What would one do to match the termination of a string?

For instance
PHP Code:
$string "A sentence. More words. Dot.End.";
$string preg_replace("#(\.[\sE])#""[INS]$1"$string);
echo 
$string
Results in:
Code:
A sentence[INS]. More words[INS]. Dot[INS].End.
How would one match the end of the string as well as "\s" and "E", so that it becomes:
Code:
A sentence[INS]. More words[INS]. Dot[INS].End[INS].