11th July, 2017
Last week we began to discuss how aptamers can be used in biosensors. If you missed this, you can read it here.
Today we outline two more 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.
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.
In these posts, we have described 4 modes where aptamers have been used in biosensors. During testing they have all shown excellent performance for the detection of both small molecules and proteins.
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