Sensor 2 was a gelatin modified screen printed electrode (Zensor
R&D, Taiwan), prepared by spreading 8 L of 6% gelatin solution
onto the carbon disk working electrode surface (3 mm diameter).
Gelatin was allowed to solidify at room temperature for 30 min.
All the electrodes: carbon counter electrode, Ag wire pseudo reference
electrode, and modified working electrode were printed on
the same support.