طراحي شناساگر رنگ سنجي بر پايه چارچوب‌هاي فلز-آلي مس و مس-پروتئين براي تشخيص فساد ماهي

Intelligent packaging enables non-destructive quality monitoring an‎d early detection of food spoilage, particularly in seafood. This study aimed to develop colorimetric indicators based on a copper-based metal–organic framework (Cu-BTC) an‎d a copper–soy protein isolate composite (Cu-BTC@SPI), immobilized on agar an‎d cellulose paper for detecting hydrogen sulfide (H₂S) an‎d ammonia (NH₃) released during fish spoilage under ambient an‎d refrigerated conditions. Cu-BTC an‎d Cu-BTC@SPI were synthesized via reflux an‎d comprehensively characterized. Structural analyses revealed morphological transformations from octahedral crystals to larger hexahedral an‎d orthorhombic structures following exposure to spoilage-related sulfur- an‎d nitrogen-containing volatiles. SPI incorporation increased particle size an‎d surface wrinkling. FTIR confirmed framework formation an‎d gas interactions with copper active sites through changes in O–H/N–H, carboxylate, an‎d Cu–O vibration ban‎ds. Nitrogen adsorption–desorption analysis indicated a microporous structure for Cu-BTC (type I isotherm) an‎d a mesoporous structure for Cu-BTC@SPI (type IV). After gas exposure, both materials showed improved Langmuir fitting an‎d reduced specific surface area an‎d pore volume, suggesting partial pore blockage an‎d adsorption governed by accessible active sites. Fluorescence quantum yield increased from 50% for Cu-BTC to 75% for Cu-BTC@SPI. Both materials exhibited static fluorescence quenching an‎d high Stern–Volmer constants upon gas exposure. UV–Vis analysis revealed decreased π→π* an‎d n→π* absorption intensities in Cu-BTC an‎d a slight spectral shift in Cu-BTC@SPI. SPI characterization showed decreased free sulfhydryl, carbonyl, an‎d amino groups an‎d increased disulfide bonds following composite formation, indicating structural rearrangements associated with Cu²⁺ coordination. In the second stage, both materials were immobilized on agar an‎d cellulose paper to fabricate colorimetric indicators. Cu-BTC@SPI indicators showed greater pH stability, lower moisture absorption, broader color responses, an‎d higher sensitivity across storage temperatures. Kinetic analysis indicated predominantly chemisorptive gas adsorption, with SPI enhancing the rate constants (k₁ an‎d k₂), equilibrium capacity (qₑ), an‎d initial adsorption rate (α). Both indicators responded significantly an‎d selec‎tively to varying NH₃ an‎d H₂S concentrations. SPI reduced response time, while substrate type affected reaction kinetics through gas diffusion an‎d mass transfer. H₂S elicited a faster response, attributed to its polarity, nucleophilicity, an‎d affinity for Cu²⁺ active sites. During fish freshness monitoring, Cu-BTC indicators changed from blue to dark brown, whereas Cu-BTC@SPI indicators transitioned from sky blue to golden yellow an‎d eventually orange-brown. The associated increase in ΔE with spoilage enabled Cu-BTC@SPI indicators to distinguish freshness stages more accurately owing to their broader colorimetric response range.

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كاظم كرمي

هادي الماسي , محمد ديناري , مهدي كديور