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Aptamer Applications: Biosensors part 2

Here we outline two strategies for utilising aptamers in biosensors.

Target Induced Displacement Mode

Target Induced Displacement (TID) mode uses an aptamer anchored via a complementary oligo, localising the target binding aptamer. When target engagement occurs, the aptamer’s conformation changes causing it to detach from its anchor as it binds to the target. TID mode biosensors can be further classified as being signal-on, signal-off or label-free modes. In signal-on TID biosensors the dissociation of aptamer causes a quenched label to be freed, showing an increase in signal. However, signal-off measures the presence of a target by detecting the reduction of signal when the labelled aptamer is released. TID biosensors can also be developed where the aptamer is not labelled. An example being micro-cantilevers, when the binding aptamer dissociates on target engagement this changes the position of the lever resulting in a signal detection of both small molecules and proteins.

Competitive Replacement

Competitive Replacement mode uses unlabelled aptamers which have been fixed to the surface of the biosensor. Initially the aptamers are incubated with a labelled molecule which is closely related to the target of interest. When the target is introduced to the biosensor, it competes with the labelled molecule. Because the aptamer is designed to have a higher affinity for the target, it will always out-compete the labelled molecule. The dissociation of the labelled molecule into solution leads to a measurable change in signal.

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