Immaculate conception refers to Mary. She was conceived without sin. Here are some biblical basis
1)Genesis 3:15 I will put enmity between you and the woman, and between your offspring and hers; They will strike at your head, while you strike at their heel.
This passage is after the fall. The woman referred to here is Mary. She will have enmity with the devil. Deep hate for the devil, being sinless.
2)Luke 1:28 28And coming to her, he said, “Hail, full of grace! The Lord is with you.
“Full of grace”, no sin.