PCR machines can be classified according to the number of samples that can be run at any one time. There are machines that can run tens or even hundreds of samples in parallel and these are designed for central laboratory use. Usually, sample preparation is not an integral part of the process and must be performed on the bench or using a separate piece of kit. At the other end of the spectrum are cartridge-based machines such as Cepheid’s GeneXpert machines that can run a single sample. These machines have integrated sample preparation capabilities. The simplicity of these machines means that, in theory, they can be used anywhere. The downside is the very fact that they can only handle one sample at a time (low throughput), and the cartridges and the machines themselves are complicated and expensive.

None of the above machines fit well with the needs of Low-Income Countries (LIC), which have a high infectious disease prevalence. There is a need, therefore, in LICs for low-cost machines that can analyse tens of samples in parallel. Such a machine hits the sweet spot for testing for TB in the community, for example. As such machines are not cartridge-based, this need is matched by the need for an accompanying low-cost and simple sample prep that can concentrate (an essential requirement for TB) and clean up the nucleic acids and deliver them to the machine. The latter should fall within the capability of minimally trained staff, as did happen in the recent COVID outbreak.

 Essential specifications for community-based PCR machines include accommodating readily available reaction tubes, multiple sample testing in parallel (8 or more samples), multiple channel detection (to accommodate internal control), low cost (<$10,000), rugged, low or no maintenance, ideally an option for battery operation but not essential as there are workarounds.

I have identified 2 PCR machines that fit the criteria for use in the LIC community. I would be pleased to hear of any other machines.

Examples of available machines

 

The ChAI Open Source QPCR machine (2 channel version)

https://www.chaibio.com/openqpcr

  • 2 channels
  • 16 wells
  • 10-50 µl sample volume
  • Uses low-profile 0.2 ml tubes
  • Wireless
  • PC Browser-driven
  • Size (cm) 20 h x 30 l x 25 w
  • 4 kg
  • Robust
  • Around $8,000

The Bio Molecular Systems Mic PCR machine

https://biomolecularsystems.com/

  • 4 channels
  • 48 wells
  • 5-30 µl sample volume
  • Uses 0.1 ml tubes
  • Bluetooth
  • PC-driven
  • Size (cm) 13 h x 15 l x 15 w
  • 2 kg
  • Robust
  • Around $10,000

*Note that this article only considers real-time PCR machines that can detect amplification in the reaction tube without opening the tube. Opening a reaction tube post-amplification will contaminate the diagnostic environment with amplicons and render the environment inappropriate for further PCR. Those promoting the detection of amplified product by lateral flow, for example, should take note of this.