Figure 18

Specific biomolecular recognition of streptavidin functionalised polystyrene spheres with biotinylated cantilever sensors. Green hatched areas depict flow of liquids at 10 μl/min. A) Frequency response of the cantilever arrays. The response of four biotin functionalised sensors was averaged and the response of the four hydroxyl functionalised sensors that act as an in situ reference was averaged as well. At t = -2 min 10 μl containing 3.42x 10⁸/μl of beads were injected for two minutes, this ensured the complete mixing/exchange of the beads in the measurement chamber. During the subsequent 10 minutes the cantilevers were exposed to the beads (light blue area) without flow. Beads were diffusing and were binding onto the sensors. After a fast initial mass uptake at 45 pg/min the curve was showing saturation with a reduced speed of ~10 pg/min. The biotinylated sensors experienced a differential frequency shift of 540 Hz. At t = 10 min the solution of the beads was rinsed out of the measurement chamber for 20 minutes and the flow stopped again. During rinsing unspecifically bound beads dissociated and the measured frequency shift corresponded to 270 Hz on the biotinylated sensors whereas on the hydroxyl functionalised sensor the reduction in frequency measured 230 Hz. B) Differential readout of specific mass uptake of the streptavidin functionalised spheres. The raw data is shown as dots in the background, the data filtered with the Savitzki–Golay filter shown as a continuous line. Data for all the eight sensors in liquid at the tenth higher oscillation mode were continuously recorded. The data acquisition for all eight sensors took 50 seconds, then the next measurement point was added. Due to the differential analysis data acquired during flow was noisier than data measured in phases where the flow was stopped.