You can create an electrical charge with rubbing.
Rubbing an object of correct composition (nonconductor) can impart a static charge. Balloons are one well known object for which this is true. Certain socks I own also avidly collect charge while in the dryer. The charged item can then attract other objects, as the balloon in the above images has done. For my socks, it is ambient pet hair.
Earlier in the story have there be some piece of equipment which is always dirty - because of its composition and that of the spacefarers gloves, it tends to accumulate charge and then attract dust; the spacefarers marvel that there is so much dust about. There could be a scene where one of them examines the dust under a microscope, suspecting that it is mostly dandruff from one particular individual - he is correct in his suspicion, but among the flakes he finds something different and very unusual - a defunct microscopic alien mote and harbinger of what is to come.
Your spacefarer is aware that this piece of dirty equipment when charged could attract (albeit defunct) alien motes. Faced with active motes, she charges up this piece of equipment and throws it into the swarm.
More than you asked, but when the above maneuver works and establishes the principle, there is something else they can use on the aliens.
The aged among you might remember using these anti-static guns on photograph records - they are also rubbed by their sleeves and collect charge and pet hair. These nifty tools sap the charge and cause the hair to fall away. A home-brew device like this would be a great weapon against motes which organize themselves and move using electical charges.