A nitrobenzoxadiazolyl(NBD)-based fluorescent dye and a photochromic spiropyran derivative are incorporated into polymeric nanoparticles via a one-step miniemulsion polymerization. The diameter of the nanoparticles can be varied from approximately 40 nm to 80 nm by adjusting the polymerization conditions. The prepared nanoparticles exhibit the spectral properties of both NBD dye and spiropyran, indicating that the two chromophores are incorporated into the nanoparticles. The determined amount of NBD and spiropyran in the nanoparticles are about approximately 85-90% of the feed amount, while the determined weight ratios of spiropyran to NBD in nanoparticles are very close to that of feed ratios, suggesting the miniemulsion polymerization is a suitable approach for incorporating multiple chromophores into individual nanoparticles with controlled amounts (content) and ratio. UV and visible light can be applied to modulate the fluorescence emission of NBD dye in nanoparticles. Upon UV irradiation, the spiropyran moieties in nanoparticles are converted to the open-ring (McH form) structure and upon visible-light irradiation they return to the closed-ring (SP form) structure; as a result, the fluorescence of NBD can be reversibly "switched off" and "switched on". Fluorescence resonance energy transfer from the excited NBD dye molecules to the McH form of the spiropyran moieties is the drives the fluorescence modulation. The nanoparticles display fairly good photoreversibility, photostability, and relatively fast photoresponsivity upon alternate UV/Vis irradiation. This class of photoresponsive nanoparticles may find applications in biological fields, such as labeling and imaging, as well as in optical fields, for example, individually light-addressable nanoscale devices.

No abstract

Fluorescent carbon nanoparticles (CNPs) with diameters of about 3 nm which can emit blue-green light were synthesized through the hydrothermal carbonization of ethylenediaminetetraacetic acid disodium salt (EDTA$2Na). Then, the CNPs were functionalized with spiropyrans to obtain the spiropyranfunctionalized CNPs. The emission of the spiropyran-functionalized CNPs centered at 510 nm could be switched off, while being turned on at 650 nm via energy transfer after UV light irradiation. The process could be reversed by using visible light irradiation. The optical switching of the fluorescence was repeated 10 times without apparent "fatigue", showing excellent photoreversibility and high stability.Spiropyran-functionalized CNPs may find potential applications in biological imaging and labeling, reversible data storage/erasing, as well as individual light-dependent nanoscale devices.

In the present study, novel polymeric nanoparticles of ca. 55 nm in diameter with reversibly photoswitchable fluorescence properties were synthesized using a facile one-step miniemulsion polymerization, in which the donor of fluorescence resonance energy transfer (FRET), 4-methamino-9-allyl-1,8-naphthalimide (MANI), and the acceptor, spiropyran-linked methacrylate (SPMA), were covalently incorporated into a polymeric matrix during the polymerization process. The fluorescence emission of MANI dye in nanoparticles can be reversibly switched using the alternating irradiation of UV and visible light, which can induce the structural interconversion between the SP form and MC form of spiropyran moieties inside nanoparticles and thus reversibly switch on and switch off the FRET process. The prepared photoswitchable fluorescent polymer nanoparticles not only show a high load capacity of dyes, controllable amount and ratio of the two dyes, and tunable FRET efficiency but also exhibit higher spectral stability because of covalent linkage between dye molecules and the particle, relatively fast photoresponsibility, and better photoreversibility compared to some previously reported systems.

Photoswitchable fluorescent polymeric nanoparticles (PFPNs) with controllable molecular weight, high contrast, biocompatibility, and prominent photostability are highly desirable but still scarce for rewritable printing, superresolution bioimaging, and rewritable data storage. In this study, novel amphiphilic BODIPY-based PFPNs with considerable merits are first synthesized by a facile onepot RAFT-mediated miniemulsion polymerization method. The polymerization is performed by adopting polymerizable BODIPY and spiropyran derivatives, together with MMA as monomer, and mediated by utilizing biocompatible PEO macro-RAFT agent as both control agent and reactive stabilizer. The amphiphilic BODIPY-based PFPNs not only exhibit reversibly photoswitchable fluorescence properties under the alternative UV and visible light illumination through induced intraparticle fluorescence resonance energy transfer (FRET) but also display controllable molecular weight with narrow polydispersity index (PDI), high contrast of fluorescence, tunable energy transfer efficiency, good biocompatibility, excellent photostability, favorable photoreversibility, etc. The as-prepared PFPNs are successfully demonstrated for rewritable fluorescence patterning and high-contrast dual-color fluorescence imaging of living cells, implying its potential for rewritable data storage and broad biological applications in cell biology and diagnostics.

Novel multicolor and photoswitchcable fluorescent polymer nanoparticles were prepared by one-step miniemulsion via methyl methacrylate (MMA) copolymerization with 4-ethoxy-9-allyl-1,8-naphthalimide (EANI), allyl-(7-nitro-benzo[1,2,5]oxadiazol-4-yl)-amine (NBDAA) and spiropyran-linked methacrylate (SPMA). Under visible-light conditions, SPMA moieties in polymer nanoparticles are colorless and nonfluorescent, by varying the incorporating ratio of two dyes (EANI and NBDAA), fluorescence resonance energy transfer (FRET)-mediated emission signatures can be tuned so that the nanoparticles exhibit multiple colors under a single wavelength excitation. Moreover, the fluorescence emission of EANI and NBDAA dyes in nanoparticles can be reversibly switched "on" and "off" through the FRET process by the alternating irradiation of UV and visible light. This class of novel photoswitchable multicolor fluorescent polymer nanoparticles may find potential applications in multiplexed bioanalysis.

No abstract

Imaging of hepatocellular nitric oxide (NO) in vivo is of great importance for understanding its roles in liver diseases, but such an imaging approach is still lacking. Herein, a hepatocyte-targeting fluorescent NO sensor has been fabricated. This sensor exhibits good water solubility, excellent selectivity, and high sensitivity (∼1.62 nM). The cells and in vivo imaging experiments reveal that Gal-RhB facilitates the visualization of hepatocellular NO in both HepG2 cells and zebrafish. These results demonstrate that Gal-RhB may be a promising tool for studying the function of NO in NO-associated liver diseases.