Fig. 1. Optical electronic-nose for screening of colorectal diseases.
Fig. 2. Experimental setup for testing optical e-nose: (a) photo of measurement system, (b) block diagram of measurement system.
Fig. 3. Voltage differences of optical gas sensor as a function of center wavelength.
Fig. 4. Cumulated output voltage difference as a function of CO2 concentrations.
Fig. 5. Principal component analysis (PCA) of CO2 and ethanol gases and mixtures of gases: Iso-propyl alcohol (IPA), methanol (M), acetone (A) and toluene (T).
Table 1. Biomarkers surveyed from the articles related to the colorectal diseases and their central absorption wavelength.