Selective Detection of Cu+ Ions in Live Cells via Fluorescence Lifetime Imaging Microscopy

Visualizing DNA/RNA, Proteins, and Small Molecule Metabolites within Live Cells

Live cell imaging is essential for obtaining spatial and temporal insights into dynamic molecular events within heterogeneous individual cells, in situ intracellular networks, and in vivo organisms. Molecular tracking in live cells is also a critical and general requirement for studying dynamic physiological processes in cell biology, cancer, developmental biology, and neuroscience. Alongside this context, this review provides a comprehensive overview of recent research progress in live-cell imaging of RNAs, DNAs, proteins, and small-molecule metabolites, as well as their applications in molecular diagnosis, immunodiagnosis, and biochemical diagnosis. A series of advanced live-cell imaging techniques have been introduced and summarized, including high-precision live-cell imaging, high-resolution imaging, low-abundance imaging, multidimensional imaging, multipath imaging, rapid imaging, and computationally driven live-cell imaging methods, all of which offer valuable insights for disease prevention, diagnosis, and treatment. This review article also addresses the current challenges, potential solutions, and future development prospects in this field.

Isolation of a copper photocatalyst on a metal-organic cage for the sulfonylation of aryl halides resulting from visible-light-mediated C(sp2)-S cross-coupling

A Ce-based metal-organic tetrahedron was assembled for preserving the uncoordinated nature of 2,2'-bipyridyl groups to form a Cu-based photocatalyst, which protected CuI centers from intermolecular deactivation and showed high photocatalytic activity for the visible-light-mediated C(sp²)-S cross-coupling.

Fluorescence and Lifetime Imaging of Endoplasmic Reticulum Polarity Change During Ferroptosis

As a new form of regulated cell death, ferroptosis is closely related to various diseases. Tracing ferroptosis related biological behavior is helpful to better understand this process and its related biology. Considering that ferroptosis is featured with remarkable lipid peroxidation which can easily change the membranes' compositions and structures, it is potential to detect intracellular environmental changes for direct assessment of ferroptosis. In view of the close relationship between endoplasmic reticulum (ER) and ferroptosis, we designed an ER-targeted and polarity-sensitive fluorescent probe SBD-CH, which has superior photostability and can respond to polarity with high selectivity without the affection of viscosity. SBD-CH can monitor the trend of ER polarity during ferroptosis by confocal laser scanning microscopy (CLSM), and analyze the distribution of polarity in ferroptosis by fluorescence lifetime imaging microscopy (FLIM). During Erastin induced ferroptosis, the polarity of ER in HT-1080 cells increased and the polarity distribution in ER was more dispersed. Our work provides an effective strategy for evaluating the process of ferroptosis by monitoring the changes of ER polarity.

Small-Molecule Fluorescent Probes for Binding- and Activity-Based Sensing of Redox-Active Biological Metals

Although transition metals constitute less than 0.1% of the total mass within a human body, they have a substantial impact on fundamental biological processes across all kingdoms of life. Indeed, these nutrients play crucial roles in the physiological functions of enzymes, with the redox properties of many of these metals being essential to their activity. At the same time, imbalances in transition metal pools can be detrimental to health. Modern analytical techniques are helping to illuminate the workings of metal homeostasis at a molecular and atomic level, their spatial localization in real time, and the implications of metal dysregulation in disease pathogenesis. Fluorescence microscopy has proven to be one of the most promising non-invasive methods for studying metal pools in biological samples. The accuracy and sensitivity of bioimaging experiments are predominantly determined by the fluorescent metal-responsive sensor, highlighting the importance of rational probe design for such measurements. This review covers activity- and binding-based fluorescent metal sensors that have been applied to cellular studies. We focus on the essential redox-active metals: iron, copper, manganese, cobalt, chromium, and nickel. We aim to encourage further targeted efforts in developing innovative approaches to understanding the biological chemistry of redox-active metals.

Tracking mitochondrial Cu(I) fluctuations through a ratiometric fluorescent probe in AD model cells: Towards understanding how AβOs induce mitochondrial Cu(I) dyshomeostasis

Mitochondrial copper signaling pathway plays a role in Alzheimer's disease (AD), especially in relevant Amyloid-β oligomers (AβOs) neurotoxicity and mitochondrial dysfunction. Clarifying the relationship between mitochondrial copper homeostasis and both of mitochondrial dysfunction and AβOs neurotoxicity is important for understanding AD pathogenesis. Herein, we designed and synthesized a ratiometric fluorescent probe CHC-NS4 for Cu(I). CHC-NS4 possesses excellent ratiometric response, high selectivity to Cu(I) and specific ability to target mitochondria. Under mitochondrial dysfunction induced by oligomycin, mitochondrial Cu(I) levels gradually increased, which may be related to inhibition of ATP7A-mediated Cu(I) exportation and/or high expression of COX. On this basis, CHC-NS4 was further utilized to visualize the fluctuations of mitochondrial Cu(I) levels during progression of AD model cells induced by AβOs. It was found that mitochondrial Cu(I) levels were gradually elevated during the AD progression, which depended on not only AβOs concentration but also incubation time. Moreover, endocytosis maybe served as a prime pathway mode for mitochondrial Cu(I) dyshomeostasis induced by AβOs during AD progression. These results have provided a novel inspiration into mitochondrial copper biology in AD pathogenesis.

K, Koner AL. Review on Lysosomal Metal Ion Detection Using Fluorescent Probes

Metal ions are indispensable and play an important role in living systems. Metal ions coordinated to metalloenzymes pocket activate the bound substrate and labile metal ions maintaining the ionic balance. The amount of metal ions present in various subcellular compartments of the cells is highly regulated for maintaining cellular homeostasis. An imbalance in the metal ion concentration is related to several diseases and results in serious pathological conditions. Mostly the internalized metal ions are processed in the lysosomal compartment of the cell. A delicate regulation of metal ions in the lysosomal compartment can modulate the lysosomal pH and inhibit hydrolytic enzymes, which ultimately causes lysosomal storage disorders. In the past decade, the understanding and regulation of lysosomal metal ions based on fluorometric methods have gained significant attention. In this review, we have comprehensively summarized the development of various fluorescent reporters over the past five years for a selective and sensitive estimation of lysosomal metal ion concentration. We believe this consolidated and timely review will help researchers working in the areas associated with lysosomal metal ions.

Chromo-Fluorogenic Rhodamine-Based Amphiphilic Probe as a Selective and Sensitive Sensor for Intracellular Cu(I) in Living Cells

Fluorescent probes are widely studied for metal ion detection because of their multiple favorable properties such as high sensitivity and selectivity, quick response, naked eye detection, and in situ monitoring. However, optical probes that can effectively detect the Cu(I) level in cell interiors are rare due to the difficulty associated with selectively and sensitively detecting this metal ion in a cell environment. Therefore, we designed and synthesized three water-soluble probes (1-3) with a 1,3,5-triazine core decorated by three substituents: a hydrophobic alkyl chain, a hydrophilic maltose, and a rhodamine B hydrazine fluorophore. Among the probes, probe 1, which has an octyl chain and a branched maltose group, was the most effective at sensing Cu+ in aqueous solution. Upon addition of Cu+, this probe showed a dramatic color change from colorless to pink in daylight and displayed an intense yellow fluorescence emission under 365 nm light. The limit of detection and dissociation constant (Kd) of this probe were 20 nM and 1.1 × 10-12 M, respectively, which are the lowest values reported to date. The two metal ion-binding sites and the aggregation-induced emission enhancement effect, endowed by the branched maltose group and the octyl chain, respectively, are responsible for the high sensitivity and selectivity of this probe for Cu+ detection, as demonstrated by 1H NMR, dynamic light scattering, and transmission electron microscopy studies. Furthermore, the probe successfully differentiated the Cu(I) level of cancer cells from that of the normal cells. Thus, the probe holds potential for real-time monitoring of Cu(I) level in biological samples and bioimaging of cancer cells.

Precisely modulating the chromatin tracker via substituent engineering: reporting pathological oxidative stress during mitosis

An in-depth understanding of cancer-cell mitosis presents unprecedented advantages for solving metastasis and proliferation of tumors, which has aroused great interest in visualizing the behavior via a luminescence tool. We developed a fluorescent molecule CBTZ-yne based on substituent engineering to acquire befitting lipophilicity and electrophilicity for anchoring lipid droplets and the nucleus, in which the low polarity environment and nucleic acids triggered a "weak-strong" fluorescence and "short-long" fluorescence-lifetime response. Meaningfully, CBTZ-yne visualized chromatin condensation, alignment, pull-push, and separation as well as lipid droplet dynamics, for the first time, precisely unveiling the asynchronous cellular mitosis processes affected by photo-generation reactive oxygen species according to the subtle change of fluorescence-lifetime. Our work suggested a new guideline for tracking the issue of the proliferation of malignant tumors in photodynamic therapy.

Natural Acceptor of Coumarin-Isomerized Red-Emissive BioAIEgen for Monitoring Cu2+ Concentration in Live Cells via FLIM

Artificial aggregation-induced emission luminogens (AIEgens) have flourished in bio-applications with the development of synthetic chemistry, which however are plagued by issues like singularity in structures and non-renewability. The unique structures and renewability of biomass moieties can compensate for these drawbacks, but their properties are hard to design and regulate due to their confined structures. Therefore, it appears to be a reasonable approach to derive AIEgens from abundant biomass (BioAIEgens), integrating the bilateral advantages of both synthetic and natural AIEgens. In this work, the blue-violet emissive coumarin with its lactone structure serving as a rare natural acceptor, is utilized to construct donor-π-acceptor typed BioAIE isomers incorporating the propeller-like and electron-donating triphenylamine (TPA) unit. The results show that Cm-p-TPA undergoes charge transfer with its keto form, emitting red light at 600 nm, which can be applied to monitor Cu2+ concentration during mitophagy using fluorescence lifetime imaging microscopy because of the excellent biocompatibility, photostability, and specific recognition to Cu2+ . This work not only demonstrates the feasibility of utilizing positional isomerization to modulate excited-state evolutions and resultant optical properties, but also provides evidence for the rationality of constructing biologically-active BioAIEgens via a biomass-derivatization concept.

Current and Future of "Turn-On" Based Small-Molecule Copper Probes for Cuproptosis

Increasing evidence shows that abnormal copper (Cu) metabolism is highly related to many diseases, such as Alzheimer's disease, Wilson's disease, hematological malignancies and Menkes disease. Very recently, cuproptosis, a Cu-dependent, programmed cell death was firstly described by Tsvetkov et al. in 2022. Their findings may provide a new perspective for the treatment of related diseases. However, the concrete mechanisms of these diseases, especially cuproptosis, remain completely unclear, the reason of which may be a lack of reliable tools to conduct highly selective, sensitive and high-resolution imaging of Cu in complex life systems. So far, numerous small-molecular fluorescent probes have been designed and utilized to explore the Cu signal pathway. Among them, fluorescence turn-on probes greatly enhance the resolution and accuracy of imaging and may be a promising tool for research of investigation into cuproptosis. This review summarizes the probes developed in the past decade which have the potential to study cuproptosis, focusing on the design strategies, luminescence mechanism and biological-imaging applications. Besides, we put forward some ideas concerning the design of next-generation probes for cuproptosis, aiming to tackle the main problems in this new field. Furthermore, the prospect of cuproptosis in the treatment of corresponding diseases is also highlighted.

Ratiometric detection of Cu2+ in water and drinks using Tb(III)-functionalized UiO-66-type metal-organic frameworks

As an important trace element in the human body, the concentration of Cu²⁺ has an important impact on the environment and human health, and its quantitative determination is of great significance in the fields of environmental protection and food safety. Here, a ratiometric fluorescent probe based on Tb(III)-functionalized UiO-66-type MOFs has been synthesized via a facile post-synthetic modification method by employing mixed linkers containing terephthalic acid and 2,6-pyridinedicarboxylic acid for Cu²⁺ detection. The blue fluorescence intensity at 440 nm from the ligands of MOFs does not change much with increasing Cu²⁺ concentrations and can be used as a reference signal, while the green fluorescence of Tb³⁺ can be rapidly and selectively quenched, causing fluorescence intensity at 547 nm to decrease. The probe can be used as a ratiometric sensor for Cu²⁺ detection with a good linear response and low detection limit. The use of the probe for the determination of Cu²⁺ in real water samples and drinks shows good practicality. This method for Cu²⁺ detection is simple, specific and visualized to meet the needs of environmental monitoring and food analysis and provides a new strategy for the construction of new copper ion fluorescent sensors to analyze complex samples.

A fluorescent sensor based on the cascade signal amplification strategy for ultra-sensitive detection of Cu2

Copper is an essential element in the human body, participating in various physiological activities in the bodies of organisms. However, an excessive load of Cu²⁺ is associated with several neurodegenerative diseases and prion diseases, also identified as a symptom of Wilson's disease (WD). A straightforward, rapid, sensitive, and specific copper sensor is highly required but remains a challenge. In this study, guided by the simulation, we developed a chemical sensor using a cascade signal amplification strategy based on the Cu-catalyzed click reaction, combined with a fluorescence-enhanced substrate with gold nanorods coupled with silver nanoislands. The sensor can selectively detect Cu²⁺ as low as 3.87 nM within 10 min. We have demonstrated that this method can be directly employed for WD diagnosis in urine samples. In addition, using antibiotic susceptibility testing (AST) as an example, we verify whether this assay can be adapted to other targets where Cu is designed as an indirect indicator.

Two quinoline-based two-photon fluorescent probes for imaging of viscosity in subcellular organelles of living HeLa cells

Two viscosity-sensitive two-photon fluorescent probes (QL and QLS) were designed and synthesized, which can be localized in lysosome and mitochondria in living HeLa cells, respectively. As the increases of viscosity from 2.55 to 1150 cP, the fluorescence quantum yield (Φ) of QL and QLS was increased by 28-fold and 37-fold, respectively. At the same time, its effective two-photon absorption cross section (Φδ_TPA) was enhanced by 15-fold and 16-fold, respectively. Fluorescence lifetime imaging (FLIM) of living HeLa cells stained with QL and QLS, revealed that lysosomal viscosity ranged from 100.76 to 254.74 cP and mitochondrial viscosity ranged from 92.21 to 286.79 cP. This type of fluorescent probe is helpful in the design and application of materials for monitoring diseases associated with abnormal viscosity.

Oxidation state-specific fluorescent copper sensors reveal oncogene-driven redox changes that regulate labile copper(II) pools

Copper is an essential metal nutrient for life that often relies on redox cycling between Cu(I) and Cu(II) oxidation states to fulfill its physiological roles, but alterations in cellular redox status can lead to imbalances in copper homeostasis that contribute to cancer and other metalloplasias with metal-dependent disease vulnerabilities. Copper-responsive fluorescent probes offer powerful tools to study labile copper pools, but most of these reagents target Cu(I), with limited methods for monitoring Cu(II) owing to its potent fluorescence quenching properties. Here, we report an activity-based sensing strategy for turn-on, oxidation state-specific detection of Cu(II) through metal-directed acyl imidazole chemistry. Cu(II) binding to a metal and oxidation state-specific receptor that accommodates the harder Lewis acidity of Cu(II) relative to Cu(I) activates the pendant dye for reaction with proximal biological nucleophiles and concomitant metal ion release, thus avoiding fluorescence quenching. Copper-directed acyl imidazole 649 for Cu(II) (CD649.2) provides foundational information on the existence and regulation of labile Cu(II) pools, including identifying divalent metal transporter 1 (DMT1) as a Cu(II) importer, labile Cu(II) increases in response to oxidative stress induced by depleting total glutathione levels, and reciprocal increases in labile Cu(II) accompanied by decreases in labile Cu(I) induced by oncogenic mutations that promote oxidative stress.

A dual-function luminescent probe for copper(II) ions and pH detection based on ruthenium(II) complex

A new ruthenium complex-based luminescent probe Ru-impa for Cu²⁺ and pH detection has been synthesized and characterized. Ru-impa could rapidly and selectively detect Cu²⁺ in aqueous solutions and the working pH ranges from weakly acidic to alkaline. The detection limit calculated using the S/N and S/B ratio was 24.7 nM and 3.4 μM, respectively. The test strips for practical detecting application were also prepared and the actual detection limit in drinking water was found to be 3 μM, which is lower than the WHO-guided drinking water limit (30 µM) and the upper limit of human serum free copper content (1.7-3.9 μM). Luminescence imaging study showed that Ru-impa could monitor Cu²⁺ level fluctuation in the cells. In addition, Ru-impa also shows a sensitive on-off luminescence response when pH > 10, indicating that it can also be used as a pH sensor under extremely alkaline conditions.

One-pot synthesis of copper nanocluster/Tb-MOF composites for the ratiometric fluorescence detection of Cu2

The increasing degradation of ecosystems due to heavy metal residues has led to environment and food contamination, prompting the development of convenient platforms for monitoring heavy metals. Here, a new dual-emission fluorescent sensor CuNCs@Tb@UiO-66-(COOH)₂ for the detection of copper ions (Cu²⁺ ) has been synthesized by one-pot encapsulation of Tb (III) and glutathione-stabilized copper nanoclusters (CuNCs) into metal-organic frameworks (MOFs) UiO-66-(COOH)₂ . In this ratiometric sensor, the fluorescence intensity of Tb³⁺ decreased significantly upon the addition of Cu²⁺ , while that of CuNCs showed good stability, together with an apparent color change. Therefore, ratiometric fluorescence detection of Cu²⁺ can be accomplished by measuring the ratio of the fluorescence intensity at the 450 nm (F₄₅₀ ) wavelength of CuNCs to the 548 nm (F₅₄₈ ) emission of Tb³⁺ in the fluorescence spectra of the CuNCs@Tb@UiO-66-(COOH)₂ suspension. Moreover, the obtained fluorescent probe shows good results in the detection of actual samples. This work can provide the basis of method for the exploration of ratiometric fluorescence and visual sensors of trace pollutants analysis in complicated samples.

Polarity-Sensitive and Membrane-Specific Probe Quantitatively Monitoring Ferroptosis through Fluorescence Lifetime Imaging

As a new form of regulated cell death, ferroptosis is closely related to various diseases. To interpret this biological behavior and monitor related pathological processes, it is necessary to develop appropriate detection strategies and tools. Considering that ferroptosis is featured with remarkable lipid peroxidation of various cell membranes, it is logical to detect membranes' structural and environmental changes for the direct assessment of ferroptosis. For this sake, we designed novel polarity-sensitive fluorescent probes Mem-C₁C₁₈ and Mem-C₁₈C₁₈, which have superior plasma membrane anchorage, high brightness, and sensitive responses to environmental polarity by changing their fluorescence lifetimes. Mem-C₁C₁₈ with much less tendency to aggregate than Mem-C₁₈C₁₈ outperformed the latter in high resolution fluorescence labeling of artificial vesicle membranes and plasma membranes of live cells. Thus, Mem-C₁C₁₈ was selected to monitor plasma membranes damaged along ferroptosis process for the first time, in combination with the technique of fluorescence lifetime imaging (FLIM). After treating HeLa cells with Erastin, a typical ferroptosis inducer, the mean fluorescence lifetime of Mem-C₁C₁₈ displayed a considerable increase from 3.00 to 4.93 ns, with a 64% increase (corresponding to the polarity parameter Δf increased from 0.213 to 0.232). Therefore, our idea to utilize a probe to quantitate the changes in polarity of plasma membranes proves to be an effective method in the evaluation of the ferroptosis process.

Synthesis and bioimaging of a BODIPY-based fluorescence quenching probe for Fe3

Iron is the main substance for maintaining life. Real-time determination of ferric ion (Fe³⁺) in living cells is of great significance for understanding the relationship of Fe³⁺ concentration changes with various physiological and pathological processes. Fluorescent probes are suitable for the detection of trace metal ions in cells due to their low toxicity and high sensitivity. In this work, a boron-dipyrromethene-based fluorescent probe (BODIPY-CL) for selective detection of Fe³⁺ was synthesized. The fluorescence emission of BODIPY-CL was determined at 516 nm. In a pH range of 1 to 10, the probe BODIPY-CL exhibits a quenching response to Fe³⁺. Meanwhile, BODIPY-CL showed a highly selective response to Fe³⁺ compared with 16 kinds of metal ions. The stoichiometry ratio of BODIPY-CL bound to Fe³⁺ was nearly 2 : 1. The fluorescence quenching response obtained by the sensor was linear with the Fe³⁺ concentration in the range of 0-400 μM, and the detection limit was 2.9 μM. BODIPY-CL was successfully applied to image Fe³⁺ in cells. This study provides a promising fluorescent imaging probe for further research on the physiological and pathological effects of Fe³⁺.

Phototoxicity of BODIPY in long-term imaging can be reduced by intramolecular motion

For long-term live-cell fluorescence imaging and biosensing, it is crucial to work with a dye that has high fluorescence quantum yield and photostability without being detrimental to the cells. In this paper, we demonstrate that neutral boron-dipyrromethene (BODIPY)-based molecular rotors have great properties for high-light-dosage demanding live-cell fluorescence imaging applications that require repetitive illuminations. In molecular rotors, an intramolecular rotation (IMR) allows an alternative route for the decay of the singlet excited state (S₁) via the formation of an intramolecular charge transfer state (CT). The occurrence of IMR reduces the probability of the formation of a triplet state (T₁) which could further react with molecular oxygen (³O₂) to form cytotoxic reactive oxygen species, e.g., singlet oxygen (¹O₂). We demonstrate that the oxygen-related nature of the phototoxicity for BODIPY derivatives can be significantly reduced if a neutral molecular rotor is used as a probe. The studied neutral molecular rotor probe shows remarkably lower phototoxicity when compared with both the non-rotating BODIPY derivative and the cationic BODIPY-based molecular rotor in different light dosages and dye concentrations. It is also evident that the charge and localization of the fluorescent probe are as significant as the IMR in terms of the phototoxicity in a long-term live-cell imaging.

A biomass-derived Schiff base material composited with polylactic acid nanofiber membrane as selective fluorescent 'turn off/on' platform for Pb2+ quantitative detection and characterization

Herein, a biomass-derived compound Z1 is synthesized via 'one pot' method for detection Pb²⁺ using fluorescence and visual dual-mode in aqueous solution. Z1 shows good response to Pb²⁺ with a limit of detection (LOD) of 13.4 nM. Importantly, the coordination mode of Z1 with Pb²⁺ is further evaluated by UV-vis and NMR spectroscopy and a 1:1 stoichiometry is identified. Furthermore, Z1 can be applied to detection Pb²⁺ in practical samples with satisfactory recoveries in range of 96.0 %-112.0 % in real samples. Besides, Z1 is added into polylactic acid (PLA) solution and made as portable fluorescence nanofiber membrane for Pb²⁺ detection. Further, Z1 responds to Pb²⁺ with high selectivity and sensitivity and has been applied for tracking Pb²⁺ changes in soil samples, zebrafish, and plant tissues. These results indicated that Z1 had great application potential in accurate detection Pb²⁺.

Surfactant-Modulated a Highly Sensitive Fluorescent Probe of Fully Conjugated Covalent Organic Nanosheets for Detecting Copper Ions in Aqueous Solution

Efficient detection of aqueous copper ions is of high significance for environmental and human health, since copper is involved in potent redox activity in physiological and pathological processes. Covalent organic frameworks (COFs) have shown advantages in efficient capturing and detecting of copper ions due to their large surface area, robust chemical stability, and high sensitivity, but most of them are hydrophobic, leading to the limitation in sensing copper ions in aqueous media. Herein, the design and synthesis of an sp² -carbon conjugated COF (sp² -TPE-COF) are reported with surfactant-assisted water dispersion for detecting traces of copper ions based on the photo-induced electron transfer (PET) mechanism. Importantly, the olefin-linked conjugated backbone of sp² -TPE-COF works as a signal amplified transducer for metal ion sensing. Notably, it is found that a surfactant-assisted strategy can greatly enhance COF's dispersion in aqueous solution and finely modulate their sensitivity with a significantly improved K_SV to 15.15 × 10⁴ m^-1 in SDBS (sodium dodecyl benzene sulfonate) solution, the value of which is larger than that of a majority of COF/MOF based sensors for copper ions. This research demonstrates the promise of surfactant modulated fully π-conjugated COFs for sensing applications.

Metal-Organic Frameworks Encapsulating Carbon Dots Enable Fast Speciation of Mono- and Divalent Copper

Copper is an essential element to play significant roles in human health associated to the strong redox properties of Cu(I) and Cu(II). The concurrent monitoring of copper species in biological matrixes is highly desired. Herein, a dual-channel fluorescence nanoprobe was designed for the speciation of mono- and divalent copper by conjugating carbon dots (CDs) with Eu-based metal-organic frameworks (Eu-MOFs). The obtained Eu-MOFs@CD nanoprobe exhibits fluorescence at λ_ex/λ_em = 380/454 nm from CDs and λ_ex/λ_em = 275/615 nm from Eu-MOFs. Bathocuproine disulfonate (BCS) specifically chelates Cu⁺ to produce a BCS-Cu⁺ adduct with absorption at 480 nm, which quenches the fluorescence of CDs at 454 nm due to the inner filter effect. On the other hand, Cu²⁺ quenches the fluorescence of Eu-MOFs due to the replacement of Eu³⁺ by Cu²⁺. Thus, Eu-MOFs@CDs enable extremely fast detection of Cu⁺ and Cu²⁺ within 1 min. Furthermore, the nanoprobe is demonstrated by monitoring the variation of Cu⁺ and Cu²⁺ in the degradation process of copper nanoparticles and Cu-based MOFs.

Chemical-Biology-derived in vivo Sensors: Past, Present, and Future

To understand the complex biochemistry and biophysics of biological systems, one needs to be able to monitor local concentrations of molecules, physical properties of macromolecular assemblies and activation status of signaling pathways, in real time, within single cells, and at high spatio-temporal resolution. Here we look at the tools that have been / are being / need to be provided by chemical biology to address these challenges. In particular, we highlight the utility of molecular probes that help to better measure mechanical forces and flux through key signalling pathways. Chemical biology can be used to both build biosensors to visualize, but also actuators to perturb biological processes. An emergent theme is the possibility to multiplex measurements of multiple cellular processes. Advances in microscopy automation now allow us to acquire datasets for 1000's of cells. This produces high dimensional datasets that require computer vision approaches that automate image analysis. The high dimensionality of these datasets are often not immediately accessible to human intuition, and, similarly to 'omics technologies, require statistical approaches for their exploitation. The field of biosensor imaging is therefore experiencing a multidisciplinary transition that will enable it to realize its full potential as a tool to provide a deeper appreciation of cell physiology.