Abstract
Prior opto-mechanical techniques to measure vibrational frequencies of viruses work on large ensembles of particles, whereas, in this work, individually trapped viral particles were studied. Double nanohole (DNH) apertures in a gold film were used to achieve optical trapping of one of the smallest virus particles yet reported, PhiX174, which has a diameter of 25 nm. When a laser was focused onto these DNH apertures, it created high local fields due to plasmonic enhancement, which allowed stable trapping of small particles for prolonged periods at low powers. Two techniques were performed to characterize the virus particles. The particles were sized via an established autocorrelation analysis technique, and the acoustic modes were probed using the extraordinary acoustic Raman (EAR) method. The size of the trapped particle was determined to be 25 ± 3.8 nm, which is in good agreement with the established diameter of PhiX174. A peak in the EAR signal was observed at 32 GHz, which fits well with the predicted value from elastic theory.
Highlights
This study demonstrates an implemented technique to directly measure the frequencies of acoustic modes of very small individual virus particles for the purpose of a fundamental understanding of their biophysics, diagnostics, or targeted destruction of the contagion
Previous work using the extraordinary acoustic Raman (EAR) technique investigated small proteins including DNA and polystyrene nanospheres [9,10,11,22], whereas here we report of the study of a virus using the technique, since the vibrational frequencies of viruses were of interest to researchers for some time [35,37,38,40,41,42,43,44,45,46,47,48,60,61,62,63,64,65,66,67]
We applied this technique to another bacteriophage, MS2, but it is not wellFor established thattype, optical trapping enables performance of experiments onevents
Summary
Optical tweezers are under development since Ashkin’s seminal work, first reported in 1970 [1]. Brillouin scattering can probe the GHz frequency range and, some Brillouin studies were done on viruses [43,46,48,59,60]; the peaks were difficult to observe possibly due to damping by water or core–shell interactions, as discussed in those works Unlike these other opto-mechanical measurement methods, the EAR technique provides a high resolution of vibrational frequencies of individual nanometer-scale particles which are confined by optical trapping, as opposed to measuring ensembles of particles in the case of. The previous EAR studies of nanometer-scale particles found peak frequencies which matched for its small size, low biological safety rating, and history of being extensively studied It makes a well with predicted values from elastic theory. Detection of such viruses can indicate the presence of fecal matter in aquatic environments [76]
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