The development of fluorescence turn-on probe for Al(III) sensing and live cell nucleus-nucleoli staining

Phenoxazine-based ambipolar luminescent room-temperature liquid crystals capable of being used in bioimaging applications

A new class of phenoxazine-based luminescent liquid crystal molecules (POs) were synthesized employing the double Knoevenagel condensation of phenoxazine dialdehyde with various alkoxy-substituted phenyl acetonitrile derivatives. This new series of molecules exhibit high solubility and excellent thermal stability. The compound with six peripheral n-alkoxy chains (PO4) stabilizes a room-temperature columnar liquid crystalline phase due to efficient space-filling interactions. The synthesized molecules exhibit high luminescence intensity in both solution and solid states. The liquid crystalline molecule PO4 exhibits positive solvatochromism with HLCT behavior, demonstrating phosphorescence at 77 K. This compound was screened for bioimaging applications due to its excellent fluorescence and high biocompatibility. Among the screened compounds, PO4 was selected due to its lower crystallization tendency and superior fluorescence and it exhibited a uniform stain distribution throughout the nematode, significantly enhancing cellular visualization. The same compound, PO4, was further explored for its potential as a fluorescent probe in bioimaging by staining MCF7 cancer cells, with cellular uptake and localization studies confirming its effectiveness in targeting and visualizing cancer cells with higher fluorescence intensity.

Strategies for the Nuclear Delivery of Metal Complexes to Cancer Cells

The nucleus is an essential organelle for the function of cells. It holds most of the genetic material and plays a crucial role in the regulation of cell growth and proliferation. Since many antitumoral therapies target nucleic acids to induce cell death, tumor-specific nuclear drug delivery could potentiate therapeutic effects and prevent potential off-target side effects on healthy tissue. Due to their great structural variety, good biocompatibility, and unique physico-chemical properties, organometallic complexes and other metal-based compounds have sparked great interest as promising anticancer agents. In this review, strategies for specific nuclear delivery of metal complexes are summarized and discussed to highlight crucial parameters to consider for the design of new metal complexes as anticancer drug candidates. Moreover, the existing opportunities and challenges of tumor-specific, nucleus-targeting metal complexes are emphasized to outline some new perspectives and help in the design of new cancer treatments.

Cell nucleus localization and high anticancer activity of quinoline-benzopyran rhodium(III) metal complexes as therapeutic and fluorescence imaging agents

Four novel rhodium(III) complexes, [Rh^III(QB1)Cl₃(DMSO)] (RhN1), [Rh^III(QB2)Cl₃(CH₃OH)]·CH₃OH (RhN2), [Rh^III(QB3)Cl₃(CH₃OH)]·CH₃OH (RhS), and [Rh^III(QB4)Cl₃(DMSO)] (RhQ), bearing quinoline-benzopyran ligands (QB1-QB4) were synthesized and used to develop highly anticancer therapeutic and fluorescence imaging agents. Compared with the QB1-QB4 ligands (IC₅₀ > 89.2 ± 1.7 μM for A549/DDP), RhN1, RhN2, RhS and RhQ exhibit selective cytotoxicity against lung carcinoma cisplatin-resistant A549/DDP (A549CDDP) cancer cells, with IC₅₀ values in the range of 0.08-2.7 μM. The fluorescent imaging agent RhQ with the more extended planar QB4 ligand exhibited high anticancer activity in A549CDDP cells and was found in the cell nucleus fraction, whereas RhS had no fluorescence properties. RhQ and RhS may trigger cell apoptosis by causing DNA damage and initiating the mitochondrial dysfunction pathway. Furthermore, RhQ has a higher antitumor efficacy (ca. 55.3%) than RhS (46.4%) and cisplatin (CDDP, 33.1%), and RhQ demonstrated significantly lower toxicity in vivo than CDDP, making it a promising Rh(III)-based anticancer therapeutic and fluorescence imaging agent.

Water-soluble optical sensors: keys to detect aluminium in biological environment

Metal ion plays a critical role from enzyme catalysis to cellular health and functions. The concentration of metal ions in a living system is highly regulated. Among the biologically relevant metal ions, the role and toxicity of aluminium in specific biological functions have been getting significant attention in recent years. The interaction of aluminium and the living system is unavoidable due to its high earth crust abundance, and the long-term exposure to aluminium can be fatal for life. The adverse Al3+ toxicity effects in humans result in various diseases ranging from cancers to neurogenetic disorders. Several Al3+ ions sensors have been developed over the past decades using the optical responses of synthesized molecules. However, only limited numbers of water-soluble optical sensors have been reported so far. In this review, we have confined our discussion to water-soluble Al3+ ions detection using optical methods and their utility for live-cell imaging and real-life application.

Performance of 2-Hydroxy-1-Naphthaldehyde-2-Amino Thiazole as a Highly Selective Turn-on Fluorescent Chemosensor for Al(III) Ions Detection and Biological Applications

The thiazole based Schiff base 2-hydroxy-1-naphthaldehyde-2-amino thiazole (receptor1) was synthesized through a single step process and characterized by spectroscopic and analytical techniques. The cation detecting ability of the receptor1 was explored by fluorescent spectroscopic methods. The receptor1 has recognized Al3+ ions by a turn-on process over a panel of other potentially competing metal ions. The binding constant of receptor1 with Al3+ was found to be 8.27 × 103 M-1. Computational studies Density Functional Theory (DFT) and Time-dependent Density Functional Theory (TD-DFT) were performed to provide detailed information on electronic states and photophysical property of receptor1 and receptor1-Al3+ ions. MTT (3-(4,5-dimethyl thiazole-2-yl)-2,5-diphenyl tetrazolium bromide) assay and bioimaging applications were made on breast carcinoma cells in humans.

Nitrogen-doped carbon dots for wash-free imaging of nucleolus orientation

Carbon dots (CDs) are a rising star in the field of cellular imaging, especially cytoplasmic imaging, attributing to the super-stable optical performance and ultra-low biological toxicity. Nucleolus can accurately reflect the expression state of a cell and is strongly linked to the occurrence and development of many diseases, so exploring bran-new CDs for nucleolus-orientation imaging with no-wash technology has important theoretical value and practical significance. Herein, nitrogen-doped carbon dots (N-CDs) with green fluorescence (the relative fluorescence quantum yield of 24.4%) was fabricated by the hydrothermal treatment of m-phenylenediamine and p-aminobenzoic acid. The N-CDs possess small size, bright green fluorescence, abundant surface functional groups, excellent fluorescence stability and good biocompatibility, facilitating that the N-CDs are an excellent imaging reagent for cellular imaging. N-CDs can particularly bind to RNA in nucleoli to enhance their fluorescence, which ensures that the N-CDs can be used in nucleolus-orientation imaging with high specificity and wash-free technique. This study demonstrates that the N-CDs have a significant feasibility to be used for nucleolus-orientation imaging in biomedical analysis and clinical diagnostic applications.

RNA-targeting low-molecular-weight fluorophores for nucleoli staining: synthesis, in silico modelling and cellular imaging

Herein we present our work on the synthesis, investigation of the photophysical properties, interactions with nucleic acids, molecular docking, and imaging application of three carbocyanine dyes.

Multifunctional rhodamine B appended ROMP derived fluorescent probe detects Al3+ and selectively labels lysosomes in live cells

There a few reports of rhodamine-based fluorescent sensors for selective detection of only Al3+, due to the challenge of identifying a suitable ligand for binding Al3+ ion. The use of fluorophore moieties appended to a polymer backbone for sensing applications is far from mature. Here, we report a new fluorescent probe/monomer 4 and its ROMP derived polymer P for specific detection of Al3+ ions. Both monomer 4 and its polymer P exhibit high selectivity toward only Al3+ with no interference from other metal ions, having a limit detection of 0.5 and 2.1 µM, respectively. The reversible recognition of monomer 4 and P for Al3+ was also proved in presence of Na2EDTA by both UV-Vis and fluorometric titration. The experimental data indicates the behavior of 4 and P toward Al3+ is pH independent in medium conditions. In addition, the switch-on luminescence response of 4 at acidic pH (0 < 5.0), allowed us to specifically stain lysosomes (pH ~ 4.5-5.0) in live cells.

Unravelling the modus-operandi of chromenylium-cyanine fluorescent probes: a case study

Small-molecule fluorescent probes having optimized optical properties, such as high photostability and brightness, local microenvironment sensitivity and specific subcellular localizations, are increasingly available. Although the basis for designing efficient fluorophores for bioimaging applications is well established, implementing an improvement in a given photophysical characteristic always tends to compromise another optical property. This problem has enormous consequences for in vivo imaging, where ensuring a specific localization and precise control of the probe response is challenging. Herein we discuss a fluorescent probe, CC334, as a case study of the chromenylium-cyanine family that commonly exhibits highly complex photophysical schemes and highly interfered bioanalytical responses. By an exhaustive and concise analysis of the CC334 optical responses including detailed spectroscopic calibrations, steady-state microenvironment effects, ultrafast photophysics analysis and computational studies, we elucidate a new strategy to apply the probe in the singlet oxygen reactive oxygen species (1O2-ROS) monitoring using in vitro and in vivo models. The probe provides a new avenue for designing fluorescent probes to understand the dynamic behavior of subcellular environments.

Aggregation-Induced Emission-Active Hydrazide-Based Probe: Selective Sensing of Al3+, HF2 -, and Nitro Explosives

(E)-N'-((2-Hydroxynaphthalen-1-yl)methylene)picolinohydrazide (H-PNAP) shows aggregation-induced emission (AIE) strictly in a 90% water/MeOH (v/v) mixture at 540 nm, and the solid-state emission is blue-shifted to 509 nm upon excitation at 400 nm. The AIE activity of H-PNAP is selectively quenched by 2,4,6-trinitrophenol (TNP) and 2,4-dinitrophenol (DNP) out of different nitroaromatic compounds with a limit of detection (LOD) of 7.79 × 10-7 and 9.08 × 10-7 M, respectively. The probe is nonemissive in aqueous medium (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, HEPES buffer, pH 7.2); however, it shows a strong emission to Al3+ (λem, 490 nm) in the presence of 17 other biological metal ions, and the LOD is 2.09 nM which is far below the WHO recommended value (7.41 mM). The emission of the [Al(PNAP)(NO3)2] complex is quenched by HF2 - (F- and PO4 3- are weak quencher), and the LOD is as low as 15 nM. The probable mechanism of the sensing feature of the probe has been authenticated by 1H nuclear magnetic resonance titration, mass spectrometry, Fourier transform infrared spectroscopy, Benesi-Hildebrand plot, and Job's plot in each case. The probe has some practical applications such as recovery of Al3+ from the drinking water sample, construction of the INHIBIT logic gate, and detection kits for Al3+ and TNP/DNP by simple paper test strips. The probe, H-PNAP, has successfully been applied to the detection of intracellular Al3+ and HF2 - ions in the human breast cancer cell, MDA-MB-468.

Surface charge controlled nucleoli selective staining with nanoscale carbon dots

Organelle selective imaging can reveal structural and functional characters of cells undergoing external stimuli, and is considered critical in revealing biological fundamentals, designing targeted delivery system, and screening potential drugs and therapeutics. This paper describes the nucleoli targeting ability of nanoscale carbon dots (including nanodiamond) that are hydrothermally made with controlled surface charges. The surface charges of carbon dots are controlled in the range of -17.9 to -2.84 mV by changing the molar ratio of two precursors, citric acid (CA) and ethylenediamine (EDA). All carbon dots samples show strong fluorescence under wide excitation wavelength, and samples with both negative and positve charges show strong fluorescent contrast from stained nucleoli. The nucleoli selective imaging of live cell has been confirmed with Hoechst staining and nucleoli specific staining (SYTO RNA-select green), and is explained as surface charge heterogeneity on carbon dots. Carbon dots with both negative and positive charges have better ability to penetrate cell and nucleus membranes, and the charge heterogeneity helps carbon dots to bind preferentially to nucleoli, where the electrostatic environment is favored.

A Highly Selective Turn-on Fluorescent Probe for the Detection of Aluminum and Its Application to Bio-Imaging

Aluminum is the most abundant metallic element in the Earth's crust and acts as a non-essential element for biological species. The accumulation of excessive amounts of aluminum can be harmful to biological species. Thus, the development of convenient and selective tools for the aluminum detection is necessary. In this work, a highly selective aluminum ion fluorescent probe N'-(2,5-dihydroxybenzylidene)acetohydrazide (Al-II) has been successfully synthesized and systemically characterized. The fluorescence intensity of this probe shows a significant enhancement in the presence of Al³⁺, which is subject to the strong quench effects caused by Cu²⁺ and Fe³⁺. The binding ratio of probe-Al³⁺ was determined from the Job's plot to be 1:1. Moreover, the probe was demonstrated to be effective for in vivo imaging of the intracellular aluminum ion in both living Drosophila S2 cells and Malpighian tubules.

An imidazole derivative-based chemodosimeter for Zn2+ and Cu2+ ions through “ON–OFF–ON” switching with intracellular Zn2+ detection

Imidazole derivative-based chemodosimeter (HL) for selective detection of Zn²⁺ and Cu²⁺ metal ions and intracellular Zn²⁺ sensing.

An amide probe as a selective Al3+ and Fe3+ sensor inside the HeLa and a549 cell lines: Pictet–Spengler reaction for the rapid detection of tryptophan amino acid

Newly synthesized amide-based probe for the selective and specific detection of (i) Al³⁺ or Fe³⁺ ions as a cation sensor and (ii) tryptophan as an amino acid sensor.

Traceable in-cell synthesis and cytoplasm-to-nucleus translocation of a zinc Schiff base complex as a simple and economical anticancer strategy

A facile and cheap strategy based on visualized in-cell synthesis of theranostic Zn Schiff base complexes realizes cancer-specific therapy.

Differential Metal Ion Sensing by an Antipyrine Derivative in Aqueous and β-Cyclodextrin Media: Selectivity Tuning by β-Cyclodextrin

β-Cyclodextrin (β-CD) is a nontoxic cyclic oligosachcharide that can encapsulate all or part of organic molecules of appropriate size and specific shape through noncovalent interaction. Herein, we report the influence of β-CD complex formation of an antipyrine derivative on its metal ion sensing behavior. In aqueous solution, the antipyrine shows a turn-on fluorescence sensing of vanadyl ion, and in cyclodextrin medium it senses aluminum ion. The compound shows an unusual fluorescence quenching on binding with β-cyclodextrin (log K_SV = 2.34 ± 0.02). The differential metal ion sensing is due to the partial blocking of the chelating moiety by the cyclodextrin molecule. The structure of the antipyrine-cyclodextrin complex is optimized by two-dimensional rotating-frame Overhauser effect spectroscopy. The binding constant is determined by isothermal titration calorimetry (log K = 2.09 ± 0.004). The metal ion binding site is optimized by quanutm mechanical calculations. The lower limit of detection of vanadyl and aluminum ions, respectively, are 5 × 10^-8 and 5 × 10^-7 mol dm^-3. This is the first report of selectivity of two different cations by a chemosensor in water and in β-CD.

Highly efficient fluorescence sensing of phosphate by dual-emissive lanthanide MOFs

The detection of phosphate (Pi) under physiological conditions is a very important issue in environmental and biological sciences. Herein, a unique fluorescent probe {[EuL(H2O)1.35(DMF)0.65]·1.9DMF}n (1) was prepared through the organic-inorganic hybridization between asymmetrical tricarboxylate ligands and Eu2O2 clusters under solvothermal conditions. The as-prepared sample 1 exhibited excellent fluorescence properties and could be designed as a self-calibrating fluorescent probe for sensitively and selectively detecting Pi which served as an essential substance in aquatic ecosystems and biological systems. The different responses of the two emission peaks caused by the addition of Pi resulted in a continuous fluorescence color change, which could be clearly observed with the naked eye under UV light lamp illumination at 302 nm. Typically, a good linearity existed between the ratio of dual fluorescence intensities and the Pi contents ranging from 0.1 μM to 15 μM with a low detection limit of 52 nM (S/N = 3). It is noteworthy that the prepared self-calibrating fluorescent probe displayed specific recognition towards Pi anions with satisfactory recovery ranging from 92.8% to 100.6% in water samples and biological fluids. Thus, we can envision that this work may open a new avenue for the detection of many other bioactive ions in environmental and biological samples.

A novel mesoionic carbene based highly fluorescent Pd(ii) complex as an endoplasmic reticulum tracker in live cells

Synthesis of new organometallic MIC based mononuclear Pd(ii) complex 1, specifically target ER of live cells and have fluorescence recovery after photobleaching (FRAP) property.

Tracking mitochondrial 1O2-ROS production through a differential mitochondria-nucleoli fluorescent probe

A dual-emissive fluorescent probe enabled unique tracking of ¹O₂-ROS species through a differential mitochondrial–nucleoli localization dynamic.

A highly selective and sensitive chemosensor forl-tryptophan by employing a Schiff based Cu(ii) complex

Construction of a new Cu(ii) complex (1) based modified glassy carbon electrode (1-GCE) for highly selective and sensitive detection ofl-tryptophan (l-Trp).

Multimodal Super-resolution Optical Microscopy Using a Transition-Metal-Based Probe Provides Unprecedented Capabilities for Imaging Both Nuclear Chromatin and Mitochondria

Detailed studies on the live cell uptake properties of a dinuclear membrane-permeable Ru^II cell probe show that, at low concentrations, the complex localizes and images mitochondria. At concentrations above ∼20 μM, the complex images nuclear DNA. Because the complex is extremely photostable, has a large Stokes shift, and displays intrinsic subcellular targeting, its compatibility with super-resolution techniques was investigated. It was found to be very well suited to image mitochondria and nuclear chromatin in two color, 2C-SIM, and STED and 3D-STED, both in fixed and live cells. In particular, due to its vastly improved photostability compared to that of conventional SR probes, it can provide images of nuclear DNA at unprecedented resolution.

Turn-on fluorescent probes that can light up endogenous RNA in nucleoli and cytoplasm of living cells under a two-photon microscope

We report two turn-on RNA probes that can light up endogenous RNA in the nucleoli and cytoplasm of living cells under a two-photon microscope.

A new multitalented azine ligand: elastic bending, single-crystal-to-single-crystal transformation and a fluorescence turn-on Al(iii) sensor

A multifunctional azine ligand with elastic bending with full phase retention, photoinduced SCSC transformation and sensitive Al³⁺ detection.