Background

I am a computer programmer working as a graduate student under a biochemistry department in a university affiliated hospital. So far I have had a very successful career, having written novel and published data mining algorithms on top of programming hardware for spectrometers. I am also tall (around 6'2") and fit at around 178 lbs. I don't think I'm particularly attractive (facially), but in the past I have not had a problem finding casual relationships.

The problem

Some people at work (school?) question my single status - particularly the female staff (the biochemistry lab is 50/50 male/female, however the hospital is heavily female dominated) and I am starting to feel that it is impacting my career and reputation. Examples:

A woman (who is married) told me directly that she feels a man who prefers singledom is not "normal".

My supervisor (PI) told a female co-worker not to talk to me (she revealed this to me the other day and asked why he would say this).

A woman whose advances I purposely ignored is accusing me of being gay.

Why I'm single

I personally have little to no interest in relationships. I have had a few short term relationships in the past and realized that relationships are not for me. I am an extremely introverted individual with clear structure in my life and in the past I have found that all the emotional needs, spontaneity, ups and downs, etc., of relationships have left me extremely depressed.

Like most humans, I have sexual needs. I found these could be met relatively easily (and on my ordered schedule) through online dating apps which further compounds my decision to avoid long term relationships.

The question

How can I reply to people in such a way that it leaves little to their imagination (i.e. prevents further rumor generation)?