Development and Optimization of Robotic Nanodroplet Dispenser with Hydrophobic Needles and Computer Vision

• The goal is to develop a robotic printer that rapidly dispenses nanoliter-scale droplets of polymer solution for evaporative deposition of thin polymer films onto spiral waveguides of biosensing chips.

• Advantages of the custom instrument include an increase of printing speed, lower cost, and no nozzle clogging issues compared to previous piezoelectric printing processes.

• A process of surface chemical treatment to RN needles was developed of gauge 28-32. They were tested with air tight syringes to eliminate dead volume.

• First, cleaned needle surface was roughed through acid etching using 3:1 hydrochloric and nitric acid mixture. After etching, the needle was dip-coated with 1H,1H,2H,2H-Perfuorodecanethiol to create a fluorinated surface.

• The purpose of hydrophobic treatment is to increase the contact angle between polymer solution droplet and nozzle wall to facilitate consistent droplet detachment.

• In the semi-contact printing process, the liquid droplet forms a bridge between the nozzle and printing surface, with the nozzle not making direct physical contact with the printing surface.

• The use of computer vision was implemented through the mounted microscope enabling more precise and automated printing processes.The onboard microscope captures the photonic chip inside the calibration pattern. Perspective warping correction and edge detection algorithms are applied to identify the shape of the chip, X/Y coordinates of the chip's edges are calculated.

• Using the known design of the chip, approximate X/Y coordinates of individual spiral waveguides are calculated, and these are superimposed on the image for precise alignment and automated printing process.

• Further research will focus on quantitatively measuring droplet sizes and optimizing the distribution of polymer solution deposition for enhanced control.

• Ongoing efforts will optimize droplet volume, solvent properties, and polymer concentration to achieve desired polymer thin film thickness and uniformity. Ways to reduce the Coffee Ring effect and improve contact pinning will be further investigated.