In biomedical research and diagnostics, it is a significant challenge to directly isolate and identify rare cells and potential biomarkers in blood, plasma and other clinical samples. Additionally, the advent of bionanotechnology is leading to numerous drug delivery approaches that involve encapsulation of drugs and imaging agents within nanoparticles, which now will also have to be identified and separated from blood and plasma. Alternating current (AC) electrokinetic techniques such as dielectrophoresis (DEP) offer a particularly attractive mechanism for the separation of cells and nanoparticles. Unfortunately, present DEP techniques require the dilution of blood/plasma, thus making the technology less suitable for clinical sample preparation. Using array devices with microelectrodes over-coated with porous hydrogel layers, AC electric field conditions have been found which allow the separation of DNA nanoparticles to be achieved under high-conductance (ionic strength) conditions. At AC frequencies in the 3000 Hz to 10,000 Hz range and 10 volts peak-to-peak, the separation of 10-microm polystyrene particles into low field regions, and 60-nm DNA-derivatized nanoparticles and 200-nm nanoparticles into high-field regions was carried out in 149 mM 1xPBS buffer (1.68 S/m). These results may allow AC electrokinetic systems to be developed that can be used with clinically relevant samples under physiological conditions.

The ability to effectively detect disease‐related DNA biomarkers and drug delivery nanoparticles directly in blood is a major challenge for viable diagnostics and therapy monitoring. A DEP method has been developed which allows the rapid isolation, concentration and detection of DNA and nanoparticles directly from human and rat whole blood. Using a microarray device operating at 20 V peak‐to‐peak and 10 kHz, a wide range of high molecular weight (HMW)‐DNA and nanoparticles were concentrated into high‐field regions by positive DEP, while the blood cells were concentrated into the low‐field regions by negative DEP. A simple fluidic wash removes the blood cells while the DNA and nanoparticles remain concentrated in the DEP high‐field regions where they can be detected by fluorescence. HMW‐DNA could be detected at 260 ng/mL, which is a detection level suitable for analysis of disease‐related cell‐free circulating DNA biomarkers. Fluorescent 40 nm nanoparticles could be detected at 9.5 × 109 particles/mL, which is a level suitable for monitoring drug delivery nanoparticles. The ability to rapidly isolate and detect DNA biomarkers and nanoparticles from undiluted whole blood will benefit many diagnostic applications by significantly reducing sample preparation time and complexity.

Dielectrophoretic (DEP) microarray devices allow important cellular nanoparticulate biomarkers and virus to be rapidly isolated, concentrated and detected directly from clinical and biological samples. A variety of sub-micron nanoparticulate entities including cell free circulating (cfc) DNA, mitochondria and virus can be isolated into DEP high-field areas on microelectrodes, while blood cells and other micron-size entities become isolated into DEP low-field areas between the microelectrodes. The nanoparticulate entities are held in the DEP high-field areas while cells are washed away along with proteins and other small molecules which are not affected by the DEP electric fields. DEP carried out on 20 µL of whole blood obtained from Chronic Lymphocytic Leukemia (CLL) patients showed a considerable amount of SYBR Green stained DNA fluorescent material concentrated in the DEP high-field regions. Whole blood obtained from healthy individuals showed little or no fluorescent DNA materials in the DEP high-field regions. Fluorescent T7 bacteriophage virus could be isolated directly from blood samples, and fluorescently stained mitochondria could be isolated from biological buffer samples. Using newer DEP microarray devices, high molecular weight (hmw) DNA could be isolated from serum and detected at levels as low as 8–16 ng/mL.

The separation of nanoparticles from micron size particles in high conductance buffers was achieved using an AC dielectrophoretic (DEP) microarray device with hydrogel over-coated microelectrodes. While nanoparticles could be selectively concentrated into high field regions directly over the platinum microelectrodes, micro-bubbling and electrode darkening was also observed. For similar experiments using un-coated microelectrodes, SEM analysis showed severe erosion of the platinum microelectrodes and fusion of nanoparticles due to the aggressive electrochemistry.