Engineered nanoparticles are a new, fast-growing technology due to their potential in drug delivery, imaging, and sensing. Their surfaces are often functionalized for stability and/or enhanced cell interactions, but the effects of these different coatings on the environmental impact of the nanoparticles are largely unknown. Polyallylamine (PAH)-coated Au nanoparticles are known to be toxic to gram-positive bacteria, likely through cell surface interactions. Isothermal titration calorimetry (ITC) was performed to determine where PAH-coated Au nanoparticles (PAH-AuNPs) bind on the gram-positive cell wall; the lipid bilayer, the thick peptidoglycan layer, or the lipoteichoic acids.  It was hypothesized that the positively charged PAH coating on the nanoparticles would cause them to bind to negatively charged lipoteichoic acids with the highest affinity through electrostatic interactions. The results showed no binding of PAH to model lipid bilayers, though binding was observed to both peptidoglycan and the lipoteichoic acid chains. Current data indicate that PAH polymer binds to the lipoteichoic acid chains with 75% higher affinity, but the thermodynamic driving force of both reactions is entropy.  Unexpectedly, the PAH-AuNPs showed binding to peptidoglycan but no binding to model lipid bilayers or lipoteichoic acids. Zeta potential data indicated the NPs are unstable, with loss of PAH over time. Therefore, synthesis of new PAH-AuNPs must be completed prior to further experimentation to confirm the ITC data collected and whether PAH-AuNPs actually do employ a different bacterial cell interaction mechanism.<br/>

Investigating the binding thermodynamics of polycation-coated Au nanoparticles to gram-positive cell walls

255th National Meeting (2018)

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