Synthesis of Rhodamine-Based Chemosensor for Fe3+ Selective Detection with off-on Mechanism and its Biological Application in DL-Tumor 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.

A Study of Small Molecule-Based Rhodamine-Derived Chemosensors and their Implications in Environmental and Biological Systems from 2012 to 2021: Latest Advancement and Future Prospects

Rhodamine-based chemosensors have sparked considerable interest in recent years due to their remarkable photophysical properties, which include high absorption coefficients, exceptional quantum yields, improved photostability, and significant red shifts. This article presents an overview of the diverse fluorometric, and colorimetric sensors produced from rhodamine, as well as their applications in a wide range of fields. The ability of rhodamine-based chemosensors to detect a wide range of metal ions, including Hg+2, Al3+, Cr3+, Cu2+, Fe3+, Fe2+, Cd2+, Sn4+, Zn2+, and Pb2+, is one of their major advantages. Other applications of these sensors include dual analytes, multianalytes, and relay recognition of dual analytes. Rhodamine-based probes can also detect noble metal ions such as Au3+, Ag+, and Pt2+. They have been used to detect pH, biological species, reactive oxygen and nitrogen species, anions, and nerve agents in addition to metal ions. The probes have been engineered to undergo colorimetric or fluorometric changes upon binding to specific analytes, rendering them highly selective and sensitive by ring-opening via different mechanisms such as Photoinduced Electron Transfer (PET), Chelation Enhanced Fluorescence (CHEF), Intramolecular Charge Transfer (ICT), and Fluorescence Resonance Energy Transfer (FRET). For improved sensing performance, light-harvesting dendritic systems based on rhodamine conjugates has also been explored for enhanced sensing performance. These dendritic arrangements permit the incorporation of numerous rhodamine units, resulting in an improvement in signal amplification and sensitivity. The probes have been utilised extensively for imaging biological samples, including imaging of living cells, and for environmental research. Moreover, they have been combined into logic gates for the construction of molecular computing systems. The usage of rhodamine-based chemosensors has created significant potential in a range of disciplines, including biological and environmental sensing as well as logic gate applications. This study focuses on the work published between 2012 and 2021 and emphasises the enormous research and development potential of these probes.

A dual channel rhodamine appended smart probe for selective recognition of Cu2+ and Hg2+ via "turn on" optical readout

A new rhodamine-6G hydrazone RHMA has been synthesized using rhodamine-6G hydrazide and 5-Allyl-3-methoxysalicylaldehyde. RHMA has been fully characterized with different spectroscopic methods and single crystal XRD. RHMA can selectively recognize Cu²⁺ and Hg²⁺ in aqueous media amongst other common competitive metal ions. A significant change in absorbance was observed with Cu²⁺ and Hg²⁺ ions with emergence of a new peak at λ_max 524 nm and 531 nm respectively. Hg²⁺ ions lead to "turn-on" fluorescence enhancement at λ_max 555 nm. This event of absorbance and fluorescence marks the opening of spirolactum ring causing visual color change from colorless to magenta and light pink.RHMA-Cu²⁺ and RHMA- Hg²⁺complexes are found to be reversible in presence of EDTA^2-ions. RHMA has real application in form of test strip. Additionally, the probe exhibits turn-on readout-based sequential logic gate-based monitoring of Cu²⁺ and Hg²⁺ at ppm levels, which may be able to address real-world challenges through simple synthesis, quick recovery, response in water, "by-eye" detection, reversible response, great selectivity, and a variety of output for accurate investigation.

Recent Advances on Iron(III) Selective Fluorescent Probes with Possible Applications in Bioimaging

Iron(III) is well-known to play a vital role in a variety of metabolic processes in almost all living systems, including the human body. However, the excess or deficiency of Fe3+ from the normal permissible limit can cause serious health problems. Therefore, novel analytical methods are developed for the simple, direct, and cost-effective monitoring of Fe3+ concentration in various environmental and biological samples. Because of the high selectivity and sensitivity, fast response time, and simplicity, the fluorescent-based molecular probes have been developed extensively in the past few decades to detect Fe3+. This review was narrated to summarize the Fe3+-selective fluorescent probes that show fluorescence enhancement (turn-on) and ratiometric response. The Fe3+ sensing ability, mechanisms along with the analytical novelties of recently reported 77 fluorescent probes are discussed.

GB, Latiyan S, Jain S. Remarkably selective biocompatible turn-on fluorescent probe for detection of Fe3+ in human blood samples and cells

The robust nature of a biocompatible fluorescent probe is demonstrated, by its detection of Fe³⁺ even after repeated rounds of quenching (reversibility) by acetate in real human blood samples and cells in vitro.

Water switched aggregation/disaggregation strategies of a coumarin–naphthalene conjugated sensor and its selectivity towards Cu2+ and Ag+ ions along with cell imaging studies on human osteosarcoma cells (U-2 OS)

A simple coumarin–naphthalene conjugated chemosensor (R1) exhibited an excellent AIE effect in methanol/water (1 : 1).