Direct quantification of Aspergillus niger spore adhesion to mica in air using an atomic force microscope

An atomic force microscope (AFM) has been used to quantify directly the adhesion between single Aspergillus niger spores and freshly cleaved mica surfaces in air, a system that is relevant to the removal of spores by filtration. The measurements used ‘spore probes’ constructed by immobilising a single spore at the end of a tipless AFM cantilever. It was found that adhesion was reproducible at a relative humidity of 64%, but that it showed substantial variability at a relative humidity of 33%, findings that are consistent with capillary forces playing a dominant role in the adhesion process. The technique should prove useful both in the evaluation of different types of filter materials and in assessing the effect of environmental conditions on spore removal efficiency.