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Sensitivity of Anthrax protective antigen (PA) detection has been improved by directly immobilizing a PA-specific peptide onto a multi-wall carbon nanotube (MWCNT). The MWCNT was covalently immobilized onto a polyaniline (PANI) electrode, which was prepared via electropolymerization of the aniline monomer onto a glassy carbon electrode (GCE). Then, the PA-specific peptide was covalently immobilized to the MWCNT layer for measurement. When comparing this technique to that of PA immobilization on an insulting self assembled organic layer, the advantages of the MWCNT are clear. The MWCNT sensor resulted in enhanced electron transfer across the sensing layer. The resulting limit of detection (LOD) was 0.4 pM, a 13-fold improvement over that of our previous self-assembled organic layer was used for immobilization of the same peptide. Neither positive nor negative interferences were observed when a sample containing both 100 pM PA and bovine serum albumin (BSA) was measured, indicating good selectivity of the proposed sensor., (Copyright © 2011 Elsevier B.V. All rights reserved.)

A short chain peptide (16mer) has been successfully utilized for the selective electrochemical detection of the protein biomarker, protective antigen (PA), for the diagnosis of Anthrax. The major motivation of using a peptide instead of an antibody for the development of a biosensor is that there are advantages associated with the smaller size, better biological stability and easy synthesizability of a peptide. PA-selective peptide was synthesized and conjugated on a binding layer previously immobilized onto gold electrode. The same sensing scheme using a conventional antibody instead of a peptide was also tested for the purpose of comparison. Since the size of the peptide is approximately 1-2 orders of magnitude smaller than that of the antibody, a more populated immobilization of peptide on the sensing layer is possible and will eventually lead to improved sensitivity for PA detection. The selectivity of the peptide-based sensor was evaluated by observing the reduction peaks of samples containing PA with different concentrations of bovine serum albumin (BSA). The resulting responses were interference-free from BSA. The results of this study demonstrate the strong analytical potential of a peptide-based biosensor for diverse applications, especially in disease diagnosis where detection of a specific protein biomarker is particularly demanding.