get the ISO 8601 with seconds.decimal-fraction-of-second date in php?

I echo this :

  php> echo date("Y-m-d\TH:i:s");
      2011-05-27T11:21:23

How can do with date function to get this date format:

2011-01-12T14:41:35.7042252+01:00 (for example)

35.7042252 => seconds.decimal-fraction-of-second

I have tried:

php> function getTimestamp()
 ... {
 ...         return date("Y-m-d\TH:i:s") . substr((string)microtime(), 1, 8);
 ... }

php> echo getTimestamp();
2011-05-27T15:34:35.6688370 // missing +01:00 how can I do?