A simple colorimetric histamine sensor based on smartphone digital image processing for fish quality assessment

Histamine (HA) is commonly employed as a marker for assessing fish spoilage. Digital image colorimetry (DIC) on a smartphone was developed to monitor HA in fish. A synthesized polyvinyl alcohol (PVA) sol-gel entrapped 2,3-naphthalenedicarboxaldehyde (NDA) that produced a blue product in the presence of HA. To fabricate the sensor, the PVA@NDA sol-gel was placed in a microtube that received sample solutions extracted from fish tissue. The intensity of the blue color produced in the presence of HA was correlated with the concentration of HA, which could be semi-quantitatively determined with the naked eye. Smartphone-enabled DIC was applied to digital images of the reaction, using the Color Lab® application to analyze the red channel of the images. Under optimum conditions, the developed sensor exhibited linearity in the range of 6.0 – 75.0 ppm of HA with a limit of detection of 0.31 ppm. Excellent stability, reproducibility, and selectivity were obtained. The developed sensor was successfully applied to detect HA in fish samples, with recoveries of 86 ± 6 – 116 ± 10%. The obtained results from HA determination in fish with the proposed method were consistent with results from the enzyme-linked immunosorbent assay. Therefore, the proposed sensor could be used to ensure the freshness of fish through on-site monitoring of HA.