One aspect of the present disclosure encompasses methods for determining a protein kinase or phosphatase activity in a biological sample, comprising: contacting in a reaction mix a first test sample and a fluorescently-labeled peptide substrate capable of being modified by a protein phosphatase or a protein kinase, contacting the reaction mix with a TiO2 matrix, thereby partitioning fluorescently-labeled phosphorylated peptide from fluorescently-labeled dephosphorylated peptide; and determining the fluorescence of the fluorescently-labeled dephosphorylated peptide, thereby determining a protein kinase or phosphatase activity.