A unique polarity-sensitive photothermal sensitizer revealing down-regulated mitochondrial polarity during photo-induced cell death.

Photothermal therapy (PTT) is a highly selective and non-invasive method to remove tumor tissues, and a promising potential method to combat cancer in the near future. However, the physical changes inside cells during photo-induced cell death have not been studied yet, due to the lack of proper tools. In this work, a polarity-sensitive PTT sensitizer was fabricated for the first time, to investigate the intracellular polarity change during photo-induced cell death. The probe targets mitochondria in live cells and can detect the polarity change induced by the addition of cholesterol in a ratiometric manner. The cell viability of live Hepg2 cells pre-incubated with the probe could be dramatically decreased after laser irradiation within 5 min. The down-regulated mitochondrial polarity during photo-induced cell death was successfully revealed by using the probe.