Schematic diagram of PCR temperature cycle using the photothermal effect in polymeric microparticles. Credit: Korea Institute of Science and Technology
Quantitative polymerase chain reaction (qPCR) is an invaluable molecular diagnostic technique that has played a central role in testing efforts throughout the COVID-19 pandemic. Due to the thermal cycling steps required to facilitate qPCR, a typical test usually takes 1 to 2 hours to complete, limiting the possibilities for definitive point-of-care screening. However, many research efforts have centered on increasing the speed of qPCR analysis, and recently, a team from the Korean Institute of Science and Technology (KIST) has developed ultrafast technology that enables the completion of a qPCR test in just five minutes through the use of photothermal nanomaterials.
Photothermal nanomaterials are able to rapidly generate heat upon light irradiation, but their application in technologies such as PCR has been limited by their low stability. The KIST team addressed this challenge by developing a novel matrix that helps overcome the instability of photothermal nanomaterials, producing microparticles they call photothermal primer-immobilized networks (pPINs). The pPINs consist of a hydrogel matrix containing both primers and reduced graphene oxide as the heat generating nanomaterial. The use of these microparticles and optical elements, rather than a Peltier element, for thermal cycling enables both faster reactions and a more compact PCR system.
The qPCR system using pPINs achieved a heating rate of 22.0 ± 3.0°C s–1 and cooling rate of 23.5 ± 2.6 °C s–1 with a reaction volume of 100 nL, enabling a qPCR run to be completed within just 5 minutes, according to the authors. The researchers further developed the system to enable multiplexing and used the system to perform a four-plex bacterial discrimination test as a proof of concept. Faster and more accurate than lateral flow tests, the pPIN qPCR technology could potentially be used for rapid point-of-care testing for COVID-19, including multiple different COVID-19 variants due to its multiplexing capabilities. This research was published in ACS Nano.
“Through additional research, we plan to miniaturize the developed ultrafast PCR technology this year, to develop a device that can be utilized anywhere,” said corresponding author Sang Kyung Kim, of the Center for Augmented Safety System with Intelligence, Sensing. “While maintaining the strength of PCR as an accurate diagnostic method, we will increase its convenience, field applicability, and promptness, by which we expect that it will become a precision diagnostic device that can be used at primary local clinics, pharmacies, and even at home. In addition, the PCR technology is a universal molecular diagnostic technology that can be applied to various diseases other than infectious disease, so it will become more applicable.”