Near-infrared fluorescent probe for selective detection of Cu2+ in living cells and in Vivo

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.

Construction of a novel ESIPT and AIE-based fluorescent sensor for sequentially detecting Cu2+ and H2S in both living cells and zebrafish

The development of effective methods for tracking Cu²⁺ and H₂S in living organisms is urgently required due to their vital function in a variety of pathophysiological processes. In this work, a new fluorescent sensor BDF with excited-state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) features for the successive detection of Cu²⁺ and H₂S was constructed by introducing 3,5-bis(trifluoromethyl)phenylacetonitrile into the benzothiazole skeleton. BDF showed a fast, selective and sensitive fluorescence "turn off" response to Cu²⁺ in physiological media, and the situ-formed complex can serve as a fluorescence "turn on" sensor for highly selective detection of H₂S through the Cu²⁺ displacement approach. In addition, the detection limits of BDF for Cu²⁺ and H₂S were determined to be 0.05 and 1.95 μM, respectively. Encouraged by its favourable features, including strong red fluorescence from the AIE effect, large Stokes shift (285 nm), high anti-interference ability and good function at physiological pH as well as a low toxicity, BDF was successfully applied for the consequent imaging of Cu²⁺ and H₂S in both living cells and zebrafish, making it an ideal candidate for detecting and imaging of Cu²⁺ and H₂S in live systems.

3A novel carbazole-based AIE-active fluorescent sensor for fast and ultrasensitive detection of Cu2+ and Co2+ in normal saline system

A novel phenyl-carbazole-based fluorescent sensor (PCBP) has been synthesized and investigated to selectively detect Cu²⁺ or Co²⁺. The PCBP molecule exhibits the excellent fluorescent property with the aggregation-induced emission (AIE) effect. In given THF/normal saline (f_w = 95%) system, the PCBP sensor shows turn-off fluorescence performance at 462 nm with Cu²⁺ or Co²⁺. It reveals excellent characteristics of good selectivity, and ultra-high sensitivity, strong anti-interference ability, wide pH applicable range, as well as ultra-fast detection response. The limit of detection (LOD) of the sensor reaches 1.1 × 10^-9 mol·L^-1 and 1.1 × 10^-8 mol·L^-1 for Cu²⁺ and Co²⁺ in turn. The formation mechanism of AIE fluorescence of PCBP molecules is attributed to the synergistic effect of intramolecular & intermolecular charge transfer (I&ICT). Meanwhile, the PCBP sensor has good repeatability for the detection of Cu²⁺, and performs excellent stability and sensitivity for the detection of Cu²⁺ in real water sample. The PCBP-based fluorescent test strips present reliable capacity for the detection of Cu²⁺ and Co²⁺⁺ in aqueous solution.

New insight into the application of fluorescence platforms in tumor diagnosis: From chemical basis to clinical application

Early and rapid diagnosis of tumors is essential for clinical treatment or management. In contrast to conventional means, bioimaging has the potential to accurately locate and diagnose tumors at an early stage. Fluorescent probe has been developed as an ideal tool to visualize tumor sites and to detect biological molecules which provides a requirement for noninvasive, real-time, precise, and specific visualization of structures and complex biochemical processes in vivo. Rencently, the development of synthetic organic chemistry and new materials have facilitated the development of near-infrared small molecular sensing platforms and nanoimaging platforms. This provides a competitive tool for various fields of bioimaging such as biological structure and function imaging, disease diagnosis, in situ at the in vivo level, and real-time dynamic imaging. This review systematically focused on the recent progress of small molecular near-infrared fluorescent probes and nano-fluorescent probes as new biomedical imaging tools in the past 3-5 years, and it covers the application of tumor biomarker sensing, tumor microenvironment imaging, and tumor vascular imaging, intraoperative guidance and as an integrated platform for diagnosis, aiming to provide guidance for researchers to design and develop future biomedical diagnostic tools.

Crystal structure of (4′E)-6′-(diethylamino)-2-[(E)-[(pyren-1-yl)methylidene]amino]-4′-{2-[(2E)-1,3,3-trimethyl-2,3-dihydro-1H-indol-2-ylidene]ethylidene}-1′,2,2′,3,3′,4′-hexahydrospiro[isoindole-1,9′-xanthene]-3-one, C54H48N4O2

C54H48N4O2, triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 11.1883(5) Å, b = 13.5364(5) Å, c = 14.3412(5) Å, α = 105.885(3)°, β = 97.710(3)°, γ = 94.126(3)°, Z = 2, V = 2056.64(14) Å3, R gt (F) = 0.0685, wR ref (F 2) = 0.1606, T = 293(2) K.

Crystal structure of (4′E)-6′-(diethylamino)-2-[(E)-[(6-methylpyridin-2-yl)methylidene]amino]-4′-{2-[(2E)-1,3,3-trimethyl-2,3-dihydro-1H-indol-2-ylidene]ethylidene}-1′,2,2′,3,3′,4′-hexahydrospiro[isoindole-1,9′-xanthene]-3-one, C44H45N5O2

C44H45N5O2, triclinic P 1 ‾ $P\overline{1}$ (no. 2), a = 11.2140(4) Å, b = 11.9932(5) Å, c = 14.2703(5) Å, α = 98.879(3)°, β = 102.025(3)°, γ = 91.122(3)°, Z = 2, V = 1851.98(12) Å3, R gt (F) = 0.0549, wR ref(F 2) = 0.1616, T = 293(2) K.

A novel fluorescent chemosensor based on coumarin and quinolinyl-benzothiazole for sequential recognition of Cu2+ and PPi and its applicability in live cell imaging

In this study, a highly selective fluorescent sensor (E)-2-((2-(benzo[d]thiazol-2-yl)quinolin-8-yl)oxy)-N'-((7-(diethylamino)-2-oxo-2H-chromen-3-yl)methylene)acetohydrazide (TQC) was synthesized from 2-methylquinolin-8-ol and 4-(diethylamino)-2-hydroxybenzaldehyde and its structure was characterized by ¹H NMR, ¹³C NMR, ESI-HR-MS and density functional theory (DFT) calculation. Sensor TQC showed an obvious "on-off-on" fluorescence response to Cu²⁺ and PPi in a DMSO/HEPES (3:2 v/v, pH = 7.4) buffer system. The detection limits of sensor TQC were 0.06 μM to Cu²⁺ and 0.01 μM to PPi. In addition, sensor TQC showed a 1:1 binding stoichiometry to Cu²⁺ and TQC-Cu²⁺ complex showed a 2:1 binding stoichiometry to PPi. The optimum pH range of sensor TQC and TQC-Cu²⁺ was 3-8. Further studies demonstrated that sensor TQC could be made into test paper strips for the qualitative of Cu²⁺ and PPi and showed sequentially "on-off-on" fluorescent bio-imaging of Cu²⁺ and PPi in HeLa cells.

A 4,5-quinolimide-based fluorescent sensor for sequential detection of Cu2+ and cysteine in water and living cells with application in a memorized device

In this study, a new 4,5-quinolimide-based fluorescent sensor BNC was synthesized and characterized. BNC showed single selectivity for Cu²⁺via the "turn-off" fluorescence among various common metal ions. After forming a 1:1 stoichiometric complex with Cu²⁺, the detection limit (LOD) of BNC for Cu²⁺ was measured to be 0.44 μM. Subsequently, the in situ generated BNC-Cu²⁺ complex had been used for sensing Cys with the LOD of 1.5 μM through the displacement strategy, resulting in the revivable emission of BNC. According to the "off-on-off" fluorescence cycle of BNC generated by the alternate addition of Cu²⁺ and Cys, a reversible memorized device with "read-write-read-erase" behavior was constructed at the molecular level. Furthermore, the recoveries of Cu²⁺ in lake water with BNC were in the range of 95.0-105%. And sequential fluorescence imagings of BNC for Cu²⁺ and Cys were successfully applied in living yeast cells.