A New Heptamethine Cyanine-Based Near-Infrared Fluorescent Probe for Divalent Copper Ions with High Selectivity

A new near-infrared fluorophore 2-(2-Aminoethyl) pyridine-tricarbocyanine (1) was rationally designed and synthe-sized as a fluorescent probe for detection of Cu2+ with high selectivity. The response of Probe 1 is based on the fluorescence quenching upon binding to Cu2+. The sensing performance of the proposed Cu2+-sensitive Probe 1 was then investigated. The probe can be applied to the quantification detection of Cu2+ with a linear concentration range covering from 4.8 × 10-7 to 1.6 × 10-4 mol/L and a detection limit of 9.3 × 10-8 mol/L. The experimental results showed that the response of 1 to Cu2+ was independent of pH in medium condition (pH 6.0-8.0), and exhibited excellent selectivity towards Cu2+ over other common metal cations.

Responsive mechanism and molecular design of di-2-picolylamine-based two-photon fluorescent probes for zinc ions

The properties of one-photon absorption（OPA）, emission and two-photon absorption（TPA） of a di-2-picolylaminebased zinc ion sensor are investigated by employing the density functional theory in combination with response functions.The responsive mechanism is explored. It is found that the calculated OPA and TPA properties are quite consistent with experimental data. Because the intra-molecular charge transfer（ICT） increases upon zinc ion binding, the TPA intensity is enhanced dramatically. According to the model sensor, we design a series of zinc ion probes which differ by conjugation center, acceptor and donor moieties. The properties of OPA, emission and TPA of the designed molecules are calculated at the same computational level. Our results demonstrate that the OPA and emission wavelengths of the designed probes have large red-shifts after zinc ions have been bound. Comparing with the model sensor, the TPA intensities of the designed probes are enhanced significantly and the absorption positions are red-shifted to longer wavelength range. Furthermore, the TPA intensity can be improved greatly upon zinc ion binding due to the increased ICT mechanism. These compounds are potential excellent candidates for two-photon fluorescent zinc ion probes.

A near-infrared fluorescent probe for visualizing transformation pathway of Cys/Hcy and H2S and its applications in living system

Sulfydryl-contained(-SH)substances including hydrogen sulfide(H_(2)S),cysteine(Cys),homocysteine(Hcy)and glutathione(GSH)play crucial roles in living systems,and their variations are closely associated with various diseases.Herein,we developed a near-infrared intramolecular charge transfer(ICT)based fluorescent probe Y-NBD,achieving detection of Cys/Hcy and H_(2)S with different fluorescent signals(green-red for Cys/Hcy,red for H_(2)S),large Stokes shifts(∼100/105nm or 191 nm)and high signal-background-ratio,but not responding to GSH.Y-NBD was successfully applied to image exogenous/endogenous Cys/Hcy and H_(2)S in various living cancer cells(HeLa,A549,and HepG2)and in zebrafish.It not only visualized the transformation pathway of several thiols in HepG2 cells but also verified that the intestine is the main site for the activation and metabolism of Y-NBD in zebrafish,as well as realized to evaluate the degree of drug-induced liver injury.This work provides a promising tool for imaging Cys/Hcy and H_(2)S in living systems and shows great potency in evaluating drug-induced liver injury and its treatment.

Syntheses and properties of photostable near-infrared cyanines and their cyclodextrin conjugates

Three fluorescent indocyanines containing p-carboxybenzyl groups on N atoms in the heterocyclic tings were synthesized under supersonic. The maxima wavelength of the absorption and emission of the dyes were 550-800 nm in water. Compared with those in aqueous solutions, the fluorescence intensity of the dyes in the α/β-cyclodextrin, Al^3＋, Zn^2＋, Sn^2＋ or the α/β-cyclodextrin in the aqueous solutions of the cations became stronger. The crystal Shapes of the dyes and their cyclodextrin inclusions were mostly acicular or polygon. The NHS-carboxyl squarylium indocyanine was prepared and used to conjugate with taurine or benzylamine, the results indicated that the dyes could couple covalently to biomass containing free NH2 group. Structure and some thermal parameters of the molecule of the trimethine cyanine were obtained by DFT method of Gaussian O3.

Near-infrared fluorescent probes for imaging of amyloid plaques in Alzheimer's disease

One of the early pathological hallmarks of Alzheimer's disease(AD) is the deposition of amyloid-β(Aβ) plaques in the brain. There has been a tremendous interest in the development of Aβ plaques imaging probes for early diagnosis of AD in the past decades. Optical imaging, particularly near-infrared fluorescence(NIRF) imaging, has emerged as a safe, low cost, real-time, and widely available technique, providing an attractive approach for in vivo detection of Aβ plaques among many different imaging techniques. In this review,we provide a brief overview of the state-of-the-art development of NIRF Aβ probes and their in vitro and in vivo applications with special focus on design strategies and optical, binding, and brain-kinetic properties.

A ratiometric near-infrared naphthalimide-based fluorescent probe with high sensitivity for detecting Fe^(2+)in vivo

Iron is one of the essential trace elements in the human body.It plays an important role in human biology and pathology.Deregulation of iron levels in cells is associated with disease development.In this work,we synthesized a novel near-infrared intramolecular charge transfer(ICT)based ratiometric fluorescent probe to detect Fe^(2+),by using naphthalimide and indole moieties as building blocks.Our work showed that the radiometric probe has excellent selectivity,sensitivity and rapid response.Moreover,we could successfully perform real-time monitoring of Fe^(2+) in He La cells and C.elegans.

Molecularly near-infrared fluorescent theranostics for in vivo tracking tumor-specific chemotherapy

Molecularly near-infrared(NIR) theranostics, combining in vivo sensing and tumor-specific therapeutic capability within one molecular system, have received considerable attention in recent years. Compared with the visible fluorescence imaging, NIR imaging(emission wavelength at 650–900 nm) possesses unique advantages including the minimum photodamage to biological samples, deep penetration, and low interference from auto-fluorescence. In over past decades, there has been an explosive development in the design of molecular imaging contrasts and imaging-guided therapeutics. In this review, we have sumarried the strategies of the NIR theranostics for imaging and tumor-specific chemotherapy applications in living systems. It is noted that the molecularly NIR theranostic design strategy could address current challenges of real-time in vivo sense-and-release for the intelligent biosensing and personalized treatment.

Near-Infrared mitochondria-targeted fluorescent probe for cysteine based on difluoroboron curcuminoid derivatives

Curcuminoid difluoroboron has attractive performance as a promising near-infrared（NIR） fluorescent dye. In this contribution, we designed and synthesized a mitochondria-targeted NIR fluorescent probe DFB1 based on difluoroboron curcuminoid scaffold for the detection of Cys（cysteine）. DFB1 employs a curcumin analog as the NIR fluorophore, an acrylate group containing a, b-unsaturated ketone as a functional trigger moiety for Cys, and a triphenylphosphonium（TPP） cation moiety for specifically targeting mitochondria. The remarkable shift of DFB1 with Cys was observed from 470 nm to 590 nm in absorption spectra and from 560 nm to 680 nm in emission spectra. Notably, DFB1 manifests significantly dual-channel and turn-on NIR fluorescent signals simultaneously in response to Cys concentration,which make it favorable for monitoring endogenous Cys activity in vivo. This probe has high sensitivity and selectivity for the detection of Cys over homocysteine（Hcy） and glutathione（GSH）. This specific response for Cys was based on differences kinetics of intramolecular adduct/cyclizations. More importantly, biological experiments indicated that this probe could be utilized for the detection of endogenous mitochondrial Cys in living cells.

Two near-infrared highly sensitive cyanine fluorescent probes for pH monitoring

Two near-infrared（NIR） p H-activated heptamethine indocyanine probes with quaternary ammonium unit were designed and synthesized. The absorption and emission titrations indicate that cationic structure improves the cyanine dye＇s aqueous solubility and these two probes exhibit highly sensitive response to p H in acid condition. Their fluorescence intensities both gradually increase about 25-fold from p H 7.60 to 3.00 with p Ka values of 4.72 and 4.45 respectively, which are suitable for studying acidic organelles in living cells. Moreover, their fluorescence intensities are linearly proportional to p H values in the range of 5.50–4.00. These results are probably attributed to the protonation of the indole nitrogen atoms, which are verified by 1H NMR spectra. Furthermore, these two probes can achieve real-time imaging of cellular p H and detection of p H in situ in living He La cells due to their excellent properties,including good reversibility, desirable photostability, high selectivity, low cytotoxicity and remarkable membrane permeability.

A near-infrared fluorescent probe for monitoring fluvastatin-stimulated endogenous H_2S production

Most reported fluorescent probes have limitations in practical applications in living systems due to the strong autofluorescence background,construction of probes with near-infrared（NIR） fluorescence emission is an accessible approach for addressing this challenge.We here designed a NIR fluorescent probe for monitoring the endogenous production of H2S in living cells.The designed probe showed significant NIR fluorescence turn-on response to H2S with high selectivity,enabling the sensitive detection H2S.Importantly,the probe could be applied in monitoring the endogenous production of H2S in raw 264.7 macrophages.This study showed that fluvastatin can promote the activity of cystathionineγ-lyase（CSE） for generation H2S.

An activatable ratiometric near-infrared fluorescent probe for hydrogen sulfide imaging in vivo

Ratiometric fluorescent probes hold great promise for in vivo imaging;however,stimuli-activatable ratiometric probes with fluorescence emissions in near-infrared(NIR)region are still very few.Herein,we report a hydrogen sulfide(H_2S)-activatable ratiometric NIR fluorescent probe(1-SPN)by integrating a H_2S-responsive NIR fluorescent probe 1 into a H_2S-inert poly[2,6-(4,4-bis-(2-ethylhexyl)-4 H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)](PCPDTBT)-based NIR semiconducting polymer nanoparticle(SPN).1-SPN shows"always on"PCPDTBT fluorescence at 830 nm and weak probe 1 fluorescence at 725 nm under excitation at 680 nm.The ratio of NIR fluorescence intensities between 725 and 830 nm(I_(725)/I_(830))is small.Upon interaction with H_2S,the fluorescence at 725 nm is rapidly switched on,resulting in a large enhancement of I_(725)/I_(830),which is allowed for sensitive visualization and quantification of H_2S concentrations in living cells.Taking advantage of enhanced tissue penetration depth of NIR fluorescence,1-SPN is also applied for real-time ratiometric fluorescence imaging of hepatic and tumor H_2S in living mice.This study demonstrates that activatable ratiometric NIR fluorescent probes hold great potential for in vivo imaging.

A near-infrared fluorescent probe for fast and precise imaging of senescent cells and ovarian cancer cells via trackingβ-galactosidase

Aging-related diseases are gradually becoming a major problem with the rapid development of aged population in human society.Although many fluorescent probes have been employed to diagnosis senescence via imaging senescence-associatedβ-galactosidase(SA-β-Gal),which is proved to be closely associated with senescent cells,the similar catalytic effectiveness of enzymatic reaction of ovarian cancer-associatedβ-Gal(OA-β-Gal)will interfere with imaging accuracy.Herein,a near-infrared(NIR)hemicyanine based fluorescent probe HCyXA-βGal was designed for light-up imaging of live cells containingβ-Gal.With the organelle-targeting morpholinyl and positive charge moieties,HCyxA-βGal was successfully applicated to image the difference of enzymatic location in senescent cells and ovarian cancer cells.Furthermore,inspired by the fast response performance,fast and precise imaging of the two cell lines was realized via covering another dimension of fluorescence signal:time-dependent intensity.

A transferrin receptor targeting dual-modal MR/NIR fluorescent imaging probe for glioblastoma diagnosis

The prognosis of glioblastoma(GBM)remains challenging,primarily due to the lack of a precise,effective imaging technique for comprehensively characterization.Addressing GBM diagnostic challenges,our study introduces an innovative dual-modal imaging that merges near-infrared(NIR)fluorescent imaging with magnetic resonance imaging(MR).This method employs superparamagnetic iron oxide nanoparticies coated with NIR fluorescent dyes,specifically Cyanine 7,and targeted peptides.This synthetic probe facilitates MRI functionality through superparamagnetic iron oxide nanoparticles,provides NIR imaging capability via Cyanine 7 and enhances tumor targeting trough peptide interactions,offering a comprehensive diagnostic tool for GBM.Notably,the probe traverses the blood-brain barrier,targeting GBM in vivo via peptides,producing clear and discermible images in both modalities.Cytotoxicity and histopathology assessments confirm the probe's favorable safet profile.These findings suggest that the dual-modal MRINIR fluorescent imaging probe could revolutionize GBM prognosis and survival rate which can also be extended to other tumors type.

Emerging applications of near-infrared fluorescent metal nanoclusters for biological imaging

Fluorescent metal nanoclusters（MNCs） have recently emerged as a novel kind of promising fluorescent probes for biological imaging because of their ultrasmall core size（〈2 nm）, strong photoluminescence,facile availability and good biocompatibility. In this review, we provide an update on recent advances in the development of near infrared（NIR）-emitting MNCs in terms of synthesis strategies and bioimaging applications. We mainly focus on the utilization of NIR-emitting MNCs（including Au, Ag, Cu and alloy NCs） either as single modal imaging（fluorescence intensity-based imaging, fluorescence lifetime imaging, two-photon imaging） probes or as multimodal imaging（such as NIR fluorescence/X-ray computed tomography/magnetic resonance imaging, NIR fluorescence/photoacoustic imaging/magnetic resonance imaging, NIR fluorescence/single photon emission computed tomography） probes in biological cells and tissues. Finally, we give a brief outlook on the future challenges and prospects of developing NIR-emitting MNCs for bioimaging.

A bifunctional, colorimetric and fluorescent probe for recognition of Cu^(2+) and Hg^(2+) and its application in molecular logic gate

A bifunctional probe 1 with iminocoumarin scaffold demonstrated different responses for Cu2+and Hg2+.In fluorescence mode of probe 1,the intensity at 528 nm was quenched severely upon the addition of Cu2+or Hg2+.Meanwhile,a new fluorescence band at 574 nm appeared in the case of Hg2+.In its UV-Vis absorption mode,significant hypochromic shift for Cu2+and bathochromic shift for Hg2+occurred,which are in agreement with the observation of distinct color changes.In addition,probe 1can be used for the construction of a molecular logic gate with NOR and INHIBIT logic functions.

Fine-tailoring the linker of near-infrared fluorescence probes for nitroreductase imaging in hypoxic tumor cells

Imaging hypoxia using fluorescence probes for nitroreductase（NTR） have attracted much attention in last decade. At least three different linkers have been commonly used to connect the recognition unit and reporting unit in reported probes for NTR. Meanwhile, the linker is known to be a key factor for achieving best sensing performance. In this work, three near-infrared fluorescence probes CyNP-1, CyNP-2 and CyNP-3 were designed and synthesized from an aminocyanine dye CyNP. The three probes have the same recognition unit and same fluorescence reporting unit, but different linkers. CyNP-1 was found to have the best sensing performance for NTR with 40-fold of fluorescence enhancement. It is well investigated how the difference of the linkers brings out the different sensing performance by HPLC, MS and docking calculations. In the end, CyNP-1 was found to have good selectivity for NTR and used to imaging hypoxia in Hela cells.

IMAGING RNA IN LIVING CELLS WITH MOLECULAR BEACONS:CURRENT PERSPECTIVES AND CHALLENGES

There is a growing realization that cell-to-cell variations in gene expression have importantbiological consequences underlying phenotype diversity and cell fate. Although analytical toolsfor measuring gene expression, such as DNA microarrays, reverse-transcriptase PCR and in situhybridization have been widely utilized to discover the role of genetic variations in governingcellular behavior, these methods are performed in cell lysates and/or on fixed cells, and thereforelack the ability to provide comprehensive spatial-dynamic information on gene expression. Thishas invoked the recent development of molecular imaging strategies capable of illuminatingthe distribution and dynamics of RNA molecules in living cells. In this review, we describe aclass of molecular imaging probes known as molecular beacons (MBs), which have increasinglybecome the probe of choice for imaging RNA in living cells. In addition, we present the majorchallenges that can limit the ability of MBs to provide accurate measurements of RNA, anddiscuss efforts that have been made to overcome these challenges. It is envisioned that withcontinued refinement of the MB design, MBs will eventually become an indispensable tool foranalyzing gene expression in biology and medicine.

Role of Interfacial Viscosity and pH in L-Phenylalanine,L-Tryptophan Molecular Rotors

Protein folding involves the aminoacid sequence to come forth and form an energy minimized structure.Recently molecular crowding leading to increase in viscosity is said to be one of the major concerns affecting protein folding.Many external fluorescent probes are used to detect such increases in viscosity.Since most of the protein sequences contain L-Phe and L-Trp,in this study we have used these aminoacids as probes to detect changes in viscosity.This study will help to advance the knowledge on molecular crowding effects in protein folding.

Recent advances in ultrasound-controlled fluorescence technology for deep tissue optical imaging

Fluorescence imaging is a noninvasive and dynamic real-time imaging technique;however,it exhibits poor spatial resolution in centimeter-deep tissues because biological tissues are highly scattering media for optical radiation.The recently developed ultrasound-controlled fluorescence(UCF)imaging is a novel imaging technique that can overcome this bottleneck.Previous studies suggest that the effective contrast agent and sensitive imaging system are the two pivotal factors for generating high-resolution UCF images ex vivo and/or in vivo.Here,this review highlights the recent advances(2015e2020)in the design and synthesis of contrast agents and the improvement of imaging systems to realize high-resolution UCF imaging of deep tissues.The imaging performances of various UCF systems,including the signal-to-noise ratio,imaging resolution,and imaging depth,are specifically discussed.In addition,the challenges and prospects are highlighted.With continuously increasing research interest in this field and emerging multidisciplinary applications,UCF imaging with higher spatial resolution and larger imaging depth may be developed shortly,which is expected to have a far-reaching impact on disease surveillance and/or therapy.

用于肼检测的新型芘基荧光分子探针的合成与性能

利用1-芘甲醛优良的荧光性质,将其作为母体进行基团修饰,经过^(1)H-NMR和HRMS对结构进行表征,证实成功构建了肼荧光分子探针PMIDO。在DMSO-H2O体系中,PMIDO只能显示弱的荧光;在加入肼后,在含水量70%的条件下,显示出强的蓝色荧光,呈现出开灯型的荧光探针特征,检出限可达1.41×10^(-7)mol/L。同时,该探针对肼的检测呈现出高选择性和稳定抗干扰性,适用于5~10的pH范围,并在30 s内完成响应。进一步阐述了其荧光检测机制,即与肼反应后生成腙,为反应型肼的荧光检测提供有益参考。