Switch-on hydrogel biosensor based on self-assembly Mn-doped ZnS QDs and cellulose nanofibrils for glutathione detection

•A novel stimuli-responsive switch-on Mn:ZnS QDs@CNHs hydrogel biosensor was designed.•The hydrogel network provides QDs with protection and improves their dispersibility.•Biosensor is self-calibrating, enabling in situ sensing without sample contamination.•The detection of glutathione in serum was realized based on static quenching of Hg2+.