Synthesis of Dual-Emissive Silicon Quantum Dots for Intracellular pH Sensing Applications

Fluorescent probes are powerful tools for biochemical analysis and imaging. Most fluorescent probes rely on a single-wavelength intensity mode and are susceptible to environmental interference. Here, a ratiometric silicon quantum dots (SiQDs) nanoprobe was developed for intracellular pH sensing. The SiQDs, synthesized through a one-pot hydrothermal treatment of 3-aminopropyltrimethoxysilane (APTMS) and carminic acid, exhibited dual emissions in the blue (∼440 nm) and green (∼520 nm) region. The properties and possible photoluminescence mechanisms of the SiQDs were investigated. The SiQDs provide sensitive pH sensing with a sigmoidal response from pH 5.0 to 9.0 and a linear range from pH 6.8 to 7.5. The SiQDs have a nearly optimal pKa value of 7.15, matching the intracellular pH of normal cells (7.2). The SiQDs nanoprobe, requiring no further modification or dye labeling, features simple synthesis, ultralow cytotoxicity, excellent photostability, pH reversibility, rapid response, and good pH sensitivity. It has been effectively utilized for ratiometric intracellular pH imaging and monitoring of stimulus-responsive pH changes in MCF-7 cells. It is a promising tool for biological applications.