Design of an Open Source, Automated Drop-Casting Device to Dispense Nanoliter Droplet Arrays

An automated method of depositing sub-μL droplets of liquids is sought after for the manufacture of chemical sensors. By depositing polymer solutions and evaporating the solvent, thin films of functional polymers can be placed in the desired pattern to create sensing elements. Traditionally, piezoelectric ink-jetting can be used to dispense picoliter-scale droplets repeatedly until the target volume is deposited. However, piezoelectric nozzles are susceptible to clogging when used with polymer solutions. Other deposition techniques include nanoplotters which can deposit nanoliter-sized droplets by imprinting dispensed liquid droplets onto materials. This method is less desirable because less control is given over the volume of the deposited droplets and damage to the sensor is made possible by impaction. In this study, an inexpensive, automatic drop-casting device is made by modifying a 4-axis CNC machine to use with a syringe pump extruder. Marlin, an open-source 3d-printing firmware, was configured to control the XYZ positioning of the syringe pump as well as the volume of liquid dispensed. The machine successfully placed an array of 38 nanoliter droplets. The minimum droplet size is limited primarily by syringe diameter. The theoretical precision of this machine is 2.5 microns per motor micro-step in the X, Y, and Z directions. Future studies may also include hydrophobic treatments to decrease droplet adhesion to the needle tip.