Surface engineering of yeast microcarriers to enhance droplet retention and antimicrobial efficacy on hydrophobic plant surfaces

Microbial contamination on plant surfaces is a major concern in both preharvest and postharvest settings. Although spraying is widely used for applying pesticides and sanitizers, poor droplet retention on hydrophobic surfaces results in significant chemical loss, environmental pollution, and health risks. Yeast-based microcarriers have shown strong potential for delivering a broad spectrum of antimicrobial agents, yet their droplet impact behavior remains poorly understood. Herein, we systematically analyzed the droplet dynamics of yeast suspensions using two retention-enhancing strategies: (1) spray modification with food-grade additives, including sodium dodecyl sulfate (SDS) and glycerol, and (2) surface engineering with ε-poly-L-lysine (ε-pLL) and SDS to form micelle-like coatings. High-speed imaging was used to visualize droplet dynamics on transparent PDMS replicas of basil leaves, enabling controlled analysis of fluid behavior on microstructured, hydrophobic surfaces. Engineered yeast droplets exhibited strong adhesion and formed large, symmetric residuals upon impact. While SDS and glycerol modifications led to modest improvements in retention, surface-engineered yeast consistently outperformed them, demonstrating the effectiveness of layer-by-layer coatings in enhancing droplet deposition on hydrophobic plant surfaces. To demonstrate delivery potential, in-situ synthesized silver–copper bimetallic nanoparticles (AgCu biNPs) were encapsulated within yeast carriers. When applied to E. coli-inoculated basil leaves inclined at 30 °, biNPs delivered via engineered yeast achieved a 2.8-log CFU/cm² reduction, compared to just 0.73-log for native yeast carriers. These findings demonstrate that surface-engineered yeast microcarriers enhance both droplet retention and antimicrobial efficacy, offering a promising, bio-based strategy to reduce spray loss and improve delivery performance in agricultural and food safety applications.