DIRECT ELECTROCHEMISTRY OF HEMOGLOBIN AT SILVER ELECTRODE MODIFIED BYLIPOIC ACID MONOLAYER

The direct electrochemistry of hemoglobin (Hb) was studied by cyclic v oltammetry(CV) and flow injection analysis(FIA) on a silver electrode modified by a self-assembled monolayer of lipoic acid(LA). Lipoic acid molecules can strongly adsorb onto the Ag electrode surface through t he cleavage of the S-H bond and the formation of the Ag-S bond, The ob served adsorption coverage of LA demonstrates that the LA molecules sp ontaneously form a self-assembled monolayer. Experimental data show th at LA can promote the redox process of Hb at the modified electrode su rface. This chemically modified electrode (CME) exhibits good stabilit y in the CV and FIA. Linear-sweep voltammetric measurement of Hb at th e CME reveals a linear relationship between the oxidative peak current and the concentration of Hb in the range of 5.0 x 10(-7)-1.5 x 10(-5) mol/L. The relative standard derivation (RSD) for six replicate measu rements of 5.0 x 10(-6) mol/L Hb in FIA is 2.8%. The detection limit i s 2.0 x 10(-7) mol/L. The reaction mechanism involves the hydrogen bon d/salt bridge formation between the carboxylate of LA and the protonat ed lysine residues of Hb that can enhance the electron transfer reacti on. It can be used to detect Hb in teal examples.