The 3DEP: 3D Electrophysiology Platform
- Label-free
- Instant results
- Minimal preparation
The 3DEP is the world’s first DEP cytometer, providing rapid, low-cost and label-free cell electrophysiology. Load cells into a disposable chip by micropipette. Insert the chip into the reader and have results in 10 seconds!
- Analyse up to 20,000 cells instantaneously
- Low-cost disposable chips require less than 100uL and 100k cells.
- Instant membrane capacitance, surface conductance, and cytoplasm conductivity measurements.
- Resting membrane potential obtainable from 2 samples.
The system is fast enough to allow real-time measurements of resting values – for example, for measuring ultradian rhythms. It is subtle enough to detect stem cell differentiation fate weeks before the same information can be detected by protein expression. It can detect what goes on inside a cell, for example during infection. It can detect early ionic events such as BK channel activity in processes such as apoptosis, much faster than by other methods.
The reason we say “electrophysiology is everywhere”, is that if you can measure electrophysiology this quickly and easily, you can use it as a marker for other things. The 3DEP can also discriminate between drug-resistant and drug-sensitive cells, or measure bacterial response to antibiotics and cancer cells to anti-cancer drugs – faster and more accurately than conventional methods such as MTT.
How does it work?
The 3DEP uses a patented chip containing 20 “wells” to analyse cells, each carrying several electrodes down the inside wall. The electrodes in each well receive a specific frequency signal, allowing 20 frequencies (user-selectable, between 1kHz and 45MHz) to be analysed simultaneously.
When the frequencies are applied to the wells, the cells inside the well move due to dielectrophoresis, if they experience “positive DEP” (that is, they are attracted to the electrodes) the cells move from the centre of the well towards the edge; if repelled from the electrodes they move towards the centre of the well.
Our image capture and analysis software maps this response to the common Clausius-Mossotti polarizability factor.
With a new cell type, there is always scope for optimising the exposure time and cell concentration to produce the best fit (highest R). Still, we have found that a 10-second exposure produces highly satisfactory results in most cases.
DEP unlocks a new world of diagnostic potential
Cells become diseased. Healthy cells become cancer cells. Blood cells become infected with malaria, macrophages with tuberculosis. Some diseases affect cell surfaces, others the membrane potential, and others the morphology, all of which can be reflected in their dielectrophoretic signatures. Moreover, Electrophysiology changes faster than molecular biology – Cells beginning apoptosis change potassium levels almost instantly; caspases and other molecular markers follow hours behind. The 3DEP determines IC50s ten times faster than MTT.
It’s not a surprise that cancer cells behave differently to normal, healthy cells at the same site. What is a surprise is that the differences include changes to the electrical signature of the cells.
Oral cancer is in the top-ten most common cancers worldwide (in India it’s no.1), but survival rates haven’t improved in decades. Part of the reason is that cases aren’t identified early enough in primary care – but the time something definitely looks like cancer, it’s too late. On average, a visual inspection is about 70% accurate; what is needed is a quick, easy, low-cost and accurate test that doctors and dentists can use to identify those needing treatment at an earlier stage.
We used a 3DEP to tell the difference between brush samples taken from patients with oral cancer and healthy control subjects, using our MDV diagnostic marker. The 3DEP could identify cancer with 92% sensitivity, and identify healthy with 95% specificity (based on >100 participants). Samples don’t need to be taken at point-of-care; they can be posted to a central lab for processing days after collection, keeping running costs down. This would work in the GP’s surgery or the dentist’s… even at home.
We have also used the same technique to detect bladder cancer, which is similar to oral cancer at a cellular level, but is the most expensive cancer to manage due to the need for lifelong, invasive monitoring for recurrence. When we applied our technique, we found very similar statistics. And there are other diseases that can be detected by this method – in fact, some that can only be detected by this method; we’re keeping some under wraps for now.
Understand the electrical world of cells
Membrane Conductance
Membrane conductance refers to how easily a membrane allows electrical charge to pass through or around it. Factors like charges on the membrane surface, activity of ion channels, and the shape of the membrane can affect conductance. This is often measured as whole-cell conductance by multiplying it with the cell’s surface area, commonly used in cell electrophysiology.
Effective Membrane Capacitance
Effective membrane capacitance refers to how well a membrane can hold electrical charge. Normally, membrane composition changes little, so the amount of charge it can store remains fairly constant. However, if the surface isn’t perfectly smooth and spherical—like when it has blebs, microvilli, or invaginations—more charge can be stored because there’s more membrane than expected. This results in a higher value for effective membrane capacitance per unit area of the cell, which indicates differences in cell surface shape. This measure is useful for studying cell differences, such as between stem cells and cancer cells. It’s also helpful for understanding changes in membrane conductance. Like conductance, whole-cell capacitance is calculated by multiplying by the cell’s surface area, commonly used in cell electrophysiology studies.
Intracellular Conductivity
Intracellular conductivity measures the concentration of charged ions within a cell’s cytoplasm, contributing to electrical conduction. It reflects the balance of positive and negative charges in the cell and is linked to membrane potential. This measure helps track changes in ion concentrations and activity of ion channels. It’s also a valuable marker for cell permeability changes; when pores form in the membrane, conductivity drops quickly. Additionally, it signals apoptosis—the first step involves ion and water movement, altering conductivity noticeably. In cell electrophysiology, dividing 1 by intracellular conductivity gives cytoplasm resistivity parameters.
Multiple Populations
Sometimes, a sample contains a mix of cell types with different electrical properties. We can model these populations, like in apoptosis where apoptotic bodies appear with distinct conductivity. The ratio of these populations indicates their relative concentrations, but this isn’t a direct comparison due to their size and properties. We can model up to three populations in a sample using high-quality spectra, obtained by averaging many spectra with software. In clinical samples with varied cell types, like oral swabs, we may not capture all properties, but 3DEP software helps differentiate samples based on dispersion characteristics. This method has classified samples as cancerous or non-cancerous without needing specific electrophysiological parameters.