Adsorbate Induced Transformations of Ovalbumin Layers in Volatile Organic Solvents: QCM Study of a Potential Bio-Sniffer for Acute Toxicity Assays

Abstract

Acute toxicity data are a necessary component of the general analysis of gaseous environments and the prediction of the possible consequences of exposure to a chemical substance on living organisms. One of the fastest ways to obtain such information is to use gas-phase chemical sensors with sensitive layers of biological origin. Here we report an experimental study of complex loadings for classical quartz crystal microbalances arising in closely packed protein layers of ovalbumin (OVA) on the surface of polycrystalline silver, silver coated with rigid carbon fullerene C60, or a soft molecular-organic crystal of copper phthalocyanine (CuPc). OVA molecules are similarly immobilized on the silver and fullerene-decorated surfaces, while the response of the OVA-CuPc layer indicates an insignificant amount of protein on the surface. A systematic study of the kinetics of the responses of these layers to saturated vapors of volatile solvents shows that the QCM resonant frequency change correlates well with the toxicity of gaseous analytes. It has been observed that saturated vapors of water, ethanol, and their mixtures are classically adsorbed with a high adsorption capacity. Benzene and isobutanol showed only a non-monotonic anti-Sauerbrey behavior, while acetone and cyclohexane had a 10-fold smaller quasi-classical response. The possibility of a gaseous analyte changing not only the QCM loading but also the mechanical behavior of the protein mass associated with the surface opens up the possibility of observing nonspecific conformational changes in proteins, which can be the cause of general cytotoxicity. This effect, combined with the native conformation of OVA in densely packed protein films, allows the use of ovalbumin in creating sensitive bio-sniffer layers for fast toxicological assays—a new class of express tests for biosafety and environmental control.

Keywords

• ovalbumin
• quartz crystal microbalances
• biosensors
• anti-Sauerbrey behavior
• adsorption
• bio-sniffer