Scientists now have a cheaper tool for probing biomolecules thanks to Japanese researchers. By measuring two different physical properties simultaneously, Yoshio Okahata and co-workers at the Tokyo Institute of Technology can study protein hydration and viscoelasticity.

 The new approach uses a sensitive mass-measuring device - a piezoelectric quartz crystal microbalance (QCM) - to detect protein immobilisation on a surface. As a protein solution flows past the QCM, covalent coupling immobilises the protein onto an activated gold face of the QCM crystal, changing the crystal's resonance frequency. In liquids, however, this resonance frequency depends not only on the change in mass accompanying protein deposition, but on protein hydration and viscoelasticity, so protein quantification becomes difficult. 

The change in blue light reflection from a gold surface indicates how much protein has been bound

To overcome this hurdle, Okhata's team followed the protein immobilisation by measuring the change in reflection of blue light from the gold surface. While the QCM resonance frequency is affected by several factors, the change in reflection corresponds only to the thickness, and so the mass, of the immobilised protein layer. Combining these two measurements means that changes in the resonance frequency due to mass can be separated from changes associated with hydration and viscoelasticity, allowing scientists to assess the effect of hydration and viscoelasticity on biomolecular adsorption. 

Previous methods to measure protein binding have involved combining the QCM with another surface measurement technique, surface plasmon resonance, which requires a complicated and expensive optical set-up. Okahata's set-up is simpler and cheaper. Looking to the future, Okahata said 'this system could be applied to other biomolecular interactions.'

Russell Johnson