Possible Clues:

• Undercover spy misplaced clue? It’s a little matter
• Small group of atoms
• Spy hugs English copper, having left bit of stuff
• Little matter of mark left in what's tipped?
• Dimmu Borgir "The Demiurge ___"
• Ion of a sort
• Bit of a compound
• Simplest unit of a chemical compound
• Spot change required in clue for 'tiny amount'
• Animal clue: odd little thing