| The femtosecond laser ablation of a gold target immersed in a liquid was used to produce gold nanoparticles intended for biosensing applications. The laser-ablated species (atoms, ions and small clusters) were rapidly cooled by the surrounding liquid to form nanoparticles. It is our intention to bind these particles, which exhibit a surface plasmon resonance peak at 520--540 nm, to biomolecules, in order to form selective and specific optical biomarkers. The gold nanoparticles necessary should have: (1) a size of 1--30 nm and a narrow size distribution, in order to exhibit similar optical properties, and (2) available chemical groups on their surfaces, which enable the further attachment of biomolecules. We showed that femtosecond laser ablation in aqueous media is a very promising approach to obtain these objectives. We found that two mechanisms contribute to the ablation of the target: the first, attributed to direct femtosecond laser ablation, is responsible for the formation of a population of smaller particles (<20 nm in diameter), while the second, associated with plasma-related ablation, and particularly important at high laser fluences, led to a population of larger particles (>20 nm in diameter). In addition, the surface chemistry study revealed that the gold nanoparticle surface was partially oxidized (i.e., AuI and AuIII), and bonded to oxygen. (Abstract shortened by UMI.). |
