Insight into Fluorescence Imaging and Bioorthogonal Reactions in Biological Analysis

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 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.

Whole-Body and Whole-Organ 3D Imaging of Hypoxia Using an Activatable Covalent Fluorescent Probe Compatible with Tissue Clearing

Elucidation of biological phenomena requires imaging of microenvironments in vivo. Although the seamless visualization of in vivo hypoxia from the level of whole-body to single-cell has great potential to discover unknown phenomena in biological and medical fields, no methodology for achieving it has been established thus far. Here, we report the whole-body and whole-organ imaging of hypoxia, an important microenvironment, at single-cell resolution using activatable covalent fluorescent probes compatible with tissue clearing. We initially focused on overcoming the incompatibility of fluorescent dyes and refractive index matching solutions (RIMSs), which has greatly hindered the development of fluorescent molecular probes in the field of tissue clearing. The fluorescent dyes compatible with RIMS were then incorporated into the development of activatable covalent fluorescent probes for hypoxia. We combined the probes with tissue clearing, achieving comprehensive single-cell-resolution imaging of hypoxia in a whole mouse body and whole organs.

Recent Advances in NIR or X-ray Excited Persistent Luminescent Materials for Deep Bioimaging

Due to their persistent luminescence, persistent luminescent (PersL) materials have attracted great interest. In the biomedical field, the use of persistent luminescent nanoparticles (PLNPs) eliminates the need for continuous in situ excitation, thereby avoiding interference from tissue autofluorescence and significantly improving the signal-to-noise ratio (SNR). Although persistent luminescence materials can emit light continuously, the luminescence intensity of small-sized nanoparticles in vivo decays quickly. Early persistent luminescent nanoparticles were mostly excited by ultraviolet (UV) or visible light and were administered for imaging purposes through ex vivo charging followed by injection into the body. Limited by the low in vivo penetration depth, UV light cannot secondary charge PLNPs that have decayed in vivo, and visible light does not penetrate deep enough to reach deep tissues, which greatly limits the imaging time of persistent luminescent materials. In order to address this issue, the development of PLNPs that can be activated by light sources with superior tissue penetration capabilities is essential. Near-infrared (NIR) light and X-rays are widely recognized as ideal excitation sources, making persistent luminescent materials stimulated by these two sources a prominent area of research in recent years. This review describes NIR and X-ray excitable persistent luminescence materials and their recent advances in bioimaging.

Nanoscale Ion-Exchange Materials: From Analytical Chemistry to Industrial and Biomedical Applications

Nano-sized ion exchangers (NIEs) combine the properties of common bulk ion-exchange polymers with the unique advantages of downsizing into nanoparticulate matter. In particular, being by nature milti-charged ions exchangers, NIEs possess high reactivity and stability in suspensions. This brief review provides an introduction to the emerging landscape of various NIE materials and summarizes their actual and potential applications. Special attention is paid to the different methods of NIE fabrication and studying their ion-exchange behavior. Critically discussed are different examples of using NIEs in chemical analysis, e.g., as solid-phase extraction materials, ion chromatography separating phases, modifiers for capillary electrophoresis, etc., and in industry (fuel cells, catalysis, water softening). Also brought into focus is the potential of NIEs for controlled drug and contrast agent delivery.

Aptameric Fluorescent Biosensors for Liver Cancer Diagnosis

Liver cancer is a prevalent global health concern with a poor 5-year survival rate upon diagnosis. Current diagnostic techniques using the combination of ultrasound, CT scans, MRI, and biopsy have the limitation of detecting detectable liver cancer when the tumor has already progressed to a certain size, often leading to late-stage diagnoses and grim clinical treatment outcomes. To this end, there has been tremendous interest in developing highly sensitive and selective biosensors to analyze related cancer biomarkers in the early stage diagnosis and prescribe appropriate treatment options. Among the various approaches, aptamers are an ideal recognition element as they can specifically bind to target molecules with high affinity. Furthermore, using aptamers, in conjunction with fluorescent moieties, enables the development of highly sensitive biosensors by taking full advantage of structural and functional flexibility. This review will provide a summary and detailed discussion on recent aptamer-based fluorescence biosensors for liver cancer diagnosis. Specifically, the review focuses on two promising detection strategies: (i) Förster resonance energy transfer (FRET) and (ii) metal-enhanced fluorescence for detecting and characterizing protein and miRNA cancer biomarkers.

Recent Progress in the Development of Organic Chemosensors for Formaldehyde Detection

Formaldehyde has become a prominent topic of interest because of its simple molecular structure, release from various compounds in the near vicinity of humans, and associated hazards. Thus, several researchers designed sophisticated instrumentations for formaldehyde detection that exhibit real-time sensing properties and are cost-effective and portable with high detection limits. On these grounds, this review is centered on an analysis of optical chemosensors for formaldehyde that specifically fall under the broad spectrum of organic probes. In this case, this review discusses different organic functionalities, including amines, imines, aromatic pillar arenes, β-ketoesters, and β-diketones, taking part in various reaction mechanisms ranging from aza-Cope rearrangement and Schiff base and Hanztch reactions to aldimine condensation. In addition, this review distinguishes reaction mechanisms according to photophysical phenomena, that is, aggregation-induced emission, photoinduced electron transfer, and intramolecular charge transfer. Furthermore, it addresses the instrumentation involved in gas-based and liquid formaldehyde detection. Finally, it discusses the gaps in existing technologies followed by a succinct set of recommendations for future research.

Fluorescent Probes as a Tool in Diagnostic and Drug Delivery Systems

Over the last few years, the development of fluorescent probes has received considerable attention. Fluorescence signaling allows noninvasive and harmless real-time imaging with great spectral resolution in living objects, which is extremely useful for modern biomedical applications. This review presents the basic photophysical principles and strategies for the rational design of fluorescent probes as visualization agents in medical diagnosis and drug delivery systems. Common photophysical phenomena, such as Intramolecular Charge Transfer (ICT), Twisted Intramolecular Charge Transfer (TICT), Photoinduced Electron Transfer (PET), Excited-State Intramolecular Proton Transfer (ESIPT), Fluorescent Resonance Energy Transfer (FRET), and Aggregation-Induced Emission (AIE), are described as platforms for fluorescence sensing and imaging in vivo and in vitro. The presented examples are focused on the visualization of pH, biologically important cations and anions, reactive oxygen species (ROS), viscosity, biomolecules, and enzymes that find application for diagnostic purposes. The general strategies regarding fluorescence probes as molecular logic devices and fluorescence–drug conjugates for theranostic and drug delivery systems are discussed. This work could be of help for researchers working in the field of fluorescence sensing compounds, molecular logic gates, and drug delivery.

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.

Electrochemically Promoted [3 + 2] Annulation of Imidazo[1,2-a]pyridine with Alkynes

The efficient electrochemically promoted [3 + 2] annulation of imidazo[1,2-a]pyridines with alkynes using traceless electrons as green reagents has been developed, leading to the synthesis of a large class of polycyclic heteroaromatics in good yields with a broad substrate scope under mild and green conditions. The scaled-up experiment, follow-up procedures, and potential biological applications show the practicability and feasibility of the electrochemical method.

Halogen-modified carbazole derivatives for lipid droplet-specific bioimaging and two-photon photodynamic therapy

Lipid droplets (LDs) are dynamic multifunctional organelles that participate in the regulation of many metabolic processes, visualization of which is necessary for biological research. In this work, a series of two-photon responsive fluorescent probes (C-H, C-Br, and C-I) based on carbazole units were designed and synthesized. Thereinto, an iodine-modified carbazole derivative C-I exhibited an exciting lipid droplet targeting ability due to its excellent lipophilicity. Meanwhile, benefiting from its larger Stokes shift and two-photon absorption cross-section, C-I was employed for two-photon confocal laser scanning microscopy (CLSM) and stimulated emission depletion (STED) microscopy imaging to observe LDs more accurately. In addition, given the heavy atom effect, C-I can effectively generate reactive oxygen species (ROS) leading to cancer cell apoptosis under near-infrared light irradiation. Notably, we explained the process of cell apoptosis through in vitro simulation experiments. This study provides a promising platform for visualization of lipid droplets.

Graphene Biodevices for Early Disease Diagnosis Based on Biomarker Detection

The early diagnosis of diseases plays a vital role in healthcare and the extension of human life. Graphene-based biosensors have boosted the early diagnosis of diseases by detecting and monitoring related biomarkers, providing a better understanding of various physiological and pathological processes. They have generated tremendous interest, made significant advances, and offered promising application prospects. In this paper, we discuss the background of graphene and biosensors, including the properties and functionalization of graphene and biosensors. Second, the significant technologies adopted by biosensors are discussed, such as field-effect transistors and electrochemical and optical methods. Subsequently, we highlight biosensors for detecting various biomarkers, including ions, small molecules, macromolecules, viruses, bacteria, and living human cells. Finally, the opportunities and challenges of graphene-based biosensors and related broad research interests are discussed.

Research Progress and Application of Bioorthogonal Reactions in Biomolecular Analysis and Disease Diagnosis

Bioorthogonal reactions are rapid, specific and high yield reactions that can be performed in in vivo microenvironments or simulated microenvironments. At present, the main biorthogonal reactions include Staudinger ligation, copper-catalyzed azide alkyne cycloaddition, strain-promoted [3 + 2] reaction, tetrazine ligation, metal-catalyzed coupling reaction and photo-induced biorthogonal reactions. To date, many reviews have reported that bioorthogonal reactions have been used widely as a powerful tool in the field of life sciences, such as in target recognition, drug discovery, drug activation, omics research, visualization of life processes or exogenous bacterial infection processes, signal transduction pathway research, chemical reaction dynamics analysis, disease diagnosis and treatment. In contrast, to date, few studies have investigated the application of bioorthogonal reactions in the analysis of biomacromolecules in vivo. Therefore, the application of bioorthogonal reactions in the analysis of proteins, nucleic acids, metabolites, enzyme activities and other endogenous molecules, and the determination of disease-related targets is reviewed. In addition, this review discusses the future development opportunities and challenges of biorthogonal reactions. This review presents an overview of recent advances for application in biomolecular analysis and disease diagnosis, with a focus on proteins, metabolites and RNA detection.

Time-resolved analysis of photoluminescence at a single wavelength for ratiometric and multiplex biosensing and bioimaging

Simultaneous analysis of luminescence signals of multiple probes can improve the accuracy and efficiency of biosensing and bioimaging. Analysis of multiple signals at different wavelengths usually suffers from spectral overlap, possible energy transfer, and difference in detection efficiency. Herein, we reported a polymeric luminescent probe, which was composed of a phenothiazine-based fluorescent compound and a phosphorescent iridium(iii) complex. Both luminophores emitted at around 600 nm but their luminescence lifetimes are 160 times different, allowing time-resolved independent analysis. As the fluorescence was enhanced in response to oxidation by hypochlorite and the phosphorescence was sensitive toward oxygen quenching, a four-dimensional relationship between luminescence intensity, fluorescence/phosphorescence ratio, hypochlorite concentration, and oxygen content was established. In cellular imaging, time-resolved photoluminescence imaging microscopy clearly showed the independent fluorescence response toward hypochlorite and phosphorescence response toward oxygen in separated time intervals. This work opens up a new idea for the development of multiplex biosensing and bioimaging.

Effective and transient mapping of protein-protein interactions: Application of novel releasable photoaffinity linkers

Herein, two novel multifunctional releasable photoaffinity linkers were developed for effective and transient tracking interacting proteins with the overall objective of understanding their in vivo biological functions in real-time. These linkers could be used for the chemical modification of protein under moderate experimental conditions to form protein photoaffinity probes. These probes incorporated with both photoaffinity labels and tag-transfer, enable photo-crosslinking of bait proteins along with the release of unrelated groups. These photoaffinity linkers can be utilized to construct probes for disease markers, which could enable rapid diagnosis in a clinical setting at minimal interference with normal physiology.

A cationic fluorescent probe for highly selective detection of sodium dodecyl sulfate (SDS) by electrostatic and hydrophobic self-assembly

Sodium dodecyl sulfate (SDS) has a wide range of applications in the chemical industry due to its excellent characteristics including good emulsification, foaming, water solubility and stability, easy synthesis and low price. However, it is a kind of anionic surfactant which is slightly toxic to the human body, and use of a large amount will cause potential pollution of the environment. Therefore, the development of a simple method to realize the monitoring of SDS in the environment is of great significance. Herein, a cationic fluorescent probe was prepared by the condensation reaction between 4-di-p-tolylamino-benzaldehyde and 3-ethylbenzothiazolium iodide. It can be used for the quantitative determination of SDS in the range of 5-50 μM showing red fluorescence and high selectivity by forming banded assemblies. This work provides an effective tool based on a new strategy for the detection of SDS.