Direct imaging of single gold nanoparticle etching: sensitive detection of lead ions

We present a highly sensitive Pb2+ detection method by in situ real-time imaging of Pb2+ catalyzed etching and size reduction of immobilized single gold nanoparticles with darkfield microscopy. The detection limit is 0.2 pM, suggesting that direct observation of the catalytic activity of ∼5 lead ions on one gold nanoparticle surface is possible.