## 4 The Role of Dielectrophoresis in the Characterization of Skin Tumor Cells
### Clinical Applications
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Method** & **Pros** & **Cons** & **References** \\ \hline \multirow{6}{*}{**DEP**} & Non-invasive detection in liquid biopsy; & \multirow{6}{*}{Low selectivity; [73, 96, 97, 98]} \\  & Both label-free and biomarker-based & & \\  & discrimination; & & \\  & Single-cell isolation possibilities; & Limited reproducibility & [73, 96, 97, 98] \\  & Cells’ evolution monitoring in real-time & & \\  & based on electrical properties & & \\ \hline \multirow{2}{*}{**Density gradient**} & Label-free; & Low specificity; [73, 96, 97, 98] & \\  & Simultaneous isolation of & Physical stress—destructive for [99] & \\  & more than two types of cells & the CTCs & \\ \hline \multirow{2}{*}{**Gas chromatography**} & Highly reproducible; & Use of high temperature (destructive for the sample); & \\  & High peak capacity molecules analysis & Limited to volatile compounds & \\ \hline \multirow{2}{*}{**Mass spectrometry**} & Accurate determination of mass; & Destructive for the sample; & \\  & High throughput & Less reproducible & [101] \\ \hline \multirow{2}{*}{**Liquid chromatography**} & Adeuate for a broad range of molecules; & Limited throughput; & \\  & High peak capacity molecules analysis & Potential longer separation time & [102] \\ \hline \multirow{4}{*}{**Capillary electrophoresis**} & Measurements possible on & \multirow{4}{*}{Sensitivity and resolution limits; [73, 96, 97, 98]} \\  & Automated method (offers the possibility & Increased immunofixation rate & \\  & to process larger batches) & & \\ \hline \multirow{2}{*}{**Immunomagnetic separation**} & High detection sensitivity (high purity) & Limitation related to surface & \\  & and effectiveness; & markers; & \\  & High-throughput & Antibody-mediated method & \\ \hline \multirow{2}{*}{**Fluorescence-activated cell sorting (FACS)**} & High-throughput; & High costs in processing and & \\  & Simultaneous isolation of more than two & pre-processing steps; & \\  & types of cells & Skilled staff required & \\ \hline \multirow{2}{*}{**Raman spectroscopy**} & High specificity; & Sensitive and highly optimized & \\  & Little sample preparation required & instrumentation; & \\  & & Use of high temperature & \\  & & (Destructive for the sample) & \\ \hline \multirow{2}{*}{**Photoacoustic flow cytometry**} & Label-free; & Limitation related to sample size & \\  & Quantitative flow cytometry imaging & and device parameters & [108] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Pros and cons of dielectrophoresis vs. other CTCs detection and separation methods. Another important aspect related to DEP is the continuous improvement of the technique, during the last couple of years, new technological breakthroughs changing also the classical DEP approach. One of the most used DEP techniques is the electrode-based DEP (eDEP) that employs metallic electrodes positioned within a micro-channel, having direct contact with the measured particles and the suspending medium [115]. The obvious disadvantage of this method is the higher risk of biological sample deterioration, as high frequencies charging is used. A simple solution to limit this negative effect is the use of insulator-based dielectrophoresis (iDEP), especially when manipulating fragile skin tumor cells. As the micro-electrodes are placed within an insulating structure, higher electric fields can be applied, offering a higher degree of selectivity of biological samples while maintaining a chemically inert environment [116]. Considering another DEP technique where particle contact is minimal, contactless DEP is a good example. The generation of a nonuniform electric field is possible in the absence of direct contact between electrodes and target particles, which is adequate when manipulating fragile biological cells [117]. Innovations regarding electric waves were also included in some DEP devices, traveling wave DEP consisting of a moving electrical field produces by the signals of shifting electrical phases.