Continuous-flow microfluidic printing of proteins for array-based applications including surface plasmon resonance imaging

Arraying proteins is often more challenging than creating oligonucleotide arrays. Protein concentration and purity can severely limit the capacity of spots created by traditional pin and ink jet printing techniques. To improve protein printing methods, we have developed a three-dimensional microfluidic system to deposit protein samples within discrete spots (250-μm squares) on a target surface. Our current technology produces a 48-spot array within a 0.5 × 1 cm target area. A chief advantage of this method is that samples may be introduced in continuous flow, which makes it possible to expose each spot to a larger volume of sample than would be possible with standard printing methods. Using BiacoreTM Flexchip (Biacore AB) surface plasmon resonance array-based biosensor as a chip reader, we demonstrate that the microfluidic printer is capable of spotting proteins that are dilute (<0.1 μg/ml) and contain high concentrations of contaminating protein (>10,000-fold molar excess). We also show that the spots created by the microfluidic printer are more uniform and have better-defined borders than what can be achieved with pin printing. The ability to readily print proteins using continuous flow will help expand the application of protein arrays.