Polymer characterisation on langasite delay lines

Detection of ever diminishing masses is currently becoming of increasing importance for chips working with small volumes in chemical applications. For the detection of small masses (10^-10 g) micro acoustic wave devices can be used. To detect specific molecules, a sensitive layer for selective binding is attached to the piezoelectric material. As a substrate for the surface acoustic wave (SAW) device, langasite (0°, 138.5°, 26.6° cut, LGS) with zero temperature coefficient delay (TCD) is used. The zero TCD allows high precision measurements using sensitive layers even without temperature compensation. A sensitive layer for the detection of cis-diols, such as sugars or neurotransmitters, has been realized by attaching a polymer layer to a LGS delay line. A change in the SAW velocity due to the presence of the polymer was detected. The third and fundamental harmonics were used for this purpose, because of their good signal strength. Also the temperature dependence of the new velocity was determined achieving no influence of the polymer on the group velocity. The polymer layer was successfully attached to LGS surfaces and has shown a long term chemical stability, making it adequate for future applications.