Antimicrobial resistance is a challenging health problem that demands alternative treatments. Nanoplatforms with antimicrobial properties, associated with photodynamic and photothermal therapies, are potential candidates for this task due to characteristics such as non-invasive, antibiotic-free, dual selectivity, and low adverse effects in therapeutic procedures. Graphene quantum dots are a possible substitute for other nanoparticles, especially by presenting low toxicity and low cost. However, graphene quantum dot properties are highly dependent on the synthesis methods, which makes it difficult to compare and improve methods using different studies. In this work, we apply spectroscopic and photothermal methods to investigate a commercially available green fluorescent graphene quantum dot (GQD) as a potential antimicrobial agent and to determine its theranostics properties. The results showed that the photoactivation of the GQD in phosphate-buffered saline solution by light sources with wavelengths shorter than the emission band can generate singlet oxygen and a heat yield of [Formula: see text] under excitation at 532 nm, showing the potential of this GQD as a photodynamic and photothermal agent.