Aptamers as affinity reagents in an integrated electrophoretic lab-on-a-chip platform.

Nucleic acid based affinity reagents (e.g., aptamers) offer several possible advantages over antibodies as specific recognition elements in biochemical assays. Besides offering improved cost and stability, aptamers are ideal for rapid electrophoretic analysis due to their low molecular weight and high negative charge. While aptamers have proven well-suited for affinity-shift electrophoretic analysis, demonstrating a fully integrated aptamer-based assay platform represents an important achievement toward low-cost point-of-care analysis, particularly for remote or resource poor settings where cost and ambient stability of reagents is a key consideration. Here we perform and evaluate the suitability of aptamer-based affinity assays for two clinically relevant target analytes (IgE using a known aptamer and NF-κB using a thio-modified aptamer) in an integrated electrophoretic gel-shift platform. Key steps of (i) mixing sample with aptamer, (ii) buffer exchange, and (iii) preconcentration of sample were successfully integrated on-chip upstream of a fluorescence-based gel-shift analysis step. This approach, utilizing a size-exclusion membrane optimized here for aptamer retention and preconcentration with sample, enables automated sample-to-answer for trace analytes in 10 min or less. We addressed notable nonspecific interference from serum proteins by adding similar nucleic acid competitors to suppress such interactions with the aptamer. Nanomolar sensitivities were demonstrated and integrated preconcentration of sample provides an important means of further improving detection sensitivities. Aptamers proved superior in many respects to antibody reagents, particularly with regard to speed and resolution of gel-shifts associated with specific binding to target.