Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Oxidized graphene nanomaterials were demonstrated to be able to serve as efficient carrier systems for the targeted delivery of chemical drugs [19-22] and biomolecules including proteins, DNA and siRNA [23-26] Furthermore, the potential of GO for biosensing [27,28] and bioimaging applications is being explored [29-32].
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