Topic 5 min read

Scanning probes & biology research

Latest updated: December 3, 2019

Overview

Scanning probe electrochemistry can be applied to the local study of biological systems. A number of biological processes result in changes in the local electrochemical characteristics of the system under study. By following local electrochemical characteristics, scanning probe electrochemistry has answered a number of questions as outlined in the table below.

 

Question Technique Information Measured Example
Can cell morphology be detected? dc-SECM The probe current in dc-SECM is dependent on sample activity and topography. When the cell is on a conductive substrate and is inactive to the selected redox mediator, it will appear as a low current region showing defined morphology. Unlike optical measurements of cells, the morphology is 3D with the lowest current regions reflecting the highest regions of the cell. F. Razzaghi, et al., Electrochimica Acta 157 (2015) 95–100
ac-SECM The ac current magnitude measured over an insulating sample, like a cell, is dependent on the probe to sample distance. When ac-SECM is used to measure cell morphology regions with low ac current magnitude relate to high topography regions of the cell. P. M. Diakowski, Z. Ding, Physical Chemistry Chemical Physics 9 (2007) 5966–5974
Is it possible to distinguish between different biomolecules? SKP Changes in conformation, hybridization, polarization, etc. of immobilized biomolecules cause changes in surface potential. This change in surface potential can be detected by SKP measurements as a change in contact potential difference. Using the contact potential difference, it is possible to distinguish between the biomolecules. D. C. Hansen, et al., Langmuir 19 (2003) 7514-7520
Can the effect of a toxin on cell membrane permeability be determined? dc-SECM dc-SECM uses the specific biasing of the SECM probe to perform chemically selective measurements. In these measurements, the current is directly related to the chemical concentration. If a toxin causes a change in permeability of a cell membrane a change in the current signal will be measured by the probe. This can be reflected in approach curves and area scans. M. S. M. Li, et al., Journal of Physical Chemistry C 120 (2016) 6094−6103
Can photosynthetic processes be followed? dc-SECM During photosynthesis, O2 is generated. The SECM probe can be biased to detect the generated O2 by oxygen reduction. Higher current magnitudes indicate a higher concentration of O2 and higher photosynthetic activity. This can be used to determine the location of stomata, and to compare light conditions on photosynthesis. M. Tsionsky, et al., Plant Physiology, 113 (1997) 895-901

 

SCAN-Lab AN #15: Introduction to the USB-PIO: measuring the effect of light on a live leaf

Vibrating Probe Vibrating probe sensitively measures the local current density of a sample in solution. Photosynthetic processes, like the opening and closing of guard cells at the plant stomata, are linked to changes in local current density as measured by the vibrating probe. By looping vibrating probe measurements, it is possible to measure the change in current density over time, to detect the influence of different light and dark conditions. J. S. Lee, Journal of Plant Biology 49 (2006) 186-192

 

SCAN-Lab AN#22: The use of the SVP470 for Vibrating Probe measurements of plants

Is it possible to follow the healing process? Vibrating Probe When wounding occurs, electric fields arise from the wounds. As healing takes place the electric fields change, and finally, disappear. The vibrating probe measures the current density arising from the natural electric fields occurring at a sample in solution. Looping area scans allow changes over time to be followed. L. Li, et al., Wound Repair and Regeneration 20 (2012) 840–851
SKP Wounding results in the presence of an electric field at, and near, the wound site. SKP measures contact potential difference between a probe and sample, which is affected by the electric field at the surface. Changes in the electric field can, therefore, be detected and followed by the SKP probe. R. Nuccitelli, et al., Wound Repair and Regeneration 16 (2008) 432-441
Can cell metabolism be measured? dc-SECM dc-SECM in generator-collector mode measures the current associated with a redox mediator produced by the sample. Higher currents indicate regions with a higher concentration of mediator produced by the sample. This is used in cell metabolism studies with a two-mediator system. One mediator enters the cell and interacts with redox-active enzymes in the cell. The converted mediator can then interact with a second mediator which is detected by the SECM probe. Higher currents, therefore, indicate areas of higher metabolic activity. A. Ramanaviciusa, et al., Colloids and Surfaces B: Biointerfaces 149 (2017) 1–6

 

Glossary

  • Scanning ElectroChemical Microscopy (SECM): Measurement of local electrochemical activity of a sample with chemical selectivity. The local impedance of a sample can also be measured.
  • Localized Electrochemical Impedance Spectroscopy (LEIS): Measurement of local impedance differences and point-by-point Electrochemical Impedance Spectroscopy
  • Scanning Kelvin Probe (SKP): Local non-contact measurement of sample work function. Topography can also be measured.
  • Scanning Vibrating Electrode Technique (SVET): Measurement of the local current distribution of a sample in the electrolyte. Also known as Vibrating Probe.
  • Scanning Droplet Cell (SDS): Local electrochemical and impedance measurements of a sample within a droplet.
  • Optical Surface Profiler (OSP): Non-contact measurement of the local sample topography.