Electrochemical biotin determination based on a screen printed carbon electrode array and magnetic beads

A biotin assay using magnetic beads (1 μm) and a re-usable 8-chanel screen printed electrochemical array is here reported. The reaction scheme is based on a one step competitive assay between biotin and biotin labeled with horseradish peroxidase (B-HRP). The mixture of magnetic beads modified with streptavidin (Strep-MB), biotin and B-HRP is left 15 min under stirring and then a washing step is performed. After that, 20 μL of the mixture is dropped twice on the electrodes and left 2 min. Then, the drop is removed and 20 μL of 3,3′,5,5′-tetramethylbenzidine (TMB) is deposited on the electrode surface. After 20 min a potential of −0.2 V is applied during 60 s, and 8 analytical signals are obtained. After washing with 0.1 M phosphate buffer the screen printed carbon electrode array can be use again. The linear range obtained is between 0.1 and 250 nM of biotin and have a sensitivity of 10−2 μA nM−1.