Abstract
In this paper we demonstrate a new scheme for optical super-resolution, inspired, in-part, by PALM and STORM. In this scheme each object in the field of view is tagged with a signal that allows them to be detected separately. By doing this we can identify and locate each object separately with significantly higher resolution than the diffraction limit. We demonstrate this by imaging nanoparticles significantly smaller than the optical resolution limit. In this case the “tag” we have used is the frequency of vibration of nanoscale “bells” made of metallic nanoparticles whose acoustic vibrational frequency is in the multi-GHz range. Since the vibration of the particles can be easily excited and detected and the frequency is directly related to the particle size, we can separate the signals from many particles of sufficiently different sizes even though they are smaller than, and separated by less than, the optical resolution limit. Using this scheme we have been able to localise the nanoparticle position with a precision of ~3 nm. This has many potential advantages - such nanoparticles are easily inserted into cells and well tolerated, the particles do not bleach and can be produced easily with very dispersed sizes. We estimate that 50 or more different particles (or frequency channels) can be accessed in each optical point spread function using the vibrational frequencies of gold nanospheres. However, many more channels may be accessed using more complex structures (such as nanorods) and detection techniques (for instance using polarization or wavelength selective detection) opening up this technique as a generalized method of achieving super-optical resolution imaging.
Highlights
Conventional optical imaging is restricted in resolution by the Rayleigh criterion to ~λoptical/NA, where λoptical is the optical wavelength and NA is the numerical aperture[1] of the objective lens
Higher resolution can be achieved using near field or super resolution techniques such as stimulated emission depletion (STED)[4] microscopy or photo activated localisation (PALM) and stochastic optical reconstruction (STORM) microscopy[5,6]
The optical point spread function (PSF) at the detector can be attributed to individual fluorophores and these fluorophores can be super-localised
Summary
Conventional optical imaging is restricted in resolution by the Rayleigh criterion to ~λoptical/NA, where λoptical is the optical wavelength and NA is the numerical aperture[1] of the objective lens. Higher resolution can be achieved using near field or super resolution techniques such as stimulated emission depletion (STED)[4] microscopy or photo activated localisation (PALM) and stochastic optical reconstruction (STORM) microscopy[5,6]. In these schemes fluorophores and switchable fluorophores are required to enable super resolution along with high photon dose at short optical wavelengths which are used to pump and switch the fluorophores. The optical point spread function (PSF) at the detector can be attributed to individual fluorophores and these fluorophores can be super-localised (localised with greater precision that the optical resolution) These techniques have produced important results, they require typically high light intensities which produce photodamage and they bleach. A wide-field interferometric phase microscopy has been implemented to create a map of the locations of gold nanoparticles in a sample without the need of scanning[9]
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