Nested json in vb.net

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JSON

I need to create a json string :
{"materials": [{""Article"":"53424","Description":"blabla","Price":25,"Unit":"3"}]}

but I only get
[{""Article"":"53424","Description":"blabla","Price":25,"Unit":"3"}]


How do I include the parent {"materials": into my string?

What I have so far:

Dim NewMaterial As New List(Of materialdetails)()
        NieuweMaterial .Add(New materialdetailsWith {.Article = "45147", .Description = "Dbla", .Price= 50, .Unit = "dfdk"}) 

        Dim materialen As New List(Of materialen)()

Public Class materialdetails
    Public Property Article As String
    Public Property Description As String
    Public Property Price As Decimal
    Public Property Unit As String
End Class
Public Class Parent
    Public Property parenttitle  As String
    Public Property materialdetails As List(Of materialdetails)()

End Class

As you can see I am struggling to get the parent of the parenttitle in the string. Please help with a simple example on how you would do this?
Thanks for any answer.