Al³⁺ ion sensing at attomole level via surface-potential mapping of gold nanoparticle complexes

Aluminum can be ionized in water by reacting with chlorides. Aluminum ions (Al³⁺) are believed to be very harmful to human health and are associated with Alzheimer's disease. The detection of Al³⁺ is extremely important, but conventional methods suffer from low sensitivity and cumbersome processes. Herein, we report ultra-sensitive and label-free detection of Al³⁺ using gold nanoparticles (AuNPs) and Kelvin probe force microscopy (KPFM). Al³⁺ was exposed on citrated AuNPs with different concentrations; Al³⁺/AuNP complexes were constructed via binding interactions between Al³⁺ and the citrates. By probing the Al³⁺/AuNP complexes, we quantified the degree of interactions between Al³⁺ and the citrated AuNPs using KPFM. As the Al³⁺ concentration decreased, KPFM succeeded in exhibiting ultra-sensitive detection as low as 2 amol (limit of detection 1 pM, single droplet 2 μL). We tested real samples from a sheet of aluminum foil, and detected ∼748 amol (∼374 pM, single droplet 2 μL) Al³⁺. The results indicate that the combination of AuNPs and KPFM offers a robust, facile, and an ultra-sensitive platform technology for detecting Al³⁺.