Rapid printing of a Bacterial array for a Solid-Phase Assay (BacSPA) of heavy metal ions

Abstract

Bacterial whole-cell biosensors have been used to detect numerous pollutants for decades. In this work, a rapid sensing method using patterned bacterial arrays on solidified agar media was reported. A printing system, which quickly patterns 384-spot bacterial arrays via inertial impact, was developed in this study. The droplet formation was observed by a high-speed camera and simulated in COMSOL software to investigate the printing conditions. We found that the droplet volume and speed were influenced by the accelerations of the impact. Following adjustment, the printer could eject discrete droplets and pattern arrays with high accuracy. The printed bacteria were incubated, and images acquired by a commercial digital camera were analyzed by the Python program. The areas of 384 spots in a single array were similar, with a high roundness and low deviations. We found that the printer plate quality influenced the printing results more than the printing conditions. Finally, the printing system was applied to determine heavy metals concentrations in solid growth media by bioluminescent sensor bacteria. The luminescence intensity patterns varied between heavy metals. We propose the printing system as a useful tool for rapid patterning of bacterial whole cell sensor arrays on solid agar.