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:Eva-green (Biotium) was used for detection, and 0.1% Tween 20, 0.1 mg/mL BSA, and 5% DMSO were added to the PCRmix as described (Khanna et al., 2007).
Category: