Polymeric assembled nanoparticles through kinetic stabilization by confined impingement jets dilution mixer for fluorescence switching imaging

Traditional fluorescence switching molecules achieving the state change between on and off states commonly based on UV irradiation. However, it is worth noting that UV irradiation is harmful to both the cancer cells and the normal cells. To achieve fluorescence switching under visible wavelength and avoid complicate molecular design, a fluorophore of 2,4,5,6-tetrakis(carbazol-9-yl)-1,3-dicyanobenzene(4Cz IPN) and a quencher of diarylethene(DAE) were physically incorporated within the biocompatible block copolymer poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)(PLGA-b-PEG) to form 4Cz IPNDAE nanoparticles(NPs) through flash nanoprecipitation(FNP). By using the FNP method, the NPs were prepared within milliseconds in a confined impingement jets dilution(CIJ-D) mixer. Quenching and recovery of fluorescence could achieve in the presence of DAE under 475 nm and 560 nm irradiation.Appropriate structure and fluorescent properties of the nanoparticles can be tuned by external conditions for their efficient fluorescence resonance energy transfer(FRET) in a kinetic stabilization process. This NPs formation process was further optimized by varying the dilution ratio, Reynolds number(Re) and polymer concentration to modulate the mixing and particle nucleation and growth process. The size and fluorescence switching properties of the NPs were systematically investigated in solution and in cellular uptake experiments. This work is anticipated to provide a simple and highly effective engineering strategy for the modulation of fluorescence switching nanoparticles and beneficial to its engineering application.

Fluorescence Switch Based on a Porphyrin-perylene Dyad

Upon excitation of porphyrin or perylene subunit, the porphyrin-perylene dyad exhibitsreversible fluorescence emitting and quenching by formation and neutralization of the protonatedporphyrin subunit, thereby providing a prototype of molecular fluorescence switch working in anexpanded spectral range.

Condensed state fluorescence switching of hexaarylbiimidazole-tetraphenylethene conjugate for super-resolution fluorescence nanolocalization

This paper reported the synthesis of hexaar- ylbiimidazole-tetraphenylethene （HABI-TPE） conjugated photochromic fluorophore, which simultaneously exhib- ited photochromic property, condensed state enhanced emission and reversible fluorescence switching. Upon UV irradiation, a green species with a broad absorption band between 550 and 800 nm（ the absorption maximum at 697 nm ） was observed, which readily faded to colorless in the darkness. HABI-TPE launched strong fluorescence with the maximum emission wavelength at 520 580 nm under the excitation with 450-500 nm visible light in condensed state, which is in contrast to nonfluorescence in solution. The maximum emission wavelength in condensed state was dependent of excitation wavelength. More interest- ingly, HABI-TPE exhibited reversible fluorescence switch- ing upon alternating irradiation with blue or near-UV light （wavelength less than 490 nm） and green light （more than 490 nm） in condensed state. Our evaluation demonstrated that HABI-TPE exhibited great photoswitchable fluores- cence, which is a promising photoswitchable fluorophore for localization-based super-resolution microscopy, evi- dencing by resolving nanostructures with sub-100nm resolution in polymethylmethacrylate films.

Fluorescent Switch Behavior of 1, 2-Bis(4-pyridyl) Ethylene Controlled by pH in Aqueous Solution

With the decrease of pH value from 8.45 to -1.0, the UV-Vis absorption and fluorescent spectra of 1,2-bis（4-pyridyl） ethylene（BPE） took on the same changing trend at four different successive pH stages： 8.45--7.20, 7.20--5.62, 5.62--2.60, and 2.60--1.0, namely, no change, decrease, increase, and decrease again. Among these, in a range of 7.20--5.62, the fluorescence wavelength blueshifted from 418 to 359 nm, but the UV-Vis absorption wavelength, in contrast, redshifted from 285 to 298 nm. The fluorescence intensity of BPE had a drop even to quench upon a decline in the pH value from 2.60 to -1.0 probably owing to its cation-re interaction to reduce the π electron cloud density of BPE. Two dissociation constants, pKa1（4.30±0.01） and PKa2（5.65±0.04）, were obtained based on fluorescence data. The changes of fluorescence spectra indicate that BPE has ＂oft-on-off＂ switch behavior. The fluorescent spectra of BPE were nearly independent on the presence of α- and β-cyclodextrins.

1-Imino Nitroxide Pyrene, a Burst-type H^(+) Fluorescent Switch

1-Imino nitroxide pyrene 1 has been characterized as a H^＋ fluorescent switch. The effects of various interfering species, solvents and the irradiation of ultraviolet light on the fluorescence intensity of 1 are also investigated. 1 fluoresces weakly in the 85% ethanol media containing no more than 4.5x10-5 mol/L of H^＋ （HCI）, but can produce a burst increase of about 4 times in the fluorescence intensity when the concentration of H＋ is increased to or over 4.9×10^-5mol/L. The extremely sharp response of 1 to H＋ occurs only within such a narrow concentration range. Moreover, the decrease of H^＋ concentration through adding sodium hydroxide causes the fluorescence quenching, suggesting that 1 may serve as a fluorescent switch for monitoring the concentration change of H＋ around the point of 4.5×10^-5 mol/L.

PHOTOSWITCHABLE NANOFLUOROPHORES FOR INNOVATIVE BIOIMAGING

Photosensitive fluorescent probes have become powerful tools in chemical biology and molecular biophysics,which are used to investigate cellular processes with high temporal and spatial resolution.Accordingly,photosensitive fluorescent probes,including photoactivatable,photoconvertible,and photoswitchable fluorophores,have been extensively developed during the past decade.The photoswitchable fluorophores have received much attention because they highlight cellular events clearly.This minireview summarizes recent advances of using reversibly photoswitchable fluorophores and their applications in innovative bioimaging.Photoswitchable fluorophores include photoswitchable fluorescent proteins,photoswitchable fluorescent organic molecules(dyes),and photoswitchable fluorescent nanoparticles.Several strategies have been developed to synthesize photoswitchable fluorophores,including engineering combination proteins,chemical synthesis,polymerization,and self-assembly.Here we concentrate on polymer nanoparticles with optically switchable emission properties:either fluorescence on/offor dualalternating-color fluorescence photoswitching.The essential mechanisms of fluorescence photoswitching enable different types of photoswitchable fluorophores to change emission intensity or wavelength(color)and thus validating the basis of the fluorescence on/offor dual-color photoswitching design.Generally the possible applications of any fluorophores are to label biological targets,followed by specific imaging.The newly developed photoswitchable fluorophores enable super-resolution fluorescence imaging because of their photosensitive emission.Finally,we summarize the important area regarding future research and development on photoswitchable fluorescent nanoparticles.

Site-specific fabrication of gold nanocluster-based fluorescence photoswitch enabled by the dual roles of albumin proteins

Fluorescence photoswitch is becoming increasingly desirable for many applications,but its controllable fabrication still remains challenging yet.In this paper,a new strategy is proposed to fabricate fluorescence photoswitch by harnessing dual roles of albumin proteins as both photochrome carriers and biotemplates of fluorophore.As an example,we demonstrated the successful fabrication of a fluorescence photoswitch by incorporating both the photochromic diarylethene dye(CMTE)and red-emitting fluorescent gold nanoclusters(AuNCs)into the specific domains of bovine serum albumin(BSA)in a highly controllable manner.Detailed spectral and photophysical characterisation showed that CMTE well-retains the photochromic properties within the CMTE–BSA–AuNC construct,although its photoconversion rate is slightly retarded.Different from previously reported photoswitches,the fluorescence of the present system is mainly modulated via the inner filter effect(IFE)mechanism,which exhibits high switching efficiency with an on-off ratio up to 90%,reversible fluorescence response and good antifatigue performance.This work provides a new,generable albumin protein-assisted strategy of fabricating advanced fluorescence photoswitch,which can find wide applications in biological,optical and information fields.

Asymmetric reversible structural switching of a diene coordination polymer promoted by UV-visible light

In natural and artificial systems,reversible reactions are commonly asymmetric with respect to the time scale and nature of the stimuli which drive the forward and backward processes.In applications for which switching behavior is required,it is desirable that the reversible reaction goes as close to symmetric as possible;however,such systems are uncommon.Herein,we report an example of ultraviolet(UV)-visible light-regulated asymmetric reversible structural switching involving a diene-based coordination polymer,CP1 and its monocyclobutane product,CP1a.It is possible to cycle at least ten times through a forward [2+2] photocycloaddition reaction and the reverse,photocleavage reaction.A single cycle can be completed within a few minutes.The transformation is accompanied by fast and distinct fluorescence changes,arising from optimisation of the reaction conditions.Density functional theory calculations allow rationalisation of the asymmetric reversible transformation between CP1 and CP1a rather than between CP1 and its dicyclobutane product CP1b.This work provides a clear illustration of reversible structural switching which approaches symmetric behaviour with respect to reaction rate and stimuli.The insights gained from this work also assist in the design of fast,reversible switching materials.

Preparation,Properties,and Applications of Low-Dimensional Molecular Organic Nanomaterials

In recent years, great progress has been made in research and development of small-molecule organic materials with various low-dimensional nanostructures. This paper presents a comprehensive review of recent research progress in this field, including preparation, electronic and optoelectronic properties and applications. First, an introduction gives to the reprecipitation, soft templates methods, and progress in synthesis and morphological control of low-dimensional small-molecule organic nanomaterials. Their unique optical and electronic properties and research progress in these aspects are reviewed and discussed in detail. Applications based on low-dimensional small-molecule organic nanomaterials are briefly described. Finally, some perspectives to the future development of this field are addressed.

Visualized thermoresponsive helix-helix switch of polyphenylacetylene with a wide-range tunable transition temperature

Polymers with tunable helicity and naked-eye structural change under external stimuli are valuable for fabricating smart materials. Herein, we report a novel thermoresponsive color and fluorescent polyphenylacetylene switch with a tunable critical temperature. It relies on the temperature and solvent sensitivity of intramolecular n→π* interactions between the vicinal carbonyl groups of ester substituents located at 3,5-positions, which are indispensable for forming the cis-cisoid helical conformation of polyene backbones. In a properly chosen solvent, a compressed cis-cisoid helix is stabilized by n→π* interactions at low temperatures and yields a colorless solution. Increasing temperature causes the conformational transition toward an extended cis-transoid helix due to the disruption of n→π* interactions and produces a yellow solution. Reducing the hydrogen bond donating ability or polarity of solvents increases the switching temperature. By introducing a fluorogenic pendant, this conformational transition can also be read out by fluorescence quenching. This work may open a new window for developing intelligent materials through precisely tuning conformational transitions.

Highly reversible photomodulated hydrosoluble stiff-stilbene supramolecular luminophor induced by cucurbituril

A photochromic molecular rotor based on stiff-stilbene(SSB-FMR)was handily prepared through coupled reaction,and further self-assembled with cucurbit[8]uril(CB[8])to form a 2:2 quaternary supramolecu-lar complex(SSB-FMR/CB[8]).Significantly,the intervention of CB[8]on SSB-FMR achieved dual functions that assembly-induced emission enhancement and assembly-induced improvement of photoisomerized performance(especially reversibility)of stiff-stilbene molecular photoswitch.The supramolecular strategy further facilitated the assembly as a photoresponsive fluorescence switch with outstanding fatigue resis-tance,which was expediently applied in high-security-level QR code anti-counterfeiting and controllable lysosome targeted imaging.The study unprecedentedly provides a supramolecular method for highly effi-ciently improving photoisomerized performance especially reversibility of molecular photoswitches based on stiff-stilbene,and is of vital significance for the construction of intelligent materials with excellent ca-pability.

Off-on-off luminescent switching of a dye containing imidazo[4,5-f][1,10]phenanthroline

A new acid-base fluorescent switch containing both imidazo[4,5-f][1,10]-phenanthroline and triphenylamine groups has been synthesized.Its fluorescence emissions and absorptions can be reversibiy changed through protonation/deprotonation of imidazole and amine moiety by controlling the intramolecular charge transfer（ICT） process,leading to off-on-off fluorescent molecular switching.

Conjugated Polyelectrolyte-Ag＋ Fluorescent Switch for Biothiol Sensing

A new ＂off-on＂ switch for sensitive and selective fluorescence detection of biothiols[glutathione（GSH）, cysteine（Cys） and homocysteine（Hcy）] was developed based on an anionic conjugated polyelectrolyte（CPE）, pyridyl-functionalized poly（phenylene ethynylene）（Pl）. The fluorescence of P1 can be significantly quenched by Ag＋ due to complexation-mediated interpolymer aggregation. Furthermore, biothiols can efficiently recover the fluorescence intensity of P1 as a result of the stronger binding between thiol group and Ag＋, which dissociates PI from the P1/Ag＋ complex and disrupts interpolymer aggregation. Under optimum conditions, a good linear relation- ship in a range of 100--4200 nmol/L is obtained for GSH with a detection limit of 80 nmol/L（S/N=3）. As a result of specific interaction between the thiol group and Ag＋, the proposed method shows a high selectivity for biothiols. In addition, the CPE-based fluorescence ＂off-on＂ switch has been used to quantitatively detect total biothiols in cell lysates.

Fulgide Derivative-Based Solid-State Reversible Fluorescent Switches for Advanced Optical Memory

Solid-state fluorescent switches with reversible luminescence characteristics have attracted considerable attention because of their broad applications in advanced photonics,such as anticounterfeiting inks,optical writing and erasing,and biological imaging.Herein,we have fabricated a solid-state reversible fluorescent switch under alternating UV(365 nm)and visible light treatments based on a fulgide(FUL)-functionalized tetraphenylethylene(TPE)derivative(TPE-FUL)containing a photochromic group FUL and aggregation-induced emission(AIE)luminogen TPE.TPE-FUL exhibited excellent reversible absorption and luminescence owing to the interconversion between open TPE-FUL(O-TPE-FUL)and closed TPE-FUL(C-TPE-FUL).Photophysical and theoretical investigations revealed that the luminescence of O-TPE-FUL is based on the local excited state of the TPE moiety,whereas the fluorescence quenching of C-TPE-FUL originates from the intramolecular charge transfer from the TPE to the FUL moiety.The excellent reversible photoswitching properties of TPE-FUL in the solid state allows for its potential use in advanced optical memory applications,such as anticounterfeiting,optical writing and erasing,and information encryption.

Efficient blue light-responsed dithienylethenes with exceptional photochromic performance

Three novel dithienylethenes modified by bifluoroboron β-diketonate fragments have been successfully developed. Upon blue light irradiation, they reached photostationary state within 2-5 s, as well as 100% conversion ratio and photocyclization quantum yield of > 0.70. Such fascinating photochromism were endowed by collaborative role of electron-withdrawing effect of BF_(2)bdk group to reduce HOMO-LUMO electronic gap for the open isomer, together with intramolecular hydrogen bonds and CH-π interactions favoring antiparallel conformation fixation. Moreover, they displayed specific discrimination and photoswitchable bacterial imaging for S. aureus.

A new fluorescent quinoline derivative toward the acid-responsivity in both solution and solid states

In this article,an acid-responsive luminescent material,1,4-di(quinoline-6-yl)buta-1,3-diyne(DQBD)is designed and synthesized.Upon different pH values,gradual changes of fluorescence colors for DQBD in both solution and solid phases are demonstrated due to the protonation effect.Moreover,such responsive characteristics can also be reversible,suggesting DQBD as a promising fluorescent material with great potential for reusable-and accurate-p H sensors in the future.

Fabricating UCNPs-AuNPs Fluorescent Probe for Sensitive Sensing Thiamphenicol

A novel fluorescent probe has been constructed based on fluorescence resonance energy transfer(FRET)between upconversion nanomaterials(UCNPs)NaYF4:Yb,Er and gold nanoparticles(AuNPs).The fluorescent“off-on”switching was formed for the detection of thiamphenicol(TAP)in egg samples.The fluorescence of UCNPs can be quenched to a certain degree by AuNPs.After adding TAP,the AuNPs generated aggregation and the fluorescence of UCNPs was recovered.The synthesized amination UCNPs and AuNPs were characterized by Fourier transform infrared spectroscopy(FTIR),UV-Vis,X-ray diffraction(XRD),energy dispersive spectrometer(EDS),and transmission electron microscope(TEM)techniques for observation and confirmation.As a model target,the detection of TAP has two linear ranges in the buffer solution within 0.01–0.1µmol/L and 0.1–1µmol/L using this fluorescent probe.The detection limit was obtained to be 0.003µmol/L(S/N=3),which is favorable for trace analysis.The recovery of TAP from 98.2%to 105.3%was obtained,and the relative standard deviation(RSD)was from 2.5%to 4.3%.Furthermore,the method established in this study based on the UCNPs auto-low background fluorescence has high selectivity and strong ability to eliminate interference,which is beneficial to analyzing complex samples.

A Highly Selective Fluorescent Chemosensor for Cu2＋

A new Zn2＋ probe L2-Zn（L2=naphthofuran carbonylhydrazone derivant） was synthesized as a fluores- cence chemosensor for Cu2＋, by which Cuz＋ ion could be detected with high selectivity and sensitivity in a wide pH range via a displacement ＂turn-off＂ signaling strategy. Whereas the coordination between Zn2＋ and L2 resulted in a considerable enhancement of typical luminescence of a naphthalofuran group in complex L2-Zn, the addition of Cu2＋ ion led to a dramatic decrease in the emission intensity of probe L2-Zn at about 503 nm（excitation at 423 nm）. The competitive fluorescent experiments showed that other metal ions, such as Hgz＋, Fe3＋, Ag＋, Ca2＋, Co2＋, Ni2＋, Cd2＋, Pb2＋, Zn2＋, Cr3＋ and Mg2＋ could not impact tile detection of Cu2＋. The detection limit of the novel probe L2-Zn for Cu2~ ion was as low as 2.3× 10 7 mol/L, which is far lower than the guideline value of 1.6× 10-5 mol/L of the United States Environmental Protection Agency.