Dilution buffer: 10 mM Tris–HCl, pH 7.0. K-aptamer binding buffer: 10 mM Tris–HCl, 50 mM NaCl, 5 mM KCl and 5 mM MgCl2, pH 7.0. Standard Kana solutions at different concentrations were prepared with dilution buffer and 1.0 μM K-aptamer solution was prepared with binding buffer.