A cysteine-selective fluorescent probe for monitoring stress response cysteine fluctuations

Coordination Synergistic-Induced J-Aggregation Enhanced Fluorescent Performance of HBT-Excimers and Imaging Applications

Developing a novel strategy to improve the optical performances of fluorescent probes is a vital factor in elevating its practical application; viz., novel biocompatible fluorescent probes with excellent multifunctions exhibited unparalleled advantages in probing functions of intracellular molecules to elucidate intracellular events in living systems. Herein, we have successfully constructed a new strategy that aggregation and coordination synergistically induce (2-hydroxylphenyl-benzothiazole) HBT derivatives to form excimers with large red-shifted fluorescence and application for insight into stress-response zinc fluctuations in living systems. We have synthesized four HBT-based derivatives and deeply investigated the response mechanism by fluorescent spectral studies, demonstrating that probes 3 and 4 showcased large red shifts in emission wavelength due to J-aggregation. More interestingly, the fluorescence of probe 4 was significantly enhanced in the presence of a zinc ion, suggesting that zinc coordination synergistically induced J-aggregation. Probe 4 was successfully applied to image zinc fluctuations in different models of living systems, proving that this probe is a powerful tool to unveil the relationship between invasive stress and diseases by monitoring endogenous zinc fluctuations.

Rapid and on-site detection of bisulfite via a NIR fluorescent probe: A case study on the emission wavelength of probes with different quinolinium as electron-withdrawing groups

The emission of venenous sulfur dioxide (SO2) and its derivatives from industrial applications such as coking, transportation and food processing has caused great concern about public health and environmental quality. Probes that enable sensitivity and specificity to detect SO2 derivatives play a crucial role in its regulations and finally mitigating its environmental and health impacts, but fluorescent probes that can accurately, rapidly and on-site detect SO2 derivatives in foodstuffs and environmental systems rarely reported. Herein, a near-infrared (NIR) fluorescent probe (ZTX) for the ratiometric response of bisulfite (HSO3-) was designed and synthesized by regulating the structure of high-performance HSO3- fluorescent probe SL previously reported by us based on structural analyses, theoretical calculations and related literature reports. The Michael addition reaction between the electronic-deficient C=C bond and HSO3- destroys ZTX's π-conjugation system and blocks its intramolecular charge transfer (ICT) process, resulting in a significant fading of the fuchsia solution and the bluish-purple fluorescence turned light blue fluorescence. Fluorescent imaging of HSO3- in live animals utilizing ZTX has been demonstrated. The quantitative analysis of HSO3- in food samples using ZTXvia a smartphone has been also successfully implemented. Simultaneously, the ZTX-based test strips were utilized to quantificationally determine HSO3- in environmental water samples by a smartphone. Consequently, probe ZTX could provide a new method to understand the physiopathological roles of HSO3-, evaluate food safety and monitor environment, and is promising for broad applications.

Activatable fluorescent probes for early diagnosis and evaluation of liver injury

With the increase in people's living standards, the number of patients suffering from liver injury keeps on increasing. Traditional diagnostic methods can no longer meet the needs of early and accurate diagnosis due to their limitations in application. However, fluorescent probes based on different fluorophores and nanomaterials have been gradually lighting up medical research due to their unique properties, such as high specificity and non-invasiveness. In addition, accurate identification of the different types of liver injury biomarkers can significantly improve the level of early diagnosis. Therefore, this review reviews the fluorescent probes used in the detection of biomarkers of liver injury over recent years and briefly summarizes the corresponding biomarkers of different types of liver injury. Impressively, this review also lists the structures and the response mechanisms of the different probes, and concludes with an outlook, suggesting directions in which improvements can be made. Finally, we hope that this review will contribute to the further development of fluorescent probes for the early diagnosis and assessment of liver injury.

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.

A dicyanoisophorone-based long-wavelength fluorescent probe for detection of cysteine in vitro and in vivo

In this research, an "off-on" long-wavelength fluorescent probe (DCMN-Cl) based on (E)-2-(3-(2-(6-hydroxynaphthalen-2-yl)vinyl)-5,5-dimethylcyclohex-2-en-1-ylidene) malononitrile (DCMN) is designed and synthesized for cysteine (Cys) detection. DCMN-Cl exhibits a large Stokes shift (211 nm) and shows rapid response and high specificity to Cys. The fluorescence initensity at 635 nm reveals a good linear relationship with Cys concentration in the 0 to 50 μM range, and the detection limit is as low as 159 nM. The probe is also used for fluorescence imaging of Cys in cells and mice. Moreover, the probe provided visual evidence of Cu2+ and curcumin-induced intracellular Cys fluctuations.

Intelligent detection strategy and bioimaging application of dual-responsive Hg2+ and ONOO- using near-infrared probes

Mercury is a highly toxic heavy metal pollutant. Mercury and its derivatives pose serious threats to the environment and the health of organisms. Numerous reports have indicated that Hg²⁺ exposure induces a burst of oxidative stress in organisms, causing severe damage to the health of the organism. A large number of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced under conditions of oxidative stress, and superoxide anions (O₂^-) and NO radicals react rapidly with each other to produce peroxynitrite (ONOO^-), an important downstream product. Therefore, developing an efficient and highly responsive screening method to monitor the fluctuations of Hg²⁺ and ONOO^- levels is particularly important. In this work, we designed and synthesized a highly sensitive and highly specific near-infrared probe W-2a, which can effectively detect and distinguish Hg²⁺ and ONOO^- through fluorescence imaging. In addition, we developed a WeChat mini-program called "Colorimetric acquisition" and built an intelligent detection platform to assess the environmental hazards of Hg²⁺ and ONOO^-. The probe can detect Hg²⁺ and ONOO^- in the body through dual signaling, as evidenced by cell imaging, and has successfully monitored fluctuations in the ONOO^- levels in inflamed mice. In conclusion, the W-2a probe provides a highly efficient and reliable method for assessing oxidative stress-induced changes in the ONOO^- levels in the body.

Fluorescent probe for highly selective detection of cysteine in living cells

Cys play an important physiological role in the human body. Abnormal Cys concentration can cause many diseases. Therefore, it is of great significance to detect Cys with high selectivity and sensitivity in vivo. Because homocysteine (Hcy) and glutathione (GSH) have similar reactivity and structure to cysteine, few fluorescent probes have been reported to be specific and efficient for cysteine. In this study, we designed and synthesized an organic small molecule fluorescent probe ZHJ-X based on cyanobiphenyl, which can be used to specifically recognize cysteine. The probe ZHJ-X exhibits specific selectivity for cysteine, high sensitivity, short reaction response time, good anti-interference ability, and has a low detection limit of 3.8 × 10^-6 M. The probe ZHJ-X was successfully applied to the visualization of Cys in living cells and had great application prospects in cell imaging and detection.

Fluorescent imaging to provide visualized evidences for mercury induced hypoxia stress

As one typical toxic and dangerous heavy metal, mercury brings incalculable hazards to the environment and human, the mechanism at the molecular level is unclear. There is no visualized evidence to support directly that mercury ions (Hg²⁺) exposure may induce secondary stress, which is associated with the risk of hypoxia microenvironment in biological systems. Hypoxia occurs in many physiological and pathophysiological processes in the living system, accompanying overexpression of various biomarkers, such as nitroreductase (NTR). Hence, we had successfully developed two NTR-selective fluorescent probes with excellent performance for evaluating the hypoxia degree in vivo and in vitro. We visualized and qualitatively monitored the fluctuations of the endogenous NTR levels in living cells and zebrafish. The imaging results exhibited that different doses of Hg²⁺ exposure elevated the NTR levels and the same trend in changes of NTR as extrinsic hypoxia exposure, suggesting that Hg²⁺ exposure induced microenvironmental changes resulting in the hypoxia stress. This is the first time to provide visual evidence to support that Hg²⁺ stress may involve in the intracellular hypoxia microenvironment through monitoring the dynamic of NTR levels in the living systems. Our results may provide a novel insight into the molecular mechanisms of typical heavy metal element induced toxicity.

A NIR fluorescence probe for monitoring Cys upregulation induced by balsam pear polysaccharide and imaging in zebrafish

In this work, we introduced the acrylate recognition group into dicyanoisophorone derivative DCI-C-OH to construct the NIR fluorescent probe DCI-C-Cys with a large Stokes shift (240 nm). DCI-C-Cys could specifically respond to Cys, resulting in a 22-fold increase in fluorescence intensity at 702 nm. Meanwhile, the probe has the advantages of good water solubility, high sensitivity (93 nM), and excellent biocompatibility. Moreover, DCI-C-Cys successfully monitored endogenous and exogenous Cys in HepG2 cells and zebrafish. Most importantly, we found that balsam pear polysaccharide could lead to the increase of intracellular Cys levels, which might be conducive to the further study of the antioxidant mechanism of balsam pear polysaccharide.

Real-time imaging of intracellular cysteine level fluctuations during Cu2+ or H2O2 induced redox imbalance using a turn-on fluorescence sensor

Redox balance is a necessary guarantee to maintain the normal physiological activities of organisms. Cysteine (Cys), a critical biological thiol, has the effect of maintaining redox balance in the body. The concentration of intracellular Cys is abnormal under redox imbalance, thereby resulting in multiple diseases. Additionally, studies have revealed that Cu²⁺ can stimulate the body to produce excess reactive oxygen species (ROS, similar to H₂O₂), and the generated ROS will consume reducing substances (such as Cys) in the body, leading to redox imbalance. Thus, finding a simple and effective method to monitor Cys under redox imbalance is pressing. Here, a turn on probe (DDNO) was proposed by connecting SBD-Cl to a red dye (HDM). The probe can specifically recognize Cys with rapid response (180 s) and low detection limit (0.61 μM) through substitution-rearrangement reaction between sulfhydryl and chlorine atom. Bioimaging experiments indicated that the probe has good biocompatibility and cell membrane permeability, which can be applied to monitor the fluctuation of Cys levels in live cells and zebrafish under the redox imbalance induced by Cu²⁺ or H₂O₂.

A bifunctional fluorescent probe based on PET & ICT for simultaneously recognizing Cys and H2S in living cells

Most reported probes that respond to Cysteine (Cys) and Hydrogen sulfide (H₂S) can only identify one analyte, or they were interfered with homocysteine (Hcy) and glutathione (GSH) when recognizing Cys and H₂S. In addition, nitrobenzoxadiazole (NBD) ether, as one of thiols recognition sites, inevitably encounters the situation that Cys, GSH and H₂S cannot be distinguished on the same channel at the cellular level. In this work, by introducing NBD ether and NBD amine, we constructed a bifunctional fluorescent probe NJB for dual-site response to Cys and H₂S via PET & ICT processes. NJB has wonderful selectivity for identifying Cys and HS^-, with limits of detection as low as 58.4 nM and 81.1 nM, respectively. Interestingly, NJB has been successfully applied to detect Cys and HS^- in MCF-7 cells. Therefore, the probe that serves as a great tool for inquiring the physiological and pathological functions of Cys and H₂S in living cells is promising.

A small molecule fluorescent probe for mercury ion analysis in broad low pH range: Spectral, optical mechanism and application studies

Development of new fluorescent probes for mercury ion analysis in environmental or living organism is undergoing quick growth due to its detrimental toxicity to environmental safety, ecological security, and human being. However, in most cases, the industrial waste water is acidic whereas it remains a great challenge to real-time monitor mercury ion directly at low pH using small molecule fluorescence probe. In this study, we have successfully designed and synthesized the Naph (1, 8-Naphthalimide derivative) -based small molecule probe termed as Naph-NSS capable of monitoring mercury ion in a broad range at low pH (from 2.0 to 7.0). The solid spectral studies demonstrated the high sensitivity and selectivity of the probe towards mercury ion among various species. After binding with Hg²⁺, the fluorescence of Naph-NSS greatly enhanced, and the mechanism of which was investigated by DFT studies. The probe was able to be loaded on paper strip for instant and fast detection of mercury ions. In addition, the probe is also suitable for detection of mercury ion in environmental samples, living cells and in vivo.

A Fluorescent Probe to Detect Quick Disulfide Reductase Activity in Bacteria

The Trx and Grx systems, two disulfide reductase systems, play critical roles in various cell activities. There are great differences between the thiol redox systems in prokaryotes and mammals. Though fluorescent probes have been widely used to detect these systems in mammalian cells. Very few methods are available to detect rapid changes in the redox systems of prokaryotes. Here we investigated whether Fast-TRFS, a disulfide-containing fluorescent probe utilized in analysis of mammalian thioredoxin reductase, could be used to detect cellular disulfide reducibility in bacteria. Fast-TRFS exhibited good substrate qualities for both bacterial thioredoxin and GSH-glutaredoxin systems in vitro, with Trx system having higher reaction rate. Moreover, the Fast-TRFS was used to detect the disulfide reductase activity in various bacteria and redox-related gene null E. coli. Some glutaredoxin-deficient bacteria had stronger fast disulfide reducibility. The Trx system was shown to be the predominant disulfide reductase for fast disulfide reduction rather than the Grx system. These results demonstrated that Fast-TRFS is a viable probe to detect thiol-dependent disulfide reductases in bacteria. It also indicated that cellular disulfide reduction could be classified into fast and slow reaction, which are predominantly catalyzed by E. coli Trx and Grx system, respectively.

Insight into sulfur dioxide and its derivatives metabolism in living system with visualized evidences via ultra-sensitive fluorescent probe

Sulfur dioxide (SO₂) and its derivatives have long been considered as hazardous environmental pollutants but commonly used as food additives in safe dose range. They also could be produced from biological metabolism process of sulfur-containing amino acids. However, their physiological roles remain extremely obscure mainly due to lack of efficient tools for monitoring and imaging strategy establishment. Furthermore, most of current studies of this aspect focus on novel probe design or just imaging them rather than on the ins and outs. Therefore, there is a high significance of establishing highly sensitive detection strategy for monitoring SO₂ derivatives in living systems, food and environment. Herein, we design a fluorescent probe MS-Bindol for sensitively detecting SO₂ derivatives with a low detection limit (0.2 nM). We have established an imaging strategy for investigation of SO₂ derivatives metabolism in living cells and zebrafish, providing visualize evidences and verified that SO₂ derivatives could be synthetized from thiosulfate and glutathione(GSH) and be hardly consumed by using sulfite oxidase inhibitors (ferricyanide or arsenite). Moreover, the probe also exhibits excellent practicability in food as well as environmental samples. Our studies may help biologist for better understanding SO₂ derivatives metabolism and deeply explore their physiological roles in biological systems.

A fluorescent probe for specifically measuring the overall thioredoxin and glutaredoxin reducing activity in bacterial cells

Both bacterial thioredoxin and glutaredoxin systems can reduce TRFS-green selectively, which confers TRFS-green to be a remarkable probe to detect the dominant disulfide reductase activity with a slow reaction rate in bacteria, e. g. E. coli Grx2&3.

Coumarin-based fluorescent probe with 4-phenylselenium as the active site for multi-channel discrimination of biothiols

Biological mercaptans, also known as biothiols, play their own roles in a number of important physiological processes, and the abnormal levels of biothiols are closely associated with a variety of...