Photoswitchable Fluorescent Nanoparticles: Preparation,Properties and Applications

This minireview highlights recent advances of research dedicated to photoswitchable fluorescent nanoparticles and their applications. Recently, several strategies have been developed to synthesize nanoparticles with optically switchable emission properties: either fluorescence on/off or dual‐alternating‐color fluorescence photoswitching. The underlying mechanisms of fluorescence photoswitching enable many different types of photoswitchable fluorescent nanoparticles to change fluorescence colors, thus validating the basis of the initial photoswitching design. Among all possible applications, the usage of photoswitchable fluorescent nanoparticles to empower super‐resolution fluorescence imaging and to label biological targets was subsequently reviewed. Finally, we summarize the important areas regarding future research and development on photoswitchable fluorescent nanoparticles.     

新型铽配合物掺杂SiO2荧光纳米粒子的制备

以荧光物质铽的配合物为核，二氧化硅为外壳，制备了大小均匀的新型稀土配合物荧光纳米粒子。实验采用油包水的反相微乳液法，在四乙氧基硅烷和3-氨丙基三乙氧基硅烷（APTEOS）的共水解下进行。通过透射电子显微镜（TEM）观察，所得的纳米粒子呈球形，大小均匀，直径在30nm左右。纳米粒子呈现很强的铽配合物发光，且发光性质十分稳定。可通过表面的氨基方便地与生物分子偶联，可作为一种优秀的时间分辨荧光标记物。     

载药荧光纳米粒子的制备及在乳腺癌MCF-7细胞系的应用及效果评价

利用两亲性聚乙二醇-聚乳酸共聚物（PEG-PDLLA）包覆荧光染料（DPBA）和紫杉醇（PTX）,通过自组装方法制得载药荧光纳米粒子DPBA/PTX@PEG-PDLLA.纳米粒子尺寸均一,具有良好的生物相容性.对纳米粒子的发光性质、载药量和体外药物释放等进行了表征,并考察了纳米粒子对乳腺癌细胞MCF-7的抑制效果,观察了MCF-7细胞对纳米粒子的摄取情况.结果表明,DPBA/PTX@PEG-PDLLA纳米粒子具有较强的红光发射,不仅可以用于MCF-7肿瘤细胞质荧光成像,而且对肿瘤细胞的增殖具有一定的抑制能力.     

聚磷腈荧光纳米粒子的制备及表征

以六氯环三磷腈(HCCP)和荧光素(FL)为单体、乙腈为溶剂、三乙胺(TEA)为缚酸剂,在室温超声作用下,通过沉淀聚合,成功制备了具有良好荧光性能的聚磷腈纳米粒子(PZF)。通过红外光谱、X射线能谱分析(EDS)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对PZF的化学结构和组成元素进行了分析。结果表明:制备的PZF是实心结构且粒径均一,具有良好的荧光性能;在365nm紫外光下照射不同时间后PZF的荧光强度几乎没有发生变化,说明制备得到的PZF具有强耐光漂白性。     

微型传感器:荧光纳米微球的制备及表征

以丙烯酰胺为基体,N,N-甲叉双丙烯酰胺为交联剂,荧光分子Fura-2作为探针,构造荧光纳米微球。考察了乳化剂用量、引发剂用量、交联剂单体浓度对纳米微球直径和油水比对乳液稳定性的影响。含Fura-2的荧光纳米微球对钙离子非常敏感,可作为钙离子传感器。     

Giant Amplification of Photoswitching by a Few Photons in Fluorescent Photochromic Organic Nanoparticles

Controlling or switching the optical signal from a large collection of molecules with the minimum of photons represents an extremely attractive concept. Promising fundamental and practical applications may be derived from such a photon‐saving principle. With this aim in mind, we have prepared fluorescent photochromic organic nanoparticles (NPs), showing bright red emission, complete ON–OFF contrast with full reversibility, and excellent fatigue resistance. Most interestingly, upon successive UV and visible light irradiation, the NPs exhibit a complete fluorescence quenching and recovery at very low photochromic conversion levels (<5 %), leading to the fluorescence photoswitching of 420±20 molecules for only one converted photochromic molecule. This “giant amplification of fluorescence photoswitching” originates from efficient intermolecular energy‐transfer processes within the NPs.     

Photoswitchable and Reversible Fluorescent Eutectogels for Conformal Information Encryption

Smart fluorescent materials that can respond to environmental stimuli are of great importance in the fields of information encryption and anti-counterfeiting. However, traditional fluorescent materials usually face problems such as lack of tunable fluorescence and insufficient surface-adaptive adhesion, hindering their practical applications. Herein, inspired by the glowing sucker octopus, we present a novel strategy to fabricate a reversible fluorescent eutectogel with high transparency, adhesive and self-healing performance for conformal information encryption and anti-counterfeiting. Using anthracene as luminescent unit, the eutectogel exhibits photoswitchable fluorescence and can therefore be reversibly written/erased with patterns by non-contact stimulation. Additionally, different from mechanically irreversible adhesion via glue, the eutectogel can adhere to various irregular substrates over a wide temperature range (−20 to 65 °C) and conformally deform more than 1000 times without peeling off. Furthermore, by exploiting surface-adaptive adhesion, high transparency and good stretchability of the eutectogel, dual encryption can be achieved under UV and stretching conditions to further improve the security level. This study should provide a promising strategy for the future development of advanced intelligent anti-counterfeiting materials.     

亲水性二芳基乙烯荧光分子开关的研究进展

二芳基乙烯荧光分子开关因具有优良的抗疲劳性和双稳态特征而被广泛地研究与应用,亲水化成为其作为荧光开关探针走向应用的关键点之一。本文综述了亲水性二芳基乙烯荧光分子开关当前的研究进展,归纳了实现亲水性的几种重要途径和结构,分析了各种亲水化方法的优缺点,并着重介绍了亲水性二芳基乙烯荧光分子开关作为荧光开关探针在化学传感、生物传感、生物成像以及超分辨成像等领域的应用现状,并指出当前应用研究中存在的一些问题,同时也对其未来的应用前景进行了展望。     

Fabrication of Double Emission Enhancement Fluorescent Nanoparticles with Combined PET and AIEE Effects

The major challenge in the fabrication of fluorescent silica nanoparticles (FSNs) based on dye-doped silica nanoparticles (DDSNs) is aggregation-caused fluorescence quenching. Here, we constructed an FSN based on a double emission enhancement (DEE) platform. A thio-reactive fluorescence turn-on molecule, N-butyl-4-(4-maleimidostyryl)-1,8-naphthalimide (CS), was bound to a silane coupling agent, (3-mercaptopropyl)-trimethoxysilane (MPTMS), and the product N-butyl-4-(3-(trimethoxysilyl-propylthio)styryl)-1,8-naphthalimide (CSP) was further used to fabricate a core–shell nanoparticle through the Stöber method. We concluded that the turn-on emission by CSP originated from the photoinduced electron transfer (PET) between the maleimide moiety and the CSP core scaffold, and the second emission enhancement was attributed to the aggregation-induced emission enhancement (AIEE) in CSP when encapsulated inside a core–shell nanoparticle. Thus, FSNs could be obtained through DEE based on a combination of PET and AIEE effects. Systematic investigations verified that the resulting FSNs showed the traditional solvent-independent and photostable optical properties. The results implied that the novel FSNs are suitable as biomarkers in living cells and function as fluorescent visualizing agents for intracellular imaging and drug carriers.     

Synthesis and Characterization of Fluorescent Silica Nanoparticles Functionalized with Collagens of Variable Lengths

Collagen, the most abundant protein in human body, has been widely used as an excellent natural material for diverse biomedical applications due to its superior properties such as ample biological interaction sites, minimal immunogenicity and high biocompatibility. Collagens of different lengths are produced by recombinant technology and utilized to functionalize fluorescent silica nanoparticles (FNPs). The collagen‐functionalized FNPs display mono‐disperse distribution, but their sizes are dependent on the length of collagen. These modified FNPs all show nice fluorescence profile as well as low cytotoxicity, suggesting promising applications in bioimaging. We have demonstrated that various types of collagen, conveniently produced by recombinant technology, can be used to modify silica nanoparticles with nice characteristics such as mono‐dispersion, non‐interference in fluorescence and low toxicity. It may endow fluorescent silica nanoparticles with broad biological applications.     

Fabrication of Novel Polymer Nanoparticle-Based Fluorescence Resonance Energy Transfer Systems and their Tunable Fluorescence Properties

In this study, two hydrophobic fluorescent dyes, nitrobenzoxadiazolyl (NBD) and 9-(diethylamino)benzo[a]phenoxazin-5-one (NR) with different doping ratios were incorporated into polymer nanoparticles to constitute novel polymer nanoparticle-based fluorescence resonance energy transfer (FRET) systems via a facile one-step mini-emulsion polymerization. Spectroscopic characteristics demonstrate that the two fluorophores have been successfully embedded into the nanoparticles, and the fluorescence emission intensity of the two hydrophobic dyes can be greatly enhanced in aqueous media. The as-prepared fluorescent nanoparticles also display a uniform small size (ca. 55 nm), high dye load, intense fluorescence, as well as controllable amount and ratio of the two dyes. The observed FRET efficiencies (16.0–75.2%), as well as the distance (r) between NBD (donor) and NR (acceptor), is closely correlated to the doping ratio of two dyes. Moreover, by varying the doping ratio of two dyes, the fluorescent nanoparticles would exhibit multicolor through FRET upon a single wavelength excitation, and the fluorescence emission signals of the dye-doped nanoparticles could be accurately tuned. These results indicate that the as-prepared uniform FRET-mediated nanoparticles are of high interest in multiplexed bioanalysis.     

Fluorescent Gold Nanoparticles: Synthesis of Composite Materials of Two‐Component Disulfide Gels and Gold Nanoparticles

Pseudoenantiomeric ethynylhelicene oligomers containing a disulfide group formed two‐component gels, which showed different solvent properties from gels without the disulfide group. The disulfide gels reacted with gold nanoparticles, and the resulting organic–inorganic composite materials exhibited fluorescence emission between 600–800 nm, along with emission from the oligomers at 450 nm. The disulfide gels and isolated gold nanoparticles loaded with the oligomers did not show the former emission. The 600–800 nm emission reversibly disappeared upon sol formation with heating, which was accompanied by an enhancement of the emission at 450 nm. The novel emission was also observed in the solid state.     

An Unconventional Polymerization Route to Hydrophilic Fluorescent Organic Nanoparticles for Multicolor Cellular Bioimaging

We demonstrated an unconventional polymerization route to synthesize hydrophilic fluorescent organic nanoparticles (FONs) for multicolor cellular bioimaging in this contribution. The route benefits from our unexpected discovery of a rapid polymerization reaction between 1,6‐hexanediol dipropiolate and 2,4,6‐triazide‐1,3,5‐triazine under the catalysis of N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA). Interestingly, the 2,4,6‐triazide‐1,3,5‐triazine and PMDETA system can also induce rapid free radical polymerization at room temperature. The as‐prepared FONs exhibited promising water solubility and stability with an average diameter of 20 nm. The excitation wavelength‐dependent fluorescent properties endow the FONs with blue, yellow, and red fluorescent emission under UV, blue, and green excitation, respectively. The cytotoxicity of FONs was investigated by using a Cell Counting Kit (CCK‐8) assay, which indicated good biocompatiblity. More importantly, the cell uptake experiment verified the FONs were excellent fluorescent nanoprobes for multicolor cellular bioimaging. Therefore, this unconventional route provides a novel fabrication strategy of highly hydrophilic FONs for biomedical applications.     

高耐光/耐化学性的核壳型荧光纳米微球的制备

选取不溶于水的、光/热稳定性优良的荧光溶剂染料, 采用改进的细乳液(Miniemulsion)聚合反应, 将染料分子以分散状态牢固地嵌入交联的纳米聚合物基质中, 然后结合种子聚合反应技术构建生物相容性壳层, 制备出发射橙、黄、绿和青色光的系列核壳型荧光纳米微球. 获得的核壳型荧光纳米微球的平均粒径小于40 nm, 粒度较均一, 其水胶体具有优异的储存稳定性, 较高的光/化学稳定性和发光效率; 纳米微球的交联壳层表面富含与蛋白质、核酸等相容的羧基. 该制备方法简便可控, 原材料易得, 成本低廉, 也可选用含氨基、巯基和羟基等化学修饰基团的壳层单体来构建多样化的纳米微球壳层.     

Photoswitchable organocatalysis in acylation of alcohol using dithienylethene-linked azoles

Three novel dithienylethenes bearing azole derivatives were synthesized and found to undergo reversible photocyclization of the dithienylethene units upon alternate irradiation with UV and visible light. Among them, the dithienylethene-linked imidazole and N-phenylimidazole exhibited a relatively high organocatalytic activity for the acylation of 2-decanol with acetic anhydride, and the catalytic activity of the dithienylethene-linked imidazole could be switched by reversible photoinduced cyclization/cycloreversion of the dithienylethene unit.     

Synthesis and characterization of photoswitchable fluorescent SiO2 nanoparticles

Switchable fluorescent silica nanoparticles have been prepared by covalently incorporating a fluorophore and a photochromic compound inside the particle core. The fluorescence can be switched reversibly between an on‐ and off‐state via energy transfer. The particles were synthesized using different amounts of the photoswitchable compound (spiropyran) and the fluorophore (rhodamine B) in a size distribution between 98 and 140 nm and were characterized in terms of size, switching properties, and fluorescence efficiency by TEM, and UV\Vis and fluorescence spectroscopy.