Colorimetric Assay of Lead Ions in Biological Samples Using a Nanogold-Based Membrane

We have developed a simple paper-based colorimetric membrane for sensing lead ions (Pb2+) in aqueous solutions. The nitrocellulose membrane (NCM) was used to trap bovine serum albumin (BSA) modified 13.3-nm Au nanoparticles (BSA-Au NPs), leading to the preparation of a nanocomposite film of a BSA-Au NP-decorated membrane (BSA-Au 1 NPs/NCM). The BSA-Au NPs/NCM operates on the principle that Pb2+ ions accelerate the rate of leaching of Au NPs induced by thiosulfate (S2O32-) and 2-mercaptoethanol (2-ME). The BSA-Au NPs/NCM allowed for the detection of Pb2+ by the naked eye in nanomolar aqueous solutions in the presence of leaching agents such as S2O32- and 2-ME. We employed the assistance of microwave irradiation to shorten the reaction time (< 10 min) for leaching the Au NPs. Under optimal solution conditions (5 mM glycine-NaOH (pH 10), S2O32- (100 mM), and 2-ME (250 mM), microwaves (450 W)), the BSA-Au NPs/NCM allowed the detection of Pb2+ at concentrations as low as 50 pM with high selectivity (at least 100-fold over other metal ions). This cost-effective sensing system allowed for the rapid and simple determination of the concentrations of Pb2+ ions in real samples (in this case, sea water, urine, and blood samples).