Visual detection of copper(ii) ions in blood samples by controlling the leaching of protein-capped gold nanoparticles

Abstract

We have developed a simple, low-cost, paper-based probe for the selective colorimetric detection of copper ions (Cu²⁺) in aqueous solutions. The bovine serum albumin (BSA)-modified 13.3-nm Au nanoparticle (BSA-Au NP) probe was designed to detect Cu²⁺ ions using lead ions (Pb²⁺) and 2-mercaptoethanol (2-ME) as leaching agents in a glycine–NaOH (pH 12.0) solution. In addition, a nitrocellulose membrane (NCM) was used to trap the BSA-Au NPs, leading to the preparation of a nanocomposite film consisting of a BSA-Au NP-decorated membrane (BSA-Au NPs/NCM). The BSA-Au NPs probe operates on the principle that Cu deposition on the surface of the BSA-Au NPs inhibits their leaching ability, which is accelerated by Pb²⁺ ions in the presence of 2-ME. Under optimal solution conditions (5 mM glycine–NaOH (pH 12.0), Pb²⁺ (50 μM), and 2-ME (1.0 M)), the Pb²⁺/2-ME–BSA-Au NPs/NCM enabled the detection of Cu²⁺ at nanomolar concentrations in aqueous solutions by the naked eye with high selectivity (at least 100-fold over other metal ions). In addition, this cost-effective probe allowed for the rapid and simple determination of Cu²⁺ ions in not only natural water samples but also in a complex biological sample (in this case, blood sample).