A Smartphone-based optical sensor with polyaniline label for quantitative determination of freshness of freshwater fish fillets

We developed a cost-effective, user-friendly smartphone-based sensor equipped with a polyaniline (PANI) label along with optical components and monitored the freshness of three different varieties of fish fillets i.e., Rohu (Labeo rohita), Mullet (Mugil cephalus), and Common Carp (Cyprinus carpio) during storage. We designed an optical cradle as an accessory for a smartphone using ZW3D software and a 3D printer. The cradle with the smartphone was used to observe the spectrum of developed polyaniline deposited labels for ascertaining fish freshness. The sensor was calibrated using a standard ammonia solution (0-400 ppm) and the method was validated with a spectrophotometer and existing conventional techniques like TVB-N (total volatile basic nitrogen), TVC (total visible count), pH, and TPA (Texture Profile Analysis). The limit of detection (LOD), the limit of quantification (LOQ), %Bias, and %RSD of the sensor were 3.83 ppm, 12.96 ppm, 0.14 %, and 1.87 % respectively. The developed smartphone-based sensor used about 1139 pixels for wavelengths between 391.84 and 633.54 nm. A strong correlation could be established between TVB-N, TVC, and pH with the findings of the developed sensor. Application of PANI made the sensor specific for the detection of spoilage of fish therefore can be utilized as a platform for monitoring the freshness of fish. We successfully developed a web application using the present findings to evaluate fish fillet quality.

Automated summary

We developed a cost-effective and user-friendly smartphone-based sensor with a PANI label to monitor the freshness of fish fillets during storage. The sensor was calibrated using a standard ammonia solution and validated with conventional techniques. The PANI label made the sensor specific for detecting fish spoilage and a strong correlation was found with traditional freshness indicators. A web application was developed for evaluating fish fillet quality based on the sensor's findings.