M. Duocastella

Laser-induced forward transfer of liquids: Study of the droplet ejection process

Laser-induced forward transfer LIFT is a laser direct-write technique that offers the possibility of printing patterns with a high spatial resolution from a wide range of materials in a solid or liquid state, such as conductors, dielectrics, and biomolecules in solution. This versatility has made LIFT a very promising alternative to lithography-based processes for the rapid prototyping of biomolecule microarrays. Here, we study the transfer process through the LIFT of droplets of a solution suitable for microarray preparation. The laser pulse energy and beam size were systematically varied, and the effect on the transferred droplets was evaluated. Controlled transfers in which the deposited droplets displayed optimal features could be obtained by varying these parameters. In addition, the transferred droplet volume displayed a linear dependence on the laser pulse energy. This dependence allowed determining a threshold energy density value, independent of the laser focusing conditions, which acted as necessary conditions for the transfer to occur. The corresponding sufficient condition was given by a different total energy threshold for each laser beam dimension. The threshold energy density was found to be the dimensional parameter that determined the amount of the transferred liquid per laser pulse, and there was no substantial loss of material due to liquid vaporization during the transfer.

Time-resolved imaging of the laser forward transfer of liquids

Time-resolved imaging is carried out to study the dynamics of the laser-induced forward transfer of an aqueous solution at different laser fluences. The transfer mechanisms are elucidated, and directly correlated with the material deposited at the analyzed irradiation conditions. It is found that there exists a fluence range in which regular and well-defined droplets are deposited. In this case, laser pulse energy absorption results in the formation of a plasma, which expansion originates a cavitation bubble in the liquid. After the further expansion and collapse of the bubble, a long and uniform jet is developed, which advances at a constant velocity until it reaches the receptor substrate. On the other hand, for lower fluences no material is deposited. In this case, although a jet can be also generated, it recoils before reaching the substrate. For higher fluences, splashing is observed on the receptor substrate due to the bursting of the cavitation bubble. Finally, a discussion of the possible mechanisms which lead to such singular dynamics is also provided.

Laser-Induced Forward Transfer: A Laser-Based Technique for Biomolecules Printing

The high focusing power of lasers makes them adequate for micropatterning applications. Laser-induced forward transfer (LIFT) is a direct-writing technique allowing the deposition of tiny amounts of material from a donor thin film to a solid substrate through the action of a pulsed laser beam. Although LIFT was originally developed to operate with solid films, it has been demonstrated that deposition is also possible from liquid films. In this case the material is directly ejected in the liquid state from the film and transferred to the receptor substrate, where it deposits in the form of a microdroplet. The relative translation of the film-substrate system respect to the laser beam enables the formation of two-dimensional patterns. This makes LIFT adequate for biomolecule printing: microdroplets of biological solutions can be transferred onto solid substrates to produce patterns of immobilized biomolecules. In this chapter a review on the LIFT technique for biomolecule printing is carried out, from its origins to the most recent developments. The characteristics and performances of the technique are described in detail, with special attention to the diverse possible modes of operation and transfer mechanisms. It is also shown that significant benefits in terms of resolution, speed, contamination, and sample consumption can be obtained through LIFT when compared to other more conventional direct-writing approaches. Finally, the feasibility of the technique for biomolecule printing is demonstrated through examples of successful deposition of a large set of different biomolecules.

The laser-induced forward transfer technique for microprinting

Abstract: The high focusing power of lasers makes them adequate for the development of direct writing techniques for micropatterning purposes. Although most laser direct-writing techniques are essentially subtractive, lasers can also be used as additive tools for microfabrication. In this context, laser-induced forward transfer (LIFT) constitutes a fast and versatile way to print materials onto solid substrates with micrometric resolution. This chapter reviews the LIFT technique from its origins to the most recent developments, which have demonstrated its feasibility for printing a wide variety of materials, from simple metals and oxides, to complex ceramics, polymers, biomolecules, and even living cells.