A shining proposal for the detection of dissolved O2 in aqueous medium: Self-calibrated optical sensing via a covalent hybrid structure of carbon-dots&Ru.

O2 is a life-supporting gas and has been widely recognized as an important analyte in life science, medical care and environmental science. Optical sensing for gaseous oxygen has been widely reported owing to the simple, cost-effective and easy-to-go procedure. On the other hand, optical sensors for dissolved oxygen in aqueous media have been rarely reported, since most of them are incompatible with water, leading to poor sensitivity and linearity. In this effort, we tried the combination of Ru(II)-bpy complex and carbon dots (CDs) via covalent bonds, where bpy = bipyridine. A hybrid structure, named as Ru@CD, was constructed for the detection of dissolved oxygen, using Ru(II)-bpy as sensing probe and CDs as water-compatible supporting matrix. Ru@CD was carefully characterized to confirm its hybrid structure. Detailed analysis suggested that its emission showed self-calibrated sensing signals for dissolved oxygen. A good linearity of 99.1% was realized. Its sensitivity (3.18) was higher than most literature values for dissolved oxygen detection. Its working equation was confirmed as a corrected Stern-Volmer equation (Lehrer mode). Good selectivity and signal stability were observed.