Analysis of bacterial growth showed that the toxicity of silver nanospheres is higher than that of gold nanospheres. The toxicity of silver nanoparticles is dependent on their concentration, whereas in the case of gold nanoparticles, there is no significant toxic effect. Therefore, the described microplate assay could be used as a rapid and sensitive method for detection of bacterial growth inhibition.

Background: Graphene magnetite nanocomposites (G/Fe 3 O 4 ) exhibit light photothermal conversion upon enhancement by 808 nm IR laser excitation. We evaluated the cytotoxic and photothermal effects of G/Fe 3 O 4 on a HepG2 human liver cancer cell model. Methods: Graphene nanosheets (rGO), magnetite nanoparticles (Fe 3 O 4 ), and G/Fe 3 O 4 were prepared by chemical methods and characterized using transmission electron microscopy, Raman spectroscopy, zeta analysis, and vibrating sample magnemeter. Dark and light cytotoxicity were screened with colorimetric Sulforhodamine B cell viability assay after 24 and 48 hours. DNA fragmentation and some apoptotic genes on a transcriptional RNA level expression were performed. All prepared nanomaterials were evaluated for their photothermal effect at concentrations of 10 and 50 µg/mL. The power density incident on the cells by 300 mW 808 IR diode laser was 0.597 W/cm 2 . Results: Treatment of HepG2 with 400 µg/mL of rGO, Fe 3 O 4 , and G/Fe 3 O 4 showed alteration in cell morphology after 24 hours of cell treatment and revealed toxic effects on cellular DNA. Evaluation of the cytotoxic effects showed messenger RNA (mRNA) in β-actin and Bax apoptotic genes, but no expression of mRNA of caspase-3 after 24 hours of cell exposure, suggesting the involvement of an intrinsic apoptotic caspase-independent pathway. A photothermal effect was observed for G/Fe 3 O 4 after irradiation of the HepG2 cells. A marked decrease was found in cell viability when treated with 10 and 50 µg/mL G/Fe 3 O 4 from 40% to 5% after 48 hours of cell treatment. Conclusion: Results indicate that G/Fe 3 O 4 nanocomposite was effective at transformation of light into heat and is a promising candidate for cancer therapy.

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