Disclosed herein is a multilayer nanocrystal structure comprising a nanocrystal alloy core comprising two or more nanocrystals and including an alloy interlayer formed at an interface between the two or more nanocrystals, and one or more layers of nanocrystal shells formed sequentially on the surface of the nanocrystal alloy core, wherein the nanocrystal shells each have different band gaps. After the switching to the insurance mode, determination is made whether or not the amount of bet credits matches the maximum bet amount. The detecting circuit can switch the connection polarity if required to correct it.