The use of the synergistic molecular assembly of an aptamer and cetyltrimethylammonium bromide (CTAB) on gold nanoparticles (AuNPs) is described for the selective and sensitive colorimetric recognition of As3+ ions in water samples. The As3+ ions coordinate with Ars-3 aptamer–AuNPs, causing aggregation in the presence of CTAB, which induces a red-shift in the surface plasmon resonance (SPR) band and a visual change in the color. The aptamer has shown a strong tendency to bind with As3+ ions using CTAB as a binder, exhibiting good linearity between the absorption ratio (A650/A520) and the concentration of As3+ ions (1.0–100 ppb) with a detection limit of 16.9 ppb. In contrast, other chemical species (metal ions and anions) did not induce these changes at all, and thus the aptasensor is highly specific for As3+ ion sensing. The spectroscopic and TEM results show high selectivity for As3+ ion sensing and the assay is completed within 30 min. The aptamer–AuNP-based colorimetric method illustrates the potential utility for screening As3+ ion levels in real samples. The developed aptasensor was successfully applied for the detection of As3+ ions in water and cosmetic samples, signifying its remarkable application for As3+ ion sensing in real samples.
