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Imparting electrical conductivity to a plastic optical fibre based on poly(methyl methacrylate)

In this study, as a preliminary work on the realisation of an optical/electrical acupuncture needle, we have attempted to impart electrical conductivity to a plastic optical fibre (POF) by coating a thin gold layer on its surface. First, we investigated the adhesion between the gold and two different substrates, poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)), which were used as the core and the cladding of POF, respectively. To enhance the interfacial adhesion between the gold layer and the substrates, the following two different approaches were applied: low-power plasma treatment and physical surface roughening. A 50 nm-thick gold layer was deposited by ion sputtering onto both the substrates and also onto the 0.5 mm-diameter POF. The variation of wettability and adhesion according to the plasma conditions were investigated through water contact angle measurement and cross-hatch cut testing. Despite the decreased contact angles of the substrates after Ar or O2 plasma treatment, both polymers exhibited very poor adhesion to the gold layer. However, substrates roughened by sandblasting showed 3B class adhesion to gold in the cross-hatch tape test results. The POF that was gold-sputtered after sandblasting showed an electrical conductivity of 1.35 × 103 S cm−1 without any significant optical loss. This fabrication technique may be used for developing a medical needle capable of simultaneously applying electrical and optical stimulus.