Driver not specified

HI,
I have add the external database into my settings.php,
but have this error
"
Driver not specified for this database connection: mysample

Here is my db config

$databases = array (
  'default' => 
  array (
    'default' => 
    array (
      'database' => 'sample_1p',
      'username' => 'sample_2p',
      'password' => 'mypass',
      'host' => 'localhost',
      'port' => '',
      'driver' => 'mysql',
      'prefix' => '',
    ),
  ),'mysample' => 
  array (
    'mysample' => 
    array (
      'database' => 'sample_dio',
      'username' => 'sample_diy',
      'password' => 'mypass',
      'host' => 'localhost',
      'port' => '',
      'driver' => 'mysqli',
      'prefix' => '',
    ),
  ),
);