The Challenge

Measuring the growth of cells is a vital task in any biology lab across the world. Thousands of dollars are spent on spectrophotometers and analysers to measure the optical densities of cell cultures. More importantly, hundreds of researcher-hours are spent taking samples, diluting them and measuring the optical density, again and again, through the long nights of running growth curves.

There do exist automatic devices that can measure OD, such as the Bioscreen C, but their prohibitive cost (in the tens of thousands of dollars), low volume capacity, and inability to handle high ODs make them non-viable as a substitute for manual pipetting in most experimental scenarios. Other machines simply lack the capabilities to ...

There has to be a better way. That way is GCODe.

GCODe (Growth Curve and Optical DEnsity) is an optical density measurement device that will not only take readings at pre-programmed intervals or continuously, but will also aerate and dilute the culture as required. It can even send you a message when the OD reaches a particular level, just in time to you to start the next stage of your experiment. Fundamentally, it automates the grunt work of growth curves, in a manner that allows you to walk away from the lab, secure in the knowledge that you will be alerted when your cells are ready for you.

Our work stemmed from our own frustrations running growth curves night after night, and was also inspired by the OD meter built by the 2014 Aachen iGEM team. We worked incrementally, starting with a rudimentary box of wiring, designing version after version in response to feedback from the iGEM wetlab team, as they trialled our device, and other labs and professors from across IISc.

We currently have two versions of GCODe manufactured, tested and fully documented.

They are:

GCODe Pro and GCODe Mini

GCODe Mini

Intro

The GCODe Mini is a sleek black acrylic cuboid that houses a test tube that will hold your culture. Connect the Mini to your laptop via USB, tell it what to do with our associated software, place it in the shaker-incubator, press Start … aaand you’re done !

The Mini can:

Take readings of the optical density at specified intervals for as long as required. Alert you via pushbullet notifications when the OD increases by a specified amount, or at regular time intervals, or when the OD reaches a desired value. Plot a graph of OD vs time.

Description

The GCODe Mini has two components, the Power Unit and the Analysis Unit. The Analysis Unit contains the Arduino, and the test tube. It will be connected to the laptop, and goes inside the shaker. The shaker should be plugged into the Power unit (which requires Mains power), so that it can be turned off during measurement to give a stable reading.

How it Works

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GCODe Pro

Intro

While the Mini needed the culture to be grown in a test tube, the GCODe Pro works perfectly with the large quantities of a standard conical flask. It will automatically do dilution for you, which means it can measure an almost unlimited range of ODs, including those that occur in yeast and other organisms not compatible with regular plate-readers. The GCODe Pro has the same analysis unit as the Mini, but uses a network of servos and a peristaltic pump to draw precise amounts of culture and dilute it to any desired level before measurement. Optical Density is measured by drawing the liquid into a standard cuvette, which allows the flexibility to grow unlimited amounts of culture in a conical flask or any other vessel.

Description

THe GCODE Pro has X main components THe Analysis unit uses a cuvette supplied and drained by a needle, but the measurement system is the same as the one used in the Mini The Sampling Unit draws liquid from the conical flask, or culture vessel, dilutes it as programmed, and delivers the culture to the cuvette. THe pipes are cleaned between every run by washing with ethanol.

How it Works

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Results

Growth Curves

As soon as the GCODe Mini was assembled and calibrated, we put it to work. To find out whether GCODe could actually measure optical densities in a reproducible manner, we tested it in Prof. Dipshikha Chakravortty’s lab under the supervision of Jeswin Joseph, her PhD student.

Our growth curves used Salmonella typhi, E.Coli with the optical density measured every three hours with GCODe and an ELISA plate-reader.

Salmonella Growth curve on Date1

Salmonella Growth curve on Date2

The dark blue line is the OD measured by GCODe, and the red line is the OD as measured at 600nm with a spectrophotometer. While the absolute values of the OD differ, due to the different wavelengths of the LEDs, normalizing with the ratio of ODs at 12 hours (green line) or 24 hours (cyan) shows near-perfect agreement !

Salmonella Growth curve on Date3

We also ran Growth curves on the Mini with E.Coli

E. Coli Growth curve on Date2

E. Coli Growth curve on Date2

Notice that the readings from the Mini form an even smooother curve than those from the spectrophotometer! This is probably because the GCODe readings were taken instantaneously, while it takes time to load the cuvette into the spectrophotometer and take a reading, allowing lots more opportunities for human error.

Assembly from Instructions

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Cost

pretty low

Testimonials

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