Reaction-based small-molecule fluorescent probes for endoplasmic reticulum-and mitochondria-targeted biosensing and bioimaging

Fluorescent probes have revolutionized modern biological research by making it possible to observe and measure an extensive range of cellular and subcellular processes.Among the subcellular compartments,the endoplasmic reticulum(ER)and mitochondria(MT)remain exciting targets owing to the information they reveal about the cellular processes.Consequently,monitoring pH,polarity,viscosity,metal ions,reactive nitrogen species(RNS),reactive sulfur species(RSS)and reactive oxygen species(ROS)in ER and MT with fluorescent probes is of great importance to understand the cellar and subcellular process.Recent years,redox-sensitive probes and ion probes are designed and synthesized for the detection and quantification of RNS/RSS/ROS(collectively as reactive oxygen/nitrogen/sulfur species,RONSS)and metal ions within ER and MT.These probes provide powerful tools for the researchers to learn more about the complex relationship between cellular redox homeostasis and organelle function,and understand the mechanism of disease processes and pathogenesis for developing potential treatments.In this review,the design principles,synthesis methods,targeting mechanism for ER-and MT-targeted RONSS,and metal-ionspecific fluorescent probes are discussed.The recent progress for the synthesis and applications of ER/MT-targeted probes,and their applications for monitoring cellular and subcellular processes are summarized,and the development trends and application prospects of the probes are analyzed.

Activatable fluorescent probes for imaging and diagnosis of rheumatoid arthritis

Rheumatoid arthritis(RA)is a systemic autoimmune disease that is primarily manifested as synovitis and polyarticular opacity and typically leads to serious joint damage and irreversible disability,thus adversely affecting locomotion ability and life quality.Consequently,good prognosis heavily relies on the early diagnosis and effective therapeutic monitoring of RA.Activatable fluorescent probes play vital roles in the detection and imaging of biomarkers for disease diagnosis and in vivo imaging.Herein,we review the fluorescent probes developed for the detection and imaging of RA biomarkers,namely reactive oxygen/nitrogen species(hypochlorous acid,peroxynitrite,hydroxyl radical,nitroxyl),pH,and cysteine,and address the related challenges and prospects to inspire the design of novel fluorescent probes and the improvement of their performance in RA studies.

Metal-organic cage as fluorescent probe for LiPF_(6)in lithium batteries

Lithium hexafluorophosphate(LiPF_(6)),the most commonly used lithium battery electrolyte salt,is vulnerable to heat and humidity.Quantitative and qualitative determination the variation of LiPF_(6)have always relied on advanced equipment.Herein,we develop a fast,convenient,high-selective fluorescence detection method based on metal-organic cages(MOC),whose emission is enhanced by nearly 20 times in the presence of LiPF_(6)with good stability and photobleaching resistance.The fluorescent probe can also detect moisture in battery electrolyte.We propose and verify that the luminescence enhancement is due to the presence of hydrogen bond-induced enhanced emission effect in cages.Fluorescent excitation-emission matrix spectra and variable-temperature nuclear magnetic resonance spectroscopy are employed to clarify the role of hydrogen bonds in guest-loaded cages.Density functional theory(DFT)calculation is applied to simulate the structure of host-guest complexes and estimate the adsorption energy involved in the system.The precisely matched lock-and-key model paves a new way for designing and fabricating novel host structures,enabling specific recognition of other target compounds.

Temperature-controlled DCP Fluorescent Probe Based on Hydrogel-immobilized Quantum Dots Composite

A composite was created by incorporating the quantum dot-enhanced SiO_(2)nanoparticles within this hydrogel.Based on this composite,a temperature-controlled fluorescent probe for DCP was developed.A meticulous examination of this probe revealed its attributes and factors affecting its performance.By using temperature modulation,the probe was adept at detecting DCP concentrations ranging between 1.0×10^(-6)and 9.0×10^(-6)mol/L.Such a probe offers remarkable selectivity,repeatability,and robust stability,so that the detection of DCP can be carried out at different temperatures,and a fast,reliable,sensitive and low-cost intelligent detection method is realized.

A highly sensitive fluorescent probe RN-NA reveals peroxynitrite as a novel biomarker for primary open angle glaucoma

AIM:To directly quantify peroxynitrite(ONOO-)using a highly sensitive fluorescence resonance energy transfer probe RN-NA,investigate the association between ONOOand primary open angle glaucoma(POAG),and clarify whether RN-NA could be used as a potential tool for POAG diagnosis.METHODS:Plasma and aqueous humor(AH)samples were collected from POAG patients(n=100,age:59.70±6.87y)and age-related cataract(ARC)patients(n=100,age:61.15±4.60y)admitted to our hospital.Next,RN-NA was used to detect ONOO-in plasma and AH samples,and the relationship between ONOO-level and POAG was analyzed using binary logistic regression.Besides,Pearson correlation analysis was applied to characterize the correlation of the levels of ONOO-with the patients’age,intraocular pressure(IOP),and mean deviation of visual field testing.The ONOO-scavenger MnTMPyP was employed to treat the 3-morpholinosyndnomine(SIN-1)-induced ocular hypertension in mice(n=7,6-8wk).Finally,the IOP and ONOO-in both eyes were measured 30min after the last drug treatment.RESULTS:ONOO-levels of AH and plasma were significantly higher in the POAG group than in the ARC group(P<0.01).Additionally,ONOO-levels were closely correlated with POAG in a binary logistic regression analysis[odds ratio(OR)=1.008,95%confidence interval(CI):1.002-1.013,P<0.01 for AH;OR=1.004,95%CI:1.002-1.006,P<0.001 for plasma].Pearson correlation analysis showed that ONOO-levels in AH or plasma were positively associated with visual field defects(R=0.51,P<0.01 for AH;R=0.45,P<0.001 for plasma),and ONOO-levels in plasma and AH were correlated in the POAG group(R=0.69,P<0.001).However,administering MnTMPyP to mouse eyes reversed the elevated IOP caused by SIN-1(P<0.05).CONCLUSION:ONOO-levels in AH and plasma,detected by RN-NA,are significantly related to POAG and positively correlated with visual field defects in POAG patients.Hence,ONOO-is a potential biomarker of POAG,especially advanced POAG.Besides,anti-nitration compounds may be novel ocular hypotensive agents based on the animal study.

A ratiometric fluorescent probe for hypoxanthine detection in aquatic products based on the enzyme mimics and fluorescence of cobalt-doped carbon nitride

A ratiometric fluorescent probe for hypoxanthine(Hx)detection was established based on the mimic enzyme and fluorescence characteristics of cobalt-doped graphite-phase carbon nitride(Co doped g-C_(3)N_(4)).In addition to emitting strong fluorescence,the peroxidase activity of Co doped g-C_(3)N_(4)can catalyze the reaction of O-phenylenediamine and H_(2)O_(2)to produce diallyl phthalate which can emit yellow fluorescence at 570 nm.Through the decomposition of Hx by xanthine oxidase,Hx can be indirectly detected by the generating hydrogen peroxide based on the measurement of fluorescent ratio I(F_(570)/F_(370)).The linear range was 1.7-272.2 mg/kg(R^(2)=0.997),and the detection limit was 1.52 mg/kg(3σ/K,n=9).The established method was applied to Hx detection in bass,grass carp,and shrimp,and the data were verified by HPLC.The result shows that the established probe is sensitive,accurate,and reliable,and can be used for Hx detection in aquatic products.

Small-molecule fluorescent probes for the detection of carbon dioxide

During the last few years, the preparation of novel fluorescent probes for the detection of carbon dioxide has attracted considerable attention since carbon dioxide plays extremely important roles in widespread fields including chemical, environmental, clinical analysis, and agri-food industry. This review focuses on the recent advances in the design principles, recognition mechanisms, and preparation of small-molecule fluorescent probes for the selective detection and monitoring of CO;. Moreover, their properties and functions will be discussed detailedly as well.

Recent advances of small-molecule fluorescent probes for detecting biological hydrogen sulfide

H_(2)S is well-known as a colorless,acidic gas,with a notoriously rotten-egg smell.It was recently revealed that H_(2)S is also an endogenous signaling molecule that has important biological functions,however,most of its physiology and pathology remains elusive.Therefore,the enthusiasm for H_(2)S research remains.Fluorescence imaging technology is an important tool for H_(2)S biology research.The development of fluorescence imaging technology has realized the study of H_(2)S in subcellular organelles,facilitated by the development of fluorescent probes.The probes reviewed in this paper were categorized according to their chemical mechanism of sensing and were divided into three groups:H_(2)S reducibility-based probes,H_(2)S nucleophilicity-based probes,and metal sulfide precipitation-based probes.The structure of the probes,their sensing mechanism,and imaging results have been discussed in detail.Moreover,we also introduced some probes for hydrogen polysulfides.

Carbon Nitride Quantum Dots:A Novel Fluorescent Probe for Non-Enzymatic Hydrogen Peroxide and Mercury Detection

The mercury species in the ocean(MeHg,Hg^(2+))will be enriched in marine organisms and threaten human health through the food chain.While the excessive H_(2)O_(2)in the metabolic process will produce hydroxyl radicals and accelerate the aging of human cells,causing a series of diseases.Hence,the cost-effective and rapid detection of mercury and H_(2)O_(2)is of urgent requirement and significance.Here,we synthesized emerging graphitic carbon nitride quantum dots(g-CNQDs)with high fluorescence quantum yield(FLQY)of 42.69%via a bottom-up strategy by a facile one-step hydrothermal method.The g-CNQDs can detect the H_(2)O_(2)and Hg^(2+)through the fluorescence quenching effect between g-CNQDs and detected substances.With the presence of KI,g-CNQDs show concentration-dependent fluorescence toward H_(2)O_(2),with a wide detection range of 1–1000μmolL^(-1)and a low detection limit of 0.23μmolL^(-1).The g-CNQDs also show sensitivity toward Hg^(2+)with a detection range of 0–0.1μmolL^(-1)and a detection limit of 0.038μmolL^(-1).This dual-function detection of g-CNQDs has better practical application capability compared to other quantum dot detection.This study may provide a new strategy for g-CNQDs preparation and construct a fluorescence probe that can be used in various systems involving H_(2)O_(2)and Hg^(2+),providing better support for future bifunctional or multifunction studies.

A Fluorescent Probe based on a Carbazole Derivative for Detecting Brilliant Blue in Food

Here a fluorescent probe based on a carbazole derivative(CNS)was developed to increase the detection range and reduce the detection limit of brilliant blue.Characteristics of CNS are studied.Due to the quenching ability of colorants,CNS shows an excellent current response to brilliant blue(from 1 to 10μM)with a detection limit of 2.7×10^(-8)mol/L(3σ/k)in the conditions of a 1:1 volume ratio of water to tetrahydrofuran.And the stability and reproducibility of CNS in the detection of actual samples indicate great potential for application.

Application and development of fluorescence probes in MINFLUX nanoscopy(invited paper)

The MINimal emission FLUXes(MINFLUX)technique in optical microscopy,widely recognized as the next innovative fluorescence microscopy method,claims a spatial resolution of 1-3 nm in both dead and living cells.To make use of the full resolution of the MINFLUX microscope,it is important to select appropriate fluorescence probes and labeling strategies,especially in living-cell imaging.This paper mainly focuses on recent applications and developments of fluorescence probes and the relevant labeling strategy for MINFLUX microscopy.Moreover,we discuss the deficiencies that need to be addressed in the future and a plan for the possible progression of MINFLUX to help investigators who have been involved in or are just starting in the field of super-resolution imaging microscopy with theoretical support.

Determination of Pesticide Residue Cartap Using a Sensitive Fluorescent Probe

The insecticide cartap （CP） is non-fluorescent in aqueous solutions. This property makes its determination through direct fluorescent method difficult. In acidic medium and at room temperature, palmatine （PAL） can react with cucurbit[7]uril （CB[7]） to form stable complexes, and the fluorescence intensity of the complex is greatly enhanced. Significant quenching of the fluorescence intensity of the CB[7]-PAL complex was observed with the addition of cartap. Based on the significant quenching of the supramolecular complex fluorescence intensity, a new spectrofluorimetric method with high sensitivity and selectivity was developed to determine cartap in aqueous solution. The fluorescence quenching values （AF） showed good linear relationship with cartap concentrations from 0.009 to 2.4 ~tg mL-~ with a detection limit 0.0029 ~tg mE-x. The proposed method had been successfully applied to the determination of cartap residues in grain and vegetable with recoveries of 87.4-103%. In addition, the association constants of the complexes formed between the host and the guest were determined. The competing reaction and the supramolecular interaction mechanisms between the cartap and PAL as they fight for occupancy of the CB[7] cavity were studied using spectrofluorimetry, xH NMR and molecular modeling calculations.

Hydroxylated graphene quantum dots as fluorescent probes for sensitive detection of metal ions

Highly sensitive methods are important for monitoring the concentration of metal ions in industrial wastewater.Here,we developed a new probe for the determination of metal ions by fluorescence quenching.The probe consists of hydroxylated graphene quantum dots(H-GQDs),prepared from GQDs by electrochemical method followed by surface hydroxylation.It is a non-reactive indicator with high sensitivity and detection limits of 0.01μM for Cu2+,0.005μM for Al3+,0.04μM for Fe3+,and 0.02μM for Cr3+.In addition,the low biotoxicity and excellent solubility of H-GQDs make them promising for application in wastewater metal ion detection.

Theoretical investigation on the fluorescent sensing mechanism for recognizing formaldehyde: TDDFT calculation and excited-state nonadiabatic dynamics

Inspired by the activity-based sensing method, the hydrazine-modified naphthalene derivative(Naph1) was synthesized and used as a fluorescent probe to detect formaldehyde(FA) in living cells. Through the condensation reaction between the probe Naph1 and analyte FA, researchers observed a ~14 folds enhancement of fluorescent signal around 510 nm in an experiment, realizing the high selectivity and sensitivity detection of FA. However, a theoretical understanding of the sensing mechanism was not provided in the experimental work. Given this, the light-up fluorescent detecting mechanism was in-depth unveiled by performing the time-dependent density functional theory(TDDFT) and the complete active space self-consistent field(CASSCF) theoretical calculations on excited-state intramolecular proton transfer(ESIPT)and non-adiabatic excited-state dynamics simulation. The deactivation channel of S_1/T_2 intersystem crossing(ISC) was turned off to successfully recognize FA. Insight into the ESIPT-based fluorescent detecting mechanism indicated that ESIPT was essential to light-up fluorescent probes. This work would provide a new viewpoint to develop ESIPT-based fluorescent probes for detecting reactive carbon species in vivo or vitio.

Ultrasensitive Detection of Glyphosate Using CdTe Quantum Dots in Sol-Gel-Derived Silica Spheres Coated with Calix[6]arene as Fluorescent Probes

We have developed a simple method for the preparation of highly fluorescent and stable, water-soluble CdTe quantum dots in sol-gel-derived composite silica spheres which were coated with calix[6]arene. The resulting nanoparticles (NPs) were characterized in terms of UV, fluorescence and FT-IR spectroscopy and TEM. The results show that the new NPs display more intense fluorescence intensity and are more stable than its precursors of the type SiO2/CdTe. Under the optimum, the novel NPs exhibit a higher selectivity and ultrasensitive fluorescence probes for the determination of gly-phosate over other pesticides, the fluorescence intensity increase with the concentration of glyphosate in the range from 1.0 to 25.0 nmol/L and the detection limit is low to 0.0725 nmol/L. A mechanism is suggested to explain the inclusion process by a Langmuir binding isotherm.

Green Fluorescent Protein Recombinant Nisin as a Probe for Detection of Gram-Positive Bacteria

A great amount of foodborne pathogens were Gram-positive (G+) bacteria, a threat to public health. In this study, considering the binding ability of nisin towards G+ bacteria and the stable fluorescent ability of EGFP protein, a fluorescent nisin–EGFP protein probe was constructed by a gene engineering method. Nisin and EGFP were used as the receptor and fluorophore, respectively, to detect G+ bacteria. The nisin and egfp gene were amplified separately according to the sequence published in GenBank using unique primers. The two genes were cloned into a pET-28b(+) vector resulting in a pET-28b(+)–nisin–egfp vector. The vector was transferred into Escherichia coli (E. coli) BL21 (DE3) for expression. The expressed protein was extracted, purified by a Ni–NTA column, and then tested by the SDS-PAGE method to confirm its molecular weight. Listeria monocytogenes (L. monocytogenes), Staphylococcus aureus (S. aureus), and Micrococcus luteus (M. luteus) were used as the representations of G+ bacteria. E. coli O157, representing the gram-negative (G−) bacteria, was used as a negative control. The binding specificity of the recombinant protein was performed on two types of bacteria and then detected through fluorescent microscopy. The results indicated that the nisin–EGFP probe could detect G+ bacteria at 108CFU/mL. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

Synthesis and application of rhodamine-based fluorescent probe dyes with spacer linker arm

When rhodamine-based fluorescent probe dyes are used to track target molecules they always perturb the behavior of target molecules because of steric hindrance effect. In order to minimize potential steric problems, a kind of rhodamine-based fluorescent probe dye with spacer linker arm was designed and synthesized and its application in immunofluorescence histochemistry was investigated.

A New Coumarin-Based Fluorescent pH Probe

A new iminocoumarin-derived colorimetric and fluorescent pH probe was developed for rapid and sensitive detection of pH changes in biological and environmental media. With the decrease of pH value( from 6. 24 to 3. 00),an obvious color change of the probe in ethanol-water solution from green to yellow was observed under nature light. The intensity of the maximum fluorescence emission peak of the probe decreased gradually with the acidity increase of the solution. While the fluorescence intensity of the emission peak of the probe did not exhibit distinct change when pH was less than 11. 00 and the fluorescence was almost quenched at pH 13. 50. Sensitivity of the fluorescent pH probe was not interfered by the presence of common metal cations and anions.

A Mechanism Study of a Novel Acid-Activatable Michael-Type Fluorescent Probe for Thiols

A Michael addition is usually taken as a base-catalysed reaction. However, our synthesized 2-（quinolin-2-ylmethylene） malonic acid （QMA） as a Michael-type thiol fluorescent probe is acid-active in its sensing reaction. In this work, based on theoretic calculation and experimental study on 7-hydroxy-2-（quinolin-2-ylmethylene） malonic acid, we demonstrated that QMA as a Michael acceptor is acid-activatable, i.e., it works only in solutions at pH〈7, and the lower the pH of solutions is, the higher reactivity QMA has. In alkaline solution, the malonate QMA[-2H＋]2- cannot react with both RSand RSH. In contrast, 2-（quinolin-2- ylmethylene） malonic ester （QME）, the ester of QMA, reveal a contrary pH effect on its sensing reaction, that is, it can sense thiols in alkaline solutions but not in acidic solutions, like a normal base-catalysed Michael addition. The values of activation enthalpies from theoretic calculation support the above sensing behavior of two probes under different pH conditions. In acidic solutions, the protonated QMA is more highly reactive towards electrophilic attack over its other ionized states in neutral and alkaline solutions, and so can react with lowly reactive RSH. In contrast, there is a big energy barrier in the interaction of QME with RSH （acidic solutions）, and the reaction of QME with the highly reactive nucleophile RS- is a low activation energy process （in alkaline solutions）. Theoretic calculation reveals that the sensing reaction of QMA undergoes a 1,4-addition process with neutral thiols （RSH）, and a 1,2-addition pathway for the sensing reaction of QME with RS-. Therefore, the sensing reaction of QMA is an acid-catalysed Michael addition via a 1,4-addition, and a normal base-catalysed Michael addition via a 1,2-addition.

Computational design of ratiometric two-photon fluorescent Zn2+probes based on quinoline and di-2-picolylamine moieties

To improve two-photon absorption(TPA)response of a newly synthesized probe,a series of ratiometric two-photon fluorescent Zn^(2+) sensors based on quinoline and DPA moieties have been designed.The one-photon absorption,TPA,and emission properties of the experimental and designed probes before and after coordination with Zn^(2+) are investigated employing the density functional theory in combination with response functions.The design consists of two levels.In the first level of design,five probes are constructed through using several electron acceptors or donors to increase accepting or donating ability of the fluorophores.It shows that all the designed probes have stronger TPA intensities at longer wavelengths with respect to the experimental probe because of the increased intra-molecular charge transfer.Moreover,it is found that the probe 4 built by adding an acyl unit has the largest TPA cross section among the designed structures due to the form of longer conjugated length and more linear backbone.One dimethylamino terminal attached along the skeleton can improve TPA intensity more efficiently than two side amino groups.Therefore,in the second level of design,a new probe 7 is formed by both an acyl unit and a dimethylamino terminal.It exhibits that the TPA cross sections of probe 7 and its zinc complex increase dramatically.Furthermore,the fluorescence quantum yields of the designed probes4 and 7 are calculated in a new way,which makes use of the relation between the computed difference of dipole moment and the measured fluorescence quantum yield.The result shows that our design also improves the fluorescence quantum yield considerably.All in all,the designed probes 4 and 7 not only possess enhanced TPA intensities but also have large differences of emission wavelength upon Zn^(2+) coordination and strong fluorescence intensity,which demonstrates that they are potential ratiometric two-photon fluorescent probes.