Solidified liquid layer model makes quartz crystal microbalance a convenient molecular ruler

Area of Science:

• Biophysics
• Materials Science
• Analytical Chemistry

Background:

• Quartz crystal microbalance (QCM) is widely used in biointerface studies.
• Quantitative interpretation of QCM data is often hindered by viscoelasticity and solution effects.
• Existing methods lack a practical solution for general and quantitative QCM data analysis.

Purpose of the Study:

• To validate a "solidified liquid layer" model for QCM analysis.
• To establish QCM as a quantitative biomolecular ruler.
• To address limitations in current QCM biointerface applications.

Main Methods:

• Application of five distinct proteins (rabbit IgG, streptavidin, lysozyme, bovine serum albumin) to validate the model.
• Measurement of effective thickness (T(eff)) of surface-immobilized, hydrated proteins.
• Investigation of protein-dependent critical parameters for "solidified liquid layer" formation.

Main Results:

• The "solidified liquid layer" model was successfully validated across proteins of varying sizes and shapes.
• Effective thickness values (T(eff)) were determined for immobilized proteins: 10.2 nm (IgG), 4.7 nm (streptavidin), 1.8 nm (lysozyme), and 4.8 nm (BSA).
• The critical number of stakes for layer formation was found to be protein-dependent.

Conclusions:

• The "solidified liquid layer" model provides a practical solution for quantitative QCM data interpretation.
• This model enhances QCM's utility as a biomolecular ruler in biointerface research.
• The findings will facilitate broader adoption of QCM for studying protein adsorption and conformational changes.