Kang, Sukhyun, Kang Min Kim, Yong Son, Sungwook Mhin, Jeong Ho Ryu, Kwang Bo Shim, Byoungsoo Lee, HyukSu Han, and Taeseup Song. “Graphene oxide quantum dots derived from coal for bioimaging: facile and green approach.” Scientific reports 9, no. 1 (2019): 1-7.