8. On some application perspectives of the technique

On the basis of the material discussed above, we can conclude that a dynamic speckle interferometry technique that allows studies of processes in thin transparent biological media has been theoretically substantiated and experimentally tested. Application of the technique is based on the formulas relating the parameters characterizing the target of research and the dynamics of speckle fields. The parameters characterizing the object are mean value 〈x〉, dispersion σu, and relaxation time τ<sup>0</sup> of the optical path difference Δu of sounding wave pairs as well as temporal energetic spectrum of a random process Δu ¼ ΔuðtÞ. The minimum sizes of the averaging regions of the above-named values are transverse and longitudinal resolution of the lens generating the object image. The parameters characterizing speckle dynamics are time-average radiation intensity ~I at a point in the image plane, relaxation time τκ of value ~I, constant level <sup>η</sup>� of temporal autocorrelation function <sup>η</sup> <sup>¼</sup> <sup>η</sup>ðt<sup>Þ</sup> of process <sup>~</sup><sup>I</sup> <sup>¼</sup> <sup>~</sup>IðtÞ, and also the temporal energetic spectrum of this process.

Using samples in the form of a cell monolayer cultured on a transparent substrate, or one precipitated on a transparent substrate after defrosting, we demonstrated that value σ<sup>u</sup> can be used as a parameter that quantitatively characterizes the activity of live cell. A technique for calibration of a relevant device and a technique for determination of value σ<sup>u</sup> were developed. So applications related to assessment of cell activity can be the nearest perspective for the application of the technique. In particular, the technique for determining σ<sup>u</sup> can be applied to study of the effect of toxic substances on live cells and determine their science-based maximum allowable doses. Such a technique can be applied to search the optimum drugs preventing penetration of viruses and bacteria into cells.

Determination of value σ<sup>u</sup> is based on creating special conditions excluding the influence of parameters 〈x〉 and τ<sup>0</sup> on speckle dynamics. In the general case, the necessity may arise for simultaneous determination of all the three parameters characterizing the processes occurring in different parts of the same cell. Further studies are needed to solve this problem.
