In-line photometer with pSi-based DBR for wavelength-selective transmittance measurement of methylene blue

An in-line photometer setup was designed to measure the transmittance and calculate the trace concentration of methylene blue (MB) in water samples. Different concentrations of MB, with a known peak absorbance at λ ~ 660 nm, were prepared. A test MB solution with known concentration was also prepared. UV-Vis spectrophotometry was initially performed to characterize the dye solutions. A porous Silicon-based (pSi) distributed Bragg reflector (DBR), with experimental peak reflectance centered at λ = 665 nm, was integrated into the setup for wavelength-selective purposes. Using the photometer setup, it was found that the proposed setup exhibited high precision in terms of transmittance measurements of the dye solutions due to low standard deviation, σ. The trace concentration of the test solution was calculated and it was found to be in good agreement with the known value with a 2.74 % deviation. The operation range of the setup was set to be from 1 × 10-5 M to 10 ×10-5 M of MB dye solutions because the measurements in these range were linear with more than 95% linearity.