Pulse oximeters’ varying performance based on skin tones has been highly publicised. Pulse oximeters tend to overestimate oxygen saturation values for people with darker skin (occult hypoxemia). The study aimed to construct a test bench to assess commercially available home based pulse oximeters. A laboratory simulator was used to mimic different oxygen saturation values (~70% to 100%). Four synthetic melanin filters were used to reproduce the effects of varying melanin attenuation levels. Three commercially available pulse oximeters (Biolight, N=13; ChoiceMMed, N = 18; MedLinket, N = 9) were reviewed and their response documented. All pulse oximeters’ responses under the effects of melanin attenuation did not change across various simulated oxygen saturation values. This does not match with the clinically observed data and one reason is that the light scattering due to tissue had not been fully replicated in the test bench. To investigate this further a Monte Carlo simulation of light propagation through the finger has been developed considering pulsatile flow and different skin tones. In reflection mode, the simulations highlight differences in measured R value and oxygen saturation with change in skin tone in the epidermal layer. However, in case of transmission mode, no change in the measured R value and oxygen saturation was observed. Further validation of these results from simulations is required to help us design pulse oximeters that are reliable and equitable for all users, regardless of skin tone.
An optical fibre temperature sensor modified with coating a thermochromic liquid crystal (TLC) film on the tip of fibre is reported. The interrogation is conducted in the wavelength domain using a CCD spectrometer and halogen light source. The TLC sensor shows a reversible wavelength shift of the reflective light peak in the detected temperature range (28 – 46°C). The response of the sensor to temperature was linear with a sensitivity of -4.52 nm/°C for temperature increasing and -4.60 nm/°C for decreasing. There is no measurable hysteresis in the temperature calibration experiment for TLC sensor.
A tip-based fiber-optic localized surface plasmon resonance (LSPR) sensor is reported for sensing of acetone. It is designed by coating the tip of multi-mode optical fiber with gold nanoparticles (size: ~ 40 nm) via a chemisorption process and further functionalization with a metal-organic framework (MOF) HKUST-1 via a layer-by-layer process. Two sensors with a different number of layers (80 and 120) corresponding to different thicknesses are reported. Both sensors show a redshift of resonance wavelength to acetone as a result of an increase in local refractive index induced by acetone adsorption into the HKUST-1 thin film. Sensors gradually saturate as acetone concentration increases and are fully reversible when the concentration decreases. The sensor with a thicker film exhibits slightly higher sensitivity to acetone than the thinner film with a wavelength shift of 5.27 nm for the concentration of 3.4 %.
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