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Mr David P Mabwa is a second year PhD student, in the Mid-Infrared (MIR) Photonics group at The University of Nottingham, UK. He has a background in Biomedical and Material Science and is now working towards developing a coherent chalcogenide-based endoscopic probe that utilises the MIR principles, to assist in the diagnosis of cancerous tissue.

David Mabwaa

David Mabwaa, Colin J. Scotchfordb, Rong Suc, David Furnissa, Zhuoqi Tanga, Teo Kubienaa, Harriet Parnella, Trevor M. Bensona, Richard Leachc, Angela B. Seddona,aMid-Infrared Photonics Group, Advanced Materials Research Group, Faculty of Engineering, University Of Nottingham, Nottingham NG7 2RD, UK bAdvanced Materials Research Group, Faculty of Engineering, University Of Nottingham, Nottingham NG7 2RD, UK
cManufacturing Metrology Team, Faculty of Engineering, University Of Nottingham, Nottingham NG8 1BB, UK

With the aim of providing point-of-care diagnosis via mid-infrared (MIR) sensing or MIR hyperspectral imaging, Ge-Sb-Se glass optical fibres may be used to transmit MIR light from 2.5-13 µm for vibrational molecular detection [1]. However, due to the presence of metalloid components, the cytotoxicity of these optical fibres require investigation. The aim of this study is therefore to investigate the cytotoxicity of Ge-Sb-Se optical glass fibres on 3T3 mouse fibroblast cells. To achieve this, fibres exposed to four different pre-conditions are used: as-drawn (A.D), propylamine etched (P.E), oxidised-and-washed (O.W) and oxidised. The oxidised fibres are treated with H2O2(aq.) and dried to produce the oxide layer; this is then either washed off, or left on the glass surface. Cellular response is investigated via 3-day elution and 14-day direct contact experiments. Cell metabolic activity and growth patterns are observed using the neutral red (NR) assay and scanning electron microscopy (SEM). In direct contact experiments, confluent cell layers are observed on as-drawn, P.E and O.W fibres after 14-days while no cells were observed on the oxidised surfaces, see Figure 1. This is reflected in the elution trials. A significantly higher cell viability is observed in A.D, P.E and O.W eluates after 3-days, when compared with oxidise eluates. The primary cause of toxicity is believed to result from the significant pH change that takes place once the oxide is dissolved into the growth media, from 7.290 to the acidic 3.463. The newly acidic extracellular environment results in the activation of the c-Jun N-terminal kinase (JNK) pathway, an important regulator of various cellular processes, including apoptosis, in 3T3 cells [2, 3]. We therefore conclude that Ge-Sb-Se glasses are not toxic towards 3T3 mouse fibroblasts and toxicity only arises when an oxide layer is forced to develop on the glass surface. Such oxide growth does not occur under normal ambient conditions, nor on exposure to pH neutral water, but on exposure to a strong oxidising agent like H2O2(aq.).

Figure 1. Scanning electron micrographs of cell growth on Ge20Sb10Se70 atomic % fibres over a 14-day time period. A1-A4 = A.D fibre, B1-B4 = P.E fibre, C1-C4 = O.W fibre, D1-D4 = O.10, E1-E4 = O.30, F1-F4 = O.60 fibre.

References
[1] A. B. Seddon, “Mid-infrared photonics for early cancer diagnosis,” in 16th International Conference on Transparent Optical Networks (ICTON), Graz, 2014.
[2] L. Xue and J. M. Lucocq, “Low extracellular pH indices activation of ERK 2, JNK, and p38 in A431 and Swiss 3T3 cells,” Biochemical and Biophysical Communications, vol. 241, pp. 236-242, 1997.
[3] J. Liu and A. Lin, “Role of JNK activation in apoptosis: A double-edged sword,” Cell Research, vol. 15, pp. 36-42, 2005.

Figure 1. Scanning electron micrographs of cell growth on Ge20Sb10Se70 atomic % fibres over a 14-day time period. A1-A4 = A.D fibre, B1-B4 = P.E fibre, C1-C4 = O.W fibre, D1-D4 = O.10, E1-E4 = O.30, F1-F4 = O.60 fibre.