Polylysine-modified MXene nanosheets with highly loaded glucose oxidase as cascade nanoreactor for glucose decomposition and electrochemical sensing

Two-dimensional (2D) nanoreactors with cascade catalytic activity for glucose oxidation and hydrogen peroxide decomposition are prepared via immobilizing glucose oxidase (GOx) on Ti3C2 MXene nanosheets. Amino-rich polypeptide, poly-l-lysine (PLL), is applied to modify the ultra-thin Ti3C2 MXene nanosheets with a compatible surface for GOx immobilization. The PLL-modified Ti3C2 nanosheets possess a positively charged surface and show an excellent GOx loading capacity as high as 50 wt% of the Ti3C2 nanosheets. The physically adsorbed enzymes are then cross-linked with the amine groups in the PLL chains to form a robust GOx-PLL network covered on the MXene nanosheets. The GOx-conjugated Ti3C2-PLL (Ti3C2-PLL-GOx) nanosheets showed superior enzymatic activities than the activities of GOx immobilized on an inert porous silica substrate, largely because that the Ti3C2 nanosheets can catalyze the decomposition of the toxic intermediate H2O2 generated from the glucose oxidation. Given the excellent electrical conductivity of Ti3C2 MXene, the Ti3C2-PLL-GOx nanosheets are further deposited on glassy carbon electrode to construct a high-performance biosensor with a glucose detection limit of 2.6 μM.