Herein, we report the first evidence showing the superior therapeutic and diagnostic effects of 2D moiré superlattice nanosheets of luminescent copper nanocluster assemblies on cancerous HeLa cells compared to the parent nanoclusters or their 2D assemblies. These superlattices, at very low concentrations of the metal (10.15 ± 2.06 μM), exhibited higher cytotoxicity, leading to cell disintegration. Importantly, this compound did not significantly impact healthy cells. This discovery suggests a potential method for designing nano-drugs and highlights the usefulness of moiré superlattices in healthcare theranostics.