Size Exclusion Redox-Labeled Immunoassay (SERI): A New Format for Homogeneous Amperometric Creatinine Determination

A homogeneous amperometric immunoassay for creatinine has been developed by using anti-creatinine antibodies, redox-labeled creatinine and a glassy carbon electrode covered with a semipermeable cellulose membrane with 20 kD cutoff. Creatinine from the sample competes with redox-labeled creatinine for the antigen binding sites of the antibody. Unbound conjugate passes through the membrane and is indicated at the electrode whereas antibody bound conjugate is size excluded. For redox labeling of creatinine a new labeling substance, 2-acetamido-3-chloro-1,4-naphthoquinone (AcClNQ), was used, which can be indicated electrochemically at an interference free working potential of – 200 mV (vs. Ag/AgCl). With the developed size exclusion redox-labeled immunoassay (SERI) creatinine can be determined within a range from 10 ng/mL to 100 µg/mL (0.09–900 µM).