Which is not a proper method for minimizing PCR contamination?

The answer is focused on the importance of maintaining strict separation between pre-PCR and post-PCR areas to prevent contamination from amplified products. Combining these two areas into the smallest practical space increases the risk that contaminants from the post-PCR area could inadvertently contaminate pre-PCR samples.

In molecular biology practices, especially in PCR procedures, any carryover contamination from a previous reaction could lead to false positives in subsequent experiments because even minute amounts of DNA can be amplified. Therefore, keeping pre-PCR workflows physically separate from post-PCR processing areas is a crucial standard in laboratory protocols to ensure the integrity and reliability of the results.

The other methods described, such as frequent cleaning with bleach, aliquotting reagents into single-use samples, and using aerosol barrier pipet tips, are established practices in PCR work aimed at reducing the likelihood of contamination. Each of these methods contributes in its own way to minimizing risk; for example, cleaning surfaces helps eliminate residual DNA, aliquotting helps prevent contamination of a stock reagent, and barrier tips can prevent aerosol transmission of contaminants between samples during pipetting. However, without a clear physical separation of work areas, even these precautions are less effective.