This has already been observed by Wörle-Knirsch et al. [24]. In their work, they showed that single-walled carbon nanotubes (SWNTs) were found to be non-toxic when using assays

such as LDH, annexin V, and PI staining, mitochondrial membrane potential, as well as other tetrazolium Silmitasertib concentration salt-based water-soluble assays such as WST-1, XTT, or INT. However, the MTT assay was the only assay which displayed SWNT cytotoxicity. In addition, real-time bright-field microscopy (Figure  3) did not show any morphological features suggestive of cytotoxicity, such as blebbing, membrane rupture, pyknosis, or fragmentation, for concentrations 1 to 10 3-MA datasheet μg/ml. Also, several cells were observed undergoing mitosis (data not shown). These findings suggest that at these low concentrations,

the sulfonation process affords protection to cells against the cytotoxic effects of graphene, similar to the observed protein corona-mediated mitigation of GO cytotoxicity recently published by Hu et al. [17]. However, there was a drastic change in cell morphology for concentrations of 100 μg/ml which shows evidence of pyknosis and fragmented, spindle-like cell features for the SNU449 cell Lonafarnib price lines. In these regard, we suggest that 10 μg/ml should be the upper concentration limit when using SGSs for full biocompatibility and that more work should be undertaken to understand the exact death mechanism of SGSs at concentrations >10 μg/ml. We initially sought to investigate this through the use of propidium iodide and annexin V FITC staining Tyrosine-protein kinase BLK with cell flow cytometry, but as mentioned in the ‘Methods’ section, we could only perform one time slot (24 h) with one cell line (SNU449) at two concentrations (10 and 100 μg/ml). Figure 3 Optical images

of SNU449 cells exposed to SGSs for 72 h. Images depict control cells (no SGSs) (A) and 1 (B), 10 (C), and 100 (D) μg/ml concentrations. Propidium iodide is a cell impermeable fluorophore that can bind to the DNA of cells which have lost nuclear and plasma membrane integrity. From our fluorescence-activated cell sorting (FACS) analysis shown in Additional file 1: Figure S5, we found that with an increasing concentration of SGS nanoparticles, the intensity of positive PI-stained cells increased from approximately 1.9% to 10.3%, suggesting slight cell membrane structural damage, while the majority of cells remain healthy and viable at approximately 93% ± 2.4%. Phosphatidylserine (PS) externalization is an early event in the apoptosis cascade. Annexin V binds to PS with high affinity. Our FACS analysis hence also demonstrates that very few cells were annexin V positive 24 h after exposure to SGS which ruled out apoptosis as a significant cell death mechanism, as was similarly reported for GO materials [16, 18]. Cellular internalization of SGSs Figure  4 depicts high-resolution SEM images of both SNU449 and Hep3B cancer cells after exposure to SGS at a concentration of 10 μg/ml for 24 h.