Acevedo, C. A., M. H. Stach, A. Amtmann, M. E. Young, J. G. Reyes, H. Huebner, and R. Buchholz. “Measuring β-Galactosidase Activity at PH 6 With a Differential PH Sensor”. Electronic Journal of Biotechnology, vol. 12, no. 2, Apr. 2009, pp. 0-0, https://preprints.pucv.cl/index.php/ejbiotechnology/article/view/v12n2-10.