...but using ctyped Ice feels like cheating, so you can make a 9-pixel nuke. 3x3 destructible square (Gold, Goo, Metl, etc.). Replace center pixel with high-life Deut, top right with a sparkable metal, top center with a Pbcn with ctype of Dest. Can be turned and flipped, still works.
2 pixels. A sparkable metal as a trigger (Metl, Ttan, Pscn, Nscn, etc.) and a pixel of high-tmp Ice with ctype of Sing (131) (aka Snow/Ice Sing), both at -1C. Spark for explosion.