Electronic Supplementary Material

An electrochemical immunosensor for anti-T. cruzi IgM antibodies, a biomarker for congenital Chagas disease, using a screen-printed electrode modified with gold nanoparticles and functionalized with shed acute phase antigen

Matías Regiart1, Sirley V. Pereira1, Franco A. Bertolino1, Carlos D. Garcia2, Julio Raba1, Pedro R. Aranda1*

1INQUISAL, Department of Chemistry. National University of San Luis, CONICET. Chacabuco 917. D5700BW, San Luis, Argentina

2Department of Chemistry, Clemson University, Clemson, SC 29631, South Carolina, USA

*Author to whom correspondence should be addressed: () (Tel.) +54-266-425385; (Fax) +54-2652-43-0224.

Concentrations of H2O2, 4-TBC and pH range

The enzymatic response was studied in the pH range from 4.00 to 7.00 and showed a maximum activity at pH 5.05. The pH value used was 5.05 in 0.01 mol L-1 phosphate–citrate buffer.

Fig. S1. Study of pH range from 4.00 to 7.00.

The effect of varying H2O2 concentration from 0.5 to 5 mmol L-1, for 1 mmol L-1 4-TBC solution and the effect of varying 4-TBC concentration from 0.1 mmol L-1 to 0.05 mol L-1 for 1 mmol L-1 H2O2 solution on the immunosensor response were also evaluated (data not shown). These experiments indicated that the optimum H2O2 and 4-TBC concentrations were found to be 1 mmol L-1, values that were selected for the remaining of the experiments herein described.

Enzyme conjugate concentration

As the last characterization step performed to maximize the response of the system, the effect of the enzyme conjugate concentration was also investigated. This factor was evaluated using anti-human IgM–HRP conjugate in the 1:1250, 1:1500, 1:2000, 1:2250, 1:2500, 1:2750 and 1:3000 dilution range. As it can be observed, the response of the electrode increased withrespect to the solution concentration until reaching a dilution factor of 1:2000. As a balance between protein consumption and electrochemical response, an anti-human IgM–HRP conjugate concentration of 1:2000 was selected as optimum for the preparation of the sensors.

Fig. S2. Study of enzyme conjugate concentration