  In recent years, the rising demand for close interaction with electronic
devices has led to a surge in the popularity of wearable gadgets. While
wearable gadgets have generally been rigid due to their utilisation of
silicon-based technologies, flexible semiconducting fibre-based transistors
will be needed for future wearables as active sensing components or within
microprocessors to manage and analyse data. Two-dimensional (2D) semiconducting
flakes are yet to be investigated in fibre transistors but could offer a route
toward high-mobility, biocompatible and flexible fibre-based devices. Here we
report the electrochemical exfoliation of semiconducting two-dimensional (2D)
flakes of tungsten diselenide (WSe2) and molybdenum disulfide (MoS2). The high
aspect ratio (>100) of the flakes achieves aligned and conformal flake-to-flake
junctions on polyester fibres enabling transistors with mobilities ~ 1 cm^2
V^-1 s^-1 and a current on/off ratio, Ion/Ioff ~ 10^2 - 10^4. Furthermore, the
cytotoxic effects of the MoS2 and WSe2 flakes with human keratinocyte cells are
investigated and found to be biocompatible. As an additional step, we create a
unique transistor knot architecture by leveraging the fibre diameter to
establish the length of the transistor channel, facilitating a route to scale
down transistor channel dimensions (100 {\mu}m) and utilise it to make MoS2
fibre transistors with a human hair that achieves mobilities as high as {\mu} ~
15 cm^2 V^-1 s^-1.
