Which of these is not a method used for introduction of plasmid into host cells?

Polymerase chain reaction

Polymerase chain reaction (PCR) is not a method used for the introduction of a plasmid into host cells.

PCR is a laboratory technique used to amplify a specific DNA sequence by producing multiple copies of that DNA segment. It does not involve the direct introduction of plasmids into host cells.

On the other hand:

• Gene gun is a biolistic method used to deliver DNA or plasmids into cells by high-speed microprojectiles.
• Microinjection involves physically injecting genetic material (such as plasmids) into cells using a fine micropipette.