An Open-Source Droplet Digital PCR (ddPCR) System for the Rapid and Accurate Detection of Bacteria from Environmental Water Samples

Droplet Digital PCR (ddPCR) is a method of rapid bacterial quantification in a liquid culture or solution. The development of an open source ddPCR system will allow this technology to become more affordable. The development of this open-source system utilized reused optical components, including a Photomultiplier Tube (PMT) from a flow cytometer, aligned using optical fittings. The signals received from the PMT were passed through a circuit containing passive bandpass filters and amplifier stages. FITC fluorescent microspheres were used to test the potential limits of the system’s ability to quantify different concentrations of positive bacterial droplets in a sample. The system provided a large cluster of counts at 100% accuracy when particles were passed at a rate slower than 50 particles per minute. The functionality of the system was assessed by utilizing microfluidic droplets containing cultured E. coli samples. Different concentrations were used to test the system’s accuracy through comparison. For each concentration the bacterial counts were within 10% of the expected values. To automate the quantification of signals from the system, a convolutional neural network is in development.