Peptide-directed synthesis of fluorescent gold nanoparticles for mitochondria-targeted confocal imaging of temperature

Gold nanoparticles (AuNPs) with strong red fluorescence (peaking at 657 nm under 365 nm excitation) were synthesized with the assistance of a bifunctional peptide. The peptide was rationally designed with two functional regions: region 1 (CCY) for synthesizing AuNPs and region 2 (MLRAALSTARRGPRLSRLL) for targeting mitochondria. The resulting AuNPs show excellent stability, low toxicity, good biocompatibility, as can target mitochondria. The AuNPs exhibit a temperature dependent fluorescence with high sensitivity and good reversibility. Fluorescence intensity drops to 56% of its initial value on elevating temperature from 20 to 55 A degrees C, while the quantum yield drops from 7.1% to 3.9% and fluorescence lifetime (which is 12.2 mu s at 20 A degrees C) drops to 8.96 mu s at 55 A degrees C. The AuNPs are shown to be viable mitochondrial thermometers for use in HeLa cells.