Alieva E.V., Konopsky V.N.
Biosensor based on surface plasmon interferometry independent on variations of liquid's refraction index. // Sensors and Actuators B, 2004, V.99/1, P.90-97.

We present a surface sensitive optical sensor based on registration of the phase of surface plasmons by such a method of the phase detection that makes it possible to essentially eliminate an undesirable sensitivity to variations of refraction index of a liquid due to temperature, composition and other changes. This objective has been achieved by detecting the interference between the surface plasmon wave and a bulk wave propagating at grazing angle just above the surface. The proposed interferometric method also does not suffer from vibrational noise.


Fig.4 The scheme of the experiment. On the insert the structure of the metal films is shown.


Fig.3 Calculated variation of the z-position of the interference extremum with number $m=17$ versus RI of the liquid (see text for details).


Fig.5 Interferograms recorded at two different temperatures: 22$^0$C and 46$^0$C (the 46$^0$C-interferogram is shifted down by 2000 a.u.).


Fig.6 The change of the "phase" and "frequency" of the interferograms during water cooling down from 46$^0$C to room temperature. One can see that the "phase" is not sensitive to the change of the liquid's RI, while "frequency" is.


Fig.7 The deposition of the SAM of 2-mercaptoethanol on gold surface. The RI change after the second drop of the thiol is the same as after the first one ($\Delta n\simeq 0.0035$). But the SAM was built up after the first drop and only this surface change is detected by the "phase" signal.