Ag–Au bimetallic nanocomposites with 5, 8, 13, 17 and 21 nm thickness of Au shell were synthesized.

SERS signal enhancement 10⁶–10¹³ using crystal violet analyte molecule was achieved.

Ag@Au NCs with 30 nm Ag core and 8 nm Au shell acts as excellent SERS substrate.

Ag@Au NCs with 30 nm core and 8 nm shell enhanced SERS signal of order 10¹³.

The maximum enhancement of Raman signals of crystal violet was observed to be of order 10¹³.