Bioimaging of thiazolidine-4-one-based new probes, fluorimetric detection of Cu2+ "on-off" sensor property, DFT calculation, molecular docking studies, and multiple real samples application

Thiazolidinones have been the subject of various research areas for their biological activities, thus they were promising scaffolds to develop new drug agents. A novel thiazolidine 4-one-based fluorescent chemosensor probes PS (thiazolidine) and BO (oxazolidine) were designed and synthesized. Both probes showed specific recognition against Cu2+ via a "turn-off" fluorescence response in ACN/H2O (v/v: 50/50) stock solution (10 mM, pH = 7.0) with a detection limit of (for BO: 1.9 nM and PS: 1.03 nM). Finally, the detection of chemosensory PS and BO showed positive potential for the determination of Cu2+ in real food samples, drinking water, and mung beans. The compounds were characterized by diferent chemical and spectroscopic methods. The proposed binding mode for PS and BO with Cu2+ was confirmed by DFT calculation, and also they elucidated by bioimaging studies against MCF-7 live cell lines. Additionally, the docking experiment was performed on XylE and hAChE targets.

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.

An amphiphilic dansyl based multianalyte sensor for the detection of Hg2+, PPi, and TNP: A three-in-one chemical sensor

A fluorescent dansyl-based amphiphilic probe, 5-(dimethylamino)-N-hexadecylnaphthalene-1-sulfonamide (DLC), was synthesized and characterized to detect multiple analytes at different sensing environments. In acetonitrile, DLC detects nitro explosives such as trinitrophenol (TNP) and 2,4-dinitrophenol (2,4-DNP) by an emission "on-off" response method, and the detection limits (LOD) were estimated to be as low as 4.3 µM and 17.4 µM, respectively. Amphiphilic long chains of the probe were embedded into lipid bilayers to form nanoscale vesicles DLC.Ves. Nanovesicular probe DLC.Ves was found to be highly selective for Hg2+ among other metal ions and for pyrophosphate (PPi) ions among various anions. DLC.Ves could detect Hg2+ with a turn "on-off" emission and PPi with ratiometric change in emission at 525 nm. It is proposed that DLC.Ves could detect Hg2+ via the Hg2+-induced aggregation quenching mechanism and PPi through the Hydrogen bonding. The LODs are estimated as 6.41 µM and 70.9 µM for Hg2+ and PPi, respectively. 1H NMR, SEM, and fluorescence lifetime measurements confirmed the binding mechanism. Thus, it is believed that the simple fluorescent probe DLC could be a prominent sensor to detect multiple analytes depending on the sensing medium.

Synthesis and Biological Characterization of Fluorescent Cyclipostins and Cyclophostin Analogues: New Insights for the Diagnosis of Mycobacterial-Related Diseases

Patients with cystic fibrosis (CF) have a significantly higher risk of acquiring nontuberculous mycobacteria infections, predominantly due to Mycobacterium abscessus, than the healthy population. Because M. abscessus infections are a major cause of clinical decline and morbidity in CF patients, improving treatment and the detection of this mycobacterium in the context of a polymicrobial culture represents a critical component to better manage patient care. We report here the synthesis of fluorescent Dansyl derivatives of four active cyclipostins and cyclophostin analogues (CyCs) and provide new insights regarding the CyC's lack of activity against Gram-negative and Gram-positive bacteria, and above all into their mode of action against intramacrophagic M. abscessus cells. Our results pointed out that the intracellularly active CyC accumulate in acidic compartments within macrophage cells, that this accumulation appears to be essential for their delivery to mycobacteria-containing phagosomes, and consequently, for their antimicrobial effect against intracellular replicating M. abscessus, and that modification of such intracellular localization via disruption of endolysosomal pH strongly affects the CyC accumulation and efficacy. Moreover, we discovered that these fluorescent compounds could become efficient probes to specifically label mycobacterial species with high sensitivity, including M. abscessus in the presence several other pathogens like Pseudomonas aeruginosa and Staphylococcus aureus. Collectively, all present and previous data emphasized the therapeutic potential of unlabeled CyCs and the attractiveness of the fluorescent CyC as a potential new efficient diagnostic tool to be exploited in future diagnostic developments against mycobacterial-related infections, especially against M. abscessus.

A "turn-on" ESIPT fluorescence probe of 2-(aminocarbonyl)phenylboronic acid for the selective detection of Cu(ii)

Herein, we report a highly selective fluorescent probe for the detection of Cu(ii). The detection mechanism relies on the Cu(ii)-catalyzed oxidative hydroxylation of 2-(aminocarbonyl)phenylboronic acid into salicylamide, thus recovering the excited-state intramolecular proton transfer (ESIPT) effect and inducing more than 35-fold fluorescence enhancement. The simple structure and readily available fluorescent probe give a novel method for quantitatively detecting Cu(ii) in the linear range of 0-22 μM, with a limit of detection down to 68 nM, and exhibiting high selectivity for Cu(ii) over 16 other metal ions.

Accelerated nucleophilic substitution reactions of dansyl chloride with aniline under ambient conditions via dual-tip reactive paper spray

Paper spray ionization (PSI) mass spectrometry (MS) is an emerging tool for ambient reaction monitoring via microdroplet reaction acceleration. PSI-MS was used to accelerate and monitor the time course of the reaction of dansyl chloride with aniline, in acetonitrile, to produce dansyl aniline. Three distinct PSI arrangements were explored in this study representing alternative approaches for sample loading and interaction; conventional single tip as well as two novel setups, a dual-tip and a co-axial arrangement were designed so as to limit any on-paper interaction between reagents. The effect on product abundance was investigated using these different paper configurations as it relates to the time course and distance of microdroplet travel. It was observed that product yield increases at a given distance and then decreases thereafter for all PSI configurations. The fluorescent property of the product (dansyl aniline) was used to visually inspect the reaction progress on the paper substrate during the spraying process. Amongst the variety of sample loading methods the novel dual-tip arrangement showed an increased product yield and microdroplet density, whilst avoiding any on-paper interaction between the reagents.

A Coumarin-Based Fluorescent Probe for Ratiometric Detection of Cu2+ and Its Application in Bioimaging

The fluorescent probe L, based on naphthalimide-modified coumarin, was designed, synthesized, and characterized, which could recognize Cu2+ from other cations selectively and sensitively in HEPES buffer (10 mM, Ph = 7. 4)/CH3CN (1:4, V/V). When the probe L interacted with Cu2+, the color and the fluorescent intensity changed obviously and it provided the naked-eye detection for Cu2+. The recognition mode between them was achieved by Job's plot, IR, MS, SEM, and 1HNMR. In addition, test strips made from L could still interact with Cu2+ in tap water effectively. The limit of detection (LOD) of L was 3.5 × 10-6 M. Additionally, the density functional theory (DFT) calculation method was used to analyze the action mechanism of L toward Cu2+. Importantly, the fluorescent probe L could demonstrate favorable selectivity toward Cu2+ in Caenorhabditis elegans. Thus, L was considered to have some potential for application in bioimaging.

Update on the development of molecular imaging and nanomedicine in China: Optical imaging

Molecular imaging has received increased attention worldwide, including in China, because it offers noninvasive characterization of widely diverse clinically significant pathologies. To achieve these goals, nanomedicine has evolved into a broad interdisciplinary field with flexible designs to accommodate and concentrate imaging and therapeutic payloads into pathological cells through selective binding to disease specific cell membrane biomarkers. This concept of personalized medicine reflects the vision of "magic bullets" proposed by German biochemist Paul Ehrlich over 100 years ago. As happening worldwide, Chinese scientists are contributing to this tsunami of science and technologies through impactful national programs and international research collaborations. This review provides a comprehensive update of Chinese innovations to address intractable unmet medical need in China and worldwide in the optical sciences. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging.

Synthesis of methionine methyl ester-modified coumarin as the fluorescent-colorimetric chemosensor for selective detection Cu2+ with application in molecular logic gate

A methionine methyl ester-modified coumarin derivative was designed and synthesized, which could discriminate Cu²⁺ from other metal ions in HEPES buffer (10 mM, pH 7.4)/CH₃CN (40:60, V/V). The detection limit of WM toward Cu²⁺ was 1.84 × 10^-7 M, which was lower than the concentration of Cu²⁺ in drinking water suggested by WHO and EPA. And the proposed coordination mode exhibiting the interaction between WM and Cu²⁺ was studied by UV-Vis, fluorescence spectrum, ESI-MS and FT-IR. Based on the fluorescent reversibility of WM, WM was considered as a molecular logic gate and molecular keypad lock. In addition, the test strips and the silica gel plates prepared from the solution of WM also demonstrate the favorable selectivity toward Cu²⁺.

Coumarin based hydrazone as an ICT-based fluorescence chemosensor for the detection of Cu2+ ions and the application in HeLa cells

We have constructed a new coumarin based fluorescence probe BENZPYR with ICT character through condensation of N, N-diethylamino-3-acetyl coumarin with 2-hydrazinobenzothiazole. The absorbance and fluorescence spectral characteristics of BENZPYR revealed that the chemosensor can specifically detect for Cu²⁺ ions over other different metal ions and the lowest limit of detection was found in nano molar range. The turn off sensor of BENZPYR is related to chelation enhanced quenching (CHEQ) and intramolecular charge transfer (ICT) processes were serve as excellent fluorescent detection of Cu²⁺ ions in DMF medium. Fluorescence microscopy experiments revealed that probe BENZPYR may have application as a fluorophore to detect the Cu²⁺ in living cells. The simulated DFT analysis of electronic and structural properties and also UV-vis absorption spectra are in well accordance with the experimental UV-vis absorption spectra.

A novel pyrene-based selective colorimetric and ratiometric turn-on sensing for copper

Detection of copper attracts important in most environmental and biological systems. In this study, a simple probe BisPyTSC containing bis-pyrene core was synthesized, and cation binding and sensing properties were studied using colorimetric and fluorometric detection. The research indicated that the specific ligand affinity for Cu²⁺ ions results in drastic color and spectral changes. According to the data obtained, while the peak intensity increases at 376 nm, the peak intensity decreased at 280 nm in the absorption spectrum of BisPyTSC and an increase in fluorescence intensity of BisPyTSC was observed in the presence of Cu²⁺ ions. The binding ratio of BisPyTSC to Cu²⁺ was found to be 1:1 according to Job's plot experiments. The binding constant was calculated using the Benesi-Hildebrand equation and found to be 3.26 × 10⁴ M^-1. Based on these concentration dependent fluorescence changes, the limit of detection (LOD) value was calculated to be 14.5 μM for Cu²⁺, which is the range of copper that should be in the blood (11.8-23.6 μM). As a result of all these studies, we can understand that BisPyTSC is a good selective candidate turn-on sensor that can be used for Cu²⁺ detection.

Modular design for fluorophore homodimer probes using diethylentriamine as a common spacer

Cationic fluorophore homodimer probes 1 and 2 bearing 7-aminocoumarin and naphthalimide dyes, respectively, connected via diethylenetriamine (DETA) spacer, have been developed to demonstrate the validity of our modular probe design on the basis of the triamine-based spacer.

Reactive Blue 4 as a Single Colorimetric Chemosensor for Sequential Determination of Multiple Analytes with Different Optical Responses in Aqueous Media: Cu2+-Cysteine Using a Metal Ion Displacement and Cu2+-Arginine Through the Host-Guest Interaction

In the current study, we reported a novel label-free and facile colorimetric approach for the sequential detection of copper ion (Cu²⁺), L-arginine (Arg), and L-cysteine (Cys) in the H₂O (10.0 mmol L^-1 HEPES buffer solution, pH 7.0) using Reactive Blue 4 (RB4). First, the presence of Cu²⁺ led to a naked-eye color and spectral changes according to the binding site-signaling subunit approach. Then, the RB4-Cu²⁺ complex was successfully applied for Cys and Arg through different recognition pathways. The optical signals for Arg were observed due to its association involving the amino group, as well as the participation of the carboxylate group in a bidentate form to the complex, while selective behavior for Cys was explained by a metal displacement mechanism. The limits of detection for Cu²⁺, Arg, and Cys were calculated to be 1.96, 1.06, and 1.33 μmol L^-1, respectively. It could also be employed for the determination of three analytes in environmental, biological, and pharmaceutical samples. Importantly, the test strips based on RB4-Cu²⁺ complex could be used as a solid-state sensor for the detection of Cys and Arg. In addition, NAND and IMPLICATION molecular logic gates were obtained by using chemical inputs and UV-Vis absorbance signal as the output. Graphical Abstract.

Colorimetric and fluorescent probes for real-time naked eye sensing of copper ion in solution and on paper substrate

In this paper, BT ((E)-2-(4-(4-(bis(pyridin-2-ylmethyl)amino)styryl)-3-cyano-5,5-dimethylfuran-2(5H)-ylidene)malononitrile) with strong donor-π-acceptor structure was synthesized, which showed both colorimetric and fluorescent sensing ability toward Cu²⁺ with high selectivity and sensitivity. Job plot and mass spectra measurement revealed a 1 : 1 coordination mode between Cu²⁺ and probe BT in ethanol/HEPES (1 : 4 v/v) buffer (pH 7.2) solution, and the binding constant was calculated to be 3.6 × 10⁴ M^-1. The colour of BT solution (10 µM) immediately turned from purple red to yellow and the red fluorescence was quenched obviously when a certain amount of Cu²⁺ was added, which enabled a dual-channel detection of Cu²⁺. A paper strip pre-stained with BT solution was further fabricated and it also showed excellent sensing ability toward Cu²⁺ with a detection limit as low as 10^-6 M with the naked eye, which represents better portability and operation simplicity that is favourable for on-site analysis of Cu²⁺ in water.

Ultrasensitive turn-on fluorescence detection of Cu2+ based on p-dimethylaminobenzamide derivative and the application to cell imaging

A new p-dimethylaminobenzamide derivative based compound BDIH has been synthesized. Cu²⁺ turned on the fluorescence of compound BDIH with a 1:2 binding stoichiometry. The fluorescent color of compound BDIH shows an evident change from colorless to bright blue upon the addition of Cu²⁺, which could be visibly detected by the naked eye under UV light at 365nm. More importantly, the detection limit was found to be 0.64nM which is far lower than the maximal allowed concentration of the WHO limit (31.5μM) for drinking water. This selective "turn-on" fluorescence sensor was used to identify Cu²⁺ in living cells using confocal fluorescence microscopy, indicating that compound BDIH has a potential application for selective detection of Cu²⁺ in organism.

Highly sensitive and selective fluorescent sensor for copper(ii) based on salicylaldehyde Schiff-base derivatives with aggregation induced emission and mechanoluminescence

The present study provides valuable information for designing materials with AIE, Cu²⁺ sensor and MFC properties based on Schiff-bases.

A β-diketonate–europium(iii) complex-based fluorescent probe for highly sensitive time-gated luminescence detection of copper and sulfide ions in living cells

A strongly fluorescent β-diketonate–europium(iii) complex was developed for highly sensitive imaging of intracellular copper and sulfide ions with time-gated luminescence mode.

A benzimidazole-based chemodosimeter for the fluorometric detection of Zn and Cu via 1,5 proton shifts and C–N bond cleavage

The new probe APBHN that we designed has been successfully used for the detection of Zn²⁺and Cu²⁺in both (1 : 1) and (1 : 2) ratios chemically as well as biologically in liver carcinoma cellsvia1,5 proton shifts and C–N bond cleavage.

A Cu2+-Selective Probe Based on Phenanthro-Imidazole Derivative

A novel fluorescent Probe 1, based on phenanthro-imidazole has been developed as an efficient chemosensor for the trace detection of copper ions (Cu²⁺). Probe 1 demonstrated sensitive fluorescence quenching upon binding with Cu²⁺ through 1:1 stoichiometric chelation. The detection limit for Cu²⁺ ions was projected through linear quenching fitting to be as low as 2.77 × 10^-8 M (or 1.77 ppb). The sensing response was highly selective towards Cu²⁺ with minimal influence from other common metal ions, facilitating the practical application of Probe 1 in trace detection.

A new hydroxynaphthyl benzothiazole derived fluorescent probe for highly selective and sensitive Cu(2+) detection

A new reactive probe, 1-(benzo[d]thiazol-2-yl)naphthalen-2-yl-picolinate (BTNP), was designed and synthesized. BTNP acts as a highly selective probe to Cu(2+) in DMSO/H2O (7/3, v/v, Tris-HCl 10mM, pH=7.4) solution based on Cu(2+) catalyzed hydrolysis of the picolinate ester moiety in BTNP, which leads to the formation of an ESIPT active product with dual wavelength emission enhancement. The probe also possesses the advantages of simple synthesis, rapid response and high sensitivity. The pseudo-first-order reaction rate constant was calculated to be 0.205min(-1). Moreover, application of BTNP to Cu(2+) detection in living cells and real water samples was also explored.

Naphthalimide-based fluorescent probe for selectively and specifically detecting glutathione in the lysosomes of living cells

A novel naphthalimide-based fluorescent probe employing a sulfonamide unit as a thiol-responsive group is reported. It is capable of efficiently distinguishing GSH from cysteine and homocysteine. Bioimaging shows that it has high selectivity in living cells and can visualize the level of GSH in lysosomes. It is worth mentioning that different groups on the imide unit can affect the selectivity and reaction dynamics of the probe towards thiols.

The structural characterization and biological activity of sulfamethoxazolyl-azo-p-cresol, its copper(ii) complex and their theoretical studies

Sulfonamide-azophenol and its copper(ii) complex exhibit antimicrobial activity and interaction with DNA. Molecular docking was used to determine the mechanism of drug action.

A new thio-Schiff base fluorophore with copper ion sensing, DNA binding and nuclease activity

Copper ion recognition and DNA interaction of a newly synthesized fluorescent Schiff base (HPyETSC) were investigated using UV-vis and fluorescent spectroscopy. Examination using these two techniques revealed that the detection of copper by HPyETSC is highly sensitive and selective, with a detection limit of 0.39 μm and the mode of interaction between HPyETSC and DNA is electrostatic, with a binding constant of 8.97×10(4) M(-1). Furthermore, gel electrophoresis studies showed that HPyETSC exhibited nuclease activity through oxidative pathway.

Proton donor modulating ESIPT-based fluorescent probes for highly sensitive and selective detection of Cu2+

Two novel ESIPT-based fluorescent probes for Cu²⁺ detection were developed. Altering the linker in probe molecules reversed their sensing behavior. Both probes exhibited high selectivity and sensitivity to Cu²⁺, and can be used for cell imaging.

A novel coumarin based molecular switch for dual sensing of Zn(ii) and Cu(ii)

New coumarin based molecular switch for Zn²⁺ and Cu²⁺ presents a tunable system comprising of two INHIBIT logic gates with Zn²⁺ and Cu²⁺ or Zn²⁺ and EDTA as chemical inputs. IMPLICATION logic gate is obtained with Cu²⁺ and EDTA as chemical inputs.

Chemodosimeter approach for nanomolar detection of Cu2+ ions and their bio-imaging in PC3 cell lines

A new rhodamine–azaindole based fluorescence probe for Cu²⁺ has been synthesized which shows fluorescence resonance energy transfer process in acetonitrile. Further, the probe undergoes Cu²⁺ promoted hydrolysis in mixed aqueous media as well as in the intracellular systems.