While chemical release approaches exist, there is a risk of glycan structure degradation during the release process . Therefore, direct analysis of intact glycoproteins without tedious sample preparation is highly desired. For the proof-of-concept, we selected fetuin and asialofetuin as a model system . Bovine fetuin is known to contain three Nglycosylation sites and five O-glycosylation sites , while asialofetuin shares the same protein structure and glycosylation sites but lacks terminal sialic acids . Sialic acid plays a crucial role in the central nervous system and the immune system, making it an essential glycan building block . Here, we used our sensing platform to directly quantify sialylation levels of fetuin/asialofetuin mixtures without sample pretreatment.