Synthesis And Properties Investigation Of Fluorescence Tunable Polymer Nanoparticles

In this work, several classes of fluorescence resonance energy transfer (FRET)systems based on polymeric nanoparticles were prepared. According to themechanism of FRET, through vary the ratio and distance of donor and acceptor, thehigh-efficient energy transfer can be occurred between donor and acceptor.Consequently, the nanoparticles exhibit the high-performance fluorescent modulation.This class of nanoparticles may find new applications in biological labeling andcellula imaging. The main contents and the results of this work are as following:1. At first, we successfully prepared a series of fluorescence tunable polymernanoparticles included two hydrophobic fluorescent dyes by a one-step mini-emulsionpolymerization. The selected dyes are two well known and widely studiedhydrophobic dyes with high quantum yield:9,10-diphenylanthracene (DPA) andnitrobenzoxadiazolyl (NBD). The as-prepared fluorescent nanoparticles exhibit thespectral properties of both DPA and NBD dye. Moreover, by changing theconcentrations of DPA and NBD, nanoparticles could show tuned fluorescent signalsunder a single wavelength excitation.2. Secondly, novel photoswitchable fluorescent polymeric nanoparticles have beensynthesized using a facile one-step miniemulsion polymerization, in which the FRETdonor,4-methamino-9-allyl-1,8-naphthalimide (MANI), and photoswitchable acceptor,spiropyran derivative, were successfully covalently incorporated into a polymericmatrix. The determined amount of MANI and spiropyran in the nanoparticles deducedfrom spectral data are about85~91%of the feed amount; while the determined weightratios of spiropyran to MANI in nanoparticles are very close to that of feed ratios. TheUV and visible light can be applied to modulate the fluorescence emission of MANIdye in nanoparticles. Upon UV irradiation, the spiropyran moieties in nanoparticlesconverted to the open-ring (MC form) structure and upon visible light irradiation theyturned back to the close-ring (SP form) structure, as a result the fluorescence ofMANI can be reversibly “switched off” and “switched on”. The fluorescenceresonance energy transfer (FRET) from the excited MANI dye molecules to the MCform of spiropyran moieties is the driving force behind the fluorescence modulation.The nanoparticles display fairly good photo-reversibility, photo-stability andrelatively fast photoresponsive property upon alternate UV/visible light irradiation.3. Thirdly, we have prepared novel amphiphilic reversible photoswitchablefluorescent nanoparticles via covalent incorporation with the fluorescent vinyliccrosslinking monomer, fluorescein-O,O-bis-propene (FBP)and spiropyran-linkedmethacrylate (SPMA) using a facile one-pot miniemulsion polymerization in thepresence of PEO-R-MA-40as a polymerizable nonionic surfactant. The fluorescence emission of FBP dye in nanoparticles can be reversibly switched "on" and switched"off" as a result of the structural inter-conversion between two states of spiropyranmoieties upon UV and visible light irradiation. Moreover, these novel amphiphilicreversible photoswitchable fluorescent polymeric nanoparticles also exhibit otheradvantages, such as improved biocompatibility and environmental stability, tunableFRET efficiency, relatively fast photoresponsibility and better photoreversibility.4. Finally, novel multicolor and photoswitchcable fluorescent polymernanoparticles were prepared by one-step miniemulsion via methyl methacrylate(MMA) copolymerization with4-ethoxy-9-allyl-1,8-naphthalimide (EANI),allyl-(7-nitro-benzo[1,2,5]oxadiazol-4-yl)-amine (NBDAA) and spiropyran-linkedmethacrylate (SPMA). Under visible-light conditions, SPMA moieties in polymernanoparticles are colorless and nonfluorescent, by varying the incorporating ratio oftwo dyes (EANI and NBDAA), fluorescence resonance energy transfer(FRET)-mediated emission signatures can be tuned so that the nanoparticles exhibitmultiple colors under a single wavelength excitation. Moreover, the fluorescenceemission of EANI and NBDAA dyes in nanoparticles can be reversibly switched“on” and “off” through the FRET process by the alternating irradiation of UV andvisible light.