This disclosure is based, at least in part, on an unexpected discovery that the novel nanobodies and variants thereof are able to specifically bind afucosylated or sialylated IgG Fc glycoforms. Glycosylation of the IgG Fc domain is a major determinant of the strength and specificity of antibody effector functions, modulating the binding interactions of the Fc with the diverse family of Fey receptors. These Fc glycan modifications, such as removal of the core fucose residue, are newfound clinical markers for predicting severity of diseases, such as diseases caused by dengue virus (DENV) or SARS-CoV-2. However, it remains challenging to accurately distinguish specific IgG glycoforms without costly and time-intensive methods. The novel glycol-specific nanobodies and variants thereof, as disclosed herein, can be used as rapid clinical diagnostics or prognostics to risk stratify patients with viral and inflammatory diseases, as well as therapeutics for patient treatment.