A fast, highly selective and sensitive dansyl-based fluorescent sensor for copper (II) ions and its imaging application in living cells

A Reversible Fluorescent Chemosensor for the Selective Detection of Cu2+ and CN- ions by Displacement Approach

A novel fluorescence chemosensor BDP (2-(1-(benzothiazol-2-yl)-5-(4-(diphenylamino)phenyl)-4,5-dihydro-1H-pyrazol-3-yl)phenol) has been synthesized and its sensing behavior has been screened towards various cations by absorption, emission and mass spectroscopic techniques. The probe BDP detects Cu2+ ions preferentially over other metal ions, and the resulting BDP-Cu2+ ensemble acts as a secondary sensor for cyanide anion detection over other anions. The fluorescence intensity of the probe BDP is quenched when it comes into contact with Cu2+ ions, but it is increased reversibly when it comes into contact with cyanide anion, according to spectroscopic measurements. Along with this, optical studies indicate that the sensor BDP has capability to sense Cu2+ and CN- ions selectively over other examined competitive ions with the LOD of 2.57×10-8 M and 2.98×10-8 M respectively. The detection limit of Cu2+ ions is lower than the WHO recommended Cu2+ ions concentration (31.5 µM) in drinking water. On the basis of "on-off-on" fluorescence change of the probe BDP upon interaction with Cu2+ and CN- ions, a possible mechanism for this selective sensing behavior was presented and IMPLICATION logic gate was successfully designed. Furthermore, cell imaging investigations were used to investigate the probe BDP's biological applicability.

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.

Dansyl-modified carbon dots with dual-emission for pH sensing, Fe3+ ion detection and fluorescent ink

In this work, a multifunctional ratiometric fluorescence (FL) nanohybrid (CSCDs@DC) was synthesized from chitosan based carbon dots (CSCDs) and dansyl chloride (DC) at room temperature. The CSCDs@DC revealed strong FL intensity, great stability and excellent anti-photobleaching properties. Herein, CSCDs@DC was responsive to pH value in the range of 1.5-4.0 and exhibited color-switchable FL properties between acidic and alkaline environments. In addition, CSCDs@DC showed good selectivity and sensitivity towards Fe³⁺ ions. A good linear relationship for the Fe³⁺ ion detection was obtained in the range from 0 μM to 100 μM, with a detection limit of 1.23 μM. What's more, CSCDs@DC can be used as a fluorescent ink. It expressed superior optical properties after 3 months of storage or continuous exposure to UV light for 24 h. This study suggested that CSCDs@DC had potential in the detection of pH and metal ions, as well as showing promising application in the anti-counterfeiting field.

Coumarin-Based Dual Chemosensor for Colorimetric and Fluorescent Detection of Cu2+ in Water Media

A novel coumarin derivative (5) was synthesized and used as a colorimetric and fluorescent probe for selective detection of Cu²⁺ ions in the presence of other metal ions, with the detection limits of 5.7 and 4.0 ppb, respectively. Cu²⁺ ion reacts with probe 5 to form a 1:1 stoichiometry complex, resulting in a remarkable redshift of absorption maximum from 460 to 510 nm, as well as almost completely quenching fluorescence intensity of probe 5 at the wavelength of 536 nm. These changes can be distinctly observed by naked eyes. In addition, the working pH range of probe 5 is wide and suitable for physiological conditions, thus probe 5 may be used for detection of Cu²⁺ ions in living cells. The stable structures of probe 5 and its 1:1 complex with Cu²⁺ ion were optimized at the PBE0/6-31+G(d) level of theory. The presence and characteristics of bonds in compounds were studied through atoms in a molecule and natural bond orbital analysis. The formation of the complex led to a strong transfer of electron density from probe 5 as a ligand to Cu²⁺ ion, resulting in breaking the π-electron conjugated system, which is the cause of fluorescence quenching and color change of 5-Cu²⁺ complex.

Design and synthesis of fluorescently labeled steroidal antiestrogens

A set of derivatives of 11β-(4-oxyphenyl)estradiol were prepared as potential fluorescent imaging agents for the evaluation of the estrogen receptor. The compounds were designed based on the established affinity and selectivity of 11β-[4-(dimethylethoxy)phenyl]estradiol (RU39411) as an estrogen receptor (ER) antagonist. The 5-(dimethylamino) naphathalene-1-sulfonyl (dansyl) and 7-nitrobenzo[c][1,2,5] oxadiaol-4-yl (NBD) moieties were selected based on their fluorescent and physicochemical properties. A convergent synthesis was developed that culminated in the [3 + 2] copper (I) assisted alkyne-azide cycloaddition coupling of the steroidal and fluorescent components. Good yields were obtained for the intermediates and final products, and the structural variations in the steroid component will permit evaluation of ER affinity and selectivity.

Review of fluorescent steroidal ligands for the estrogen receptor 1995-2018

The development of fluorescent ligands for the estrogen receptor (ER) continues to be of interest. Over the past 20 years, most efforts have focused on appending an expanding variety of fluorophores to the B-, C- and D-rings of the steroidal scaffold. This review highlights the synthesis and evaluation of derivatives substituted primarily at the 6-, 7α- and 17α-positions, culminating with our recent work on 11β-substituted estradiols, and proposes an approach to new fluorescent imaging agents that retain high ER affinity.