Developing robust organic afterglow emulsion for dissolved oxygen sensing

The concentration of dissolved oxygen is of vital importance for many biological processes such as cancer occurrence and stem cell development. Aqueous afterglow materials, which feature longer-lived excited states than metal complex-based phosphorescence materials, would possess higher sensitivity in oxygen sensing, and would allow visual and direct observation of oxygen concentration by human eyes and low-cost instrument. However, it remains challenging to fabricate aqueous afterglow materials because of the intrinsic problem of the disruption of rigid microenvironment during processing of solid-state afterglow materials. Here we report the fabrication of aqueous afterglow materials from liquid precursor via emulsion polymerization, which eliminate solid-state afterglow material processing and consequently result in 1.7 s phosphorescence lifetimes (2.0 s in deuterated system) at room temperature. The organic afterglow emulsion exhibits high solid content and colloidal stability, and is robust against large pH change, high salt concentration, and organic solvents. Interestingly, the afterglow emulsion has been found to display oxygen sensing property which can be dually monitored by afterglow intensity and lifetime changes. In-depth study reveals that the oxygen sensing property originates from the labile nature of organic triplets and also the oxygen permeability within the polymer latex in the aqueous emulsion system.