ODX: A Fitness Tracker-Based Device for Continuous Bacterial Growth Monitoring

Abstract

Continuous monitoring of bacterial growth in aqueous media is a crucial process in academic research as well as in the biotechnology industry. Bacterial growth is usually monitored by measuring the optical density of bacteria in liquid media, using benchtop spectrophotometers. Due to the large form factor of the existing spectrophotometers, they cannot be used for live monitoring of the bacteria inside bacterial incubation chambers. Additionally, the use of benchtop spectrometers for continuous monitoring requires multiple samplings and is labour intensive. To overcome these challenges, we have developed an optical density measuring device (ODX) by modifying a generic fitness tracker. The resulting ODX device is an ultra-portable and low-cost device that can be used inside bacterial incubators for real-time monitoring even while shaking is in progress. We evaluated the performance of ODX with different bacterial types and growth conditions and compared it with a commercial benchtop spectrophotometer. In all cases, ODX showed comparable performance to that of the standard benchtop spectrophotometer. Finally, we demonstrate a simple and useful smartphone application whereby the user is notified Page 1 of 18 ACS Paragon Plus Environment Analytical Chemistry when the bacterial concentration reaches the targeted value. Due to its potential for automation and mass production, we believe that the ODX has a wide range of applications in biotechnology research and industry.

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“…using an ultraviolet spectrophotometer [28,29]. A significant positive correlation was identified between the OD and bacteria concentrations [30].…”

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“…It was the trainees who presented alternatives that allowed the completion of experiments. These experiences also triggered our own creativity, and some scientific solutions for enabling laboratory work in low-income countries are now being investigated by our group (Yallapragada et al, 2019).…”

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“…Maintaining strictly anaerobic conditions, while quantifying gaseous substrates or products, requires incubation in gas-tight, closed incubation vessels, such as Hungate tubes, serum vials, or closed medium bottles ( Widdel and Bak, 1992 ). A few research groups have developed and published promising online OD measurement devices for tubes using 3D printed tube holders ( Lamb et al, 2013 ; Maia et al, 2016 ; Kutschera and Lamb, 2018 ; Sasidharan et al, 2018 ; Mauerhofer et al, 2019 ; Yallapragada et al, 2019 ), or a fitness-tracker based device with the promise to be attachable to a variety of culture vessels ( Yallapragada et al, 2019 ). However, these devices rely on access to a 3D printer ( Maia et al, 2016 ; Kutschera and Lamb, 2018 ; Sasidharan et al, 2018 ; Yallapragada et al, 2019 ) or availability of discontinued parts ( Yallapragada et al, 2019 ).…”

“…A few research groups have developed and published promising online OD measurement devices for tubes using 3D printed tube holders ( Lamb et al, 2013 ; Maia et al, 2016 ; Kutschera and Lamb, 2018 ; Sasidharan et al, 2018 ; Mauerhofer et al, 2019 ; Yallapragada et al, 2019 ), or a fitness-tracker based device with the promise to be attachable to a variety of culture vessels ( Yallapragada et al, 2019 ). However, these devices rely on access to a 3D printer ( Maia et al, 2016 ; Kutschera and Lamb, 2018 ; Sasidharan et al, 2018 ; Yallapragada et al, 2019 ) or availability of discontinued parts ( Yallapragada et al, 2019 ). Further, the heat sensitivity of many electronic devices inhibits their use for online measurements of thermophilic microbes.…”