A lot of people have rather negative things to say. I think in the Muslim community there needs to be a greater discussion on what 'free-mixing' actually means. As a nurse, you are a health care professional. In the UK, this is heavily emphasised and is one of the statements as part of the Code (NMC). This would not be considered free-mixing. The free-mixing that Islam prohibits is the same free-mixing that the NMC board would be against. Flirting, excessive and unnecessary touching, etc. As a nurse if this happens I would be concerned regardless of religion and spirituality.
So, yes. It is 'halal' to be a nurse. Islam is not there to make life complicated. There are times you will have to work with male patients, this is fine unless you personally feel uncomfortable for any reason (which does happen especially in adult nursing where some male patients get 'excited' by nurses who are majority female (but even in these situation, as hard as it is try your best to keep professional unless it gets out of hand, and then escalate).
Saving one persons life is like saving all of mankind. Nursing has given me such stress sometimes but the empathy and beauty of the world that I've picked up make me appreciate life, nursing practices, mankind and God more. It is crazy how much the human body can compensate when something is wrong and it is crazier how far we've come with us medical technology and as a society caring for individuals.
Trust me, our Muslim community here in the West need a lot more discussing and education regarding simple things like 'free-mixing' but I would say if there's any career that enraptures what it means to biologically be a woman, it is nursing. That's not to say its a 'woman's job', Hell no! We need more male nurses! In the same way that women may feel uncomfortable with a male providing care, male patients may also feel uncomfortable with a female providing care.