Plate-Q: A Frugal Microplate-Reader for Bacterial Signal Quantification

Abstract

Microplate readers are laboratory instruments used to measure biological properties and reactions within a microplate. A microplate consists of small wells in which separated reactions take place. These reactions convert the progression of biochemical processes into optical signals. A microplate reader detects these signals and quantifies a parameter of interest. Most lab-grade microplate readers can cost up to $20,000, making them unaffordable for underfunded labs and developing countries. In light of this, we developed Plate-Q, a $150 frugal microplate reader capable of quantifying green fluorescence protein and optical density of bacterial samples from 96-hole microplates. Rather than using optical sensors found in laboratory microplate readers, Plate-Q takes advantage of a Raspberry-Pi camera to capture images of a microplate and manually extract brightness values using computer vision algorithms. Plate-Q utilizes 440nm excitation lights with a 510nm emission filter to measure GFP expression and 600nm lights for optical density readings. However, camera-based technologies have three main problems: lens distortion, signal interference, and brightness calculations. Plate-Q addresses these problems through camera movement over the well-plate, image optimization, 3D printed well-plate covers and mathematical regression algorithms. In testing with fusarium dual-plasmid biosensors, Plate-Q showed comparable accuracy to commercial microplate readers with an average error of .034 and a root mean squared error of .012 for fluorescence and an average error of .045 and root mean squared error of .023 error for optical density. Users can scan for other fluorescent proteins by changing the light source and filter for different wavelengths. With all aspects of Plate-Q being open source, labs worldwide can quantify samples in an affordable and time-efficient manner.