The Kaiju drift reveals the breach is secured by DNA fingerprinting. From what I can tell, the DNA matching doesn't require taking a sample from Kaiju.
I'm only familiar with DNA matching through taking samples:
- blood from finger prick
- cells from cheek swab
- hair follicle
- (and fictional) blood from ambered mosquito
Is there DNA matching research on which this is based? Can (Kaiju) DNA be scanned from a distance?