Colorimetric detection of arsenite using Tris-mediated gold nanoparticle aggregation and chitosan lateral flow strip-based signal enhancement

Abstract

Globally, over 200 million people are at risk of exposure to high levels of arsenic due to increasing environmental pollution; thus, there is high demand for detection methods to monitor arsenic contamination in the natural environment. In this study, we developed a cost-effective method for detecting arsenite [As(III)] ions using sodium dodecyl sulfate (SDS)-coated gold nanoparticles (AuNPs) and Tris. Positively charged Tris molecules induce aggregation of AuNPs by neutralizing the negative charge of SDS; however, this is prevented by the presence of As(III), which has a high affinity for AuNPs. This proposed method is able to detect 5 parts per billion (ppb) and 1.85 ppb of As(III) through naked eye and spectrophotometric measurements, respectively. Furthermore, a chitosan-based lateral flow (LF) strip was devised to enhance the visual signal intensity by concentrating AuNPs on its test zone, since AuNPs of lower concentration were more effective for detecting low As(III) concentrations. As a result, As(III) was detected at 500 parts per trillion (ppt) without any interference from other metal ions, which is a 10-fold improvement from solution-based assays. Importantly, the colorimetric signal amplification strategy (using the chitosan-based LF strip) is versatile and can be applied to many other AuNP- or nanomaterial-based technologies. The proposed system enables the detection of As(III) in facility-limited or point-of-care settings, making it ideal for use in underdeveloped countries because it requires a small sample volume (approximately 20–30 µL) with a small amount of AuNPs, and takes only 10 min to generate colorimetric results.