Here we address an important roadblock that prevents the use of bright fluorescent nanoparticles as individual ratiometric sensors: the possible variation of fluorescence spectra between individual nanoparticles. Ratiometric measurements using florescent dyes have shown their utility in measuring the spatial distribution of temperature, acidity, and concentration of various ions. However, the dyes have a serious limitation in their use as sensors; namely, their fluorescent spectra can change due to interactions with the surrounding dye. Encapsulation of the d, e in a porous material can solve this issue. Recently, we demonstrated the use of ultrabright nanoporous silica nanoparticles (UNSNP) to measure temperature and acidity. The particles have at least two kinds of encapsulated dyes. Ultrahigh brightness of the particles allows measuring of the signal of interest at the single particle level. However, it raises the problem of spectral variation between particles, which is impossible to control at the nanoscale. Here, we study spectral variations between the UNSNP which have two different encapsulated dyes: rhodamine R6G and RB. The dyes can be used to measure temperature. We synthesized these particles using three different ratios of the dyes. We measured the spectra of individual nanoparticles and compared them with simulations. We observed a rather small variation of fluorescence spectra between individual UNSNP, and the spectra were in very good agreement with the results of our simulations. Thus, one can conclude that individual UNSNP can be used as effective ratiometric sensors.
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Ultrabright fluorescent nanothermometers
Here we report on the first ultrabright fluorescent nanothermometers, ∼50 nm-size particles, capable of measuring temperature in 3D and down to the nanoscale. The temperature is measured through the recording of the ratio of fluorescence intensities of fluorescent dyes encapsulated inside the nanochannels of the silica matrix of each nanothermometer. The brightness of each particle excited at 488 nm is equivalent to the fluorescence coming from 150 molecules of rhodamine 6G and 1700 molecules of rhodamine B dyes. The fluorescence of both dyes is excited with a single wavelength due to the Förster resonance energy transfer (FRET). We demonstrate repeatable measurements of temperature with the uncertainty down to 0.4 K and a constant sensitivity of ∼1%/K in the range of 20–50 °C, which is of particular interest for biomedical applications. Due to the high fluorescence brightness, we demonstrate the possibility of measurement of accurate 3D temperature distributions in a hydrogel. The accuracy of the measurements is confirmed by numerical simulations. We further demonstrate the use of single nanothermometers to measure temperature. As an example, 5–8 nanothermometers are sufficient to measure temperature with an error of 2 K (with the measurement time of >0.7 s).
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- NSF-PAR ID:
- 10341678
- Date Published:
- Journal Name:
- Nanoscale Advances
- Volume:
- 3
- Issue:
- 17
- ISSN:
- 2516-0230
- Page Range / eLocation ID:
- 5090 to 5101
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)The mesoporous nature of silica nanoparticles provides a novel platform for the development of ultrabright fluorescent particles, which have organic molecular fluorescent dyes physically encapsulated inside the silica pores. The close proximity of the dye molecules, which is possible without fluorescence quenching, gives an advantage of building sensors using FRET coupling between the encapsulated dye molecules. Here we present the use of this approach to demonstrate the assembly of ultrabright fluorescent ratiometric sensors capable of simultaneous acidity (pH) and temperature measurements. FRET pairs of the temperature-responsive, pH-sensitive and reference dyes are physically encapsulated inside the silica matrix of ~50 nm particles. We demonstrate that the particles can be used to measure both the temperature in the biologically relevant range (20 to 50 °C) and pH within 4 to 7 range with the error (mean absolute deviation) of 0.54 °C and 0.09, respectively. Stability of the sensor is demonstrated. The sensitivity of the sensor ranges within 0.2–3% °C−1 for the measurements of temperature and 2–6% pH−1 for acidity.more » « less
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Abstract Ultrabright fluorescent nanoparticles (NPs) hold great promise for demanding bioimaging applications. Recently, extremely bright molecular crystals of cationic fluorophores were obtained by hierarchical coassembly with cyanostar anion‐receptor complexes. These small‐molecule ionic isolation lattices (SMILES) ensure spatial and electronic isolation to prohibit aggregation quenching of dyes. We report a simple, one‐step supramolecular approach to formulate SMILES materials into NPs. Rhodamine‐based SMILES NPs stabilized by glycol amphiphiles show high fluorescence quantum yield (30 %) and brightness per volume (5000 M−1 cm−1/nm3) with 400 dye molecules packed into 16‐nm particles, corresponding to a particle absorption coefficient of 4×107 M−1 cm−1. UV excitation of the cyanostar component leads to higher brightness (>6000 M−1 cm−1/ nm3) by energy transfer to rhodamine emitters. Coated NPs stain cells and are thus promising for bioimaging.
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Abstract Ultrabright fluorescent nanoparticles (NPs) hold great promise for demanding bioimaging applications. Recently, extremely bright molecular crystals of cationic fluorophores were obtained by hierarchical coassembly with cyanostar anion‐receptor complexes. These small‐molecule ionic isolation lattices (SMILES) ensure spatial and electronic isolation to prohibit aggregation quenching of dyes. We report a simple, one‐step supramolecular approach to formulate SMILES materials into NPs. Rhodamine‐based SMILES NPs stabilized by glycol amphiphiles show high fluorescence quantum yield (30 %) and brightness per volume (5000 M−1 cm−1/nm3) with 400 dye molecules packed into 16‐nm particles, corresponding to a particle absorption coefficient of 4×107 M−1 cm−1. UV excitation of the cyanostar component leads to higher brightness (>6000 M−1 cm−1/ nm3) by energy transfer to rhodamine emitters. Coated NPs stain cells and are thus promising for bioimaging.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1NA00449B
