Nano-priming of lettuce seeds using Chitosan Stabilized iron oxide nanoparticles with tunable interfacial properties

Polymer molecular weight plays a central role in determining the balance between electrostatic and steric stabilization in polymer-coated colloidal systems, yet its influence on nanoparticle accessibility at soft, hydrated interfaces remains insufficiently resolved. Here, we examine the effect of chitosan molecular weight (1000, 10,000, and 50,000 g/mol) on the electrosteric stabilization and colloidal behavior of iron oxide nanoparticles. Nanoparticles stabilized with low-molecular-weight chitosan exhibit smaller hydrodynamic diameters (≈ 110 nm) and higher positive zeta potentials (≈ + 35 mV), leading to enhanced suspension stability and slower sedimentation relative to higher-molecular-weight formulations. Increasing chitosan molecular weight produces thicker polymer layers that enhance steric contributions while partially screening surface charge, resulting in larger hydrodynamic sizes (≈ 150-160 nm) and reduced colloidal stability. These trends indicate a molecular-weight-dependent transition from electrostatic-dominated to steric-dominated stabilization. Using hydrated seed coats as polysaccharide-rich soft interfaces to probe interfacial accessibility, micro-X-ray fluorescence mapping revealed enhanced nanoparticle surface association under conditions of optimal electrosteric balance. This interfacial behaviour correlated with increased germination responses (up to ≈ 92%) without detectable adverse physiological effects. Collectively, these results demonstrate that chitosan molecular weight provides a tunable parameter for controlling electrosteric stabilization and nanoparticle accessibility at soft interfaces.