ABSTRACT
The amplified sensing of (18) by the (19)-labeled liposomes was also transduced by microgravimetric quartz-crystal-microbalance measurements [42]. The sensing interface of oligonucleotide (17) was assembled on an Au-quartz crystal (9 MHz). Figure 14(A) exemplifies the crystal frequency changes upon the amplified sensing of (18). Interaction of the sensing interface with the analyte (18), 5×10−6 M (step a) results in a frequency change of ∆f=−17 Hz, implying a surface coverage of the analyte as a result of hybridization that corresponds to 1.2×10−11 mole·cm−2. Reaction of the resulting interface with the (19)-labeled liposomes (step b), yields a frequency change that corresponds to ∆f=−120 Hz. Figure 14(A) shows also the control experiment, where the sensing interface is interacted with the non-complementary DNA, (18a), (step c) and then with the (19)-labeled liposomes (step d). The crystal frequency is almost unaltered, implying that the sensing protocol reveals high selectivity. The extent of the association of the (19)-labeled liposomes to the sensing array is controlled by the amount of hybridized (18) that forms the ds-assembly. In turn, the amount of (18) linked to the surface is dependent on the bulk concentration of the analyte DNA in the sample. For example, when the bulk DNA concentration is 5×10−9 M, the association of the (19)-tagged liposomes to the interface results in a frequency change of ∆f=−70 Hz, Figure 14(A) (inset). The lower sensitivity limit for the piezoelectric transduction of the amplified sensing of (18) by the (19)-labeled liposomes was estimated to be 5×10−12 M, where a frequency change of ∆f=−20 Hz was observed after the amplification step.
