Upconversion nanoparticles as intracellular pH messengers

Abstract

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.

A ratiometric luminescence pH sensor based on YAG:V3+,V5+ nanoparticles

“…As presented, the Eu 3+ ions can act as an internal reference signal with the pH stable emission, whereas the fluorescein luminescence, deposited on Eu 3+ -doped inorganic NaGd(WO 4 ) 2 nanoparticles, is a sensing probe. 71 Concerning the upconverting pH sensor, Yb 3+ , Ho 3+ , Tm 3+ -doped NaCaY(MoO 4 ) 3 ; 72 Yb 3+ , Er 3+ -doped NaYF 4 73–75 and Yb 3+ , Tm 3+ -doped NaYF 4 52 conjugated with organic compounds should be distinguished. A very broad pH operating range, namely 1–10, has been found for Yb 3+ , Er 3+ -doped NaYF 4 with the PEI polyelectrolyte.…”

Synthesis of tetrahedron DNA nanostructures for detecting the activation of cell signal transduction via their specific binding to transcriptional factors

“…3C). 28,29 However, clathrin-mediated endocytosis and lipid rafts might not play key roles in the internalization of TDNs into cells, because the clathrin-mediated endocytosis inhibitor chlorpromazine hydrochloride (CPZ) 28,30 and the lipid raft inhibitor methyl-β-cyclodextrin (mβ-CD) 31,32 had few effects on the internalization of FAM-labeled TDNs into cells (Fig. 3A and B).…”

The Art of Fluorescence Imaging with Chemical Sensors: The Next Decade 2012–2022

“…The UCNP-pHAb composites were found to be colocalized with the lysosome marker LysoBrite. The drug inhibitors chlorpromazine and nystatin, which interfere with clathrin-mediated endocytosis and caveolae-mediated endocytosis, were applied to elucidate the mechanism of nanoparticle uptake into the cell [115]. mentalization, compartment acidification, and the processing of endocytos (Figure 14).…”