Table 1 Main characteristics, strengths and weaknesses of the three technologies compared.
Raman | Fluorescence | Terahertz | |
|---|---|---|---|
Origin of the signal | Intrinsic chemical composition of the cell | Amount of fluorescent dye inside the cell | Amount of diverse metabolites and proteins inside the cell |
Signal acquired | Vibrational spectrum | Fluorescence intensity | THz peak magnitude |
Origin of the signal evolution after the delivery of µsPEF | Changes in the molecular composition of the cell | Internalization of non-permeant fluorescence dye into the cell | Leakage of molecules across the membrane |
Detection threshold (V/cm) in comparison with control group | ≤ 500 | > 500 and ≤ 750 | ≤ 500 |
Dose effect | Signal maybe related to the permeabilization state of the plasma membrane | Signal increases with the electric field magnitude for electric field magnitude above the detection threshold | Signal increases with the electric field magnitude |
Label | No | Yes | No |
Time resolution | Very low (~ 60 s) | Good (~ 0.3 s) | Low (~ 10 s) |
Spatial resolution | Very good (~ 1 μm) | Very good (~ 1 μm) | Very low (~ 2500 μm) |
Requirements for signal quantification | Normalization of the spectrum | Internal references necessary | Internal reference necessary |
Signal stability | Excellent (~ hours) | Low (~ 10 s) (photobleaching) | Excellent (~ hours) |
Data processing | Multivariate analysis | Univariate analysis | Univariate analysis |
Sample preparation | Specific substrate and solution | Labeling protocol | Specific substrate and solution |
Technology maturity | Research set-up | Commercialized equipment | Research set-up |
