If you're going to bring in, put it in a professional looking binder. The interviewers will see it and might ask to see the contents. If not, there may be an opportunity to refer to a piece in it as a response to a question. Ask if they would like to see the artifact. Don't push it on them. If that opportunity doesn't arise or they reject your offer, you'll have an opportunity at the end of the interview when they ask if you have any questions. Again, ask them If they'd like to see it. Personally, when I'm interviewing I find portfolios to be a distraction.

As an interviewer, I have also found portfolios to be cumbersome when introduced by the candidate, especially on a first round interview.  Usually, first rounds are short and meant to screen candidates.  The interviewers are meeting many candidates, and are  on  a tight schedule.  A portfolio will slow the pace at which the interview team must work, and will therefore be a negative in the minds of the team.   It is better used in a one to one situation, with conversation about how supervisors on your reference list would comment about the work in the portfolio.  This gives the interviewer content for the reference call. 

Thank you for the advice. I agree with you on the time constraints. There never seemed to be an opportunity, during the interviews I have been on, to present it, so I wondered of their importance. I think I will create one just to have for myself. It will be helpful to have a record of what I've done to help me prepare for future interviews. Sometimes it's hard to remember everything you've done over the course of your career.