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Quantum Dot Dissemination and Behavior in Bacterial Biofilms

J.B. Morrow, R.D. Holbrook and C.J. Zeissler
National Institute of Standards and Technology, US

quantum dots, bacterial biofilms, interaction energy

Quantum dots (QDs) are colloidal semiconductor nanocrystals that photoluminescence emission is proportional to the dot size and have been utilized in fluorescent imaging in biological systems. Biofilms are communities of microorganisms attached to surfaces encased in extracellular polymeric substances and serve as a survival mechanism in diverse environments including water distribution systems. Dots of two different sizes (5 and 20 nm) and two different surface chemistries (amine and carboxyl modified) were utilized to measure diffusion in bacterial cells and biofilms as a function of fluid shear. Interaction energies of QDs with bacterial biofilms, governed by interfacial forces include van der Waals, electrostatics and hydrophobicity (including Lewis acid/base contributions), are predicted to be largely attractive, -2575 kT, for 5 nm diameter COOH QDs with drinking water biofilms grown on PVC pipe. Small QDs (<5 nm), capable of entering bacterial cells, can strongly associate with biofilm bacteria. Attractive interaction energies are significantly reduced for larger QDs, -16.6 kT, for 20 nm diameter QDs contacted with drinking water biofilms. Confocal Laser Scanning Microscopy (CLSM) and epifluorescent microscopy measurements of diffusion coefficients for QDs in single (Pseudomonas aeruginosa PAO1) and native drinking water bacterial biofilms were dependent on the size and chemistry of the quantum dots and agreed well with predicted attractive interaction energies.

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