A new functionalized fluorosensor detects enteroviral RNA with high sensitivity in real time. It marks a major step in safer, more effective viral diagnostics.
In a notable breakthrough, researchers at the Nanoscience Center (NSC) of the University of Jyväskylä, Finland, have developed an innovative, label-free ratiometric fluorosensor capable of detecting enteroviral RNA with high sensitivity and selectivity. This advancement represents a significant step forward in viral diagnostics and highlights the value of interdisciplinary collaboration in tackling global health challenges.
Viruses continue to pose a serious threat to public health, as seen in recent pandemics. Early detection and accurate identification are essential for controlling the spread of infections. While traditional diagnostic methods are effective, they often fall short in providing detailed spatiotemporal information about viral genome release, limiting their utility in dynamic or early-stage detection scenarios.
“This interdisciplinary effort, combining expertise from biology, chemistry, and physics, marks a significant advancement in viral detection technology. We have developed an enhanced ratiometric fluorosensor using carbon dots (CDs) functionalized with Probe (single-stranded complementary oligonucleotide fragment) and ethidium bromide (EB), for detection of enteroviral RNA,” says professor of physics Jussi Toppari from the University of Jyväskylä.
Innovative ratiometric fluorosensor for viral detection
Fluorescent nanoparticles have emerged as powerful tools for bioanalyte sensing, with CDs leading the way due to their simple synthesis, exceptional photostability, tunable photoluminescence, excellent aqueous solubility, biocompatibility, and versatile surface functionalities for ligand conjugation. These unique properties position CDs as a game-changer in the field of biosensing.
“This so-called Functionalized Sensor (Func Sensor), where CDs are functionalized i.e., covalently bonded with the probe clearly outperforms the more traditional approach of Non-Functionalized Sensor (Non-Func Sensor) which is a simple mixture of CDs, probe, and EB,” explains Doctoral Researcher Amar Raj from University of Jyväskylä.
In both sensors, the presence of target DNA, hybridizing with the probe, enhances EB fluorescence, while CDs fluorescence changes slightly due to electron transfer, enabling ratiometric detection, and were ultrasensitive.
“The Non-Func Sensor showed a lower sensitivity with target DNA and was not effective with real enteroviral RNA samples, while the Func Sensor showed a higher sensitivity with DNA and real viral RNA, exhibiting clearly improved selectivity,” comments Postdoctoral Researcher Abhishek Pathak. He worked earlier as a Postdoctoral Researcher at the University of Jyväskylä.
The superior performance of the Func Sensor is attributed to enhanced charge transfer due to covalent functionalization.
“Our proof-of-principle study highlights the importance of covalent immobilization of the probe for improved electron transfer between CDs and EB and thus enhanced performance and demonstrate the suitability of the Func sensor for practical applications in rapid, real-time and precise in situ detection of viral RNA,” tells Professor of Cell and Molecular Biology Varpu Marjomäki from University of Jyväskylä.
Especially, the research shows that the Func sensor can detect enteroviral RNA release from the capsid in real-time in vitro.
“This means that the Func sensor can be used as a novel viral RNA sensing platform which offers a much-needed possibility to detect real-time viral RNA appearance during infection,” says Marjomäki.
Towards safer research
This groundbreaking research introduces a novel method for detecting viral RNA and provides new insights into charge transfer mechanisms between fluorophores. Building on these findings, the team is now working to enhance the system’s safety and reliability by replacing the potentially hazardous dye ethidium bromide with safer, less cytotoxic, and more biocompatible alternatives.
“This enhancement will further improve the safety and efficacy of in vivo viral RNA detection,” rejoices Pathak.
Reference: “Ultrasensitive ratiometric fluorosensor for enteroviral RNA detection based on improved electron transfer between carbon dots and ethidium bromide” by Abhishek Pathak, Amar Raj, Sylva Larsson, Ajay B. Patil, Atul K. Singh, Mira Laajala, Tatu Kumpulainen, Varpu S. Marjomäki and J. Jussi Toppari, 11 March 2025, Carbon.
DOI: 10.1016/j.carbon.2025.120222
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