May 27 2021
In the event of the COVID-19 pandemic, reverse transcription-polymerase chain reaction (RT-PCR) has been the benchmark for diagnosis.
This tiny PCR chip can amplify DNA much more quickly than conventional, benchtop PCR systems. Image Credit: Adapted from ACS Nano, 2021.
But the PCR part of the test necessitates heavy, costly machines and takes nearly an hour to complete, which makes it difficult to rapidly diagnose someone at a testing site. Scientists recently reported in ACS Nano about the development of a plasmofluidic chip with the ability to perform PCR in just around 8 minutes, which could expedite diagnosis during current and future pandemics.
Fast diagnosis of COVID-19 and similar highly contagious viral diseases is crucial for timely medical care, contact tracing, and quarantining. At present, RT-PCR –– which involves the use of enzymes to reverse transcribe minuscule amounts of viral RNA to DNA and then amplifying the DNA for it to be identified by a fluorescent probe –– is the most sensitive and reliable diagnostic method.
However, since the PCR portion of the test necessitates 30–40 cycles of heating and cooling in exclusive machines, it requires nearly an hour to perform, and samples should essentially be sent away to a lab, implying that a patient normally must wait a day or two to receive their diagnosis.
Ki-Hun Jeong and collaborators intended to create a plasmofluidic PCR chip with the ability to quickly heat and cool minuscule volumes of liquids, thereby enabling accurate point-of-care diagnosis within a fraction of the time.
The researchers developed a postage-stamp-sized polydimethylsiloxane chip including a microchamber array for the PCR reactions. Adding a drop of sample to the chip makes the vacuum pull the liquid into the microchambers, which are placed above glass nanopillars with gold nanoislands.
Any microbubbles that might interfere with the PCR reaction diffuse out through an air-permeable wall. Upon switching on a white LED beneath the chip, the gold nanoislands on the nanopillars instantly transform light into heat and then quickly cool when the light is turned off.
The team tested the device using a piece of DNA with a SARS-CoV-2 gene, thus achieving 40 heating and cooling cycles and fluorescence detection in just 5 minutes, with 3 more minutes for sample loading. The amplification efficiency was found to be 91%, but a comparable traditional PCR process exhibits an efficiency of 98%.
The reverse transcriptase step was added before sample loading, restricting the total testing time by the new method to 10–13 minutes, as against approximately an hour for standard RT-PCR testing. According to the researchers, the new device could offer several opportunities for fast point-of-care diagnostics during a pandemic.
The researchers acknowledge financial support from the Korea Advanced Institute of Science and Technology (KAIST) and the National Research Foundation of Korea.
Journal Reference:
Kang, B.-H., et al. (2021) Ultrafast and Real-Time Nanoplasmonic On-Chip Polymerase Chain Reaction for Rapid and Quantitative Molecular Diagnostics. ACS Nano. doi.org/10.1021/acsnano.1c02154.