ABSTRACT
Similarly, the dendritic-type amplification of the analyte DNA, (18), by the biotinlabeled liposome can be transduced by microgravimetric quartz-crystal microbalance measurements. Figure 14(B) shows the two-step amplified sensing of (18), 5×10−6 M. Association of the (18)-analyte/20 ds-system to the sensing interface results in a frequency decrease of approximately 25 Hz (step a). Binding of avidin to the biotinylated assembly yields a frequency change of ∆f~−50 Hz (step b). Linkage of the biotin-tagged liposome to the system amplifies the primary association of (18), and a very high frequency change, ∆f~−500 Hz, is observed (step c). Additional treatment of the interface
with avidin, ∆f~−50 Hz (step d), and then with the biotin-labeled liposome (step e) results in a second amplification corresponding to ∆f=−690 Hz. Note that the amplification in the
econd step is higher than that in the first step, due to the multiligation affinity of avidin for the biotinylated liposome. The sensing of (18) is specific, Figure 14(B). Treatment of the sensing interface with the noncomplementary DNA, 18a/20 complex, does not yield any significant frequency change (step f) and subsequent interaction of the resulting assembly with avidin and the biotin-tagged liposome, (21), results in a frequency change of only approximately −30 Hz, (steps g and h, respectively) that is attributed to the nonspecific association of the liposome to the interface. Using the dendritic amplification route, the lower sensitivity limit for the sensing of (18) is 1×10−13 M (or 1×10−16 mol·mL−1). Note that by additional binding steps of the avidin-biotinylated liposome, the sensitivity of the analysis could be further enhanced.
