jQuery Search in specific td class

My search currently searches through all the table fields - I would like it to only search the ones that have a td class of test.

Im using

$('input#SearchBox').quicksearch('table#tablesorter-demo tbody tr');

This searches all the fields in the table, I have tried:

$('input#SearchBox').quicksearch('table#tablesorter-demo tbody tr td.test');

but this just stops the whole search from working.

I also tried:

'$('input#SearchBox').quicksearch('table#tablesorter-demo tbody tr', {'selector': 'td.test'});

But this doesnt find anything…

Ideas appreciated?