A novel approach to banana ripeness monitoring: Aluminum and nitrogen-doped carbon quantum dots nanoparticle-based colorimetric indicator for ethylene detection

In the present study, an ethylene-sensitive indicator was developed based on aluminum and nitrogen-doped carbon quantum dots (Al-N@CDs) embedded in agar film (AF/Al-N@CDs) to detect banana ripening at ambient (25°C) and refrigerated (4°C) temperatures. The LSPR spectrum and TEM images of Al-N@CDs revealed a red shift and nanoparticle aggregation upon contact with ethylene gas, respectively. The designed colorimetric indicator had a smooth and dense surface, was pH-resistant, and exhibited antibacterial properties against E. coli and S. aureus bacteria. The addition of Al-N@CDs nanoparticles to the agar film reduced its permeability to water vapor and oxygen. The AF/Al-N@CDs indicator demonstrated high selectivity and specificity for ethylene gas in the presence of other volatile gases. There was a strong correlation between the concentration of ethylene gas and the color change of the AF/Al-N@CDs indicator. As a result, it was able to detect ethylene gas from banana ripening at both ambient and refrigerated temperatures, with the indicator color changing from light yellow to dark orange at ambient temperature and to brownish cream on the last day under refrigeration. XPS and FTIR spectra confirmed bond formation between aluminum nanoparticles and ethylene gas. During storage, the texture of the bananas became softer, and the amount of sugars increased, with higher sugar levels in bananas stored at room temperature. In addition, the skin color became darker and browner, with more pronounced browning occurring under refrigeration. The results demonstrated the effectiveness of the AF/Al-N@CDs colorimetric indicator in qualitatively detecting ethylene gas produced during banana ripening.