help.... regex to validate password.

Hi All,
I have a password strength validator regex ;- "^(?=.*\d)(?=.*[a-z])(?=.*[A-Z])(?!.*\s).{8,16}$"

This validates as ;-
requires one lower case letter, one upper case letter, one digit, 8-16 length. (mandatory)
allows all special characters but optional.
do not allow any spaces in between.
But allows leading or trailing spaces (this i dont want this actually)......


Please tell me how to modify this regex to avoid from allowing leading or trailing spaces....
TIA

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