regex/preg_replace() difficulty

Regular Expressions: How can I indicate that the contents of a term (user input*) needs to be treated as 'non-operators/control characters' (as *word* to match in that exact way)? (* Because the term is a user's input I can't escape the control characters manually.) Example: $result = preg_replace('/('.$termWithOptionalBold.')(<\/?span[^>]*>)*()/si', '<span class="highlight">\1</span>', $result); [If $termWithOptionalBold is a "." (period) for example, any char will be matched--instead of only the "."] Any suggestions? Thanks a lot for your effort! Best wishes, jonas PS: Somewhere I read that '\Q' would do something like that but it didn't work.