Virus detection

Detection of viruses is of enormous importance in medical research as well as in clinical diagnosis. A great number of detection methods have been devised, ranging from the very quick and simple to the very advanced, but there is still much room for improvement and we have a novel and very promising method to propose.  

Most methods for virus detection are indirect and involve detecting DNA/RNA or antibodies, or studying the effect of the virus on cells in a cell culture. Molecular-based methods, such as PCR and ELISA and Western blot, can detect residues of DNA/RNA even after an infection has ended, but do not accurately measure the concentration of intact virus particles in a sample. Electron microscopes can count virus particles, but require expensive equipment and extensive training to use. Fluorescent dyes and techniques like NTA, fluorescence microscopy and flow cytometry can also be used to detect viruses, but dyes can bleach under laser illumination. In complex biological samples such as blood serum which contains much protein and particles, fluorescent dyes can cause too much background signal by attaching to all the other material in addition to the targeted viruses. Our innovative and patent-pending method to address these shortcomings is to label viruses with nanoparticles of gold rather than fluorescent dyes, and to detect them selectively with our twilight holographic particle tracking method. 

The advantages are the following:

1. Selectively detecting only virus particles with gold particles attached, whereas individual virus and gold are below detection limit and do not disturb the measurement. This makes use of that holographic particle tracking is insensitive to particles below detection limit, which blend into the background. 
2. Particles above detection limit, but without gold nanoparticles attached, are readily differentiated from those with gold attached.
3. Comparably few gold nanoparticles need to be attached to enable detection, whereas many fluorescent molecules would be needed. 
4. Combined with size measurement, intact virus particles can be differentiated from virus debris.
5. Whereas the current detection limit for individual virus particles is about 150nm, with gold nanoparticles attached the detection limit is pushed down to below 100nm. Individual gold nanoparticles as small as 50nm can be directly detected. 

While further work is needed to optimize the chemical surface coating on the gold particles and test the method in various biological fluids, initial results have been promising and the method is considered to have a high chance of success. Research is ongoing.  

The method may also be useful for detection of other small particles, for example exosomes, which are small particles of similar size as virus and which are produced by live cells. Exosomes have the potential to be used as biomarkers for e.g. cancer diagnosis and can also be produced in cell cultures for use as drug delivery vehicles. Exosomes is currently a very hot research topic.