Developing an Improved Procedure for Monitoring the Heart Rate of D. Magna

Overview

Daphnia magna is an aquatic invertebrate and a well-established model organism for toxicological studies. It is transparent, allowing heart rate monitoring to be used as a toxicological assay. Monitoring the heart rate of D. magna is complicated by the movement of the organism and the speed of their heart rate, making it nearly impossible to count reliably with the naked eye. This study presents a procedure for video capture of D. magna heart rate as well as the design of instruments to aid the researcher in this procedure. To restrict movement of D. magna for video capture, a round bottom 96-well microtiter plate was used with one D. magna per well. The majority of the liquid in each well was pipetted out, leaving the D. magna stationary so that a 10-second video could be captured. Video was originally captured at 120fps or greater using a modified dissecting scope and an iPhone. To improve image quality, a dissecting scope with a darkfield base and a Sony a6500 digital camera were used. To improve ease of pipetting for video capture, a specialized tip and automated pipetting system were developed. The tip was formed from a glass Pasteur pipette melted to a 90˚ angle and a lifter that could actuate the tip’s movement in and out of the well was designed and 3D printed. This lifter was actuated by a micro servo motor. To further automate the pipetting process, a device to control a 100-1000µl micropipette was designed and prototyped with 3D printing. This device allows the plunger and volume setting of the pipette to be controlled with stepper motors. The proposed method of heart rate assay provides a reliable quantitative measurement of D. magna heart rate, while allowing the organism mobility during the course of the experiment, only restricting movement for 10-second observations. The use of servo and stepper motors allows for customizable control over pipetting functions with a microcontroller. Future directions include automation of microtiter plate movement, a plug-and-play solution for control of the proposed devices, and developing an integrated system for easy deployment in research and laboratory settings.

Competition history

• AJAS 2020 Category not listed

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