RESUMO
Fluorescently labelled nanoparticles are routinely used in Correlative Light Electron Microscopy (CLEM) to combine the capabilities of two separate microscope platforms: fluorescent light microscopy (LM) and electron microscopy (EM). The inherent assumption is that the fluorescent label observed under LM colocalises well with the electron dense nanoparticle observed in EM. Herein we show, by combining single molecule fluorescent imaging with optical detection of the scattering from single gold nanoparticles, that for a commercially produced sample of 10 nm gold nanoparticles tagged to Alexa-633 there is in fact no colocalisation between the fluorescent signatures of Alexa-633 and the scattering associated with the gold nanoparticle. This shows that the attached gold nanoparticle quenches the fluorescent signal by ~95%, or less likely that the complex has dissociated. In either scenario, the observed fluorescent signal in fact arises from a large population of untagged fluorophores; rendering these labels potentially ineffective and misleading to the field.
RESUMO
The ability to characterize the Point Spread Function(PSF) is crucial in practical microscopy, but requires knowledge of the complex PSF for approaches that detect fields instead of intensities. Here we experimentally measure and theoretically model the volumetric amplitude and phase response of an Interferometric Cross-polarisation Microscope to demonstrate the technique's capability to provide confocal-like images of weakly birefringent structures in living cells. We find the axial FWHM of the amplitude PSF to be 0.70 ± 0.01 µm and 0.83 µm for model and measurement, respectively, on par with confocal microscopy. Ultimately retaining both amplitude and phase information will however enable approaches for improved localisation of objects.
