Response of Single-Walled Carbon Nanotubes to Dopamine and Serotonin.

Modulating the optical response of fluorescent nanoparticles through rational modification of their surface chemistry can yield distinct optical signatures upon the interaction with structurally related molecules. Herein, we present a method for tuning the fluorescence response of single-walled carbon nanotubes (SWCNTs) toward dopamine (DA) and serotonin, two structurally related monoamine-hydroxylated aromatic neurotransmitters, by introducing oxygen defects into (6,5) chirality-enriched SWCNTs suspended by sodium cholate (SC). This modification facilitated opposite optical responses toward these neurotransmitters, where DA distinctly increased the fluorescence of the defect-induced emission of SWCNTs (D-SWCNTs) 6-fold, while serotonin notably decreased it. In contrast, pristine, defect-free SWCNTs exhibited similar optical responses to both neurotransmitters. The underlying mechanisms for the divergent fluorescence response were found to be polydopamine (PDA) surface adsorption in the case of the fluorescence enhancement in response to DA, while the fluorescence decrease in response to serotonin was attributed to enhanced solvent relaxation effects in the presence of defects. Importantly, the divergent optical response of D-SWCNTs to DA and serotonin, via the introduction of defects, was validated in complex biological environments such as serum. Further, the generality of our approach was confirmed by the demonstrations of a divergent fluorescence response of D-SWCNTs suspended by an additional dispersant, namely lipid-polyethylene glycol (PEG). This study offers promising avenues for the broad applicability of surface functionalization of SWCNTs to achieve divergent responses toward structurally related molecules and advance applications in sensing, imaging, and diagnostic technologies.

A new Conjugated mesoporous polymer as fluorescence sensor for the detection of nerve agent simulant dimethyl chlorophosphonate via specific nucleophilic substitution reaction

Conjugated micro/mesoporous polymers (CMPs) represent a category of porous organic materials formed via covalent bonds. Here, DAC-TFP CMP was synthesized using 3,6-diaminocarbazole (DAC) and 2-hydroxy-1,3,5-benzenetricarbaldehyde (TFP) as building blocks. DAC-TFP CMP is a porous conjugation polymer with remarkable thermal and chemical stability. DAC-TFP CMP suspension demonstrates selective "on-off" fluorescence response towards nerve agent simulant dimethyl chlorophosphonate (DMCP) in 1,4-dioxane with exceptionally low detection limits. DMCP and DAC-TFP CMP undergo a nucleophilic substitution reaction, leading to the formation of an N-P bond between N atom on carbazole of DAC-TFP CMP and P atom of DMCP. The new polymer DAC-TFP CMP@DMCP has electron donor-acceptor structure and the fluorescence quenching can be ascribed to the intramolecular charge transfer (ICT) from DAC-TFP CMP unit to DMCP group, as supported by XPS results and DFT calculation. Upon the addition of DMCP to the 1,4-dioxane suspension of DAC-TFP CMP, a subtle blue shift is observed in both the fluorescence emission spectra and UV-vis absorption spectra, providing further validation of the ICT mechanism. DAC-TFP CMP shows excellent recoveries in detecting DMCP in both soil and pesticide samples containing mesotrione and atrazine, highlighting its strong potential as a reliable chemosensor for DMCP detection and analysis.

RhB intercalated Zr(VI)-bipyridine architecture for efficient ratiometric fluorescent response toward Cr(VI) analyte and decontamination of Cr(VI) and reactive dye via photochemical REDOX

It is extremely‌ imperative to enhance the sensing accuracy of water-stable Zr-MOFs for Cr(VI), because the single emission signal in a sole Zr-MOF is rather vulnerable to external factors. Interpolation of guest luminous species into Zr-MOF crystals presents a feasible way to achieve dual-emission signals. In this contribution, a highly water-stable Zr-MOF (Zr-bcu-22bipy44dc) which emits bright-blue fluorescence was deployed as matrix to intercalate fluorochrome Rhodamine B (RhB), creating a novel dual-emission (at 410 and 580 nm) luminescent platform, RhB@Zr-MOF. Then, it was utilized as a fluorescence probe to accurately detect trace-level Cr(VI) ions, by assessing the relative fluorescence intensity (IR) difference between the host Zr-MOF (I410) and the guest RhB (I580). Interestingly, the septal interpolation of luminescent species within Zr-MOF matrix effectively suppresses aggregation-induced quenching (ACQ), which tends to occur easily for RhB molecules. Moreover, its determined detection limits (DL) for CrO42- (6.13 ppb) and Cr2O72- (10.04 ppb) ions have been remarkably enhanced by approximately 4.92-fold and 3.66-fold, respectively, compared to the initial Zr-MOF (30.11 and 36.76 ppb). DFT and TD-DFT calculations have confirmed that the orange-yellow photoluminescence exhibited by RhB@Zr-MOF should be attributed to the PET process inherent to the intercalated RhB molecules, rather than the commonly accepted intermolecular Förster resonance energy transfer (FRET) mechanism or the photo-induced electron transfer (PET) effect previously identified by us. Efficient antenna effect of RhB module synergizes with Zr-MOF's appropriate band structure, also enables RhB@Zr-MOF convincing ability to photochemically deoxidize Cr(VI) and bleach reactive dark blue K-R (K-R)

Exploring the rhodanine universe: Design and synthesis of fluorescent rhodanine-based derivatives as anti-fibrillar and anti-oligomer agents against α-synuclein and 2N4R tau

Tau and α-synuclein (α-syn) are prone-to-aggregate proteins that coprecipitate in the brains of Alzheimer’s disease (AD) and Parkinson’s disease (PD) patients. The early-stage oligomers and protofibrils of tau are believed to be strongly linked to human cognitive impairment while the toxic α-syn oligomers are associated with behavioral motor deficits. Therefore, concurrent targeting of both proteinaceous aggregates and their lower dense oligomers are very challenging. Herein, rhodanine-based compounds were designed and synthesized to tackle the fibrils and oligomers of tau and α-syn proteins. In particular, the indole-containing rhodanines 5l and 5r displayed significantly high anti-aggregation activity towards α-syn fibrils by reduction of the thioflavin-T (ThT) fluorescence to lower than 5 %. Moreover, 5r showed a remarkable decrease in the fluorescence of thioflavin-S (ThS) when incubated with the non-phosphorylated tau 0N4R and 2N4R as well as the hyperphosphorylated tau isoform 1N4R, respectively. Transmission electron microscopy (TEM) analyses validated the powerful anti-fibrillar activity of 5l and 5r towards both protein aggregates. In addition, both 5l and 5r highly suppressed 0N4R tau and α-syn oligomer formation using the photo-induced cross-linking of unmodified Protein (PICUP) assay. The fluorescence emission intensity of 5l was quenched to almost half in the presence of both protein fibrils at 510 nm. 5r showed a similar fluorescence response upon binding to 2N4R fibrils while no quenching effect was observed with α-syn aggregates. Ex vivo disaggregation assay using extracted human Aβ plaques was employed to confirm the ability of 5l and 5r to disaggregate the dense fibrils. Both inhibitors showed no promising activity towards the cell-based α-syn inclusion formation. However, another indolyl derivative 5j prevented the α-syn inclusion at 5 µM. Collectively, the indolyl-rhodanine scaffold could act as a building block for further structural optimization to obtain dual targeting disease-modifying candidates for AD and PD.

A facile synthesis of polyethyleneimine based fluorescent polymeric nanorods using vitamin B6 cofactor as cross-linker for ratiometric detection of doxorubicin.

Polyethyleneimine (PEI) based fluorescent polymeric nanorods with high quantum yield (87.21%) were synthesized by crosslinking and self-assembly of PEI by vitamin B6 cofactor pyridoxal 5'-phosphate (PLP). The fluorescent PEIPLP polymeric nanorods were employed for the ratiometric detection of doxorubicin (DOX). With the addition of DOX to the PEIPLP nanorods, the fluorescent intensity was decreased at 510nm and concomitantly enhanced at 590nm due to the fluorescence resonance energy transfer (FRET) process. The selective and specific ratiometric fluorescence response from the PEIPLP nanorods can be employed to detect DOX down to 10 nM. Thepractical utility of the PEIPLP nanorods was examined by detecting DOX in human serum.

High-Performance Chemigenetic Potassium Ion Indicator.

Potassium ion (K+) is the most abundant metal ion in cells and plays an indispensable role in practically all biological systems. Although there have been reports of both synthetic and genetically encoded fluorescent K+ indicators, there remains a need for an indicator that is genetically targetable, has high specificity for K+ versus Na+, and has a high fluorescent response in the red to far-red wavelength range. Here, we introduce a series of chemigenetic K+ indicators, designated as the HaloKbp1 series, based on the bacterial K+-binding protein (Kbp) inserted into HaloTag7 self-labeled with environmentally sensitive rhodamine derivatives. This series of high-performance indicators features high brightness in the red to far-red region, large intensiometric fluorescence changes, and a range of Kd values. We demonstrate that they are suitable for the detection of physiologically relevant K+ concentration changes such as those that result from the Ca2+-dependent activation of the BK potassium channel.

Synthesis of π-Extended Imidazo[1,2-a]quinolines via Carboxylic Acid-Assisted Ru(II)-Catalyzed Dual C-H Activation and Alkyne Annulation.

Ru(II)-catalyzed, carboxylic acid-assisted oxidative annulation of N-aryl azoles with alkynes via double C-H activation to produce highly functionalized π-extended imidazo[1,2-a]quinolines is reported. The reaction features a broad substrate generality and tolerates various biologically relevant scaffolds. Interestingly, annulated products showed strong fluorescence properties and an AgIE effect and exhibited a selective fluorescent response toward the Cu2+ ion. Further photocatalytic properties of the product are demonstrated in the photochemical coupling of azoles and arenes.

Stimuli-Responsive Photoluminescent Molecular Tweezers for Highly Enantioselective Discrimination of Chiral Primary Amines.

To address the challenge of chiral recognition in terms of efficiency and generality, we propose a novel fluorescence sensing approach by rationally designing metal-ion-responsive chiral molecular tweezers. The flexible and adaptable molecular tweezers enable facile recognition of 31 structurally varied chiral primary amine compounds, including amino acids, amino acid esters, and chiral amines. Notably, upon stimulation by zinc ions, the chiral molecular tweezers demonstrate a higher enantioselective fluorescence response. Combined density functional theory calculations reveal that the chiral sensing mechanism relies on differential reaction rates and potential hydrogen-bonding interactions between the two enantiomers and the chiral receptor, which results in one of the enantiomers forming a more abundant, stable, and structurally rigid complex with the receptor, resulting in a significant increase in the fluorescence intensity and enantioselectivity. The stimuli-responsive molecular tweezers approach provides a novel strategy for precise stereocontrol and universality of chiral recognition, offering a promising tool for applications in various fields.

Deep-Red and Near-Infrared Compact Cyanine Dyes for Sensitive NAD(P)H Sensing in Live Cells and Kidney Disease Tissues.

Cyanine dyes constructed for NAD(P)H near-infrared sensing utilize extended π-conjugation but often exhibit delayed fluorescence responses to NAD(P)H due to reduced positive charge density in 3-quinolinium acceptors. This study introduces deep-red and near-infrared compact cyanine dyes represented by probes A and B for mitochondrial NAD(P)H detection in live cells. Probes A and B feature a unique structural design with a double bond connection linking 3-quinolinium to strategically positioned 1-methylquinolinium acceptor units at 2- and 4-positions, correspondingly. Probe A absorbs at 359 and 531 nm, while probe B absorbs at 324 and 370 nm, emitting subtle fluorescence at 587 and 628 nm, respectively, with no NADH present. Upon NADH exposure, probes A and B exhibit significant emission enhancements at 612 and 656 nm, correspondingly, attributed to the efficient reduction of 3-quinolinium units to electron-donative 1-methyl-1,4-dihydroquinoline units. Probe B, chosen for its near-infrared emission and fast response to NAD(P)H, effectively monitored dynamic intracellular NAD(P)H levels throughout diverse experimental conditions. In HeLa cells, minimal basal fluorescence increased upon NADH stimulation. It also identified increased NAD(P)H levels following chemical treatments with acesulfame potassium, cisplatin, carboplatin, and temozolomide, CoCl2-induced hypoxia, and TLR4 activation in macrophages and in disease models of kidney pathology, where diseased tissues exhibited higher fluorescence than normal tissues. In fruit fly larvae under starvation conditions, probe B tracked NAD(P)H increases triggered by exogenous NADH, demonstrating its in vivo applicability for metabolic studies. These findings highlight probe B's utility in elucidating dynamic NAD(P)H fluctuations in diverse biological contexts, offering insights into mitochondrial function and cellular metabolism.

NIR‐II Fluorescence/Photoacoustic Dual Ratiometric Probes with Unique Recognition Site for Quantitatively Visualizing H2S2in Vivo

AbstractHydrogen persulfide (H2S2) plays a significant role in redox biology and signal transduction; therefore, quantitative visualization of H2S2 in the deep tissue of living organisms is essential for obtaining reliable information about relevant pathophysiological processes directly. However, currently reported H2S2 probes are unsuitable for this purpose because of their poor selectivity for many polysulfide species or their short wavelength, which hinders precise imaging in deep tissues. Herein, for the first time, we report a unique H2S2‐mediated dithiole formation reaction. Based on this reaction, we construct the first NIR‐II fluorescence (FL) and photoacoustic (PA) dual‐ratiometric probe (NIR‐II‐H2S2) for quantitatively visualizing H2S2 in vivo. This probe shows dual‐ratiometric NIR‐II fluorescence (I840/I1000, 107‐fold) and photoacoustic (PA800/PA900, 6.5‐fold) responses towards Na2S2 species with high specificity, excellent sensitivity (1.8 nM), improved water solubility, and deep‐tissue penetration. More importantly, using NIR‐II dual‐ratiometric FL/PA imaging, we successfully demonstrated that the probe could be used to accurately quantify the fluctuating H2S2 levels in the liver‐injury mouse models induced by lipopolysaccharides or metformin drugs. Overall, this study not only presents a promising tool for H2S2‐related pathological research, but also provides a unique recognition site that may be generalized for designing more useful H2S2 imaging agents in the future.

Ultrafast ppb-Level Detection of Nitro-Furan Based Antibiotics in Aqueous Medium by an Oxadiazole-Grafted Luminescent Sensor.

This work is primarily focused on the utilization of an oxadiazole grafted 2D luminescent metal-organic framework, {[Zn2(4-tpom)2(oxdz)2].4H2O}n (1), in the detection of trace amounts of nitrofuran-based antibiotics such as nitrofurantoin (NFT) and nitrofurazone (NFZ) in aqueous medium. The π-electron rich moieties and the H-bond accepting sites in the dual linkers (4-tpom and oxdz2-) enable the framework to interact efficiently with NFT and NFZ exhibiting a turn-off fluorescence response with the respective KSV (6.55 x 104 M-1 and 4 x 104 M-1) and LOD (89 ppb and 78 ppb) values. Furthermore, the efficiency of 1 in sensing commercially sold antibiotic tablet, Martifur-100 (contains nitrofurantoin as an active ingredient), is demonstrated as an example with an LOD value of 277 ppb. Its multicycle reusability and the ultrafast response toward these antibiotics are also reported. The nature of quenching of 1 by NFT and NFZ has been investigated with experimental and theoretical considerations.

Synthesis and Characterizations of Dibenzo-Fused Perioctacene.

Dibenzoperioctacene (DBPO) with extended zigzag edges was synthesized and unambiguously characterized by a combination of nuclear magnetic resonance (NMR), mass spectrometry, and single-crystal X-ray diffraction analysis. Variable-temperature (VT) NMR analysis indicated the closed-shell character of DBPO, yet an electron paramagnetic resonance (EPR) signal was observed at room temperature suggesting its potential open-shell diradicaloid nature. The bond lengths in the single-crystal structure of DBPO aligned more closely with those of open-shell teranthene than closed-shell bisanthene. Spin-unrestricted density functional theory (DFT) calculations using various methods supported that ground state of DBPO might be on the borderline between closed- and open-shell singlet states, with a large singlet-triplet energy gap (ΔEST), consistent with the VT-NMR and EPR results. UV-vis-near infrared (NIR) absorption spectrum showed the longest-wavelength peak at 905 nm, marking the NIR optical properties of DBPO. DBPO exhibited a tendency to react with atmospheric oxygen, which additionally hinted at its possible open-shell character. Furthermore, the oxidized species of non-fluorescent DBPO exhibited strong emission at 820 and 915 nm, which opens its potential for oxygen detection via a "turn-on" NIR fluorescence response.

Precision Synthesis of Conjugated Polymer Films by Surface-Confined Stepwise Sonogashira Cross-Coupling.

Thin films of poly(arylene ethynylene)-conjugated polymers, including low-energy-gap donor-acceptor polymers, can be prepared via stepwise polymerization utilizing surface-confined Sonogashira cross-coupling. This robust and efficient polymerization protocol yields conjugated polymers with a precise molecular structure and with nanometer-level control of the organization and the uniform alignment of the macromolecular chains in the densely packed film. In addition to high stability and predictable and well-defined molecular organization and morphology, the surface-confined conjugated polymer chains experience significant interchain electronic interactions, resulting in dominating intermolecular π-electron delocalization which is primarily responsible for the electronic and spectroscopic properties of polymer films. The fluorescent films demonstrate remarkable performance in chemosensing applications, showing a turn-off fluorescent response on the sub-ppt (part per trillion) level of nitroaromatic explosives in water. This unique sensitivity is likely related to the enhanced exciton mobility in the uniformly aligned and structurally monodisperse polymer films.

An Ultrasensitive Self‐Calibrating Terbium Metal Organic Framework for the Detection of Amphotericin B

ABSTRACTWe successfully synthesized a 3D porous lanthanide metal–organic framework, [Tb (obdb)][Tb1/3(H2O)7/3]·NMP (Tb‐MOF) with hydrated terbium ions in the pores by solvothermal method using 4′,4″′‐oxybis[1,1′‐biphenyl]‐3,5‐dicarboxylic acid (H4obdb) as ligand. It is worth mentioning that Tb‐MOF exhibits excellent performance in structural stability and fluorescence response. Even after soaking in various solvents and pH solutions for 3 months, Tb‐MOF can maintain its structural integrity and excellent stability. The fluorescence spectra show that Tb‐MOF not only exhibits the luminescence of the ligand centered at 368 nm (IL), but also emits the characteristic emissions of the metal terbium, among which the luminescence at 542 nm is the strongest. In the detection of antibiotic amphotericin B (AB), Tb‐MOF showed significant detection efficiency. Upon increasing the concentration of AB, the fluorescence intensity at 542 nm gradually decreased, whereas the fluorescence at 368 nm decreased rapidly. The I542/IL value showed a very high linear correlation with AB concentration, with the slope reaching 1.29 × 108 M−1 (0–100 μM). In the field of fluorescent sensors for AB detection, Tb‐MOF is notable not only for its impressively low LOD (limt of detection) of 0.072 nM but also for pioneering the application of a self‐calibrating ratio‐based detection method. To better elucidate this fluorescence sensing phenomenon, we also conducted a detailed discussion of the sensing mechanism for AB.

A Novel Rhodamine B Fluorescent Probe Derived from Carboxymethyl Chitosan for the Selective Detection of Fe3.

In this study, we synthesized a fluorescent material by modifying the C-2 amino group of carboxymethyl chitosan with a rhodamine B derivative, which was proposed and demonstrated using 1H NMR and FT-IR measurements. A series of experiments including selectivity, sensitivity, reversibility, pH, and water content were conducted to investigate the fluorometric and colorimetric properties of the grafted polymer. Utilizing a Fe3+-induced ring-opening mechanism of the rhodamine B spirolactam, we found that the grafted polymer exhibited a highly selective fluorescence response to Fe3+, with enhanced fluorescence at 583 nm compared to other tested metal ions and anions, accompanied by the characteristic absorption peak of rhodamine B that appeared at 561 nm with a noticeable color change from colorless to pink, facilitating visual observation. Additionally, the modified probe, composed of carboxymethyl chitosan, was easily regenerated through treatment with EDTA.

A Tandem-Locked Fluorescent Probe Activated by Hypoxia and a Viscous Environment for Precise Intraoperative Imaging of Tumor and Instant Assessment of Ferroptosis-Mediated Therapy.

Noninvasive fluorescence detection of tumor-associated biomarker dynamics provides immediate insights into tumor biology, which are essential for assessing the efficacy of therapeutic interventions, adapting treatment strategies, and achieving personalized diagnosis and therapy evaluation. However, due to the absence of a single biomarker that effectively reflects tumor development and progression, the currently available optical diagnostic agents that rely on "always-on" or single pathological activation frequently show nonspecific fluorescence responses and limited tumor accumulation, which inevitably compromises the accuracy and reliability of tumor imaging. Herein, based on intramolecular charge transfer (ICT) and twisted intramolecular charge-transfer (TICT) hybrid mechanisms, we report a tandem-locked probe, NTVI-Biotin, for simultaneously specific imaging-guided tumor resection and ferroptosis-mediated tumor ablation evaluation under the coactivation of nitro reductase (NTR)/viscosity. The dual-stimulus-responsive design strategy ensures that NTVI-Biotin exclusively activates near-infrared (NIR) fluorescence signals upon interaction with both NTR and elevated viscosity levels through triggering ICT on while inhibiting the TICT process. Meanwhile, functionalization with a tumor-targeting hydrophilic biotin-poly(ethylene glycol) moiety enhances tumor accumulation. The probe's dual-response and tumor-targeting design minimizes nonspecific tissue activation, allowing for precise tumor identification and lesion removal with a superior tumor-to-normal tissue (T/N > 6) ratio. More importantly, NTVI-Biotin was capable of evaluating ferroptosis-mediated chemotherapeutics by real-time monitoring of the alternations of NTR/viscosity levels. The results reveal that the increased tumor signals of NTVI-Biotin following the combination of ferroptosis and chemotherapy correlate well with the tumor growth inhibition, demonstrating the potential of NTVI-Biotin to assess therapeutic efficacy.

Fluorometric detection of quinolones via AIE and FRET with terbium-doped carbon dots and copper nanoclusters

Terbium and nitrogen co-doped carbon dots (Tb@N-CDs), combined with α-lipoic acid-functionalized copper nanoclusters (LA@CuNCs), were proposed for the ratiometric detection of quinolone (QA) antibiotics. In this system, Tb@N-CDs facilitate the aggregation of LA@CuNCs, enhancing its fluorescence emission at 670 nm via aggregation-induced emission enhancement (AIEE). Meanwhile, the fluorescence emission of Tb@N-CDs at 460 nm diminishes due to Förster resonance energy transfer (FRET). Upon the introduction of QA, the binding between Tb3+ ions and N-CDs weakens, disrupting both AIEE and FRET processes. This disruption results in a reduction in fluorescence emission at 670 nm and a concurrent increase at 460 nm. The fluorescence response ratio (F460/F670) increases with higher concentrations of ciprofloxacin (CFX), demonstrating a linear range from 0.008 to 120 μmol L−1 and LOD of 1.6 nmol L−1. The method successfully detected CFX in milk and urine samples, achieving recoveries between 97.7 % and 103.8 %, RSD of less than 3.79 %.

An ultrasensitive lysosome-targeting NIR fluorescence probe for detection of hydroxyl radical during ferroptosis and cuproptosis

Hydroxyl radical (•OH) is one of the most destructive reactive oxygen species in biosystems, mainly produced by the participation of transition metals. Lysosomes, the major metabolic center of intracellular metals, may accelerate the generation of •OH by metal-participated reactions due to their acidic microenvironment, which may make lysosomes a major intracellular site for •OH production. In this work, an ultrasensitive NIR lysosome-targeting •OH fluorescence probe, Lyso-OH, was developed for in situ detection of •OH in lysosomes. The reaction of Lyso-OH and •OH leads to a large spectroscopic red-shift and a significant NIR fluorescence response at 655 nm. Such large changes in π-conjugation and spectroscopic properties can achieve an extremely low background fluorescence, which is helpful to obtain a high-contrast and ultrasensitive NIR fluorescence response, enabling Lyso-OH to detect the trace •OH produced by autoxidation of low-valent metals (e.g. Fe2+ and Cu+). Lyso-OH has good lysosome-targeting ability and has been used for the fluorescence imaging of two transition metal-dependent regulated cell death processes, ferroptosis and cuproptosis. The results revealed that both ferroptosis and cuproptosis were accompanied by lysosomal •OH level increase. Moreover, Lyso-OH was also capable of monitoring the •OH level fluctuations in mice models of inflammation and tumor. The good analytical performance of Lyso-OH may allow it to be widely used in more •OH-associated physiological and pathological processes.

Bioinspired peptide sensors with tailorable structure for specific and in-situ tracking of Hg2+ biodistribution in living cells upon acute exposure

Metal-biomolecule interactions that are ubiquitous in nature provide fundamental knowledge and rich structural motifs for the development of functional molecules and smart sensors. In this work, inspired by the active sites in metalloproteins, a biomimetic peptide sensor was designed for the selective recognition and activatable sensing of Hg2+ in living biosystems. Tetraphenylethylene (TPE) with typical aggregation-induced emission (AIE) behavior, was introduced as the activatable signal transducer to enable high signal-to-background signaling. The tailorable side chains and flexible peptide linkage were exploited to tune the coordination affinity, selectivity, and fluorescence response toward Hg2+. Benefiting from the rapid response (1 min), high specificity and nanomolar sensitivity, the peptide sensor allows investigating the mechanism of acute toxicity of Hg2+. Capable of penetrating plasma membrane, the peptide sensor revealed the dosage-dependent and dynamic subcellular biodistribution behavior of Hg2+. The finding that Hg2+ preferentially accumulates and rapidly enriches in nucleoli of cells upon short exposure, evidences the adverse effect toward ribosome biogenesis and the resultant genetic deficiencies. These results highlight the peptide sensors as promising tools for not only on-site detection, but also studying the cell biology and toxicology of this metal ion in living biosystems.

A Ratiometric Fluorescence Probe for Visualized Detection of Heavy Metal Cadmium and Application in Water Samples and Living Cells.

Heavy metal cadmium (II) residuals have inflicted severe damage to human health and ecosystems. It has become imperative to devise straightforward and highly selective sensing methods for the detection of Cd2+. In this work, a ratiometric benzothiazole-based fluorescence probe (BQFA) was effortlessly synthesized and characterized using standard optical techniques for the visual detection of Cd2+ with a change in color from blue to green, exhibiting a significant Stokes shift. Moreover, the binding ratio of BQFA to Cd2+ was established as 1:1 by the Job's plot and was further confirmed by FT-IR and 1HNMR titrations. The ratiometric fluorescence response via the ICT mechanism was confirmed by DFT calculations. Furthermore, the limit of detection for detecting Cd2+ was determined to be 68 nM. Furthermore, it is noteworthy that BQFA showed good performance in real water samples, paper strips, smartphone colorimetric identification, and cell imaging.