Upconversion nanoparticles for sensing pH

Tsai, Evaline S.; Himmelstoß, Sandy F.; Wiesholler, Lisa M.; Hirsch, Thomas; Hall, Elizabeth A. H.

doi:10.1039/c9an00236g

Cited by 33 publications

(29 citation statements)

References 52 publications

(62 reference statements)

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“…2e). Aggregation, causing the bimodal distribution, was consistent with the average zeta potential of +22 mV, which was a decrease from the zeta potential of +36 mV before dye attachment [31]. Particles with zeta potentials within the range seen here may agglomerate.…”

Section: Preparation and Characterization Of Ucnp-phab Sensorsupporting

confidence: 75%

“…The succinimidyl ester group here (enclosed by red dashed box) can react with primary amines to form an amide bond. Structure created with ChemDraw (b) The absorption (dashed) and emission (solid) spectra of pHAb (in color) are overlaid with the emission spectrum of thin-shell, PEI-coated UCNP [ 31 ] upon 980 nm excitation (in black). (c) Emission spectra at various pHs when UCNP-pHAb in phosphate/citrate buffer is excited at 532 nm (direct excitation of the dye).…”

Section: Resultsmentioning

confidence: 99%

“…A thin shell (1 nm thick) was grown to protect the UCNP from quenching effects. Core-shell particles are known to have brighter luminescence than core-only particles [31]. The synthesis protocol is described in the Electronic Supplementary Material (ESM).…”

Section: Synthesis Of Ucnpsmentioning

confidence: 99%

“…The UCNPs were modified with PEI to enable the formation of an amide bond between UCNP and dye. A two-step ligand exchange process was used to replace the oleate on the surface of the UCNPs with PEI [31]. The nanoparticles were dispersed in a cyclohexane/DMF system with NOBF 4 (1 mg per 1 mg UCNPs), and the resulting mixture was stirred for 20 min at 30°C.…”

Section: Ucnp Surface Modification With Peimentioning

confidence: 99%

“…As shown by us and others previously, the multiple emissions of the UCNPs at different wavelengths allow ratiometric sensing to be achieved. Depending on the chemistry of the indicator and distance from the UCNP linked via surface modification, it is possible to use one band of the UCNP (eg green emission) to excite a pH-sensitive moiety through the inner filter effect or energy transfer, while the other UCNP band (eg red emission) acts as a reference for quantitative ratiometric measurements [18,23,24,31]. This could also "turn-on" a separate analyte-dependent peak relative to a reference UCNP emission band.…”

Section: Preparation and Characterization Of Ucnp-phab Sensormentioning

confidence: 99%

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Upconversion nanoparticles as intracellular pH messengers

et al. 2020

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Upconversion nanoparticles (UCNPs) should be particularly well suited for measurement inside cells because they can be imaged down to submicrometer dimensions in near real time using fluorescence microscopy, and they overcome problems, such as photobleaching, autofluorescence, and deep tissue penetration, that are commonly encountered in cellular imaging applications. In this study, the performance of an UCNP modified with a pH-sensitive dye (pHAb) is studied. The dye (emission wavelength 580 nm) was attached in a polyethylene imine (PEI) coating on the UCNP and excited via the 540-nm UCNP emission under 980-nm excitation. The UC resonance energy transfer efficiencies at different pHs ranged from 25 to 30% and a Förster distance of 2.56 nm was predicted from these results. Human neuroblastoma SH-SY5Y cells, equilibrated with nigericin H + /K + ionophore to equalize the intra-and extracellular pH‚ showed uptake of the UCNP-pHAb conjugate particles and, taking the ratio of the intensity collected from the pHAb emission channel (565-630 nm) to that from the UCNP red emission channel (640-680 nm), produced a sigmoidal pH response curve with an apparent pK a for the UCNP-pHAb of~5.1. The UCNP-pHAb were shown to colocalize with LysoBrite dye, a lysosome marker. Drug inhibitors such as chlorpromazine (CPZ) and nystatin (NYS) that interfere with clathrin-mediated endocytosis and caveolae-mediated endocytosis, respectively, were investigated to elucidate the mechanism of nanoparticle uptake into the cell. This preliminary study suggests that pH indicator-modified UCNPs such as UCNP-pHAb can report pH in SH-SY5Y cells and that the incorporation of the nanoparticles into the cell occurs via clathrinmediated endocytosis.

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Section: Preparation and Characterization Of Ucnp-phab Sensorsupporting

confidence: 75%

Section: Resultsmentioning

confidence: 99%

Section: Synthesis Of Ucnpsmentioning

confidence: 99%

Section: Ucnp Surface Modification With Peimentioning

confidence: 99%

Section: Preparation and Characterization Of Ucnp-phab Sensormentioning

confidence: 99%

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Upconversion nanoparticles as intracellular pH messengers

et al. 2020

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Application of Optical Nanoprobes for Supramolecular Biosensing

Das,

Pal,

Bej

et al. 2023

Biosensors Nanotechnology

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True FRET‐Based Sensing of pH via Separation of FRET and Photon Reabsorption

Bagot

Rappeport

Das

et al. 2022

Advanced Optical Materials

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Among the most promising sensors being developed are those that rely on Förster resonance energy transfer (FRET). FRET is a non-radiative process where energy can be transferred from a donor (ion or molecule) to an acceptor. [3][4][5] The rate of this exchange is highly distance-dependent and fades rapidly with increasing donoracceptor separation. Thus sensors that utilize FRET are capable of measuring local variations in critical biological parameters.Of the possible FRET-based sensors, those based on upconverting nanoparticles (UCNPs) are among the most promising. UCNPs are unique nanoparticles that can emit at several distinct visible wavelengths from a single, near-infrared excitation source. UCNPs exhibit many advantageous characteristics for bioimaging and sensing such as no photobleaching, no blinking, and no background autofluorescence. [6,7] In particular, many groups have attempted to utilize UCNPs as a FRET-based sensor by conjugating a fluorescent dye to the UCNP surface. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] The key advantage of this configuration over other FRET-based schemes is that the multimodal emission of UCNPs allows for ratiometric sensing in which the relative intensities of two distinct peaks are compared rather than just the enhancement or quenching of a single one. Such ratiometric sensing reduces the sensing error due to variations in excitation intensity or nanoparticle concentrations, and thus makes these sensors much more robust against both sensor inhomogeneity and environmental noise. [26] However, FRET is not the sole process occurring that can affect the collected emissions. Unless a single UCNP can be measured directly, there exists a non-negligible chance that a photon emitted by one UCNP can be absorbed by a dye molecule on another nanoparticle. Such photon reabsorption (PR) would in turn lead to a decrease in the collected emission, thereby obscuring the true, localized FRET response of the original nanoparticle. An additional complication also arises from the fact that many of the visible UCNP emission lines originate from the same energy level. Since FRET acts as a decay pathway for an excited state electron, all emissions from this level should be affected equally by FRET, not just the one that overlaps with the dye's absorption band. To our knowledge, although the distinction between FRET and photon reabsorption has been discussed before, [27][28][29] no FRET-UCNP sensor has yet been proposed that accurately accounts for these complications.

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Upconversion nanoparticles for sensing pH

Abstract: pH sensing IR-excited dye-linked upconversion nanoparticles, via inner field effect quenching at 540 nm referenced to emission at 650 nm.

Cited by 33 publications

References 52 publications

Upconversion nanoparticles as intracellular pH messengers

Upconversion nanoparticles as intracellular pH messengers

Application of Optical Nanoprobes for Supramolecular Biosensing

True FRET‐Based Sensing of pH via Separation of FRET and Photon Reabsorption

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