Silver nanoparticles (AgNPs) are well-known for their antimicrobial effects and several groups are proposing them as active agents to fight antimicrobial resistance. A wide variety of methods is available for nanoparticle synthesis, affording a broad spectrum of chemical and physical properties. In this work, we report on AgNPs produced by laser ablation synthesis in solution (LASiS), discussing the major features of this approach. Laser ablation synthesis is one of the best candidates, as compared to wet-chemical syntheses, for preparing Ag nano-antimicrobials. In fact, this method allows the preparation of stable Ag colloids in pure solvents without using either capping and stabilizing agents or reductants. LASiS produces AgNPs, which can be more suitable for medical and food-related applications where it is important to use non-toxic chemicals and materials for humans. In addition, laser ablation allows for achieving nanoparticles with different properties according to experimental laser parameters, thus influencing antibacterial mechanisms. However, the concentration obtained by laser-generated AgNP colloids is often low, and it is hard to implement them on an industrial scale. To obtain interesting concentrations for final applications, it is necessary to exploit high-energy lasers, which are quite expensive. In this review, we discuss the pros and cons of the use of laser ablation synthesis for the production of Ag antimicrobial colloids, taking into account applications in the food packaging field.

We study the incubation effect during laser ablation of stainless steel with ultrashort pulses to boost the material removal efficiency at high repetition rates. The multi-shot ablation threshold fluence has been estimated for two pulse durations, 650-fs and 10-ps, in a range of repetition rates from 50kHz to 1 MHz. Our results show that the threshold fluence decreases with the number of laser pulses N due to damage accumulation mechanisms, as expected. Moreover, approaching the MHz regime, the onset of heat accumulation enhances the incubation effect, which is in turn lower for shorter pulses at repetition rates below 600 kHz. A saturation of the threshold fluence value is shown to occur for a significantly high number of pulses, and well fitted by a modified incubation model.