Detecting Hg²⁺ Ions with an ICT Fluorescent Sensor Molecule: Remarkable Emission Spectra Shift and Unique Selectivity

A fluorescent ratiometric Hg2+ ion sensor RMS, based on a coumarin platform coupled with a tetraamide receptor, is presented. This sensor, employing the ICT mechanism, could be used to specifically detect Hg2+ ions in a neutral buffered water solution with an ∼100-nm blue shift in emission spectra

Colorimetric and Ratiometric Fluorescent Chemosensor with a Large Red-Shift in Emission: Cu(II)-Only Sensing by Deprotonation of Secondary Amines as Receptor Conjugated to Naphthalimide Fluorophore

A new fluorescent probe N-butyl-4,5-di[2-(phenylamino)ethylamino]-1,8-naphthalimide 1 senses only Cu(II) among heavy and transition metal (HTM) ions by means of a colorimetric (primrose yellow to pink) method with a large red-shift in emission (green to red) attributed to the deprotonation of the secondary amines as a receptor conjugated to the naphthalimide fluorophore

Ratiometric and Selective Fluorescent Sensor for Cu^II Based on Internal Charge Transfer (ICT)

A CuII-sensing, ratiometric, and selective fluorescent sensor 1, N-butyl-4,5-di[(pyridin-2-ylmethyl)amino]-1,8-naphthalimide, was designed and synthesized on the basis of the mechanism of internal charge transfer (ICT). In aqueous ethanol solutions of 1, the presence of CuII induces the formation of a 1:1 metal−ligand complex, which exhibits a strong, increasing fluorescent emission centered at 475 nm at the expense of the fluorescent emission of 1 centered at 525 nm

A Lysosome-Targetable Fluorescent Probe for Imaging Hydrogen Sulfide in Living Cells

In this work, a 1,8-naphthalimide-derived fluorescent probe for H2S based on the thiolysis of dinitrophenyl ether is reported. This probe exhibits turn-on fluorescence detection of H2S in bovine serum and lysosome-targetable fluorescent imaging of H2S with excellent selectivity

Ratiometric and Highly Selective Fluorescent Sensor for Cadmium under Physiological pH Range: A New Strategy to Discriminate Cadmium from Zinc

In a neutral aqueous environment, a new ratiometric Cd2+ fluorescent sensor 1a can successfully discriminate Cd2+ from Zn2+ by undergoing two different internal charge transfer (ICT) processes, and the high selectivity of sensor 1a to Cd2+ over some other metals was also observed. Moreover, through structure derivation and a series of NMR studies, the unique role of the 2-picolyl group (the part in red in the abstract graphic) in the sensor 1a−Cd2+ complexation was disclosed

Constructing a Local Hydrophobic Cage in Dye-Doped Fluorescent Silica Nanoparticles to Enhance the Photophysical Properties

Aggregation-caused quenching (ACQ) and poor photostability in aqueous media are two common problems for organic fluorescence dyes which cause a dramatic loss of fluorescence imaging quality and photodynamic therapy (PDT) failure. Herein, a local hydrophobic cage is built up inside near-infrared (NIR) cyanine-anchored fluorescent silica nanoparticles (FSNPs) in which a hydrophobic silane coupling agent (n-octyltriethoxysilane, OTES) is doped into FSNPs for the first time to significantly inhibit the ACQ effect and inward diffusion of water molecules. Therefore, the obtained optimal FSNP-C with OTES-modification can provide hydrophobic repulsive forces to effectively inhibit the π–π stacking interaction of cyanine dyes and simultaneously reduce the formation of strong oxidizing species (•OH and H2O2) in reaction with H2O, resulting in the best photostability (fluorescent intensity remained at 90.1% of the initial value after 300 s of laser scanning) and a high PDT efficiency on two- and three-dimensional (spheroids) HeLa cell culture models. Moreover, through molecular engineering (including increasing covalent anchoring sites and steric hindrance groups of cyanine dyes), FSNP-C exhibits the highest fluorescent intensity both in water solution (12.3-fold improvement compared to free dye) and living cells due to the limitation of molecular motion. Thus, this study provides an effectively strategy by combining a local hydrophobic cage and molecular engineering for NIR FSNPs in long-term bright fluorescence imaging and a stable PDT process

Zn²⁺-Triggered Amide Tautomerization Produces a Highly Zn²⁺-Selective, Cell-Permeable, and Ratiometric Fluorescent Sensor

It is still a significant challenge to develop a Zn2+-selective fluorescent sensor with the ability to exclude the interference of some heavy and transition metal (HTM) ions such as Fe2+, Co2+, Ni2+, Cu2+, Cd2+, and Hg2+. Herein, we report a novel amide-containing receptor for Zn2+, combined with a naphthalimide fluorophore, termed ZTRS. The fluorescence, absorption detection, NMR, and IR studies indicated that ZTRS bound Zn2+ in an imidic acid tautomeric form of the amide/di-2-picolylamine receptor in aqueous solution, while most other HTM ions were bound to the sensor in an amide tautomeric form. Due to this differential binding mode, ZTRS showed excellent selectivity for Zn2+ over most competitive HTM ions with an enhanced fluorescence (22-fold) as well as a red-shift in emission from 483 to 514 nm. Interestingly, the ZTRS/Cd2+ complex showed an enhanced (21-fold) blue-shift in emission from 483 to 446 nm. Therefore, ZTRS discriminated in vitro and in vivo Zn2+ and Cd2+ with green and blue fluorescence, respectively. Due to the stronger affinity, Zn2+ could be ratiometrically detected in vitro and in vivo with a large emission wavelength shift from 446 to 514 nm via a Cd2+ displacement approach. ZTRS was also successfully used to image intracellular Zn2+ ions in the presence of iron ions. Finally, we applied ZTRS to detect zinc ions during the development of living zebrafish embryos

Near-Infrared Fluorescence Probe for Monoamine Oxidase A with a Large Stokes Shift for Intraoperative Navigation

Monoamine oxidase A (MAO-A) is a dimeric flavoprotein that is found in the mitochondrial membrane. Currently, there is a lack of near-infrared fluorescent probes (NIR-FPs) with good specificity and high sensitivity for detecting MAO-A, making it difficult to accurately recognize and image cells in vitro and in vivo. In this study, the NIR-FP DDM-NH2 was designed and synthesized in order to detect MAO-A specifically in live biological systems. The probe comprised two functional components: dicyanoisophosphone as an NIR dye precursor and alanine as a recognition moiety. After identifying MAO-A, the probe exhibited an NIR emission peak at 770 nm with a significant Stokes shift (180 nm), 11-fold response factor, low detection limit of 99.7 nM, and considerably higher affinity toward MAO-A than that toward MAO-B, indicating high sensitivity. In addition, DDM-NH2 was effective when applied to the image-based assessment of MAO-A activity in HeLa cells, zebrafish, and tumor-bearing mice, demonstrating great potential for visualization-based research and MAO-A application in vivo

Endoplasmic Reticulum-Targeting Near-Infrared Fluorescent Probe for CYP2J2 Activity and Its Imaging Application in Endoplasmic Reticulum Stress and Tumor

CYP2J2 as an endoplasmic reticulum (ER)-expressed vital cytochrome P450 isoform participates in the metabolism of endogenous polyunsaturated fatty acids. Its abnormal expression and function are closely related to the progress of cancer and cardiovascular diseases. Herein, an ER-targeting near-infrared (NIR) fluorescent probe ER-BnXPI was developed for monitoring CYP2J2 activity, which possessed a high selectivity and sensitivity toward CYP2J2 among various CYP450 isoforms and exhibited excellent subcellular localization for ER. Then, the CYP2J2 variation behavior under the ER stress model was imaged by ER-BnXPI in living cells and successfully used for the in vivo imaging in different tumors that well distinguished tumor tissues from para-cancerous tissues. All these findings fully demonstrated that ER-BnXPI could be used as a promising tool for exploring the physiological function of CYP2J2 and provided some novel approach for the diagnosis and therapy of CYP2J2-related vascular inflammation and cancer