Highly conductive wet-spun poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) fibres, a prior concept developed by Reid et al., were adopted for pH analysis. With an optimised polyaniline (PANi) coating, these fibres displayed Nernstian responses (in a solid-state sensor containing a fabricated quasi-reference electrode) across a pH range of 3.0 to 9.0 when in contact with both pH-adjusted artificial sweat matrix and human plasma; the fibres had additional desirable antibacterial and biocompatible properties. To date, wet-spun PEDOT:PSS fibres have not been adopted in a chemical sensing capacity. This invention provides opportunities for future wearable, fibre-based sensors capable of real-time, on-body pH sensing (to monitor wound healing and skin disease). However, a primary limitation was poor tensile strength (32 ± 11 MPa), which could lead to fibre breakages in real-life wearable applications. To overcome this limitation, another substrate, modified electrically conductive cotton, was explored.
A simple and effective ?dipping and drying? approach involving cotton yarns in a dispersion of PEDOT:PSS and multi-walled carbon nanotubes (MWCNT) resulted in the development of a flexible, highly conductive cotton fibre. Subsequent PANi deposition yielded electrodes with significant biocompatible and antibacterial properties that could be fabricated (alongside quasi-reference electrodes) into a solid-state wearable pH sensor, which achieved rapid, selective, and Nernstian responses (-61 ± 2 mV pH-1) over a wide pH range (2.0 ? 12.0), even in pH-adjusted artificial sweat matrix and human plasma. To date, there is no prior published research that reports on this combination of conductive materials and cotton in such a sensing capacity. Furthermore, few previous reports have described conducting cotton threads with low enough electrical resistances to allow the electrodeposition of functional polymers, like PANi, whilst retaining the necessary flexibility for wearable applications. Thus, this development represents an important progression towards the realisation of real-time, on-body, wearable sensors.