Preparation and methodology for chemical mapping of sol–gel thin films containing lysozyme

Sol–gels are seeing widespread interest as suitable materials for the immobilization of biomolecules in applications ranging from optical coatings to specialty biocatalysts. Although there are numerous studies that have characterized these materials in terms of their macroscopic properties, few studies have examined and correlated these properties at the microscopic level. This study describes a spin-coating technique for the preparation of aluminum-supported sol–gel thin films containing immobilized lysozyme [E.C. 3.2.1.17] that are suitable for chemical mapping using FTIR microscopy operating in reflectance mode. This type of information can then be used to understand a variety of aspects of these materials which can be used for optimal engineering of these materials, as well as insightful design and modeling. A data analysis method was developed to extract information on chemical speciation and domain information on the materials from FTIR data matrices. Results from these studies indicated that, contrary to what might be expected, these sol–gels are not homogeneous on the microscopic level. Instead, they are heterogeneous in both the distribution of lysozyme and hydrophobic monomers at the scale investigated (20 μm resolution). The method described here has promise in terms of providing a non-invasive approach of chemically mapping concentrations of proteinaceous and related substances as well as chemical domains in situ in sol–gel thin films.