# Synergistic Integration of Spin Crossover and Zinc Oxide in Transparent Films for Active Intelligent Packaging

## TL;DR

A transparent film combining temperature-sensitive and antimicrobial properties is developed for smart packaging applications.

## Contribution

A synergistic integration of spin crossover and zinc oxide in a transparent film for active intelligent packaging is demonstrated.

## Key findings

- The SCO transition broadens and hysteresis width decreases with increasing ZnO loading.
- The film maintains low active agent release and shows antiproliferative activity against MCF-7 cells at high concentrations.
- The material offers scalable potential for food and pharmaceutical packaging with real-time thermal and antimicrobial functions.

## Abstract

The development of multifunctional smart packaging materials capable of simultaneously monitoring temperature and suppressing microbial contamination is critical for next-generation food and pharmaceutical safety systems. In this study, we report the design and characterization of a polymeric film integrating a spin crossover (SCO)-based thermochromic sensor with zinc oxide (ZnO) nanoparticles serving as an antimicrobial agent. Beyond the individual functionalities, we demonstrate a synergistic effect between SCO and ZnO components. Notably, the SCO transition of the pristine SCO complex is broadened, and the hysteresis width of the transition is decreased (i.e., from 6 K to 1.5 K, 2 K, and 1.5 K for ZnO loading of 0.5%, 1%, and 2%, respectively), in the polysulfone–SCO–ZnO composites. Migration studies reveal that the co-existence of SCO and ZnO does not disrupt the low release profile of active agents, which remains low across ZnO loadings. The polymeric film exhibited dose-dependent antiproliferative activity against MCF-7 breast cancer cells, with a significant reduction in cell viability observed only at the highest tested concentration, indicating cytotoxic potential. This multifunctional platform represents a promising advancement in smart packaging design, enabling real-time thermal indication combined with the integration of ZnO as a literature-established antimicrobial component, within a non-toxic, and visually transparent system. Collectively, the material’s properties offer promising scalability for both food and pharmaceutical packaging applications where visual clarity, antimicrobial integrity, and temperature monitoring are imperative.