I am looking for a way to check if an exact string match exists in another string using Regex or any better method suggested. I understand that you tell regex to match a space or any other non-word character at the beginning or end of a string. However, I don't know exactly how to set it up.

Search String: t

String 1: Hello World, Nice to see you! t
String 2: Hello World, Nice to see you!
String 3: T Hello World, Nice to see you!

I would like to use the search string and compare it to String 1, String 2 and String 3 and only get a positive match from String 1 and String 3 but not from String 2.

Requirements:
Search String may be at any character position in the Subject.
There may or may not be a white-space character before or after it.
I do not want it to match if it is part of another string; such as part of a word.

For the sake of this question: I think I would do this using this pattern: /\bt\b/gi

/\b{$search_string}\b/gi

Does this look right? Can it be made better? Any situations where this pattern wouldn't work?
Additional info: this will be used in PHP 5