Specific targeting of ultrasound contrast agent (USCA) for diagnostic application: an in vitro feasibility study based on SAW biosensor

The present study described a new strategy to examine the interaction between the targeted ultrasound contrast agent (USCA) and its target under flow conditions with a surface acoustic wave (SAW) transducer. The sensing principle is based on the measurement of the phase change on the sensing element upon the binding of specific biomolecules. Love-wave biosensor array was consisting of sensor elements and reference elements. The sensor elements have been prepared by coating the sensor surface with tumor marker EDB-fibronectin by means of SAM technique and carbodiimide chemistry. Reference elements were left blank or coated with fibronectin and used to eliminate thermal drift, unspecific binding, and turbulence from injection of liquids by calculating the differential phase shift with respect to the sensor elements. The binding of targeted USCA to the sensor surface was constantly recorded by monitoring the phase shift on the sensor element. The binding of targeted USCA generated a high phase shift on the sensor elements, but almost no change on the reference elements. Control experiments using non-targeted and isotype-targeted USCA confirmed the specificity of binding due to anti-EDB-fibronectin scFv-antibody-fragment-EDB-fibronectin antigen interaction. The suitability of the SAW technique to monitor the specific binding behavior of targeted micron-sized USCA in real time has been well established.