2.5.1. MTT Cell Viability Assay

The MTT assay is used to measure cellular metabolic activity as an indicator of cell viability, proliferation and cytotoxicity. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) is a yellow dye, which is reduced by cellular enzymes to the blue product formazan. As the transformation is possible in viable cells only, the amount of blue formazan formed is proportional to the number of viable cells.

To evaluate the viability of cells grown with T-RGO, MTT assay was carried out using the human macrophage cell lines (Raw 264.7, ATCC, TIB-71). As per the instructions of the manufacturer (Thermo Fisher Scientific, USA), cells were grown in 96 well plates and treated with different volumes of 1 mg/mL of nanocomposite. After incubation, cells were treated with 100 μL of MTT dye solution and incubated at 37 °C for a period of 4 h. Thereafter, solvent dimethyl sulfoxide (DMSO) was added to dissolve the formazan crystals. Readings were taken at a wavelength of 570 nm. The absorbance was converted into cell viability (%) using Eq. (3) [22, 23].

where OD is the optical density for absorbance measurements.