Abstract.
A high-precision optical biosensor technique capable of independently determining
the refractive index (RI)
of liquids is presented.
Photonic crystal surface waves were used to detect
surface binding events, while an independent registration of the critical angle
was used for accurate determination of the liquid RI.
This technique was tested using binding of biotin molecules
to a streptavidin monolayer at low and high
biotin concentrations.
The attained baseline noise is 5×10-13 m/Hz1/2
for adlayer
thickness changes and 9×10-8 RIU/Hz1/2 for RI changes.
Fig.1 A sketch of the biosensor. The typical reflection profiles are shown near the photodiode array.
Fig.2 Immobilization of streptavidin on a biotinylated surface (top left) with subsequent binding of free biotin to this streptavidin monolayer (top right) and corresponding changes of RI of the buffer during these injections (bottom). The measurement time was 1 second per point (no posterior data averaging and smoothing). In color inserts corresponding processes are illustrated.
Fig.3 The injection of a high concentration of free biotin: changes in the thickness of the streptavidin-biotin complex (left) and the corresponding change of RI of the buffer (right). In color insert the possible corresponding process is illustrated. Enlarged views of the baseline noises are presented as inserts at the bottom.