When searching for BINARY data (such as an Active Directory objectGUID) you need to escape each hexadecimal character with a backslash.
The following command line run of ldapsearch shows:
ldapsearch -b "dc=blahblah,dc=com" "(objectGUID=\AE\C3\23\35\F7)"
In PHP, you need to escape the escape for the backslash:
ldap_search($ds,"dc=blahblah,dc=com", "(objectGUID=\\AE\\C3\\23\\35\\F7)");