A cancer cell-specific fluorescent probe for imaging Cu2+ in living cancer cells

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.

Recent advances in small-molecule fluorescent probes with the function of targeting cancer receptors

Cancer is "the sword of Damocles" that threatens human life and health. Therefore, the diagnosis and treatment of cancer have been receiving much attention. Many overexpressed receptors on the surface of cancer cells provide us with an effective way to specifically identify the cancer cells, and receptor targeting strategies are becoming one of the hot ideas to enhance the ability of fluorescent probes to target tumors. Fluorescent probes connected to ligands are targeted at cancer cell surfaces through receptor-mediated endocytosis. Receptor-targeting probes can image and track cancer cells, determine tumor boundaries, monitor deep lesions, and play a role in clinical medicine, such as fluorescent imaging-guided surgery. In this review, based on the perspective of small molecule fluorescent probes, we reviewed the design ideas, photophysical properties, and applications of receptor-targeting probes for detecting biomarkers in imaging and tracing cancer cells and prospected the future developmental direction of such probes. We hope that this review will provide more ideas for the design and development of active targeting probes for receptors and lead to more applications in the medical field.

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.

An efficient tetrahydroquinazolin-2-amine derivative-grafted cellulose fluorescent probe for detection of Cu2+ and Zn2

Cu²⁺ and Zn²⁺ play crucial roles in many physiological processes, and their disorder will cause harm to human health. An efficient difunctional fluorescent probe CMC-GE-PQA for simultaneous detection of Cu²⁺ and Zn²⁺ was synthesized based on carboxymethyl cellulose. The probe CMC-GE-PQA exhibited a moderate blue fluorescence color. Interestingly, this probe showed a distinct fluorescence enhancement response toward Zn²⁺, while it displayed a significant fluorescence quenching response toward Cu²⁺. The detection limits of CMC-GE-PQA for Cu²⁺ and Zn²⁺ were calculated as low as 5.0 × 10^-8 M and 1.0 × 10^-7 M, respectively. The detection mechanisms of CMC-GE-PQA for Cu²⁺ and Zn²⁺ were fully verified by Job's plot, X-ray photoelectron spectroscopy analysis. The probe CMC-GE-PQA was applied to determine the trace amounts of Cu²⁺ and Zn²⁺ in environmental water samples. In addition, the probe CMC-GE-PQA-based fluorescent film and hydrogel were manufactured to achieve the portable detection of Cu²⁺ and Zn²⁺.

Facile synthesis of sulfur and oxygen co-doped graphitic carbon nitride quantum dots for on-off detection of Cu2+in real samples and living cells

A fluorescent sulfur and oxygen co-doped graphitic carbon nitride quantum dots (S,O-CNQDs) were prepared from ethylenediaminetetraacetic acid disodium salt dihydrate and thiourea as the carbon and sulfur sources. The morphology and surface functional groups of S,O-CNQDs were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The fluorescence of S,O-CNQDs could be quenched efficiently by Cu²⁺under the optimum conditions. The S,O-CNQDs could function as an excellent fluorescent probe for Cu²⁺detection with a wide linear range of 0.50-15μM and a low detection limit of 0.58 nM. In addition, this fluorescent probe was employed for monitoring Cu²⁺in samples of tap water, lake water, human serum and urine with good recoveries from 99.0% to 110.0%. Moreover, the S,O-CNQDs with high cell penetration and low cytotoxicity were utilized for Cu²⁺detection in living cells. Owing to the excellent properties of S,O-CNQDs, the as-prepared S,O-CNQDs can be a potential candidate for biological applications.

Evaluation of Fluorescent Cu2+ Probes: Instant Sensing, Cell Permeable Recognition and Quantitative Detection

By incorporating a rhodamine spirolactam structure as the recognition site for Cu2+, two novel probes were synthesized through a connection of rhodamine 6G acylhydrazine and 5-formyl-6-hydroxyl-4-methylcoumarin/2,4-dihydroxybenzaldehyde. In the recognition process of probes towards Cu2+, the spirolactam ring exhibited opening and closing, accompanying an instant and specific change in fluorescence and in color, which could also achieve a naked-eye and semiquantitative recognition of aqueous Cu2+ besides the fluorescent Cu2+ detection method. Fluorescent analyses and ECV304 cell imaging further revealed the probes' good optical stability, instant response, low toxicity, and membrane permeability, which offers future possibilities for the probes' instant detection and the real-time tracking of Cu2+ in biological systems.

Novel polysiloxane-based rhodamine B fluorescent probe for selectively detection of Al3+ and its application in living-cell and zebrafish imaging

Polysiloxanes have excellent stability and biological relevance and are suitable for biological research. However, there were few polysiloxane-based fluorescent probes for bioimaging. This report successfully designed a new polysiloxane-based polymer fluorescent probe (RB-1) for the first time as a "turn-on" fluorescent probe response to Al³⁺ ion with highly sensitive and selectivity. Importantly, this probe could also apply both in cell and zebrafish imaging, indicating the huge application development prospects of polysiloxane-based fluorescent probes in future.

A highly sensitive and fast responsive naphthalimide-based fluorescent probe for Cu2+ and its application

The response of the probe L to Cu²⁺ is reversible and very fast (20 s). L has a low detection limit of 49 nM and was used for imaging of Cu²⁺ in MCF-7 cells with satisfying results. The sensor L can be analyzed with a molecular logic gate.