An air filter system and an air filter therefor are provided for use in a building with first and second zones separated by a wall-door system having a wall with a door therein. The head has a vibrating mechanism which, in conjunction with the motor, vibrates the distal portion at a sonic frequency. A bistable multivibrator reverses the direction of the charge current, to charge the internal capacitor when the voltage decreases below the second threshold level, and to decharge the internal capacitor when the voltage increases above the first threshold level. The processing circuit generates an internal atomic operation to replace the atomic sequence. These features render the assay and screening methods that employ the labeled substrates especially suited for use in high throughput assay formats. The present invention also describes methods of using such an apparatus to supply oxygen to a wound for improved wound healing.