Fabrication of Photoswitchable and Thermotunable Multicolor Fluorescent Hybrid Silica Nanoparticles Coated with Dye-Labeled Poly(N-isopropylacrylamide) Brushes

Abstract

We report on the fabrication of hybrid silica nanoparticles densely grafted with thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) brushes with inner and outer layers selectively labeled with fluorescence resonance energy transfer (FRET) donors, 4-(2-acryloyloxyethylamino)-7-nitro-2,1,3benzoxadiazole (NBDAE), and photoswitchable acceptors, 1 0 -(2-methacryloxyethyl)-3 0 ,3 0 -dimethyl-6-nitro-spiro(2H-1-benzo-pyran-2,2 0 -indoline) (SPMA), respectively, via surface-initiated sequential atom transfer radical polymerization (ATRP). P(NIPAM-co-NBDAE)-b-P(NIPAM-co-SPMA) brushes at the surface of silica core exhibit collapse in the broad temperature range of 20-37 °C. UV irradiation of the aqueous dispersion of hybrid silica nanoparticles induces the transformation of SPMA moieties in the outer layer of polymer brushes from nonfluorescent spiropyran (SP) form to fluorescent merocyanine (MC) form, leading to occurrence of the FRET process between NBDAE and SPMA residues. Most importantly, the FRET efficiency can be facilely tuned via thermoinduced collapse/swelling of P(NIPAM-co-NBDAE)-b-P(NIPAM-co-SPMA) brushes by changing the relative distance between donor and acceptor species located within the inner and outer layers of polymer brushes, respectively. Thus, hybrid silica nanoparticles coated with P(NIPAM-co-NBDAE)-b-P(NIPAM-co-SPMA) brushes can serve as a sensitive ratiometric fluorescent thermometer. On the other hand, when the hybrid nanoparticle dispersion was irradiated with visible light again after UV irradiation, the MC form of SPMA moieties reverts back to the nonfluorescent SP form, leading to the turn-off of FRET process. Overall, aqueous dispersion of this novel type of hybrid silica nanoparticle is capable of emitting multicolor fluorescence, which can be facilely tuned by UV irradiation, visible light, and temperatures or a proper combination of these factors.

Thermometry at the nanoscale

“…The most explored polymers are PNIPAM, which has a lower critical solution transition at 305 K, 6,20,78,[127][128][129][130][131][132][133][134][135][136][137][138][139] together with others polymers of the same family, such as NNPAM or NIP-MAM. 134 Other examples include PEG-based polymers, Table 2 and Fig.…”

Remote Hyperthermia, Drug Delivery and Thermometry: The Multifunctional Platform Provided by Nanoparticles

“…While Figure 3a shows the trend of the ratio between harmonics (h5/h3) of the sample's magnetization response versus temperature over amplitude of the AC field (T/H o ) [34] Figure 3b presents the typical trend of the inverse AC susceptibility (1/χ) versus temperature (T) at increasing amplitudes of the AC field (H o ) [32]. The three optical-based nanothermometric properties emphasized include the trends reported for the temperature (T) dependence of the optical emission intensity (I) in Figure 3c for a typical semiconductor nanoparticle (SNP) [15,17], the shift in the emission wavelength (λ) for a typical GNP [26] in Figure 3d and the lifetime (τ) variation for a typical luminescent supported moiety (LSM) [30].…”

“…The population of the vibrational mode increases as the temperature increases, resulting in the increase of the oscillator strength [132]. Hybrid silica nanoparticles decorated with fluorescent precursor were used as a nanothermometer to probe temperature in the range of 20 to 37°C, with accuracy of about 0.1°C [17]. Finally, the iron oxide nanoparticle surface-decorated with a luminescent and thermo-sensitive organic molecule can be used as a nanothermometer, providing spatial resolution in the subnanometer range [23].…”

“…Nanoprobes allowing remote temperature-sensing using optical or magnetic properties are among the most promising directions nowadays. Most of the optical-based nanothermometers use the light-emitting intensity [15][16][17][18][19][20][21][22][23], light-emitting peak shift [24][25][26], or lifetime decay of a suitable optical band as the thermometric property [27][28][29][30]. As far as the clinical use is concerned the drawbacks of the actual optical-based nanothermometers rely on biocompatibility (usual semiconductor-based core nanoprobes or dye-based shell moieties are toxic), robustness (typical bleaching of organic-based shell moieties) or temperature accuracy (no better than 0.3°C nowadays), or even combination of these factors.…”

Preparation and characterization of dual-responsive spiropyran-based random copolymer brushes via surface-initiated atom transfer radical polymerization

“…[12][13][14][15] Therefore, surface-initiated atom transfer radical polymerization (SI-ATRP) is one kind of the effective method for preparing structure-controlled polymer brushes. [16][17][18][19][20][21][22][23] With the development of the research on the smart material, stimuli-responsive polymers have attracted significant interest. When they are subjected to external environmental stimuli, [24] such as the changes of solvent, [25] temperature, [26][27][28] ionic strength, [29] pH, [30,31] and light irradiation, [32,33] the molecular chains of the corresponding stimuli-responsive polymer brushes will generate a conformational change, leading to the changes in the properties of polymer brushes.…”