Graphene-based materials are promising building blocks for future nanodevices owing to their superior electronic, thermal, and mechanical properties as well as their chemical stability [1]. However, currently available graphene-based materials produced by typical physical and chemical routes, including micromechanical cleavage [2], reduction of exfoliated graphene oxide (GO) [3], and solvothermal synthesis [4], are generally micrometer-sized graphene sheets (GSs), which limits their direct application in nanodevices. In this context, it has become imperative to develop effective routes for cutting large GSs into nanometer-sized pieces with a well-confined shape, such as graphene quantum dots (GQDs).