Printing Inks for Security Applications Containing Bacteriorhodopsin

M. Neebe and N. Hampp

Institute of Physical Chemistry, Philipps-University, Hans-Meerwein-St., D-35043 Marburg, Germany


The biological photochrome bacteriorhodopsin (BR) occurs in nature in the form of a two-dimensional crystalline lattice. In this form, so-called purple membranes (PM), it is astonishingly stable towards chemical and thermal degradation. Variants of the naturally occuring bacteriorhodopsin can be switched with low light levels between a purple and a yellowish states with yellow and blue light - no UV light is required. The application of bacteriorhodopsin in the form of a photochromic ink is described. In addition to the optical effect, which can be checked easily without instrumentation, additional security elements can be realized with the same material which are very hard to detect and to copy. Among them is the alteration of the aminoacid sequence of the bacteriorhodopsin in positions which do not interact with its photochemical properties. By this and related methods even single production batches may be identified.