Dipojono, H. K., I. Safitri, N. Nugraha, E. M. Budi, N. Nuryanti, A. G. Saputro, M. Y. David, and H. Kasai. “Immobilization of Amino Acids Leucine and Glycine on Polypyrrole for Biosensor Applications: A Density Functional Theory Study”. Journal of Mathematical and Fundamental Sciences, vol. 43, no. 2, July 2013, pp. 113-22, doi:10.5614/itbj.sci.2011.43.2.4.