Real-Time SE/QCM-D Characterization of Biomolecule Adsorption within Sculptured Thin Films

Recent improvements in nanofabrication strategies have led to the development of precisely crafted nanostructures with intricate features. Incorporating biomolecules such as proteins, DNA, drugs, and even whole cells could allow for functionalization of nanostructured surfaces for biological applications including biosensing, tissue engineering scaffolds, as well as drug and gene delivery. Along with the nanofabrication of biological devices, there is a need to develop instruments that are able to probe and characterize the dynamic evolution of these bio-functionalized interfaces. Spectroscopic ellipsometry combined with quartz crystal microbalance with dissipation (SE/QCM-D) is a non-destructive optical/mechanical characterization technique that when run in tandem, reveal dynamic characteristics of functional nanostructure development including film thickness, adsorbed mass, and porosity with sub-angstrom resolutions. Nanostructures in the form of sculptured thin films (STF) were fabricated by glancing angle deposition via electron beam evaporation of titanium onto gold-coated QCM-D crystals. The crystals were then mounted within the QCM-D liquid chamber and proteins of varying sizes were deposited and characterized in situ. Protein adsorption was detected shortly after introducing the protein solutions with both QCM-D and SE as an increase of mass and change in the optical response, respectively. The QCM-D reports greater adsorbed mass for larger proteins (fibronectin) than smaller proteins (bovine serum albumin). The total adsorbed mass of proteins within the nanostructured scaffold exceeded the total absorbed mass of their respective depositions on flat surfaces, confirming that these nanostructures are capable of trapping proteins. Analysis of the anisotropic optical response from the nanostructures, which is very sensitive to environmental changes, adds complementary information on protein adsorption and the optical quantification is in agreement with QCM-D results. In addition, deposition of other biomolecules such as cells and DNA complexes have also been probed on these surfaces. The use of combinatorial SE/QCM-D to characterize and monitor the deposition of biomolecules on complex nanotopographies will improve the design and fabrication strategies for a wide array of biotechnological devices.