ZIF-8 nano-enhanced spiral fiber optic evanescent wave sensor for high-sensitivity ethanol monitoring and application for early detection of mango anthracnose

Early detection of mango anthracnose is of great significance for reducing postharvest losses, yet non-invasive and sensitive monitoring methods remain limited. In this work, a ZIF-8 nano-enhanced spiral fiber optic evanescent wave (FOEW) sensor is developed for ethanol vapor detection and applied to early diagnosis of mango anthracnose. Three probe configurations, including a U-shaped FOEW probe, an uncoated spiral probe, and a ZIF-8/PVP-coated spiral probe, are systematically compared. The spiral geometry significantly increases the effective sensing length (from 1.9 cm to 9.4 cm), leading to enhanced ethanol sensitivity, while ZIF-8 nano-coating further amplifies the sensing response through adsorption enrichment. Using an estimated headspace concentration defined by a fixed liquid injection protocol (1 μL injection into a 50 mL sealed chamber), the ZIF-8/PVP-coated spiral probe exhibits a linear response over the range of 80–8000 ppm, with a sensitivity of 2.34 × 10⁻⁴ Abs/ppm, a limit of detection of 1.31 ppm, and a limit of quantification of 4.36 ppm. Proof-of-concept experiments on mango samples demonstrate that ethanol emission from infected fruit is consistently higher than that from healthy samples, and increases with disease progression. These results indicate that the proposed ZIF-8 nano-enhanced spiral FOEW sensor provides a promising non-invasive platform for sensitive ethanol monitoring and early detection of mango anthracnose.