Dissolved oxygen monitoring using coating-free, surface-activated, intensity-modulated coreless termination fibre sensors and transducers

•Structural change of the optical fibre played a significant role in dissolved oxygen sensing and monitoring performance.•Surface modification through wet cleaning has improved optical responses, surface activation, wettability, surface morphology, and surface roughness.•Coreless termination fibre treated with 1 M of H2SO4 has produced a good sensitivity, repeatability, selectivity, stability and detection limit.•Absorbance-evanescent field sensing principle for detecting dissolved oxygen is revealed.