The short answer is "Not that was ever admitted" the long answer is much more complex than this.

So we know that during WW2 British forces used Mustard Gas^1 on their Irish and native British Indian Army soldiers to see if "Indian" skin compared to "British" skin in regards to the damage Mustard Gas inflicted on it^2. It is unclear if all of the subjects involved in these tests were volunteers or not.

We also know that on May 6th 1953 Ronald Maddison^3 a 20 YO Royal Air Force engineer died after volunteering to be part of a Sarin gas test. An inquest 51 years after his death^4 found that volunteers testing chemical weapons(some of which may have been prisoners, most of which were volunteer airmen) between 1939 and 1989 were not properly informed of the risks of the experiments and exactly what the experiments were. The inquest found that Ronald Maddison had been "Unlawfully killed" and the MOD accepted that he had died due to "gross negligence in the planning and conduct of the experiment"^5 they did challenge that it was due to lack of informed consent.

We know the USA has done extensive research on prisoners (volunteered or otherwise^7). The obvious candidates are, of course, Nazi Germany^8 the subsequent trial and conviction of the Doctors involved^9 and Unit 731 but there are many more experiments conducted post WW2 including:

Stanford^10 Prison^11 Experiment^12 (Didn't actually take place in a prison, but very interesting reading all the same)

Project MKULTRA^13

The Tuskegee Syphilis Study^14

A little more info on how lack of informed consent can have disastrous results^15.

Hope this partially answers your question. Sorry I couldn't dig up direct evidence either way.