Modular droplet-based fluidics for large volume libraries of individual multiparametric codes in lab-on-chip systems

Droplet-based lab-on-a-chip systems offer vast possibilities in manipulation, guidance, tracking and labeling of individual droplet-based bioreactors. One of the targeted application scenarios is in drug discovery where millions of unique codes are required, which is out of reach for current technologies. Here, we propose and validate a concept for the realization of multiparametric codes, where information is stored in distinct physical and chemical parameters. Exemplarily we focus on the use of impedance and magnetic sensing by monitoring ionic concentration as well as magnetic content per droplet and droplet volume. Codes based on aqueous ferrofluid droplets were prepared using a tubing-based millifluidic setup and consist of up to 6 droplets of different combinations of volumes and magnetic concentration. We demonstrate that a droplet chain of 3 single droplets of different volume with 9 different magnetic nanoparticle concentrations accompanied with 4 different ionic concentrations per droplet offers up to 3 million unique codes. The developed fluidic platform can be readily extended to other types of sensors including optical ones to boost the coding capacity even further.