High-throughput drug screening by Printing Biology

Printing biology is our way to define a novel field employing material printing techniques generally used in plastic electronics to solve important issues of biology by miniaturized and high-throughput platforms. In this field, we already showed the possibility to use Dip Pen Lithography to fabricate single-cell biochips [1]. Also,we employed non-contact patterning methods such as inkjet printing methods to fabricate microarrays for drug screening at solid-liquid interfaces [2] or in picoliter-scale liquid droplets [3] so enabling high-throughput screening of chemical libraries onto disease-based targets. In this regard, printing methods would greatly reduce times and costs of standard drug screening campaigns which are commonly based on complex liquid handling robotics and are time and reagent consuming (micro-, nanoliter scale). In this work, we show a low-cost, general and miniaturized printing biology approach for drug screening, by combining Inkjet Printing and Dip Pen Lithography to develop the biochip. We show the possibility to precisely deliver femtoliter scale droplets of protein targets by Dip Pen Lithography by finely tuning the deposition parameters and ink formulation. Protein solutions are spiked with glycerol at 30 % v/v and are deposited at defined values of humidity (50 % -70 % R.H.). This permits to obtain microscale droplet arrays where picoliter volumes of drug candidates solutions are readily deposited by inkjet printing. In this way, it is possible to produce different drug targets concentration directly on-chip. Fluorescence confocal microscopy is here used to quantify drug-ligand interaction by means of standard intensity based imaging and fluctuation techniques that permit mapping concentration and important biophysical parameters including diffusion coefficients of fluorolabeled (or intrinsically fluorescent) ligands at nanomolar concentration. Outputs obtained on different systems by means of such a miniaturized approach are compared with the ones obtained on standard microliters volumes samples, confirming the ability of our biochip printing methodology to discriminate ligand-target interactions in different compounds. MiUR and the PRIN2012 program are acknowledged for fudings.