The presented method of surface modification of single-crystal silicon by chemical etching makes it possible to obtain homogeneous nanostructured silicon layers with a thickness from 3 to 60 nm for application in micro- and nano-electronics as new multifunctional material. These results could be applied to the creation of sensitive photodetectors for visible and ultraviolet ranges. The method of scanning tunneling spectroscopy shows, that the changes in the thickness of nanostructured silicon layers affect the type of conductivity, and it opens new prospective for a practical application of nanostructured silicon in nano-electronics. The obtained current-voltage characteristics of nanostructured silicon layers showed different degrees of filling of the valence band, the conduction band and the appearance on the curve of the tunneling conductance of new peaks in the gas environment. The latter gives the possibility to use the method of scanning tunneling spectroscopy for a generation of gas and biosensors. The immune biosensor is proposed in the lab on a chip form based on the nanostructured silicon for the simultaneous analysis of numerous samples. The developed biosensor based on nanostructured silicon is very promising for use in so-called systems of lab-on-chip because it can be used for rapid analysis of various immune responses and is fully compatible with silicon planar technology used in the manufacturing of the semiconductor devices.