<![CDATA[It is necessary to design a fast, inexpensive, and portable method for detecting formalin to support food safety screening and halal-tayyib principles. This study aims to develop and characterize a formalin detection system using a smartphone, an optical fiber sensor, an evanescent wave, and a diffraction grating. The sensor medium comprises a multi-mode step-index plastic-clad silica optical fiber (core diameter 400 µm; NA 0.48), with modifications in the sensing area to enhance interaction between the evanescent field and the medium. The optical fiber used in the detection system has its end polished to a 45-degree angle and its cladding section scratched at five locations over a 1 cm length. The optical system uses the smartphone’s rear LED as a light source, the camera as a detector, and a diffraction grating from a DVD to disperse the output light, enabling intensity changes to be recorded. The spectral image is analyzed in ImageJ to obtain the intensities of the R, G, and B channels, then converted to a single grayscale intensity value using a weighted luminance model and evaluated using linear regression. The results show that RGB and grayscale intensities increase monotonically with formalin concentration from 0 to 10 ppm. The grayscale calibration curve is given by the equation. . The sensor's sensitivity indicates that a 1 ppm change in concentration corresponds to a 1.7481 pixel change. The regression value (R2) of 0.9565 demonstrates good linearity across the test range. Per-channel analysis indicates that the green channel exhibits the highest linearity, whereas the blue channel shows the greatest response. These findings confirm that the proposed optical fiber-smartphone sensor platform has the potential to be a compact, low-cost, and viable solution for portable formalin detection. It is necessary to design a fast, inexpensive, and portable method for detecting formalin to support food safety screening and halal-tayyib principles. This study aims to develop and characterize a formalin detection system using a smartphone, an optical fiber sensor, an evanescent wave, and a diffraction grating. The sensor medium comprises a multi-mode step-index plastic-clad silica optical fiber (core diameter 400 µm; NA 0.48), with modifications in the sensing area to enhance interaction between the evanescent field and the medium. The optical fiber used in the detection system has its end polished to a 45-degree angle and its cladding section scratched at five locations over a 1 cm length. The optical system uses the smartphone’s rear LED as a light source, the camera as a detector, and a diffraction grating from a DVD to disperse the output light, enabling intensity changes to be recorded. The spectral image is analyzed in ImageJ to obtain the intensities of the R, G, and B channels, then converted to a single grayscale intensity value using a weighted luminance model and evaluated using linear regression. The results show that RGB and grayscale intensities increase monotonically with formalin concentration from 0 to 10 ppm. The grayscale calibration curve is given by the equation. . The sensor's sensitivity indicates that a 1 ppm change in concentration corresponds to a 1.7481 pixel change. The regression value (R2) of 0.9565 demonstrates good linearity across the test range. Per-channel analysis indicates that the green channel exhibits the highest linearity, whereas the blue channel shows the greatest response. These findings confirm that the proposed optical fiber-smartphone sensor platform has the potential to be a compact, low-cost, and viable solution for portable formalin detection.]]>
