Acoustic waves have a typical wavelength of few tenths of micrometers. The study of the intrinsic properties of nano-entities attached to the device surface is carried out in our lab using acoustic wave devices operating at several frequencies, i.e., from 35 to 300 MHz. In order to have spatial control of the immobilized molecules, the latter are bound through a single anchor (normally a PEG, thiol or DNA) to specific attachment points separated from each other by a certain distance. Through this single point attachment, biomolecules are presented to the surface in a suspended way as discrete particles, allowing the preservation of their native conformation. The above methodology is used for the immobilization of proteins and DNA molecules and subsequent study of dynamic changes of their conformation under well-controlled conditions.
Molecular nano-switches have been developed and studied as part of our nano-biotechnology studies. One such example is the DNA Holliday-junction; structure transitions between an “open” and “closed” state (mediated by magnesium) have been measured acoustically and the actual shape was deduced by independent intrinsic viscosity measurements (Nano Lett 2010). It has to be noticed that such a change is hard to be observed with label-free methods or even microscopy given the very small size (~ 10 nm) of the molecule.
Structural changes of intrinsically disordered proteins
Acoustic wave devices’ sensitivity to molecular hydrodynamic properties can be applied to the study of conformational changes of proteins such as the intrinsically disordered E.coli membrane protein ZipA. By attaching the protein to a supported lipid bilayer through a His-tag anchor, we showed that the protein was sensitive to the solution’s ionic strength, through the corresponding stretching or contraction of the unstructured domain (Chem Comm 2016). This conformational change was reflected on the change of the acoustic signals as they also followed the ionic-change induced change of ZipA conformation, with an impressive sensitivity of 1.8 nm or less.
Bacteria detection on modified surfaces
Over the past decade there has been an immense effort to develop new bioassays and biosensors for the rapid detection of food- and water-borne pathogens which remain a major cause of disease and mortality throughout the world. Within this framework, Abs are used as the means to achieve bacterial capturing to the sensor substrate. Present work in our group focuses on the development of optimized acoustic device surfaces for bacterial detection by employing different types of protocols using monoclonal/polyclonal antibodies or aptamers, prior to the addition of the bacteria-containing sample (Salmonella Typhimurium and mutant strains). In collaboration with Dr E. Gogolides group from the NCSR-Demokritos, plasma micro- and nano-textured surfaces have been developed and used as alternative means for enhancing Ab binding, leading potentially to higher bacteria attachment on corrugated immuno-surfaces (Sens Actuat B: Chemical 2016).