Figure 3. NutriPhone image acquisition and processing for vitamin B₁₂ quantification.

(A) Colorimetric variation of the test and control line regions on the silver enhanced B₁₂ lateral flow test strip at different known concentrations of standard vitamin B₁₂ samples (B) image processing algorithm used by our NutriPhone platform (C) Test and control line signals detected by the NutriPhone app as local intensity minima for 0 and 369 pmol/L of B₁₂ standard samples (D) Calibration curve showing the T/C ratios of the colorimetric signals at different standard B₁₂ concentrations: T/C ratio = d + (a–d)/(1+([B₁₂]/c)^b), where a = 0.99, b = 3, c = 303.7, and d = 0.3. Four parameter curve was fitted with R² = 0.8776. At each concentration 3 strips were used and the maximum and minimum deviation from the average were shown as error bars.