**5. Conclusions**

252 Acoustic Waves – From Microdevices to Helioseismology

The properties of the medium were determined at t1 = 10 and t2 = 70 minutes. At t1 = 10, the system is modeled as MTSM sensor loaded with semi-infinite Newtonian medium ( DIwater) (fig 10A). The height of the column (2 mm) was much higher than the penetration

At t2 = 10 min., the MTSM/GA determined properties of the layer at 15, 25 and 35 MHz are presented in table 5. The variations in the determined thickness values were very high (ranging from 300 nm to 5 μm due to the fact that column height was much larger than the penetration depth. Solution range for thickness values was set to be between 1 nm to 10 μm in genetic algorithm. Thus any thickness value larger than the penetration depth will satisfy the solution because the MTSM sensor is not sensitive to the changes beyond the penetration depth. However, the solutions were always higher than penetration depth as expected. Due to the high fluctuations in thickness values, it was not presented here. In contrast the solutions for ρ1, η1 and C1 match with the literature values very well. (Literature values are ρ1 = 1000 kg/m3, η1 = 0.001 kg/m.s and C1 = 0 N/m2 at room temperature (Greczylo and

depth of the acoustic wave at 5 MHz (~250 nm in DI water).

Fig. 10. Physical model for MTSM sensor system at A) t=10 and B) t=70

measured the average height of the antibody layer as 10.1±3.3 nm.

MTSM Frequency Density (kg/m3) CI (N/m2) η (kg/m.s)

Table 5. Determined properties for semi-infinite Newtonian medium layer by MTSM/GA at

At t = 70 min., the physical model is presented in fig 10b. A viscoelastic layer (protein layer) with finite thickness and semi-infinite Newtonian medium were loaded on MTSM sensor. The properties for diwater layer were entered into the algorithm as known variables and the unknown properties (ρp, ηp, C1 and dp) of viscoelastic layer were determined using the MTSM/GA method. The results are presented in table 6. The thickness of the layer was determined to range from 10.3 to 11 nm for the harmonics. This number correlates well with the values presented by the other researches. Westphal et al (Westphal and Bornmann 2002) calculated the height of antibody layer as 9.2 nm. Furthermore Liao et al (Liao et al 2004)

15 1006±5 (2.00±1.00) x102 (1.05±.004) x10-3 25 1003±2 (5.00±3.00) x102 (1.08±0.03) x10-3 35 1004±4 (1.00±1.00) x102 (1.06±0.04) x10-3

Deboswka 2005)).

15, 25 and 35Hz

It was shown that MTSM sensor combined with genetic algorithm can be used to extract mechanical and geometrical properties of biological layers. The developed technique was first experimentally tested with SU8-2002 polymer layers with known properties having two different thicknesses. It was shown that the developed technique was successfully determined the mechanical and geometrical layers of thin polymer layers. MTSM/GA technique was then applied to extract the properties of antibody layer coated on MTSM sensor. The obtained data support our hypothesis about use of MTSM/GA technique can be a powerful tool for quantitative characterization of interfacial biological interfacial processes.
