Nightshade (Nightshade Series #1)

Jillian Conrad never believed in vampires-until she was unwillingly injected with a serum that was supposed to act as a deadly poison to them. Now, tormented half-vampire Declan Reese wants her blood to destroy the undead kingdom. Unfortunately, the serum has also made her blood irresistible to all vampires-including Declan, whose desire for Jillian is more than mere hunger.