The manipulation of minute volumes of fluids -in the nl to pl range- in microfabricated channels, which is the operation principle of microfluidics, is made possible by the realization of miniaturized devices characterized by high portability and integration. Microfluidic devices aim to the reduction of the dimensions of a conventional macroscopic laboratory at micrometer scale, to carry out complex chemical reactions and analytical assays in a compact chip (Fig. 1). The miniaturization presents many advantages in terms of reduction in reagents, sample and waste volumes, more homogeneous reaction conditions and shorter times for diffusion-driven reactions, automation, and massive parallel processing. By analogy with electronic integrated circuits, microfluidic elements, such as fluid injectors, filters, valves, mixers, separation elements, detectors, can be used as building blocks for lab-on-chip devices. Microfluidic devices offer a high degree of integration with potential applications in biomolecular separations, enzymatic assays, polymerase chain reaction, immunohybridization reactions, high-throughput drug screening, DNA sequencing, gene-expression profiling, protein analysis, and cell-based assays. Moreover, microfluidic devices are interesting systems for basic studies of fluid dynamics, since they allow one to explore a wide range of flow conditions in terms of interfacial free energies, flow rates, fluid viscosity, and geometries.

Fig. 1 Lab-on-chip concept. The reduction in size offers a series of advantages for chemical and biological applications

The realization of highly-integrated multifunctional microfluidic chips (lab-on-chips or micro-total analysis systems) requires coordinated technological efforts in order to fabricate all the functional components (valves, heaters, sensors, etc.). The materials to be used are an important issue, since they have to be suitable for nanofabrication and compatible with the reactions to be performed in the device. We focus our attention on elastomeric (poly(dimethylsiloxane), PDMS, and its derivatives), and thermoplastic polymers (polymethylmethacrylate, PMMA, cyclic-olefin based copolymers, TOPAS®), which are characterized by easy manufacturing, good transparency properties in the ultraviolet-visible region of the e.m. spectrum, and mechanical properties variable over a wide range (Young’s modulus in the range 3 MPa-2 GPa).
Moreover, a fundamental requirement for fabricating microfluidic networks is the possibility of sealing irreversibly two separate layers (typically one textured with the microfabricated channels and a flat surface operating as support). The above-mentioned materials offer a high flexibility and ease of bonding both with other polymers and with silicon and glass, thus facilitating the realization of monolithic and hybrid devices. We developed different types of bonding procedures based both on thermal approaches and on chemical superficial treatments, such as plasma oxidation. A part of our experimental activity in microfluidics is, in fact, focused on the optimization of high-throughput sealing approaches for polymeric and hybrid devices. 
Another important aspect to take into account is the capability of connecting microdevices with external elements for controlling the fluid injection, such as tubing and mechanical syringe pumps. The use of external pumping machines offers a good control of the flow rate (down to a few tens of nL/min) and of the delivered volumes of liquid, so far almost impossible by relying on spontaneous capillarity. Connections between chips and macro-equipments are watertight, in order to avoid liquid losses during the analytical procedures, compatible with the liquid to be injected, in particular in the case of biological samples, and easy to be manufactured (Fig. 2).

Fig. 2 Microfluidic chip connected with external tubes for controlling the flow rates through external pumping.

Fig. 3 Changes in the meniscus of water in an hydrophobic microchannel under external pressure. The arrow indicates the flow direction in infusion mode (a), and under withdraw (b, c).

 

sensors, and heaters. All of these elements are necessary for accomplishing and detecting bio-chemical reactions. For instance, lab-on-chip devices for polymerase chain reaction integrate microfluidic networks and heaters for reaching the temperature values required for denaturation, extension, and annealing. We realize temperature sensors and heaters by photolithographic techniques, evaporation of Ti and Pt layers, and lift-off. The temperature range accessible to these heaters is usually 20-120 °C.

For more information, please contact: Dr. Dario Pisignano ( This e-mail address is being protected from spam bots, you need JavaScript enabled to view it )