The F# dynamic operator (?)
allows you to pass string parameters without using the quotes, achieving a similar syntax to C# dynamic, but you need to define it first for your concrete use case, the compiler just provides the syntax. Try this:
let (?) (parameters:obj) param =
(parameters :?> Nancy.DynamicDictionary).[param]
type ParameterModule() as this =
inherit NancyModule("/{about}")
do this.Get.["/"] <- fun parameters -> sprintf "Hello %O" parameters?about :> obj