Credit: © 2009 Wiley

The surface and channels of the aluminosilicate known as zeolite L have been modified for a variety of applications. When coated with amino moieties, for example, the zeolite adheres to Escherichia coli cells and acts as a non-toxic carrier. Dyes have also been incorporated into the pores of zeolite L. Cristian Strassert, Luisa De Cola and co-workers at the Westfälische Wilhelms-Universität Münster in Germany have now combined these two approaches, and further functionalized the zeolite's surface with a photosensitizer, to prepare a material that labels, targets and kills bacteria1.

A green fluorescent dye was first loaded in the zeolite's channels by gas-phase insertion. A silicon(IV) phthalocyanine — known to be a biocompatible photosensitizer that generates singlet oxygen on irradiation — was then covalently attached to the zeolite's surface; steric hindrance prevents the phthalocyanines from aggregating. No energy transfer occurrs between the chromophores, so the dyes and phthalocyanine moieties can be independently used as labels and photosensitizers, respectively, controlled by different irradiation wavelengths.

Amino groups were subsequently attached to the zeolite's surface. Fluorescent studies revealed that the resulting hybrid material adheres to the negatively charged membrane of E. coli cells through hydrogen bonding and electrostatic interactions, thus efficiently targeting the bacteria. On irradiation, the phthalocyanine derivatives generate singlet oxygen radicals that kill the bacteria.