A lab on a chip device includes a whole blood inlet port and microchannels to transport a whole blood sample or plasma skimmed from the whole blood sample into a detection chamber that includes at least one 3-electrode set of a counter electrode, a working electrode and a reference electrode. The counter electrode, the working electrode and the reference electrode may present bare, unmodified surfaces that are disposed so that clozapine present in the whole blood sample is detected via a reduction-oxidation reaction. Alternatively, the working electrode surface may include catechol grafted to chitosan. A method of detecting analytes and biomarkers includes collecting a whole blood sample, loading the sample into a point-of-care testing (POCT) device that includes at least one working electrode; testing the sample for the occurrence of a redox reaction; and calculating the total oxidative charge when the working electrode is bare or modified as before.