Integrated Device Combines Techniques to Detect Malaria

Recombinase polymerase amplification (RPA) is promising for further development since it operates in a short time frame and produces a product that can be visually detected on a lateral flow dipstick.

Isothermal amplification techniques are emerging as a promising method for malaria diagnosis since they are capable of detecting extremely low concentrations of parasite target while mitigating the need for infrastructure and training required by other nucleic acid based tests.

Bioengineers at Rice University (Houston, TX, USA) developed an integrated device capable of carrying out isothermal amplification using the RPA reaction, post-amplification dilution, and lateral flow detection of the resulting product. The paper and plastic device developed amplified the target using RPA; diluted the resulting product; and detected the product using a lateral flow sandwich assay. In addition, the device transferred the product between the amplification, dilution, and detection modules. A sequence of paper pads loaded with various reagents was used to carry out these functions.

The device is made of simple components, can be assembled by the user and uses a novel slider method to transport reagents through the system. The equipment needed beyond the device itself and the sample to be tested are a hot plate capable of 37 °C, a reusable 25 gram metal weight, the RPA master mix, the running/dilution buffer and pipettes to load these reagents onto the device dilution, running buffer, RPA and sample pads. This device runs the entire assay, including detection, in around an hour and has a limit of detection equivalent to when the assay is run using conventional methods on the bench top. The total run time for the device is 55 minutes, and including the loading and operation of the device, the entire assay can be carried out in about an hour.

The authors concluded that the fabricated device amplified a sequence which is common to the human infectious species of Plasmodium and operated an isothermal amplification reaction which is rapid and has an easy visual readout. A paper and plastic device was also developed which carries out the amplification of the samples, dilutes the product and runs the result on a lateral flow strip. When tested on synthetic targets, a limit of detection of 5 copies/µL (50 total copies) was found, which matches the performance of the same assay run on the bench top. The study was published on November 26, 2015, in the Malaria Journal.

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