You can't give up an attack to cast Detect Evil.
A paladin can use a move action to Detect Evil on a single target.
Assuming the paladin also has a way of attacking said target without moving (for example because they're already adjacent to the target, or because they can attack from a distance), or to move to the target as a swift action (note: Smite Evil is also a swift action, so this way you don't get to Smite this round), then they can use the remaining standard action for a single attack. But it would be just one attack, even if you usually had three, four or five.