A novel mitochondrial-targeted two-photon fluorescent probe for ultrafast monitoring of SO2 derivatives and its applications

A FRET-based ratiometric fluorescent probe for sensing bisulfite/sulfite and viscosity and its applications in food, water samples and test strips

A FRET-based ratiometric dual-response fluorescent probe, CQI, constructed by combining quinolinium-indole as the acceptor and coumarin as the donor, was developed for sensing HSO3-/SO32- and viscosity. After the interaction of probe CQI with the analyte, we achieved a green channel for the response to HSO3-/SO32- and an orange channel for the response to viscosity. We comprehensively evaluated the ability of CQI to detect SO2 derivatives and viscosity using fluorescence spectroscopy. Probe CQI exhibited a large Stokes shift (196 nm), a high energy transfer efficiency (99.6 %) and a wide detection range (0-250 μM). The fluorescence intensity of the probe increased up to 14-fold with increasing viscosity, and CQI could detect the viscosity of food thickeners. More importantly, probe CQI could not only successfully monitor SO2 derivatives in various food and water samples, but also be prepared as bisulfite test strips.

High-selective two-site fluorescent probe for Cys/SO2 detection and cell imaging

A fluorescent probe has been designed using cyanine phenothiazine and 7-nitro-1,2,3-benzoxadiazole (NBD) for selective detection of Cys-SO2 components. The probe utilizes the NBD structure to achieve specificity towards Cys and employs a reaction mechanism between the double bond of cyanine and phenothiazine with SO32- to achieve selectivity towards SO2. Importantly, the NBPI phenothiazine structure incorporates a large C-O bond energy attached to NBD, effectively eliminating interference from Hcy and ensuring highly selective response to Cys. The optimized design of the probe enables excellent linearity and extremely low detection limits for Cys-SO2 components in vitro experiments. The probe NBPI allows separate detection of Cys-SO2 in the presence of both components. Furthermore, the probe NBPI demonstrated successful imaging of endogenous and exogenous Cys and SO2 in cell studies.

Organelle-targeting ratiometric fluorescent probes: design principles, detection mechanisms, bio-applications, and challenges

Biological species, including reactive oxygen species (ROS), reactive sulfur species (RSS), reactive nitrogen species (RNS), F-, Pd2+, Cu2+, Hg2+, and others, are crucial for the healthy functioning of cells in living organisms. However, their aberrant concentration can result in various serious diseases. Therefore, it is essential to monitor biological species in cellular organelles such as the cell membrane, mitochondria, lysosome, endoplasmic reticulum, Golgi apparatus, and nucleus. Among various fluorescent probes for species detection within the organelles, ratiometric fluorescent probes have drawn special attention as a potential way to get beyond the drawbacks of intensity-based probes. This method depends on measuring the intensity change of two emission bands (caused by an analyte), which produces an efficient internal referencing that increases the detection's sensitivity. This review article discusses the literature publications (from 2015 to 2022) on organelle-targeting ratiometric fluorescent probes, the general strategies, the detecting mechanisms, the broad scope, and the challenges currently faced by fluorescent probes.

Theoretical study on a series of naphthalimide-contained two-photon fluorescent hypochlorite probe targeting endoplasmic reticulum: response mechanism and receptor effect

The development of detecting hypochlorous acid (HClO) in living endoplasmic reticulum has attracted much attention in the fields of biology, medicine, and pharmacy. In the present work, the one-photon absorption (OPA), one-photon emission (OPE), and two-photon absorption (TPA) properties of a series newly synthesized chemosensors with naphthalimide as the fluorophore were systematically investigated using time-dependent density functional theory in combination with response theory. Special emphasis is placed on evolution of the probes' optical properties in the presence of HClO. These compounds show drastic changes in their photoabsorption and photoemission properties when they react with HClO, indicating them to be excellent candidates as fluorescent chemosensors. To further understand the mechanisms of the two probes, we have employed the hole and electron analysis to investigate the charge transfer process for the photoemission of the molecules. The receptor effect is found to play a dominant role in the sensing performance of these probes. Specifically, two-photon absorption properties of the molecules are calculated. We have found that all probes show significant two-photon responses in the near-infrared light region. And the maximum two-photon absorption cross section of probe 2 is greatly enhanced with the presence of HClO, indicating that probe 2 can act as a potential two-photon excited fluorescent HClO probe. The theoretical investigations would be helpful to build the structure-property relationships for the naphthalimide-contained probes, providing information on the design of efficient two-photon fluorescent sensors that can be used for biological imaging of HClO in endoplasmic reticulum.

Natural flavylium-inspired far-red to NIR-II dyes and their applications as fluorescent probes for biomedical sensing

Fluorescent probes that emit in the far-red (600-700 nm), first near-infrared (NIR-I, 700-900 nm), and second NIR (NIR-II, 900-1700 nm) regions possess unique advantages, including low photodamage and deep penetration into biological samples. Notably, NIR-II optical imaging can achieve tissue penetration as deep as 5-20 mm, which is critical for biomedical sensing and clinical applications. Much research has focused on developing far-red to NIR-II dyes to meet the needs of modern biomedicine. Flavylium compounds are natural colorants found in many flowers and fruits. Flavylium-inspired dyes are ideal platforms for constructing fluorescent probes because of their far-red to NIR emissions, high quantum yields, high molar extinction coefficients, and good water solubilities. The synthetic and structural diversities of flavylium dyes also enable NIR-II probe development, which markedly advance the field of NIR-II in vivo imaging. In the last decade, there have been huge developments in flavylium-inspired dyes and their applications as far-red to NIR fluorescent probes for biomedical applications. In this review, we highlight the optical properties of representative flavylium dyes, design strategies, sensing mechanisms, and applications as fluorescent probes for detecting and visualizing important biomedical species and events. This review will prompt further research not only on flavylium dyes, but also into all far-red to NIR fluorophores and fluorescent probes. Moreover, this interest will hopefully spillover into applications related to complex biological systems and clinical treatments, ranging in focus from the sub-organelle to whole-animal levels.

A dual-response fluorescent probe for discriminative sensing of hydrazine and bisulfite as well as intracellular imaging with different emission

Bisulfite and hydrazine are harmful to the environment safety and human health. Therefore, it is of great value to develop a smart fluorescent probe with high selectivity for detection of bisulfite and hydrazine. In our report, a dual-response fluorescent probe EDBI with high selectivity, rapid response, and low detection limit for discriminative determination HSO₃^- and N₂H₄ was exploited. The probe EDBI is capable of distinctive sensing HSO₃^- and N₂H₄ based on nucleophilic addition reactions by taking advantage of ratiometric fluorescence and fluorescence "on-off" mode, respectively. The dual-responses behaviors of probe EDBI toward HSO₃^- and N₂H₄ were attribute to different reaction sites, which it has been confirmed by HRMS. More importantly, cytotoxicity experiment authenticated that probe possesses low toxicity and good penetration. The probe EDBI with excellent performance, it was successfully employed to distinguishable sense HSO₃^- and N₂H₄ in living cells by diverse channel patterns. Therefore, this simple dual-response fluorescence probe is expected to be used for real-time monitoring bisulfite and hydrazine in biological samples.

Optimizing the framework of indolium hemicyanine to detect sulfur dioxide targeting mitochondria

Endogenous sulfur dioxide (SO₂) is mainly produced by the enzymatic reaction of sulfur-containing amino acids in mitochondria, which has unique biological activity in inflammatory reaction, regulating blood pressure and maintaining the homeostasis of biological sulfur. It is more and more common to detect monitor SO₂ levels by fluorescence probe. In recent years, the indolium hemicyanine skeleton based on the D-π-A structure has been widely used in the development of fluorescent sensors for the detection of SO_2. However, subtle changes in the chemical structure of indolium may cause significant differences in SO₂ sensing behavior. In this article, we designed and synthesized two probes with different lipophilicities to further study the relationship between the structure and optical properties of hemicyanine dyes. On the basis of previous studies, the structure of indolium hemicyanine skeleton was optimized by introducing -OH group, so that MC-1 and MC-2 had the best response to SO₃^2- in pure PBS system. In addition, the lipophilicity of MC-2 was better than that of MC-1, which enabled it to respond quickly to SO₃^2- and better target mitochondria for SO₂ detection. Most importantly, the low detection limits of MC-1 and MC-2 conducive to the detection of endogenous SO₂. This work provided an idea for developing SO₂ fluorescent sensors with excellent water solubility and low detection limit.

A turn-on fluorescent probe based on indolizine for the detection of sulfite

Numerous SO32−/HSO3− fluorescent probes have been reported based on various mechanisms.

A near-infrared fluorescent probe targeting mitochondria for sulfite detection and its application in food and biology

Sulfur dioxide (SO2) is the main air pollutant in the environment, causing great harm to human health. Abnormal SO2 levels are usually associated with some respiratory diseases, cardiovascular diseases, and neurological disorders (even brain cancer). Therefore, monitoring SO2 levels is helpful to better understand its special physiological and pathological role. Although many fluorescent probes for SO2 have been reported, many of them were not ideal for in vivo imaging due to the short emission wavelength. In this work, a near-infrared fluorescent probe NIR-BN with emission wavelength of 680 nm was constructed by conjugating the benzopyrylium moiety and 6-hydroxy-2-naphthaldehyde. NIR-BN had high selectivity and rapidity for SO2 detection. In addition, the detection limit of NIR-BN was relatively low, which can be used for the determination of sulfite in different sugar samples with high accuracy. Of course, due to the excellent spectral and structural properties of NIR-BN, we have applied NIR-BN to the detection of SO2 in biological systems.

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.

Design of a FRET-based fluorescent probe for the reversible detection of SO2and formaldehyde in living cells and mice

Design of a FRET-based fluorescent probe for the reversible detection of SO₂and formaldehyde in living cells and mice.