Yingdan Qian

Facile synthesis of nitrogen-doped graphene for measuring the releasing process of hydrogen peroxide from living cells

Modulating the electronic characteristics of graphene is of great technological importance for improving and expanding its applications. Chemical doping with other elements is a promising way to achieve this goal. This work reports a facile synthesis of nitrogen-doped graphene (N-graphene) at low temperature. This method, which involves the steps of graphite oxidation, exfoliation, and chemical reduction with the use of hydrazine as a reducing agent, can simultaneously realize the reduction of graphene oxide and doping graphene with nitrogen atoms. The spectroscopic results demonstrate that N-graphene with N/C atomic ratio up to ∼4.5% can be prepared, and the doping N atoms consist of pyridinic, pyrrolic, graphitic, and oxidized nitrogen structures with the surface atomic compositions of ∼28%, 49%, 19%, and 4%, respectively. The prepared N-graphene exhibits superior electrocatalytic activity toward H2O2 reduction, and the contribution of the doped N atoms to the enhanced electrocatalytic activity is explained in detail based on density functional theory (DFT) calculations. Moreover, N-graphene is further used to study the dynamic process of H2O2 (a common representative of reactive oxygen species, ROS, in living cells) release from living cells such as neutrophil, RAW 264.7 macrophage, and MCF-7 cells. The results presented here open a new way to synthesize N-graphene, and also developed a new platform for a reliable collection of kinetic information on cellular ROS release. The approach established in this work could be potentially useful in study of downstream biological effects of various stimuli in physiology and pathology.

Graphene oxide-induced conformation changes of glucose oxidase studied by infrared spectroscopy.

The adsorption of proteins on the surface of nanomaterials can induce changes in the structure and biological activity of the proteins. Although there have been a number of studies aimed at developing an understanding of the interactions of proteins with surfaces of nanomaterials, a detailed description of the actual state of the adsorbed proteins or the functional consequences of protein adsorption onto nanomaterials has yet to be reported. In this study, the conformation changes of glucose oxidase (GOx) induced by adsorption on graphene oxide (GO) sheets were investigated by quantitative second-derivative infrared analysis and two-dimensional infrared correlation spectroscopy (2D IR). The adsorption of GOx on GO sheets resulted in the conversion of α-helix to β-sheet structures and therefore led to substantial conformation changes of GOx, even the unfolding of the protein. These alterations in the conformation of GOx caused a significant decrease in the catalytic activity of the enzyme for glucose oxidation. This study demonstrates that nanomaterials can strongly influence the conformation and activity of adsorbed proteins. In addition to the importance of this effect in cases of the direct adsorption of proteins on nanomaterials, the results have implications for proteins adsorbed on materials with nanometer-scale surface roughness.

Probing the anticancer-drug-binding-induced microenvironment alterations in subdomain IIA of human serum albumin.

The binding interaction of anticancer drug (using 5-fluorouracil (FU) as an example) with the model protein human serum albumin (HSA), and the FU-binding-induced microenvironment alterations in subdomain IIA of HSA molecule were studied by a combination of spectroscopic techniques and molecular docking method. The results indicated that the nature of forces involved in binding interaction between HSA and FU molecule were mainly van der Waals forces and hydrogen bonding interactions. These interactions resulted in the formation of FU-HSA complex, making the local microenvironment in subdomain IIA of the protein more hydrophobic than its native state. Moreover, the interaction caused the large conformation changes of HSA, leading to the increase of the compact α-helix structures at low concentration of FU (less than 150 μM). However, the high concentration of FU (higher than 150 μM) made the compact α-helix structure decreasing, probably due to the protein undergoing some sort of distortion. Molecular docking study revealed that FU could enter the inside a hydrophobic cavity of subdomain IIA (Sudlows site I) in proximity of Trp214 residue with the formation of specific hydrogen bonding with Trp214 and Lys199 residues, causing the fluorescence quenching of Trp214 through a static quenching mechanism. The study essentially provides an effective way for investigating the microenvironment alterations of protein induced by the drug molecules, and this approach can further be used in development of biomedicines and assessment of the safety-engineered drug delivery.