It's probably technically feasible to use this ink as an antenna for an implanted RFID chip, they're not much larger than a grain of sand after all, but do you

It's probably technically feasible to use this ink as an antenna for an implanted RFID chip, they're not much larger than a grain of sand after all, but do you REALLY want to do that? Once you have your key of identification implanted you just created a seriously disturbing incentive for someone (without a reader to clone your RFID) to do you grievous harm when they simply want to steal your stuff. It probably won't happen to you or many other people but it's enough of a concern that I'll put up with the occasional misplaced key instead. tl;dr I'd love to hack your tattoo and get in your front door.