Immobilisation of Semliki forest virus for atomic force microscopy

Semliki Forest virus (SFV), an alphavirus, is a single-stranded positive-sense RNA virus. The RNA genome is surrounded by a protein shell known as the capsid which itself is surrounded by a lipid envelope of host cell origin. In this study, SFV strain L10 enveloped virus and its capsid were immobilised onto silicon wafer supports which had been pre-coated with a monolayer of the relevant anti-viral antibody. After drying, the samples were imaged in air, using non-contact mode atomic force microscopy (AFM). Quantification of the AFM images has revealed that both the strain L10 enveloped virus and capsid collapse when immobilised in this manner. The capsid undergoes more significant collapse compared to the enveloped virus. The dimensions of the immobilised enveloped virus and capsid have been compared to a model where the free spherical particles collapse into ellipsoids during immobilisation. For the immobilised capsid the dimensions are consistent with this model whereas for the enveloped virus the model is less effective. The dimensions of the enveloped virus appear to be affected by the antibody used for immobilisation.