Development of a label-free gold nanoparticle-based colorimetric aptasensor for detection of human estrogen receptor alpha

The increasing demand for easily available and low-cost diagnostics has fuelled the development of aptasensors as platforms for rapid, sensitive, and point-of-care testing of target analytes. Recently, gold nanoparticle (AuNP)-based aptasensors have attracted wide recognition owing to their color transition properties which allow real-time rapid sensing of targets. In this study, we utilized the color transition property of aptamer-functionalized AuNPs to detect and quantify estrogen receptor alpha (ER alpha), a key biomarker protein in breast cancer. We found that the coating of AuNPs with unmodified ER alpha-RNA aptamer (GGGGUCAAGGUGACCCC) makes them resistant to salt-induced aggregation. However, addition of ERa to the aptamer-protected AuNPs results in their spontaneous aggregation as evident from a color transition from wine red to deep blue. On the basis of this, we developed an ERa aptasensor, with limits of detection and quantification of 0.64 and 2.16 ng/mL, respectively; the aptasensor can efficiently detect and quantify ERa in a working range of 10 ng/ mL-5 mu g/mL protein. Validation of the aptasensor on cellular extracts of ER alpha-positive MCF-7 and ER alpha-deficient MDA-MB-231 breast cancer cells showed a target-selective response in ER alpha-positive samples but not in cellular extracts of ERa-deficient breast cancer cells. Further, the small size and simple fabrication chemistry of aptamers provide an additional benefit to make the ERa aptasensor a potentially useful and cost-effective tool in point-of-care analyses of ER alpha.