Long-decay near-infrared-emitting doped quantum dots for lifetime-based in vivo pH imaging.

pH-responsive doped quantum dots with an ultrasmall size (∼3.5 nm), near-infrared emission (∼720 nm) and long lifetime (∼1 μs), which exhibit a linear response range from pH 5.5 to 7.0 with the maximum change in the fluorescence lifetime up to ∼600 nm, were synthesized as lifetime-based pH nanosensors for in vivo imaging.