New test reduces time to diagnose viral infections from hours to minutes

A team led by the CSIC's Institute of Microelectronics of Barcelona (IMB-CNM-CSIC) has presented a new diagnostic platform for the detection of viral RNA sequences. The device allows shortening the detection process by not requiring previous sample treatment steps, such as the genetic amplification that is done in current molecular diagnostics. Its ability to detect the virus directly in clinical samples represents a significant change by combining speed, versatility and low cost.

The instrument, the results of which were recently published in Analytical Chemistry, is designed to diagnose viral infections in nasopharyngeal samples. Although its feasibility has so far been demonstrated in the detection of the SARS-CoV-2 virus, the researchers emphasize that the versatility of the new test allows it to be adapted to identify other infectious diseases.

“The device includes microfluidics on paper, using a miniaturized electrochemical cell produced on a silicon chip, and the use of functionalized magnetic nanoparticles complementary to the viral RNA sequences, selected as biomarkers, allowing detection in a maximum time of 40 minutes," says César Fernández-Sánchez, principal investigator of the project in the Chemical Transducers Group at IMB-CNM-CSIC. The innovative development gives the device “portability and simplicity, resulting in an estimated price per analysis of less than one euro".

This time savings is significant compared to the more than 24 hours that can elapse between sample collection and PCR results. The analytical standard for covid-19 detection during the pandemic was based on polymerase chain reaction (PCR), which involved transporting samples to the laboratory after extraction. The instrument developed by IMB-CNM seeks to improve this molecular diagnosis, bringing it to the point of patient care. “It is a very simple, inexpensive and energy-efficient electrochemical device,” adds Fernández.

System sensitivity and application

The system has demonstrated a sensitivity of 100% and a specificity of 93%, a percentage that refers to the ability of the test to correctly identify people who are not infected, thus avoiding "false positives". These figures have been verified in the detection of SARS-CoV-2 RNA, demonstrating its great potential as a molecular diagnostic tool.

"It is a very versatile tool that could be easily adapted to detect other infectious diseases that require the rapid and efficient implementation of mass screening programs. If, in addition, we consider its low cost, the platform could be used in low-resource countries," explains Manuel Gutiérrez-Capitán, researcher at IMB-CNM-CSIC. “It is a breakthrough because it does not require previous treatment stages and can be applied at the point-of-care by non-specialized personnel," he concludes.

Device combining electrochemistry with fluidics on paper

It consists of three components: a silicon chip containing an electrochemical cell with two gold electrodes, manufactured with microelectronic technology; a fluidic paper component; and a methacrylate cartridge (case) for aligning and contacting the electrochemical cell (the chip) and the paper. The only disposable and interchangeable component is the paper, which can be recycled as normal.

In addition, the device employs functionalized magnetic nanoparticles, i.e. intentionally modified to provide them with new capabilities, through the use of oligonucleotide strands (synthetic DNA or RNA molecules) complementary to the viral RNA sequences. These make it possible to separate the biomarker of interest from the sample matrix and, in turn, to preconcentrate it in the medium suitable for analysis.

Currently, a pre-industrial prototype that integrates the measurement electronics powered by the battery of a mobile device, together with a control app, is currently undergoing validation. In this way, a completely autonomous, interconnected and portable device would be achieved.

The electrochemical cell technology of the chip is manufactured in the Micro and Nanofabrication Clean Room, a Unique Science and Technology Infrastructure (ICTS) recognized by the Ministry of Science, Innovation and Universities.

Collaboration to improve public health

The device is the result of work that began at the height of the covid-19 pandemic in 2020, in collaboration with several groups from the Institute of Advanced Chemistry of Catalonia (IQAC-CSIC), the University of Barcelona, the Severo Ochoa Center for Molecular Biology (CBMSO-CSIC) and the Germans Trias i Pujol University Hospital in Badalona. It has been financed with CSIC's own funds, through donations, and with recovery funds obtained by the CSIC's Plataforma Temática Interdisciplinar (PTI) Salud Global.

_{Reference article: Manuel Gutiérrez-Capitán, Eva Balada, Anna Aviñó, Lluïsa Vilaplana, Roger Galve, Alícia Lacoma, Antonio Baldi, Antonio Alcamí, Véronique Noé, Carlos J. Ciudad, Ramón Eritja, María-Pilar Marco, César Fernández-Sánchez. Unraveling the Amplification-Free Quantitative Detection of Viral RNA in Nasopharyngeal Swab Samples Using a Compact Electrochemical Rapid Test Device. Analytical Chemistry. DOI: doi/10.1021/acs.analchem.5c01605}

• Mounting of paper detection device in a methacrylate cartridge connected to a cell phone for diagnostics.
• Hand with pliers to hold the silicon chip with gold electrodes for detection.
• Base of the methacrylate cartridge, with the chip on one side to insert the paper and close the device.
• César Fernández, Manuel Gutiérrez-Capitán and Antoni Baldi in the laboratory. Gutiérrez-Capitán holds the rapid diagnostic device.