When antibodies do a pirouette
Functionalized nanoparticles could soon revolutionize point-of-care diagnostics. Researchers at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) and Julius-Maximilians-Universität Würzburg have developed a method for binding specific molecules in samples and serums, such as antibodies in the blood, to the surface of iron oxide particles thus allowing them to be identified using an inexpensive and compact detector. The researchers have now published their findings in the journal Nature Communications.
The last few months have demonstrated how important it is to have functioning diagnostics to detect infectious diseases, while simultaneously presenting us with a dilemma: Antigen rapid tests are comparably inexpensive, easy to use and provide a result within a matter of minutes, but are not nearly as reliable as a PCR test. PCR tests, on the other hand, are very reliable, but difficult to use and expensive and the result is only available after a few hours or even several days in some cases. A team of researchers from Universitätsklinikum Erlangen (UKER) and Würzburg University has developed a method that could solve this dilemma and combine high sensitivity with simple and rapid point-of-care diagnostics.
Nanocompounds with specific fingerprints
This method is based on magnetic nanoparticles – particles of iron oxide that are a few hundred nanometers in size to which specific surfaces have been applied. “We can change the surfaces of these particles in such a way that only specific molecules from the samples dock on to them,” explains Prof. Dr. Christoph Alexiou, senior physician at the Department of Otorhinolaryngology – Head and Neck Surgery at UKER, Endowed Professorship for Nanomedicine, Else Kröner-Fresenius-Stiftung and head of the Section of Experimental Oncology and Nanomedicine (SEON). Binding nanoparticles with specific antibodies or antigens creates molecules that have a unique movement pattern, for example in rotating magnetic fields. PD Dr. Rainer Tietze, deputy head of SEON, compares it to a pirouette in ice skating: “If the skater holds their arms close to their body, they turn more quickly. If they stretch their arms out to the side, they turn more slowly.”
The limited mobility of the compounds can be detected using a suitable device. This is where the researchers in Würzburg come in. A team led by Dr. Patrick Vogel from the Chair of Experimental Physics V has developed a new measurement technique called COMPASS, which stands for “Critical Offset Magnetic PArticle SpectroScopy”. The nanoparticles are excited using permanent and time-varying magnetic fields. Since the particles themselves act like small permanent magnets, these magnetic fields cause them to vibrate or rotate. At the same time, this method has an amplifying effect, similar to that of optical interferences, where slight modifications to the signal source lead to greater changes in the magnetization response. Rainer Tietze: “If we measure the entire range of functionalized nanoparticles in a sample, we get a specific fingerprint and can make reliable statements about the concentration of specific molecules.”
Alternative to complex diagnostic methods
The researchers have demonstrated that it is possible to make highly sensitive measurements in a very short space of time with little technical outlay. For example, they were able to reliably detect SARS-CoV-2 antibodies within a few seconds using a rapid test. Since the diagnostic device fits into a small case and the materials only cost a few hundred euros, the COMPASS set could soon become part of the standard equipment for point-of-care-diagnosis and become a genuine alternative to complex and costly methods of analysis such as ELISA or flow cytometry. Christoph Alexiou, however, envisages a much wider range of applications: “Rapid testing in the field of preventive medicine in humans is only one feasible area. Further conceivable applications include large-scale screening of farm animals for reportable diseases and also applications in biochemistry or pharmacy in research on receptor compounds and substances.”
The Section of Experimental Oncology and Nanomedicine (SEON) at UKER is a leading specialist in the design of functional nanoparticles, which are not only supplied with excellent properties when a special coating is applied to them, but are also easily reproducible and must also be safe to use in in-vivo applications. “This success is unimaginable without funding,” says Christoph Alexiou. “I would like to express my particular gratitude to the Manfred Roth Stiftung in Fürth that has been providing financial support to us for several years and is thus making top-level research into nanomedicine possible.”
Prof. Dr. Christoph Alexiou
Head of the Section of Experimental Oncology and Nanomedicine (SEON)
Phone: +49 9131 85 33142
* DOI: 10.1038/s41467-022-34941-y
Critical Offset Magnetic PArticle Spectro-Scopy for rapid and highly sensitive medical point-of-care diagnostics