Fluorescing aptamer-gold nanosensors for enhanced sensitivity to bisphenol A

An insufficient sensitivity of aptamer-integrated colorimetric gold nanoparticles (AuNPs) is a common challenge in the detection of environmental chemicals. We report the use of a modified aptamer/AuNP-based sensor in conjunction with a fluorescing single-stranded DNA aptamer for the sensitive detection of bisphenol A (BPA), which is a major endocrine disruptor (EDC). While an anti-BPA single-stranded DNA aptamer was bound with BPA, a weak fluorescence signal was observed upon the addition of SYBR Green-I (SG-I), which is specific to a duplex region of the free aptamer. This reaction was accompanied by a subsequent aggregation of unmodified AuNPs (citrate-stabilized AuNPs) at high salt concentrations, leading to a color change from reddish to purple. In contrast, the absence of BPA elicited a high fluorescence signal from SG-I and produced no color change in the AuNP solution even upon the addition of salt ions. Unlike aptamers that are labeled at their ends with fluorophores, our strategy gave rise to neither a loss of target-binding affinity nor a perturbation of the AuNP colorimetry. Thus, a quantitative analysis with a broad dynamic range was achieved by combining the fluorescent and colorimetric measurements at BPA concentrations ranging over four orders of magnitude. Our approach also yielded a greater detection sensitivity (as low as 9 pg·mL−1) than classical AuNP colorimetry or other aptamer-combined methods Moreover, this method enabled the detection of BPA in a small fraction extracted from thermal paper with a high specificity among EDCs. We anticipate that this approach will facilitate further advances in the design of traditional AuNP colorimetric sensors using different aptamers for chemical sensing in the environmental and clinical fields.