Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA.
ACS Nano. 2012 Jan 24;6(1):63-73. doi: 10.1021/nn202355p. Epub 2011 Dec 23.
Aqueous dispersions of graphene oxide are inherently unstable in the presence of electrolytes, which screen the electrostatic surface charge on these nanosheets and induce irreversible aggregation. Two complementary strategies, utilizing either electrostatic or steric stabilization, have been developed to enhance the stability of graphene oxide in electrolyte solutions, allowing it to stay dispersed in cell culture media and serum. The electrostatic stabilization approach entails further oxidation of graphene oxide to low C/O ratio (~1.1) and increases ionic tolerance of these nanosheets. The steric stabilization technique employs an amphiphilic block copolymer that serves as a noncovalently bound surfactant to minimize the aggregate-inducing nanosheet-nanosheet interactions. Both strategies can stabilize graphene oxide nanosheets with large dimensions (>300 nm) in biological media, allowing for an enhancement of >250% in the bioconjugation efficiency of streptavidin in comparison to untreated nanosheets. Notably, both strategies allow the stabilized nanosheets to be readily taken up by cells, demonstrating their excellent performance as potential drug-delivery vehicles.
氧化石墨烯在电解质存在的情况下本质上是不稳定的，因为电解质会屏蔽这些纳米片的静电表面电荷，从而导致不可逆的聚集。为了提高氧化石墨烯在电解质溶液中的稳定性，使其在细胞培养基和血清中保持分散状态，已经开发了两种互补的策略，分别利用静电或空间稳定化。静电稳定化方法需要进一步氧化氧化石墨烯，使其 C/O 比达到较低水平（约 1.1），并提高这些纳米片的离子耐受性。空间稳定化技术则采用两亲性嵌段共聚物作为非共价结合的表面活性剂，以最小化诱导聚集的纳米片-纳米片相互作用。这两种策略都可以在生物介质中稳定大尺寸（>300nm）的氧化石墨烯纳米片，与未经处理的纳米片相比，生物素化蛋白的生物偶联效率提高了>250%。值得注意的是，这两种策略都允许稳定的纳米片被细胞轻易摄取，证明了它们作为潜在药物输送载体的优异性能。
