Fluorescent and Photostable Silicon Nanoparticles Sensors for Real-Time and Long-Term Intracellular pH Measurement in Live Cells

Abstract

Fluorescent sensors suitable for dynamic measurement of intracellular pH (pHi) fluctuations should feature the following properties: feeble cytotoxicity, wide-pH range response, and strong fluorescence coupled with good photostability, which are still remaining scanty to date. Herein, by functionalizing fluorescent silicon nanoparticles (SiNPs) with pH-sensitive dopamine (DA) and pH-insensitive rhodamine B isothiocyanate (RBITC), we present the first demonstration of fluorescent SiNPs-based sensors, simultaneously exhibiting minimal toxicity (cell viability of treated cells remains above 95% during 24-h treatment), sensitive fluorescent response to a broad pH range (∼4-10), and bright fluorescence coupled with robust photostability (∼9% loss of fluorescence intensity after 40 min continuous excitation; in contrast, fluorescence of Lyso-tracker is rapidly quenched in 5 min under the same experiment conditions). Taking advantage of these merits, we further employ the resultant fluorescent SiNPs sensors for the detection of lysosomal pH change mediated by nigericin in live HeLa and MCF-7 cells in long-term (e.g., 30 min) manners. Interestingly, two consecutive stages, i.e., alkalization lag phase and logarithmic growth phase, are observed based on recording the whole process of pH change, offering important information for understanding the dynamic process of pHi fluctuations.