'Particular' is usually used as an adjective to indicate one definite item. 'I wanted that particular car because I liked the color." It can also be used in the negative, to say that there is no item that we are definitely talking about, or that what we are talking about could be any number of items. 'I'm not looking for any pen in particular - I just need one right now to finish my notes." = Any pen will be satisfactory. It can also be used to describe a person as being very careful in their choices. "She was very particular about her clothes and made sure that there was never a wrinkle or loose thread on what she wore." 'Detail' is used to as a noun describe some element that is part of a whole. It is used many times as a general term. 'He gave the report in full detail." = He gave all the individual items in the report. Usually if we are talking about a single item that is part of a whole, we will talk about 'one detail' or 'one or two details'.

particular = adjective detail = noun