Electric polarization properties of single bacteria measured with electrostatic force microscopy. Theoretical and practical studies of Dielectric constant of single bacteria and smaller elements

• Autores: Daniel Esteban Ferrer
• Directores de la Tesis: Antonio Juárez (dir. tes.), Gabriel Gomila Lluch (dir. tes.)
• Lectura: En la Universitat de Barcelona ( España ) en 2014
• Idioma: inglés
• Tribunal Calificador de la Tesis: Manel Puig Vidal (presid.), Jaime Virgilio Colchero Paetz (secret.), Juan José Sáenz Gutiérrez (voc.)
• Materias:
  • Física
    • Electromagnetismo
      • Magnitudes eléctricas y su medida
  • Ciencias de la vida
    • Microbiología
  • Ciencias tecnológicas
    • Ingeniería y tecnología eléctricas
      • Aplicaciones eléctricas
    • Tecnología electrónica
• Enlaces
  • Tesis en acceso abierto en: Dipòsit Digital de la UB
• Resumen

  • The present thesis is included in the field of nanobioelectricity. That is, understanding the electrical properties of biological specimens at the nanoscale (< 200 nm). To do so we used an electrical variation of the Atomic Force Microscope called Electrostatic Force Microscope (EFM). By the application of a novel methodology (experimental and theoretical) we were able to obtain electrical polarization properties of single bacteria. Firstly the methodology was applied to calibration samples were the dielectric constant was already known. The obtained value for a silicon nitride sample was 7.6 and the nominal value for this material is 6-8 (depending on stoichometry). Also a silicon oxide sample was studied obtaining a dielectric constant of 3.9 while the nominal value is 4. Both calculations validate the used methodology. Moving to bacteria we found that the effective dielectric constant, for the four bacterial types investigated (Salmonella typhimurium, Escherchia coli, Lactobacilus sakei, and Listeria innocua) is around 3-5 under dry air conditions. Under ambient humidity, it increases to 6-7 for the Gram-negative bacterial types (S. typhimurium and E. coli) and to 15-20 for the Gram-positive ones (L. sakei and L. innocua). We show that the measured effective dielectric constants can be consistently interpreted in terms of the electric polarization properties of the biochemical components of the bacterial cell compartments and of their hydration state. These results demonstrate the potential of electrical studies of single bacterial cells. Finally a comparison of these results with smaller ones (namely nanoparticles and viruses) was performed in the theoretical side obtaining that the geometrical factors of the sample have a larger influence in the small objects. Also it was concluded that while there exist some analytical approximations to work with them, these are not applicable to larger objects like bacteria. This work confirms that dielectric measurements of single bacterial cells can be correlated with the electric polarization response of their biochemical constituents and their internal structure, thus opening interesting possibilities for analytical studies based on the biological electric polarization properties (also with smaller biological entities).