Protein-receptor-functionalized field-effect transistor sensors designed for <i>in vivo </i>applications suffer from the inability to circumvent limitations due to screening under physiological conditions due to the large sizes of the protein/antibody-based molecular recognition elements in combination with small (&lt;1 nm) Debye lengths. The Debye length is the distance beyond semiconducting channel surfaces wherein changes in local electric fields affect the distributions of channel free charge carriers to the greatest extent. We overcome this limitation through the use of short, rationally designed oligonucleotide sequences, termed aptamers for molecular recognition. Structure-switching aptamers undergo large conformational changes upon target capture that involve rearrangement of their highly negatively charged backbones in close proximity to semiconducting channels resulting in measurable changes in channel conductances. Coupling aptamers to field-effect transistors, we detected singly charged (serotonin and dopamine), neutral (glucose), and zwitterionic (sphingosine-1-phosphate) small-molecule targets under physiological concentrations. Fluorescence resonance energy transfer studies of glucose and serotonin aptamers indicate that they undergo significant conformational changes, which in the case of glucose also include repositioning of double-helical stems. Further, circular dichroism spectroscopy indicates that some of these aptamers (serotonin and dopamine) adopt new specific-binding motifs, such as G quartets, that are stabilized by target binding. We also systematically altered: (1) the distances at which these repositioning changes in stems occur from the surfaces of channels by increasing aptamer stem lengths, with longer stem lengths leading to decreased signal responses; (2) the densities at which aptamers are positioned on surfaces. These experiments provide new understanding of interactions between aptamers and charge carriers in semiconductors, leading to tunable signals and sensitivities.

Mechanistic investigations of stem-loop aptamer field-effect transistors

256th National Meeting (2018)

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