Vortex mixer

The images of the surface morphology of the gold nanorods (AuNRs) were obtained using an Hitachi HT 7800 transmission electron microscopy system (TEM) (Hitachi, Japan). An incubator was purchased from Shanghai Bosun Industrial Co., Ltd. The constant temperature water bath was provided by Shanghai Yiheng Scientific Instrument Co., Ltd. The blue-shifts of the longitudinal localized surface plasmon resonance (LLSPR) of the AuNRs were measured using a Bio-Tek Synergy HTX microplate reader (Winooski, USA), and using a Vortex Mixer purchased from Eppendorf Company (Hamburg, Germany).

Faecal steroids were extracted using the methanol-based procedure outlined in Palme et al. (2013 ). Lyophilisation was not necessary due to the consistency of golden hamster faeces. After homogenisation of each faecal sample (by using a mortar), 50 mg were weighed and stored at − 20 °C until assayed. Each faecal sample was shaken on a vortex (Velp Scientifica Vortex mixer, USA) at 20 rpm with 1 ml of 80% methanol and subsequently on a thermomixer (Eppendorf Thermomixer compact 5350, Eppendorf, Germany) at 500 rpm for 15 min. The suspension was then centrifuged at 2500×g for 5 min (Eppendorf centrifuge 5424, Eppendorf, Germany). Faecal cortisol metabolites were quantified in an aliquot of the extract (50 μl further diluted 1:10 with assay buffer) using a group specific 11-oxoaetiocholanolone enzyme immunoassay (EIA measuring glucocorticoid metabolites with a 5β-3α-ol-11-one structure) successfully validated for the golden hamster (Chelini et al. 2010 (link)). Details of this assay were first described by Möstl et al. (2002 (link)). Concentrations of FCM are expressed as nanograms per gram faecal dry matter.