In biological systems, many processes in cell signaling function by the release and uptake of chemical species, such as neurotransmitters, ions or reactive oxygen species. The qualitative and quantitative study of these processes give new insights on how biological systems work. Nano electrochemistry offers powerful tools in the fields of biophysics, electrophysiology as well as neurochemistry where either electric currents or chemical species can be detected. Additionally, the study of cell morphology is possible in ion conductance measurements.
Commonly, carbon microelectrodes are used due to good chemical stability under physiological conditions. Chronoamperometric measurements or fast scan cyclic voltammetry can be used for the detection and quantification of chemical species from single cells. These methods offer temporal resolution of the processes under investigation.
Scanning electrochemical microscopy (SECM) enables the exact positioning of the microelectrode and adds lateral resolution by scanning of the microelectrode. With this, 2D and 3D concentration profiles of chemical species after release can be mapped.
Scanning ion conductance microscopy (SICM) can be used for contact-less topography imaging of sensitive biological samples. The high resolution and performance under physiological conditions allows the imaging of single live cells.
The release of many neurotransmitters (e.g. dopamine, epinephrine or serotonin) can be investigated electrochemically by oxidation at a microelectrode upon application of a suitable potential. The recorded current can be used to quantify the released neurotransmitters.
The study of morphological features of cells can help to understand disease. Scanning ion conductance microscopy (SICM) uses an ionic current between a quasi-reference electrode within a micropipette and a quasi-reference electrode in the bulk solution to map the topography of sensitive biological samples with lateral resolution greater than 100 nm. SICM can be easily combined seamlessly with fluorescence imaging.
In living systems, free radicals and reactive oxygen / nitrogen species (ROS/RNS) play important roles, because they can cause oxidative damage and tissue dysfunction and serve as molecular signals activating stress responses that are beneficial to the organism. Scanning electrochemical microscopy (SECM) and spatially-resolved electrochemical methods were effectively applied to image and quantify extracellular local concentrations of ROS and RNS, as well as other redox active signaling molecules. Stable long-term (>3 h) quantification measurements with high temporal (>1 Hz) and spatial (<1 µm) resolutions have been achieved from individual live cell in the ROS production and degradation processes.