'cannot be duplicated' is correct and can be used in written English.
For example, "This unique item cannot be duplicated."
The local phone companies have networks that cannot be duplicated.
Note: Assignments currently cannot be duplicated for discussions and quizzes.
Bone is a nanoscale composite with mechanical properties which cannot be duplicated by monolithic materials.
The kinship you establish with those with whom you share this camaraderie cannot be duplicated.
Much of what he needs in a case, he added, cannot be duplicated.
In South America, it's axiomatic that our structure and style cannot be duplicated.
This approach, however, has a built-in dilemma since nature cannot be duplicated in captivity.
Richard Williams did not relinquish control, and this is the part of the Williams-sister model that cannot be duplicated.
RIM's network, however, has one significant feature that probably cannot be duplicated.
Bermuda's climate cannot be duplicated, but you can provide the other things that make island nasturtiums glad.
Many specialty stores have carved out niches that cannot be duplicated online, selling rare records or used discs.
