Assay Development and Screening
Virus Particle Mobility Measurement for High Throughput Analysis
Monday, February 5
3:30 PM - 4:00 PM
In initial tests a newly demonstrated differential mobility analyzer (DMA) air-electrophoresis instrument now achieves high-resolution (1/FWHM ~30) for particle size classification in the 0-70 nm size range. The target application of this size range is to survey insect viruses (20-60 nm diameter). The integrated analytical process sequence exploits the extreme size uniformity of virion-particles within a virus species. This relatively monodisperse distribution is readily separated from the matrix. Parent samples may be pre-processed using centrifugation, ultrafiltration, dialysis etc. This pre-processing generated refined retentate biofluid that has been enriched as much as 1000-fold in virion content. This tool is favored in mosquito analysis by two factors: 1) infected insects display high viral load thereby enhancing signal strength and 2) insects are infected by only one virus at a time, thus reducing potential complexity of virion particle size distribution spectra. Once the sample is preprocessed, the instrument operates as follows: (i) dissolved virus particles are introduced in the gas phase via electrospray (ES); (ii) the large initial charge on the virus particles is reduced to one elementary unity via carefully controlled contact with oppositely charged ions; (iii) particle sizes present are determined by mobility analysis in the gas using the differential mobility analyzer (DMA); (iv) particles in each selected size are individually counted with a condensation nucleus counter (CNC), providing information on virus concentration. Step (ii) neutralization is now possible using a bipolar electrospray neutralizer source of free electrons, a relatively simple, compact device that eliminates previous reliance on radioisotope neutralizers, permitting safe, portable operation. The air-recirculating fully-contained DMA instrument (no high vacuum) is intended for service in high throughput analysis. It may be challenged with large series of unique refined biofluid samples with target throughput of 10 samples per hour along with frequent calibration runs and target cost of ≤$1 per analyte. Principles of device operation will be reviewed. Representative high resolution DMA viral spectra will be presented along with outline of future work.