Carbon nanodots (CDs) with a low cytotoxicity have been synthesized by one-step microwave-assisted pyrolysis of citric acid in the presence of various amine molecules. The primary amine molecules have been confirmed to serve dual roles as N-doping precursors and surface passivation agents, both of which considerably enhanced the fluorescence of the CDs.

Significance: A protein modification technology has been developed in this study to overcome current problems faced by protein therapy. After being individually encapsulated in a super-hydrophilic zwitterionic gel, a therapeutic protein showed exceptional stability and long in vivo circulation half-life. More importantly, no immune response against either the protein or the polymer was observed following repeated injections. This technology will benefit patients by reducing administration frequency and mitigating adverse reactions and could allow more immunogenic proteins to enter into human therapeutic or protective applications.