Exploiting Greener Formulations of Benzalkonium Chloride with Enhanced Antibacterial Properties

In recent years, the extensive use of benzalkonium chloride (BKC) as a disinfectant has raised significant concerns due to its toxicity and its potential to promote environmental impact and antimicrobial resistance. In order to reduce the toxicity associated with BKC in spray disinfectants, the antimicrobial agent was coencapsulated into vesicle-like nanosystems, known as nanodroplets (NDs), with limonene, a natural essential oil renowned for its antimicrobial properties and commonly used in cleaning product formulations. The aim was to reduce the required concentration of BKC in the disinfectant formulation by enhancing its antimicrobial activity through encapsulation in nanodroplets (BKC-NDs) and by loading limonene within the core of the nanodroplets. The vesicles consist of two distinct phases: an organic core composed of decafluoropentane and limonene and an outer aqueous shell stabilized at the interface by BKC. In this formulation, therefore, BKC plays both a functional role as an antimicrobial agent and a technological role as a surfactant, allowing for the formation of the NDs. Moreover, a more sustainable formulation was obtained by removing decafluoropentane and retaining limonene in the vesicle core. A library of BKC-NDs with varying BKC concentrations (0.008, 0.08, and 2.4% w/v), with or without a decafluoropentane core, was prepared to finally select the minimum concentration with the highest antimicrobial activity. BKC-NDs demonstrated superior antimicrobial properties compared to BKC in aqueous solution against Staphylococcus aureus and Escherichia coli and, in particular, the formulation at 0.08% w/v, while maintaining comparable in vitro biocompatibility. The efficiency of BKC-NDs spray disinfectants was also assessed from a physicochemical perspective, demonstrating high wettability, wide spray angle, and long-term stability upon storage while retaining antimicrobial efficacy. A novel green spray disinfectant based on BKC, which exploits materials of natural origin to reduce the concentration of chemicals, was developed to minimize its related toxicity and environmental contamination.