Development and Challenge of Fluorescent Probes for Bioimaging Applications: From Visualization to Diagnosis

Multifunctional near-infrared fluorescent probe for sensing of lysine and Cu2+/Fe3+ and relay detection of biothiols

Lysine (Lys), Cu2+ and Fe3+ ions and biothiols are essential to a myriad of biological and pathological pathways, and their dysregulation is implicated in a variety of diseases. Development of fluorescent probes capable of detecting multiple analytes may be of great significance for early and accurate diagnosis of diseases and remains a huge challenge. In this context, a novel coumarin-dicyanoisophorone-based probe, engineered for the concurrent sensing of Lys, Cu2+, Fe3+ and biothiols was developed. The probe exhibited turn-on response to Lys, colorimetric and turn-off response to Cu2+ by formation of the probe-Cu2+ complex, and ratiometric sensing of Fe3+. In addition, the probe-Cu2+ complex served colorimetric and fluorescence turn-on sensor for biothiols. The limit of detection (LOD) values for the analytes were in the range of 0.30-4.40 μM. Sensing mechanisms based on intramolecular charge transfer (ICT) and iron-mediated hydrolysis of Schiff base were proposed and substantiated through density functional theory (DFT) calculations. Application of the probe for living cell bioimaging was demonstrated.

Research Progress of Fluorescent Probes for Detection of Glutathione (GSH): Fluorophore, Photophysical Properties, Biological Applications

Intracellular biothiols, including cysteine (Cys), glutathione (GSH), and homocysteine (Hcy), play a critical role in many physiological and pathological processes. Among them, GSH is the most abundant non-protein mercaptan (1-10 mM) in cells, and the change in GSH concentration level is closely related to the occurrence of many diseases, such as Parkinson's disease, Alzheimer's disease, and neurological diseases. Fluorescent probes have attracted much attention due to their advantages of high specificity, high sensitivity, high selectivity, low cost, and high quantum yield. Methods that use optical probes for selective detection of GSH in vitro and in vivo are in high demand. In this paper, we reviewed the most recent five years of research on fluorescence probes for the detection of GSH, including the specific detection of GSH, dual-channel identification of GSH and other substances, and the detection of GSH and other biothiols. According to the type of fluorophore, we classified GSH fluorescent probes into eight classes, including BODIPY, 1,8-Naphthalimide, coumarin, xanthene, rhodamine, cyanine, benzothiazoles, and others. In addition, we roundly discuss the synthesis, detection mechanism, photophysical properties, and biological applications of fluorescent probes. We hope that this review will inspire the exploration of new fluorescent probes for GSH and other related analyses.

Highly specific GSH-triggered bifunctional molecules to enable precise imaging and targeted therapy of cancer

The utilization of diagnostic-integrated molecules can enable targeted delivery and controlled release to significantly enhance therapeutic effectiveness and minimize toxic effects. Herein, we developed a novel class of glutathione (GSH)-activated bifunctional molecules that respond to elevated levels of GSH in tumor microenvironment. These bifunctional molecules retained the pharmacodynamic effects of parent molecules and mitigated cytotoxicity. Meanwhile, controlled release was monitored using fluorescent signals, enabling detection of drug distribution and accumulation in situ and in real time. Moreover, the correlation between GSH levels and fluorescence intensity offers the possibility of monitoring the effectiveness of responsive drugs. In conclusion, bifunctional molecules, as novel diagnostic-integrated molecules with both fluorescence imaging and therapeutic effects, exhibited potential applications in cancer therapy and imaging.

Supercritical Fluids: An Innovative Strategy for Drug Development

Nanotechnology plays a pivotal role in the biomedical field, especially in the synthesis and regulation of drug particle size. Reducing drug particles to the micron or nanometer scale can enhance bioavailability. Supercritical fluid technology, as a green drug development strategy, is expected to resolve the challenges of thermal degradation, uneven particle size, and organic solvent residue faced by traditional methods such as milling and crystallization. This paper provides an insight into the application of super-stable homogeneous intermix formulating technology (SHIFT) and super-table pure-nanomedicine formulation technology (SPFT) developed based on supercritical fluids for drug dispersion and micronization. These technologies significantly enhance the solubility and permeability of hydrophobic drugs by controlling the particle size and morphology, and the modified drugs show excellent therapeutic efficacy in the treatment of hepatocellular carcinoma, pathological scarring, and corneal neovascularization, and their performance and efficacy are highlighted when administered through multiple routes of administration. Overall, supercritical fluids have opened a green and efficient pathway for clinical drug development, which is expected to reduce side effects and enhance therapeutic efficacy.

Nanoparticles Encapsulated in Red Blood Cell Membranes for Near-Infrared Second Window Imaging-Guided Photothermal-Enhanced Immunotherapy on Tumors

Photothermal therapy (PTT), which uses the high thermal conversion ability of photothermal agents to ablate tumor cells at high temperatures, has gained significant attention because it has the advantages of high selectivity and specificity, precise targeting of tumor sites, and low invasiveness and trauma. However, PTT guided by the NIR-I has limitations in tissue penetration depth, resulting in limited imaging monitoring and therapeutic effects on deep-seated tumor tissues. Moreover, nanoparticles are easily cleared by the immune system and difficult to passively target tumor sites during the process of treatment. To address these issues, we prepared nanoparticles using NIR-II dyes IR1048 and DSPE-PEG-OH and further encapsulated them in red blood cell membranes derived from mice. These biomimetic nanoparticles, called RDIR1048, showed reduced clearance by the immune system and had long circulation characteristics. They effectively accumulated at tumor sites, and strong fluorescence could still be observed at the tumor site 96 h after administration. Furthermore, through mouse thermal imaging experiments, we found that RDIR1048 exhibited good PTT ability. When used in combination with an immune checkpoint inhibitor, anti-PD-L1 antibodies, it enhanced the immunogenic cell death of tumor cells caused by PTT and improved the therapeutic effect of immunotherapy, which demonstrated good therapeutic efficacy in the treatment of tumor-bearing mice. This study provides a feasible basis for the future development of NIR-II nanoparticles with long circulation properties.

All-in-one nanotheranostic platform based on tumor microenvironment: new strategies in multimodal imaging and therapeutic protocol

Conventional tumor diagnosis and treatment approaches have significant limitations in clinical application, whereas personalized theranostistic nanoplatforms can ensure advanced diagnosis, precise treatment, and even a good prognosis in cancer. Tumor microenvironment (TME)-targeted therapeutic strategies offer absolute advantages in all aspects compared to tumor cell-targeted therapeutic strategies. It is essential to create a TME-responsive all-in-one nanotheranostic platform to facilitate individualized tumor treatment. Based on the TME-responsive multifunctional nanotheranostic platform, we focus on the combined use of multimodal imaging and therapeutic protocols and summary and outlooks on the latest advanced nanomaterials and structures for creating the integrated nanotheranostic system based on material science, which provide insights and reflections on the development of innovative TME-targeting tools for cancer theranostics.

Novel angiogenesis inhibitors with superoxide anion radical amplification effect: Surmounting the Achilles' heels of angiogenesis inhibitors and photosensitizers

Angiogenesis inhibitors and photosensitizers are pivotal in tumor clinical treatment, yet their utilization is constrained. Herein, eleven novel angiogenesis inhibitors were developed through hybridization strategy to overcome their clinical limitations. These title compounds boast excitation wavelengths within the "therapeutic window", enabling deep tissue penetration. Notably, they could generate superoxide anion radicals via the Type I mechanism, with compound 36 showed the strongest superoxide anion radical generating capacity. Biological evaluation demonstrated remarkable cellular activity of all the title compounds, even under hypoxic conditions. Among them, compound 36 stood out for its superior anti-proliferative activity in both normoxic and hypoxic environments, surpassing individual angiogenesis inhibitors and photosensitizers. Compound 36 induced cell apoptosis via superoxide anion radical generation, devoid of dark toxicity. Molecular docking revealed that the target-recognizing portion of compound 36 was able to insert into the ATP binding pocket of the target protein similar to sorafenib. Collectively, our results suggested that hybridization of angiogenesis inhibitors and photosensitizers was a potential strategy to address the limitations of their clinical use.

A highly sensitive ratiometric fluorescent probe for detecting HSO3-/SO32- and viscosity change based on FRET/TICT mechanism

BACKGROUND

Sulfur dioxide (SO2) is a significant gas signaling molecule in organisms, and viscosity is a crucial parameter of the cellular microenvironment. They are both involved in regulating many physiological processes in the human body. However, abnormalities in SO2 and viscosity levels are associated with various diseases, such as cardiovascular disease, lung cancer, respiratory diseases, neurological disorders, diabetes and Alzheimer's disease. Hence, it is essential to explore novel and efficient fluorescent probes for simultaneously monitoring SO2 and viscosity in organisms.

RESULTS

We selected quinolinium salt with good stability, high fluorescence intensity, good solubility and low cytotoxicity as the fluorophore and developed a highly sensitive ratiometric probe QQD to identify SO2 and viscosity changes based on Förster resonance energy transfer/twisted intramolecular charge transfer (FRET/TICT) mechanism. Excitingly, compared with other probes for SO2 detection, QQD not only identified HSO3-/SO32- with a large Stokes shift (218 nm), low detection limit (1.87 μM), good selectivity, high energy transfer efficiency (92 %) and wide recognition range (1.87-200 μM), but also identified viscosity with a 26-fold fluorescence enhancement and good linearity. Crucially, QQD was applied to detect HSO3-/SO32- and viscosity in actual water and food samples. In addition, QQD had low toxicity and good photostability for imaging HSO3-/SO32- and viscosity in cells. These results confirmed the feasibility and reliability of QQD for HSO3-/SO32- and viscosity imaging and environmental detection.

SIGNIFICANCE

We reported a unique ratiometric probe QQD for detecting HSO3-/SO32- and viscosity based on the quinolinium skeleton. In addition to detecting HSO3-/SO32- and viscosity change in actual water and food samples, QQD could also monitor the variations of HSO3-/SO32- and viscosity in cells, which provided an experimental basis for further exploration of the role of SO2 derivatives and viscosity in biological systems.

Aminoguanidine-based bioactive proligand as AIEE probe for anticancer and anticovid studies

The emission features of a novel bioactive compound, 1,3-bis(2-hydroxy-3,5-diiodophenyl-methylideneamino)guanidine is found impressive with aggregation induced emission enhancement. The nitrogen and iodine rich multidentate proligand was characterized physicochemically. SCXRD and Hirshfeld surface investigation have revealed the presence of significant triangular iodine bonding apart from hydrogen bonding, weak C-H⋯π and π⋯π intermolecular interactions. These interactions collectively contribute to the solid-state packing arrangement of the molecules within the crystal lattice. The band gap of the compound was estimated experimentally and is supported with theoretical calculations. The solid-state fluorescence quantum yield of Φ = 0.36 emphasizes the utility of the proligand and the AIEE characteristics is attributed to restricted intramolecular motions as indicated by fluorescence lifetime decay studies. Strong interaction of the compound with calf thymus DNA was explored experimentally and found to align with in silico docking results. Notably, in vitro anticancer assessment on MCF-7 breast cancer cells show an IC50 value of 181.05 μg mL-1 and signifying its potent cytotoxic properties. Also, the compound is found to have lesser cytotoxicity against L929 normal cell line with an IC50 value of 356.54 μg mL-1. Computational studies further underscore the exceptional binding affinity with active sites in the SARS-CoV-2 main protease 3CLpro, surpassing established repurposed drugs. Furthermore, the proligand demonstrates excellent putative affinity towards the SARS-CoV-2 spike glycoprotein, accompanied by its distinctive AIEE attributes, drug likeness and DNA binding capability rendering it a valuable tool for prospective research investigations.

Novel multi-target angiogenesis inhibitors as potential anticancer agents: Design, synthesis and preliminary activity evaluation

Based on the crucial role of histone deacetylase (HDAC) and receptor tyrosine kinase in angiogenesis, in situ assembly, skeletal transition, molecular hybridization, and pharmacophore fusion were employed to yield seventy-six multi-target angiogenesis inhibitors. Biological evaluation indicated that most of the compounds exhibited potent proliferation inhibitory activity on MCF-7 cells, with the TH series having the highest inhibitory activity on MCF-7 cells. In addition, the IC50 values of TA11 and TH3 against HT-29 cellswere 0.078 μmol/L and 0.068 μmol/L, respectively. The cytotoxicity evaluation indicated that TC9, TA11, TM4, and TH3 displayed good safety against HEK293T cells. TH2 and TH3 could induce apoptosis of MCF-7 cells. Molecular modeling and ADMET prediction results indicated that most of target compounds showed promising medicinal properties, which was consistent with the experimental results. Our findings provided new lead compounds for the structural optimization of multi-target angiogenesis inhibitors.

Quantum Dot Fluorescent Imaging: Using Atomic Structure Correlation Studies to Improve Photophysical Properties

Efforts to study intricate, higher-order cellular functions have called for fluorescence imaging under physiologically relevant conditions such as tissue systems in simulated native buffers. This endeavor has presented novel challenges for fluorescent probes initially designed for use in simple buffers and monolayer cell culture. Among current fluorescent probes, semiconductor nanocrystals, or quantum dots (QDs), offer superior photophysical properties that are the products of their nanoscale architectures and chemical formulations. While their high brightness and photostability are ideal for these biological environments, even state of the art QDs can struggle under certain physiological conditions. A recent method correlating electron microscopy ultrastructure with single-QD fluorescence has begun to highlight subtle structural defects in QDs once believed to have no significant impact on photoluminescence (PL). Specific defects, such as exposed core facets, have been shown to quench QD PL in physiologically accurate conditions. For QD-based imaging in complex cellular systems to be fully realized, mechanistic insight and structural optimization of size and PL should be established. Insight from single QD resolution atomic structure and photophysical correlative studies provides a direct course to synthetically tune QDs to match these challenging environments.

A near-infrared emitting "off-on" fluorescent probe for bioimaging of Pd(Ⅱ) ions in living cells and mice

BACKGROUND

The surging consumption of palladium in modern industry has given rise to its accumulation in the ecosystem, posing conspicuous toxicity to aquatic organisms and human health. The investigation of palladium in biological systems is highly demanded for the in-depth understanding of its dynamics and behaviors. Fluorescence imaging serves as a powerful approach to assess palladium species in biological systems, and currently most of the sensing probes are applicable to living cells. Effective tracking of palladium species in living organisms is challenging, which requires sufficient hydrophilicity and imaging depth of the probes.

RESULTS

Based on an intramolecular charge transfer (ICT) mechanism, a distyryl boron dipyrromethene (BODIPY) derivative (DISBDP-Pd) has been prepared for the near-infrared (NIR) fluorescence imaging of Pd2+ ions. Two additional methoxy triethylene glycol (TEG) chains could serve as flexible and hydrophilic moieties to enhance the aqueous solubility and cell permeability of the extended conjugate. Solution studies revealed that DISBDP-Pd exhibited a NIR fluorescence enhancement signal exclusively to Pd2+ ions (detection limit as low as 0.85 ppb) with negligible interference from Pd0 species and other closely related metal ions. Computational calculations have been performed to rationalize the binding mode and the mechanism of action. Fluorescence imaging assays have been conducted on A549 human non-small cell lung carcinoma cells and mouse models. Exhibiting negligible cytotoxicity, DISBDP-Pd demonstrated concentration-related fluorescence enhancement signals in response to Pd2+ ions in living cells and mice.

SIGNIFICANCE

DISBDP-Pd exhibits advantages over many small molecule palladium probes in terms of satisfactory aqueous solubility, high sensitivity and selectivity, and biocompatible NIR emission property, which are particularly favorable for the sensing application in biological environments. The design strategy of this probe can potentially be adopted for the functionalization of other BODIPY probes implemented for NIR fluorescence bioimaging.

Analyzing MC-LR distribution characteristics in natural lakes by a novel fluorescence technology

The death of aquatic and terrestrial organisms caused by cyanobacterial blooms has been a topic of considerable concern since the 19th century. Microcystin-LR (MC-LR) produced by cyanobacterial blooms threaten natural ecosystems and human health. Therefore, establishing an effective monitoring and early warning system to detect MC-LR in water bodies is crucial. However, rapidly and intuitively assessing the distribution traits of MC-LR in lakes is a challenging task due to the complexities and expenses associated with conventional detection methods. To overcome these technical limitations, we introduce a novel and effective method for evaluating the distribution of MC-LR in lakes. This method is achieved by using a fluorescence probe (BAD) technology, marking the first application of this technology in evaluating the distribution of MC-LR in natural lake environments. The probe BAD is endowed with unique functions through clever functionalization modification. Experimental results exhibit that BAD has different fluorescence signals at various lake sampling points. The correlation analysis of fluorescence data and physicochemical indicators determines that the fluorescence data of the probe exhibit good correlation with MC-LR, implying that BAD is capable of detecting MC-LR in lakes. Moreover, the introduction of fluorescence technology to achieve the intuitive distribution of MC-LR in the entire plateau lake. This study provides a new method for evaluating the distribution of MC-LR in plateau lakes. It opens a new avenue for exploring the relationship between cyanobacterial blooms and MC-LR in natural waters.

Spindle Monitor: A Tool for Real-Time Assessment and Concurrent Treatment of Postoperative Tumor Prognosis

Cancer surgery remains a mainstay in clinical treatment. However, the efficacy of subsequent therapies largely depends on the precise evaluation of postoperative prognoses, underscoring the critical need for a comprehensive and accurate assessment of surgical outcomes. Nanoprobes targeting tumors offer a promising solution for visual prognostic assessment. In this study, we developed a "Spindle Monitor" system, designated as APPADs (Au NBPs@PDA-pep-AS1411-Dox), composed of core-shell nanoparticles. The core was made up of gold nanobipyramids (Au NBPs), coated with polydopamine (PDA), and subsequently loaded with peptide chains, AS1411, and doxorubicin (Dox). Upon deployment in the acidic tumor microenvironment (TME), APPADs released substantial amounts of Dox, initiating the apoptotic process. This triggered the activity of caspase-3, which is a crucial executor in the apoptotic pathway. Consequently, DEVD, a specific recognition site for caspase-3, was cleaved, enabling the disconnection of FITC-conjugated peptide chains and the recovery of fluorescence. Through assessing this fluorescence imaging effect, local laser irradiation could be precisely guided to the postoperative site, facilitating a synergistic combination of photothermal therapy and chemotherapy. Specifically, our "Spindle Monitor" APPADs had been validated to achieve accurate fluorescence imaging in vitro and in vivo, which demonstrated its potential value as a versatile tool for evaluating postoperative prognosis in surgical treatments, such as thyroid cancer, and assessing chemotherapy efficacy in difficult cases, like late-stage osteosarcoma. This promising tool lays a good foundation for development in visual prognosis evaluation after tumor surgery.

Internalization of Pegylated Er:Y2O3 Nanoparticles inside HCT-116 Cancer Cells: Implications for Imaging and Drug Delivery

Lanthanide-doped nanoparticles, featuring sharp emission peaks with narrow bandwidth, exhibit high downconversion luminescence intensity, making them highly valuable in the fields of bioimaging and drug delivery. High-crystallinity Y2O3 nanoparticles (NPs) doped with Er3+ ions were functionalized by using a pegylation procedure to confer water solubility and biocompatibility. The NPs were thoroughly characterized using transmission electron microscopy (TEM), inductively coupled plasma mass spectrometry (ICP-MS), and photoluminescence measurements. The pegylated nanoparticles were studied both from a toxicological perspective and to demonstrate their internalization within HCT-116 cancer cells. Cell viability tests allowed for the identification of the "optimal" concentration, which yields a detectable fluorescence signal without being toxic to the cells. The internalization process was investigated using a combined approach involving confocal microscopy and ICP-MS. The obtained data clearly indicate the efficient internalization of NPs into the cells with emission intensity showing a strong correlation with the concentrations of nanoparticles delivered to the cells. Overall, this research contributes significantly to the fields of nanotechnology and biomedical research, with noteworthy implications for imaging and drug delivery applications.

New Fluorophore and Its Applications in Visualizing Polystyrene Nanoplastics in Bean Sprouts and HeLa Cells

In the domain of environmental science, pollutants of nanoscale plastic dimensions are acknowledged as subjects of intricate significance. Such entities, though minuscule, present formidable challenges to ecological systems and human health. The diminutive dimensions of these contaminants render their detection arduous, thus demanding the inception of avant-garde methodologies. The present manuscript postulates the employment of the tetraphenylethylene functional group with a fused xanthene (TPEF), a distinguished fluorophore, as an exemplary system for the discernment of nanoplastic particulates. The synthesis and characterization of TPEF have been exhaustively elucidated, revealing its paramount fluorescence attributes and inherent affinity for interaction with nanoplastics. When subjected to comparison with TPEF, nanoplastics are observed to manifest a more pronounced fluorescent luminescence than when associated with the conventional Nile Red (NR). Particularly, the TPEF has shown exceptional affinity for polystyrene (PS) nanoplastics. Further, the resilience of nanoplastics within the hypocotyl epidermis of soybeans, as well as their persistence in mung bean sprouts subsequent to rigorous rinsing protocols, has been meticulously examined. Additionally, this investigation furnishes empirical data signifying the existence of nano-dimensional plastic contaminants within HeLa cellular structures. The urgency of addressing the environmental ramifications engendered by these diminutive yet potent plastic constituents is emphatically highlighted in this manuscript. TPEF paves the way for prospective explorations, with the aspiration of devising efficacious mitigation strategies. Such strategies might encompass delineating the trajectories undertaken by nanoplastics within trophic networks or their ingress into human cellular architectures.

Investigating the Use of Coumarin Derivatives as Lasers

A benzene ring and a lactone ring combine to form the chemical coumarin. Dye lasers have made significant advances in laser technology. The coumarin molecule itself is a non-fluorescent but it displays high fluorescence when electron-denoting substituents such as sulfonamide, benzopyrone, amine, benzothiazole, hydroxyl, methoxy are substituted at various positions. Substituted coumarin possesses the highest energy properties, photostability, and alteration in electron mobility, and therefore could be effectively used as dye lasers. These are considered some of the best fluorophores due to their outstanding photophysical and photochemical properties, which include high fluorescence quantum yields, great photostability, good functionality, and a wide spectrum range. Various inorganic materials are used in classic laser technology to generate the necessary emission. Inorganic lasers come in various types and can emit light in the electromagnetic spectrum's ultraviolet, visible, or infrared parts. Inorganic lasers have certain limitations, which is why coumarin lasers are becoming increasingly popular due to their many advantages. Compared to inorganic lasers, dye lasers offer far better tunability and cover the entire visible and near-infrared range. They only emit at very few specific wavelengths and in extremely narrow bands. The property is therefore presented in this review.

A mitochondria-targeted dual-response sensor for monitoring viscosity and peroxynitrite in living cells with distinct fluorescence signals

Viscosity and peroxynitrite (ONOO-) are two significant indicators to affect and evaluate the mitochondrial functional status, which are nearly relational with pathophysiological process in many diseases. Developing suitable analytical methods for monitoring mitochondrial viscosity changes and ONOO- is thus of great importance. In this research, a new mitochondria-targeted sensor DCVP-NO2 for the dual determination of viscosity and ONOO- was exploited based on the coumarin skeleton. DCVP-NO2 displayed a red fluorescence "turn-on" response toward viscosity along with about 30-fold intensity increase. Meanwhile, it could be used as ratiometric probe for detection of ONOO- with excellent sensitivity and extraordinary selectivity for ONOO- over other chemical and biological species. Moreover, thanks to its good photostability, low cytotoxicity and ideal mitochondrion-targeting capability, DCVP-NO2 was successfully utilized for fluorescence imaging of viscosity variations and ONOO- in mitochondria of living cells through different channels. In addition, the results of cell imaging revealed that ONOO- would lead to the increase of viscosity. Taken together, this work provides a potential molecular tool for researching biological functions and interactions of viscosity and ONOO- in mitochondria.

Development and Validation of Nerve-Targeted Bacteriochlorin Sensors

We report an innovative approach to producing bacteriochlorins (bacs) via formal cycloaddition by subjecting a porphyrin to a trimolecular reaction. Bacs are near-infrared probes with the intrinsic ability to serve in multimodal imaging. However, despite their ability to fluoresce and chelate metal ions, existing bacs have thus offered limited ability to label biomolecules for target specificity or have lacked chemical purity, limiting their use in bio-imaging. In this work, bacs allowed a precise and controlled appending of clickable linkers, lending the porphyrinoids substantially more chemical stability, clickability, and solubility, rendering them more suitable for preclinical investigation. Our bac probes enable the targeted use of biomolecules in fluorescence imaging and Cerenkov luminescence for guided intraoperative imaging. Bacs' capacity for chelation provides opportunities for use in non-invasive positron emission tomography/computed tomography. Herein, we report the labeling of bacs with Hs1a, a (NaV1.7)-sodium-channel-binding peptide derived from the Chinese tarantula Cyriopagopus schmidti to yield Bac-Hs1a and radiolabeled Hs1a, which shuttles our bac sensor(s) to mouse nerves. In vivo, the bac sensor allowed us to observe high signal-to-background ratios in the nerves of animals injected with fluorescent Bac-Hs1a and radiolabeled Hs1a in all imaging modes. This study demonstrates that Bac-Hs1a and [64Cu]Cu-Bac-Hs1a accumulate in peripheral nerves, providing contrast and utility in the preclinical space. For the chemistry and bio-imaging fields, this study represents an exciting starting point for the modular manipulation of bacs, their development and use as probes for diagnosis, and their deployment as formidable multiplex nerve-imaging agents for use in routine imaging experiments.

Polyaromatic Hydrocarbon (PAH)-Based Aza-POPOPs: Synthesis, Photophysical Studies, and Nitroanalyte Sensing Abilities

1,4-Bis(5-phenyl-2-oxazolyl)benzene (POPOP) is a common scintillation fluorescent laser dye. In this manuscript, the synthesis of 2-Ar-5-(4-(4-Ar'-1H-1,2,3-triazol-1-yl)phenyl)-1,3,4-oxadiazoles (Ar, Ar' = Ph, naphtalenyl-2, pyrenyl-1, triphenilenyl-2), as PAH-based aza-analogues of POPOP, by means of Cu-catalyzed click reaction between 2-(4-azidophenyl)-5-Ar-1,3,4-oxadiazole and terminal ethynyl-substituted PAHs is reported. An investigation of the photophysical properties of the obtained products was carried out, and their sensory response to nitroanalytes was evaluated. In the case of pyrenyl-1-substituted aza-POPOP, dramatic fluorescence quenching by nitroanalytes was observed.

Natural-product-based fluorescent probes: recent advances and applications

Fluorescent probes are attractive tools for biology, drug discovery, disease diagnosis, and environmental analysis. In bioimaging, these easy-to-operate and inexpensive probes can be used to detect biological substances, obtain detailed cell images, track in vivo biochemical reactions, and monitor disease biomarkers without damaging biological samples. Over the last few decades, natural products have attracted extensive research interest owing to their great potential as recognition units for state-of-the-art fluorescent probes. This review describes representative natural-product-based fluorescent probes and recent discoveries, with a particular focus on fluorescent bioimaging and biochemical studies.

Fluorescent "AND" logic gates for simultaneous detection of thiols and protons: photophysical properties, mechanism and bioimaging of living cells

Five fluorescent probes TP1-5 were demonstrated as two-input "AND" molecular logic gates for the detection of thiols and protons. The molecules were designed based on "thiol receptor-spacer₁-fluorophore-spacer₂-proton receptor" mode. The logic gates were constructed by employing maleimide, naphthalimide and morpholine (TP1-3)/N-methyl piperazine (TP4-5) as the thiol receptor, fluorophore and proton receptor, respectively. All probes show significant fluorescence enhancements upon addition of both protons and thiols. However, much weaker spectral responses were observed with the addition of only one single analyte. The fluorescence outputs, based on photoinduced electron transfer (PET) and (twisted) intramolecular charge transfer (TICT/ICT), were modulated by the proton receptor and linker. The length of spacer₁ affects the responses toward thiols, whereas spacer₂ influences the sensing performance toward protons. The difference between the pK_a values of morpholine (∼5.80) and N-methyl piperazine (∼7.10) enables us to detect thiols in divergent pH circumstances. TP1-3 exhibit an excellent "AND" logic function for simultaneous detection of protons and thiols as well as bioimaging thiols in weakly acidic living cells. However, TP4 and TP5 are not good candidates for executing "AND" logic operation possibly due to the stronger electron donating properties and steric effect of N-methyl piperazine.

Er:Y2O3 and Nd:Y2O3 Nanoparticles: Synthesis, Pegylation, Characterization and Study of Their Luminescence Properties

Lanthanide-doped yttrium oxide nanoparticles can display selective upconversion properties, rendering them invaluable in the field of nanomedicine for both sensing and diagnostics. Different syntheses of Er:Y2O3 and Nd:Y2O3 nanoparticles (NPs) were studied and optimized to obtain small particles of regular shape and good crystallinity. The morphological and compositional characterizations of the nanoparticles were obtained with different techniques and showed that both Er:Y2O3 and Nd:Y2O3 NPs were well dispersed, with dimensions of the order of a few tens of nanometers. The photoluminescence and cathodoluminescence measurements showed that both Er:Y2O3 and Nd:Y2O3 NPs had good emission as well as upconversion. The nanophosphors were functionalized by a pegylation procedure to suppress unwanted reactions of the NPs with other biological components, making the NP systems biocompatible and the NPs soluble in water and well dispersed. The pegylated core/shell nanoparticles showed the same morphological and optical characteristics as the core, promoting their strategic role as photoactive material for theragnostics and biosensing.

Designs and Applications of Multi-stimuli Responsive FRET Processes in AIEgen-Functionalized and Bi-fluorophoric Supramolecular Materials

Materials capable of displaying strong ratiometric fluorescence with Förster resonance energy transfer (FRET) processes have attracted much research interest because of various chemosensor and biomedical applications. This review highlights several popular strategies in designing FRET-OFF/ON mechanisms of ratiometric fluorescence systems. In particular, the developments of organic and polymeric FRET materials featuring aggregation-induced emission-based luminogens (AIEgens), supramolecular assemblies, photochromic molecular switches and surfactant-induced AIE/FRET mechanisms are presented. AIEgens have been frequently employed as FRET donor and/or acceptor fluorophores to obtain enhanced ratiometric fluorescences in solution and solid states. Since AIE effects and FRET processes rely on controllable distances between fluorophores, many interesting fluorescent properties can be designed by regulating aggregation states in polymers and supramolecular systems. Photo-switchable fluorophores, such as spiropyran and diarylethene, provide drastic changes in fluorescence spectra upon photo-induced isomerizations, leading to photo-switching mechanisms to activate/deactivate FRET processes. Supramolecular assemblies offer versatile platforms to regulate responsive FRET processes effectively. In rotaxane structures, the donor-acceptor distance and FRET efficiency can be tuned by acid/base-controlled shuttling of the macrocycle component. The tunable supramolecular interactions are strongly influenced by external factors (such as pH values, temperatures, analytes, surfactants, UV-visible lights, etc.), which induce the assembly and disassembly of host-guest systems and thus their FRET-ON/FRET-OFF behavior. In addition, the changes in donor or acceptor fluorescence profiles upon detections of analytes can also sufficiently alter the FRET behavior and result in different ratiometric fluorescence outputs. The strategies and examples provided in this review offer the insights and toolkits for future FRET-based material developments.

New insight into the application of fluorescence platforms in tumor diagnosis: From chemical basis to clinical application

Early and rapid diagnosis of tumors is essential for clinical treatment or management. In contrast to conventional means, bioimaging has the potential to accurately locate and diagnose tumors at an early stage. Fluorescent probe has been developed as an ideal tool to visualize tumor sites and to detect biological molecules which provides a requirement for noninvasive, real-time, precise, and specific visualization of structures and complex biochemical processes in vivo. Rencently, the development of synthetic organic chemistry and new materials have facilitated the development of near-infrared small molecular sensing platforms and nanoimaging platforms. This provides a competitive tool for various fields of bioimaging such as biological structure and function imaging, disease diagnosis, in situ at the in vivo level, and real-time dynamic imaging. This review systematically focused on the recent progress of small molecular near-infrared fluorescent probes and nano-fluorescent probes as new biomedical imaging tools in the past 3-5 years, and it covers the application of tumor biomarker sensing, tumor microenvironment imaging, and tumor vascular imaging, intraoperative guidance and as an integrated platform for diagnosis, aiming to provide guidance for researchers to design and develop future biomedical diagnostic tools.