Carbon Dots Synergizing with Phosphate Starch to Construct Dual Conduction Pathways for High-Performance Smart Packaging Films

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Abstract
The advancement of smart packaging technology demands high-performance and sustainable sensing materials. While starch is a biodegradable natural polymer, its inherent high crystallinity restricts charge transport capability. This study developed a novel smart sensing film by incorporating ellagic acid-derived blue, fluorescent carbon dots (CDs) into phosphate starch (PS), which is rich in phosphorus. The effects of silver ions (Ag+), sodium carboxymethyl cellulose (CMC), and CDs on the film properties were systematically investigated. Results indicate that CDs act as flexible nano-crosslinkers, forming hydrogen bonds with PS molecular chains and effectively balancing strength and toughness—achieving a tensile strength of 5.1 MPa and an elongation at break of 24.1%. Phosphorus, in synergy with CDs, facilitates an efficient dual conduction pathway for ions and electrons: phosphate groups enable ion transport, while the conjugated carbon cores of the CDs provide electron transport channels. This synergistic effect significantly reduces the film’s electrical impedance from 6.93 × 106 Ω to 1.12 × 106 Ω (a reduction of 84%) and enhances thermal stability, increasing the char residue from 1.1% to 18.3%. The PS/CDs composite film exhibits a strong linear current response to pH in the range of 2–7 (R2 = 0.9450), and shows enhanced discrimination between fresh orange juice (pH = 3.38) and spoiled orange juice (pH = 2.68), with a current change of 0.62 × 10−5 A. Moreover, the film exhibits strong blue fluorescence at 427 nm, with an intensity that shows a pronounced pH-dependent response. This study elucidates the mechanism by which phosphorus and CDs synergistically enhance the sensing performance of starch-based films, offering a new strategy for developing high-performance starch-based materials for smart packaging.
Funding Information
  • Scientific Research Fund Project of Yunnan Provincial Department of Education (2023Y0691)
  • Yunnan Provincial Programs (202301AT070217)
  • Yunnan Provincial Programs (202404BU090031)
  • Open Research Fund of the Key Laboratory of Efficient Utilization of Forestry Biomass Resources in Southwest China
  • National Forestry and Grassland Administration (2021-KF09)

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