Au nanoparticles were generated by laser ablation in PBS buffer and conjugated to immunoglobulin E (IgE) during ablation (in situ) and after ablation (ex situ). Exposure for 5 min to 532 nm pulses with a duration of 150 ps, an energy of 8 mJ and a repetition rate of 10 Hz yielded nanoparticles with a mean diameter of about 4 nm for in situ conjugation and of about 5 nm for ex situ conjugation. ELISA analysis showed that the conjugation efficiency was comparable for in situ and ex situ fabrication. ELISA for cytokine (IL-6) production by IgE-activated mast cells showed that the Au-IgE conjugates induced a response which coincided within error for conjugates prepared in situ and ex situ. (C) 2012 Elsevier B.V. All rights reserved.