Noninvasive monitoring of intracellular pH change induced by drug stimulation using silica nanoparticle sensors

Abstract

We have synthesized and applied a nanoparticle-based pH sensor for noninvasive monitoring of intracellular pH changes induced by drug stimulation. The pH sensor is a two-fluorophore-doped nanoparticle sensor (2DFNS) that contains a pH-sensitive indicator (fluorescein isothiocyanate, FITC) and a reference dye (tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate, RuBPY). The nanoparticles have an average diameter of 42 +/- 3 nm and can easily be taken up by cells for noninvasive intracellular pH measurement. The 2DFNS exhibited excellent pH sensitivity, reversibility, and a dynamic range of pH 4-7 for biological studies. We have used 2DFNS to monitor pH changes in living cells by drug stimulation. Both lysosomal pH changes in murine macrophages stimulated by chloroquine and intracellular acidification in apoptotic cancer cells were monitored in real time and with high pH sensitivity. Hela cells underwent intracellular acidification with a drop in pH from 7.2 to 6.5 after 8 h of treatment with 2 mumol/L dexamethasone, and this intracellular pH drop in the apoptotic cells was not influenced by the addition of zinc ions. The application of 2DFNS to intracellular pH measurements yields some important advantages: excellent pH sensitivity, little environmental effect on the pH dye, excellent quantification, high stability and excellent reversibility.

Optical Chemical Sensors:Design and Applications

“…In this case the pH sensor is composed of a shell of covalently bound indicator-dye molecules surrounding a core of sequestered, covalently bound, reference-dye molecules. What is interesting is that although both authors used covalent immobilization, Peng et al, 2007, reported an extensive dye leakage.…”

“…In the field of biology and medicine, sensors able to monitor pH in real time are in great demand, as they can be used for the general understanding of biological processes and for biomedical diagnostics (Doussineau et al, 2009). Recently, a lot of work has been done on optical pH-sensitive micro- (Borisov et al, 2008a;Doussineau et al, 2009;Schulz et al, 2009 ;Hornig et al, 2008) and nano-sensors (Allard & Larpent, 2008;Burns et al, 2006;Gao et al, 2005;Gao et al, 2007;Kim et al, 2006;Peng et al, 2007;Sun et al, 2006;). Here, the latter will be discussed, since they are less than 100 nm in size.…”

“…Several sol-gel pH NSs were prepared using a microemulsion procedure (Allard & Larpent, 2008;Gao et al, 2005;Gao et al, 2007;Kim et al, 2006;Peng et al, 2007;Sun et al, 2006) and one by Stöber (Burns et al, 2006). Gao et al, 2007, designed pH sensors using the doping technique for the immobilization of indicators in sol-gel NPs.…”

“…Kim et al, 2006, designed ormosil NPs (33±6 nm) in which the ratiometric pH-responsive dye is covalently immobilized. Peng et al, 2007, andBurns et al, 2006, developed twofluorophore-immobilized NPs sensors. The first author used fluorescein isothiocyanate as an indicator dye that was covalently crosslinked with the network formed by the hydrolysis of tetraethoxysilane and aminoproplytriethoxysilane, while tris(2,2′-bipyridyl) dichlororuthenium(II) hexahydrate (reference) was entrapped simultaneously inside the same NSs (42 nm) by electrostatic interaction.…”

Two‐Dye Core/Shell Zeolite Nanoparticles: A New Tool for Ratiometric pH Measurements

“…monodisperse dye-doped silica nanoparticles capable of noninvasive insertion into living cells. [35][36][37] Compartmented two-dye nanosensors have been described, allowing quantitative real-time pH monitoring based on the principle of ratiometric measurements. By placing a pH-insensitive reference dye in the silica core and a pH-indicator dye in the shell, such sensor systems circumvent problems associated with intensity-based measurements, i.e., dependence on the probe concentration or fluctuations in the light source intensity.…”