Neat deep eutectic solvents exhibit potent antibiofilm activity: overcoming dilution bias in eutectic solvent antimicrobial assays

<b>Aims </b>Chronic wound infections are driven by multidrug‑resistant, biofilm‑forming bacteria that impede antimicrobial penetration and limit therapeutic success. This study aimed to evaluate deep eutectic solvents (DESs) as intrinsically active antimicrobial and antibiofilm agents and to determine how their physicochemical properties influence biological performance.<b>Methods and Results </b>Four DESs based on choline chloride or betaine paired with lactic or malonic acid were characterised to assess relationships between viscosity, ionic conductivity and hydrogen‑bond network dynamics. Choline chloride‑based DESs exhibited the lowest viscosities and highest conductivities, indicative of enhanced ionic mobility. Antimicrobial testing against six clinical wound isolates showed strong inhibitory and bactericidal activity across all DESs, surpassing ethanol and pH‑matched controls and confirming activity was not attributable to acidity alone. In colony biofilm assays, neat DESs produced multi‑log reductions, frequently approaching complete eradication of mature biofilms.<b>Conclusions </b>A clear structure–transport–activity relationship was identified, demonstrating that hydrogen‑bond architecture and ionic mobility govern DES antimicrobial potency. These findings support the potential of DESs as solvent‑active therapeutic platforms for topical management of biofilm‑mediated wound infections.