A method for regulating sample surface charge has been proposed in this invention. In some implementations, a method includes determining a triggering event associated with a subject person. An indexing drive system controls incremental rotation of the Ferris wheel mechanism through a predetermined sequence of steps, and a cork feeder introduces a single synthetic cork stopper into each of the carriers as empty ones of the carriers are presented one-by-one at the cork feeder. The at least one processor further obtains a determination result as to whether a sample which has been tested by the at least one first module is necessary to be processed by the at least one second module.