What is DEP?
What You Need to Know About Dielectrophoresis
Dielectrophoresis 101
Beginnings
Dielectrophoresis was first observed in the early 20th century, and predicted by Maxwell in the late 19th. But it wasn't until 1951 that Prof Herb Pohl of Oklahoma State University first reported it, came up with an equation to describe it, and gave it a name and its acronym (DEP). In 1966 he published (with Masters student Ira Hawk) that it also worked on cells - in that case live and dead yeast.
Expansion
DEP research took off in the late 80s, when microengineering technology enabled researchers to make suitable electrodes for cell analysis and separation. However, most of the designs were aimed more at the scientific literature than the market, and DEP platforms remained low-throughput, cumbersome, complicated to use, and prone to being jammed by bubbles.
Towards 3D
More recently, researchers have looked to building 3D devices to overcome these issues. Many are still encumbered by low throughput, difficulty of use and high operating cost.
In the 2000s, a new approach from a research lab in the UK, called DEP-Well, changed the way we do DEP and led to the 3DEP and Deparator.
Electrophoresis
Most people in the life sciences are familiar with electrophoresis, where an electric field is used to separate molecules with different sizes and amounts of charge. This works because of Coulomb's law, that force is equal to charge times electric field. This forms the basis of gel electrophoresis, commonly known for DNA profiling (the famous "DNA barcode").
Dielectrophoresis
DEP works on things with capacitance and resistance - things that can polarise. This means that in an electric field they acquire positive and negative charge on either side, a bit like the poles of a magnet. If the field is the same everywhere, the forces on the poles are equal and opposite and the particle does not move. But if the field is nonuniform, one force is bigger than the other and there is a net force up or down the field gradient. This is DEP.
Frequency dependence.
The magnitude and direction of the force (up or down) depends on whether the particle is more or less polarisable than its suspending medium at the applied field frequency. By determining this force at a range of different frequencies, we can produce a DEP spectrum that we can use to estimate the separate properties of the particle. If the particle consists of a thin "shell" surrounding an inner "core" we can determine the properties of these different components.
DEP of cells
Cells in suspension can polarise and are amenable to DEP. They are complex structures but the dominant electrical properties are the membrane and the cytoplasm, both of which have conductance and capacitance values. This means we can determine these values if we measure the DEP at different frequencies, producing the DEP spectrum. We then fit a standard model to this to determine the electrical properties. The 3DEP measures at 20 user-selectable frequencies between 1kHz and 45MHz.
If a mixture contains two cell types with different electrical properties, they may be separable by DEP. If a frequency window exists where one type of cell experiences positive DEP it will move up the field gradient to the electrodes, where it will be trapped. The other experiences negative DEP and is pushed into the flow; only the negative DEP cells will exit the chip. Afterwards the field can be turned off and the positive DEP fraction can be recovered separately.
The DEP-Well system
DEPtech products achieve their unique performance due to the patented DEP-Well technologies at their cores. By using a completely new approach to dielectrophoresis chip design, we have developed 3D dielectrophoretic characterization and separation using low-cost, disposable chips that are stil a thousand times faster than what came before. It is this approach that has led to the development of the 3DEP and DEParator.