A simple displacement aptamer assay on resistive pulse sensor for small molecule detection.

A universal aptamer-based sensing strategy is proposed using DNA modified nanocarriers and Resistive Pulse Sensing (RPS) for the rapid (≤20 min) and label free detection of small molecules. The surface of a magnetic nanocarrier was first modified with a ssDNA (anchor) which is designed to be partially complimentary in sequence to the ssDNA aptamer. The aptamer and anchor form a stable dsDNA complex on the nanocarriers surface. Upon the addition of the target molecule, a conformational change takes place where the aptamer preferentially binds to the target over the anchor; causing the aptamer to be released into solution. The RPS measures the change in velocity of the nanocarrier as its surface changes from dsDNA to ssDNA, and its velocity is used as a proxy for the concentration of the target. The length of the aptamer and the ability to extract and preconcentrate the nanocarriers using a magnet, is shown to affect the sensitivity. We illustrate the versatility of the assay using the same anchor sequence and Aptamers to the antibiotic Moxifloxacin, and chemotherapeutics Imatinib and Irinotecan. In addition, the proposed assay can be easily extended to detect multiple analytes simultaneously, by utilizing nanocarriers with different diameters. Each sized particle is functionalised with a the same anchor but a unique aptamer. We illustrate this with the simultaneous detection of Imatinib and Moxifloxacin. The strategy could be easily adapted to a range of targets and unlike previous strategies that use aptamer modified nanocarriers, the signal is not dependent upon the tertiary structure of the aptamer-target interaction.