Rapid "turn-on" photoluminescence detection of bisulfite in wines and living cells with a formyl bearing bis-cyclometalated Ir(iii) complex

A fluorescent probe with serum albumin as a signal amplifier for real-time sensing of HSO3- in solution, mitochondria of animal cells and rice roots

Endogenous release of HSO3- during the enzymatic oxidation of sulfur containing amino acids in mitochondria or insufficiency of sulfite oxidase results in the accumulation of sulfite and thiosulfate in biological fluids affecting mitochondrial homeostasis of brain mitochondria associated with serious clinical symptoms related to neurological disorders. The red fluorescent probe MGQ undergoes self-assembly in water and reveals aggregation induced quenching of fluorescence. MGQ reveals 143-fold and 179-fold increases in fluorescence intensity at 645 nm, respectively, in the presence of HSA and BSA and does not significantly differentiate between two albumins. The detailed studies of MGQ have been performed in the presence of BSA. The presence of other enzymes/proteins and amino acids, viz. pepsin, trypsin, lysozyme, Bromelain, lysine, histidine, hemoglobin, etc., does not affect the fluorescence of MGQ or MGQ-BSA solutions and points to high selectivity towards BSA. The limit of detection for BSA is 10 nM. In PBS buffer, MGQ in the absence of BSA does not react with HSO3- and sluggishly in a 1 : 1 ethanol-water mixture. However, in the confined space of BSA/HSA, MGQ displays a signal amplification, undergoes instantaneous Michael type addition of HSO3- and results in a ratiometric change in fluorescence intensity in ≤1.5 min with the decrease of red fluorescence at 645 nm and emergence of green fluorescence at 515 nm. The LOD for the detection of HSO3- is 4 nM.

Shining New Light on Biological Systems: Luminescent Transition Metal Complexes for Bioimaging and Biosensing Applications

Luminescence imaging is a powerful and versatile technique for investigating cell physiology and pathology in living systems, making significant contributions to life science research and clinical diagnosis. In recent years, luminescent transition metal complexes have gained significant attention for diagnostic and therapeutic applications due to their unique photophysical and photochemical properties. In this Review, we provide a comprehensive overview of the recent development of luminescent transition metal complexes for bioimaging and biosensing applications, with a focus on transition metal centers with a d6, d8, and d10 electronic configuration. We elucidate the structure-property relationships of luminescent transition metal complexes, exploring how their structural characteristics can be manipulated to control their biological behavior such as cellular uptake, localization, biocompatibility, pharmacokinetics, and biodistribution. Furthermore, we introduce the various design strategies that leverage the interesting photophysical properties of luminescent transition metal complexes for a wide variety of biological applications, including autofluorescence-free imaging, multimodal imaging, organelle imaging, biological sensing, microenvironment monitoring, bioorthogonal labeling, bacterial imaging, and cell viability assessment. Finally, we provide insights into the challenges and perspectives of luminescent transition metal complexes for bioimaging and biosensing applications, as well as their use in disease diagnosis and treatment evaluation.

A near-infrared fluorescent probe for imaging of bisulfite in living animals and its application in food samples

Bisulfite (HSO₃^-) has been widely used as an antioxidant, enzyme inhibitor and antimicrobial agent in foodstuffs, pharmaceutical and beverages industries. It is also a signaling molecular in the cardiovascular and cerebrovascular systems. Nevertheless, a high level of HSO₃^- can cause allergic reactions and asthmatic attacks. Accordingly, the monitoring of HSO₃^- levels possesses momentous significance from the perspectives of biological technology and food security supervision. Herein, a near-infrared fluorescent probe LJ is rationally constructed for sensing HSO₃^-. The fluorescence quenching recognition mechanism was realized by the addition reaction of electron-deficient CC bond in probe LJ and HSO₃^-. Probe LJ revealed multifarious preponderances such as longer wavelength emission (710 nm), low cytotoxicity, larger Stokes shift (215 nm), better selectivity, higher sensitivity (72 nM) and short response time (50 s). Encouragingly, probe LJ can detect HSO₃^- in living zebrafish and mice in vivo by fluorescence imaging techniques. In the meantime, probe LJ was also successfully employed to semi-quantitatively detect HSO₃^- in real foodstuff samples and water samples by the "naked-eye" colorimetry without the help of any special instruments. More importantly, quantitative detection of HSO₃^- in practical food samples was achieved through a smartphone application software. Consequently, probe LJ is expected to provide an effective and convenient way for the detection and monitoring of HSO₃^- in organisms and for food safety detection, which has tremendous application potential.

Small-Molecule Fluorescent Probe for Detection of Sulfite

Sulfite is widely used as an antioxidant additive and preservative in food and beverages. Abnormal levels of sulfite in the body is related to a variety of diseases. There are strict rules for sulfite intake. Therefore, to monitor the sulfite level in physiological and pathological events, there is in urgent need to develop a rapid, accurate, sensitive, and non-invasive approach, which can also be of great significance for the improvement of the corresponding clinical diagnosis. With the development of fluorescent probes, many advantages of fluorescent probes for sulfite detection, such as real time imaging, simple operation, economy, fast response, non-invasive, and so on, have been gradually highlighted. In this review, we enumerated almost all the sulfite fluorescent probes over nearly a decade and summarized their respective characteristics, in order to provide a unified platform for their standardized evaluation. Meanwhile, we tried to systematically review the research progress of sulfite small-molecule fluorescent probes. Logically, we focused on the structures, reaction mechanisms, and applications of sulfite fluorescent probes. We hope that this review will be helpful for the investigators who are interested in sulfite-associated biological procedures.

Synthesis of pH-responsive cyclometalated iridium(III) complex and its application in the selective killing of cancerous cells

Cyclometalated iridium(III) complexes are promising candidates as photosensitizers (PSs) in photodynamic therapy (PDT). The challenge in PDT is the selective killing of cancerous cells over the neighboring normal cells. In this work, a pH-responsive cyclometalated iridium(III) complex (probe 1) was designed and synthesized as an effective PS to selectively kill cancerous cells, with 3-(2-pyridyl)benzaldehyde used as the main ligand and 1-(2-pyridyl)-β-carboline used as an ancillary ligand. Probe 1 shows enhanced photoluminescence emission and higher ¹O₂ quantum yield in an acidic environment compared to a neutral solution, which led to remarkable phototoxicity toward cancerous cells and high selectivity for killing cancerous cells over normal cells within 10 min. This work demonstrates that the cyclometalated iridium(III) complex with acidic pH-responsive photoluminescence emission and high ¹O₂ generation is an effective alternative PS for selectively killing cancerous cells.

A Novel Fluorescence Probe for the Reversible Detection of Bisulfite and Hydrogen Peroxide Pair in Vitro and in Vivo

The detection of changes in the reactive oxygen species (ROS)/reactive sulfur species (RSS) couple is important for studying the cellular redox state. Herein, we developed a 1,8-naphthalimide-based fluorescence probe (NI) for the reversible detection of bisulfite (HSO₃ ^- ) and hydrogen peroxide (H₂ O₂ ) in vitro and in vivo. NI has been designed with a reactive ethylene unit which specifically reacts with HSO₃ ^- by a Michael addition reaction mechanism, resulting in the quenching of yellow fluorescence at 580 nm and the appearing of green fluorescence at 510 nm upon excitation at 500 nm and 430 nm, respectively. The addition product (NI-HSO₃ ) could be specifically oxidized to form the original C=C bond of NI, recovering the fluorescence emission and color. The detection limits of NI for HSO₃ ^- and NI-HSO₃ for H₂ O₂ were calculated to be 2.05 μM and 4.23 μM, respectively. The reversible fluorescence response of NI towards HSO₃ ^- /H₂ O₂ couple can be repeated for at least five times. NI is reliable at a broad pH range (pH 3.0-11.5) and features outstanding selectivity, which enabled its practical applications in biological and food samples. Monitoring the reversible and dynamic inter-conversion between HSO₃ ^- and H₂ O₂ in vitro and in vivo has been verified by fluorescence imaging in live HeLa cells, adult zebrafish and nude mice. Moreover, NI has been successfully applied to detect of HSO₃ ^- levels in food samples.

Colorimetric and Ratiometric Fluorescence Detection of HSO3- With a NIR Fluorescent Dye

Bisulfite (HSO₃^-) has been widely used in food and industry, which has brought convenience to human life, but also seriously endangered human health. In this work, the probe PBI was designed and synthesized to detect bisulfite (HSO₃^-) through nucleophilic addition reaction. The probe PBI showed a selective reaction to HSO₃^- and can quantitatively detect HSO₃^-. At the same time, the color of the probe PBI changed significantly, which provided a simple method for the naked eye to identify HSO₃^-. Finally, it was successfully applied to the fluorescence imaging of HSO₃^- in living cells.

An efficient hemicyanine dyes-based ratiometric fluorescence probe for sulfur dioxide derivatives in live-cells and seawater

In life systems, sulfurdioxide (SO₂) has very important function in several physiological processes, which can be generated endogenously during the biosynthesis of sulfur-containing amino acids. Herein, a ratiometric fluorescence probe CY carried with the structure of hemicyanine dyes has been developed to track SO₂ derivatives through Michael-addition reaction. The solution of CY shows significant changes from yellow to colorless after adding the SO₃^2-/HSO₃^- in day light within 2 min. Successfully, probe CY can detect SO₂ derivatives in living cells and seawater. Furthermore, probe CY also be used to monitor the change of SO₂ derivatives in seawater. These results give evidence of the potential application of CY in future biomedical diagnosis and marine environment research.

Novel Platinum(II) Complex-based Luminescent Probe for Detection of Hypochlorite in Cancer Cells

Hypochlorite (ClO⁻) is of great importance either for the metabolism of living organisms or as disinfectant in daily life. However, improper concentration levels of ClO⁻ lead to serious health problems including erythrocyte damage, cardiovascular problems, neuron degeneration, lung/kidney injury and cancer. Therefore, a sensitive and selective detection method is required for the visualization and measurement of ClO⁻. In this work, a novel platinum(II) complex-based luminescent probe Pt-CHO was synthesized and utilized to detect ClO⁻. This "turn-off" probe exhibits high sensitivity, excellent selectivity, good pH stability, low limit of detection and instantaneous response ability. Moreover, the luminescent response is caused by the oxidation of aldehyde into carboxyl groups combined with the coordination of hydroxyl groups at the Pt center, which is rarely reported. The cell imaging of HeLa cells proved the considerable potential of the probe for ClO⁻ imaging in living cells.

Red-Emission Probe for Ratiometric Fluorescent Detection of Bisulfite and Its Application in Live Animals and Food Samples

Key roles of bisulfite (HSO3 -) in food quality assurance and human health necessitate a reliable analytical method for rapid, sensitive, and selective detection of HSO3 -. Herein, a new red-emitting ratiometric fluorescence probe, BIQ, is reported for sensitive and selective detection of HSO3 - in food samples and live animals. Probe BIQ recognizes HSO3 - via a 1,4-nucleophilic addition reaction. As a result of this specific reaction, emission intensities at 625 and 475 nm are dramatically changed, allowing the detection of HSO3 - in a ratiometric fluorescence model in an aqueous solution. The obvious changes of solution color from pink to transparent and fluorescence color from rose-red to cyan allow the detection of HSO3 - by naked eyes. Furthermore, probe BIQ has fast response in color and fluorescence (<2 min), excellent selectivity, and a low detection limit (0.29 μM), which enables its application in HSO3 - detection in food samples and live organisms. The practical applications of probe BIQ are then demonstrated by the visualization of HSO3 - in live animals (zebrafish and nude mouse) as well as the determination of HSO3 - in white wine and sugar.

An Efficient Probe of Cyclometallated Phosphorescent Iridium Complex for Selective Detection of Cyanide

A cyclometallated phosphorescent iridium-based probe to detect CN^- was prepared through a cyanide alcoholize reaction based on the C^N type main ligand and N^N type ancillary ligand (2-phenyl pyridine and 1,10-phenanthroline-5-carboxaldehyde, respectively). The efficient probe exhibited good sensitivity in response to CN^- in an CH₃CN and H₂O (95/5) mixture within a 1.23 μM detection limit. The response of PL is directly in line with the concentration of CN^- from 0 to 2.0 equiv. The PL investigation of other reactive anions proved the great selectivity to CN^-. Additionally, upon adding 1.0 equiv. of cyanide, the formation of cyanohydrin was correctly elucidated in ¹H NMR, FT-IR, and mass spectra studies. The conspicuous results indicate that the iridium complex has the potential possibility of application in other biosystems related to CN^-.