Helios zeta uv vis spectrophotometer

The absorption spectrum of each nanocomposite was detected using a Helios Zeta UV-Vis spectrophotometer (ThermoFisher, Pittsfield, MA, USA). The range of the wavelength was from 400 to 600 nm, where 520 nm is the typical absorption wavelength of Au nanoparticles. Origin Pro 8 (OriginLab Corporation, Northampton, MA, USA) software was applied to further quantify the data.

The methodology proposed by Miller [20 (link)] and Sansano et al. [21 (link)] for reducing sugars determination was used. An amount of 0.3 g of sample was mixed with 2 mL of 80% ethanol, vortexed, and allowed to stand for 30 min. It was centrifuged at 5000× g for 5 min (5810R, Eppendorf, Hamburg, Germany). The extraction was repeated twice, and the extracts were pooled. An aliquot of 500 µL was taken and mixed with 1 mL of DNS reagent (10 g/L of 3,5-dinitrosalicylic acid, containing 300 g potassium sodium tartrate tetrahydrate and 16 g sodium hydroxide). It was heated in a water bath (J.P.Selecta, Barcelona, Spain) at 100 °C for 5 min and then cooled to room temperature. The sample was diluted with 6 mL of distilled water and the absorbance was measured at 546 nm (Helios Zeta UV-VIS Spectrophotometer, Thermo Fisher Scientific, Waltham, MA, USA). Results were expressed as g glucose/100 g dry basis using a standard curve.