Recent advances in dielectrophoresis toward biomarker detection: A summary of studies published between 2014 and 2021

Enhancing the efficiency of lung cancer cell capture using microfluidic dielectrophoresis and aptamer-based surface modification

Metastasis remains a significant cause to cancer-related mortality, underscoring the critical need for early detection and analysis of circulating tumor cells (CTCs). This study presents a novel microfluidic chip designed to efficiently capture A549 lung cancer cells by combining dielectrophoresis (DEP) and aptamer-based binding, thereby enhancing capture efficiency and specificity. The microchip features interdigitated electrodes made of indium-tin-oxide that generate a nonuniform electric field to manipulate CTCs. Following three chip design, scenarios were investigated: (A) bare glass surface, (B) glass modified with gold nanoparticles (AuNPs) only, and (C) glass modified with both AuNPs and aptamers. Experimental results demonstrate that AuNPs significantly enhance capture efficiency under DEP, with scenarios (B) and (C) exhibiting similar performance. Notably, scenario (C) stands out as aptamer-functionalized surfaces resisting fluid shear forces, achieving CTCs retention even after electric field deactivation. Additionally, an innovative reverse pumping method mitigates inlet clogging, enhancing experimental efficiency. This research offers valuable insights into optimizing surface modifications and understanding key factors influencing cell capture, contributing to the development of efficient cell manipulation techniques with potential applications in cancer research and personalized treatment options.

Fabricating a dielectrophoretic microfluidic device using 3D-printed moulds and silver conductive paint

Dielectrophoresis is an electric field-based technique for moving neutral particles through a fluid. When used for particle separation, dielectrophoresis has many advantages compared to other methods, like providing label-free operation with greater control of the separation forces. In this paper, we design, build, and test a low-voltage dielectrophoretic device using a 3D printing approach. This lab-on-a-chip device fits on a microscope glass slide and incorporates microfluidic channels for particle separation. First, we use multiphysics simulations to evaluate the separation efficiency of the prospective device and guide the design process. Second, we fabricate the device in PDMS (polydimethylsiloxane) by using 3D-printed moulds that contain patterns of the channels and electrodes. The imprint of the electrodes is then filled with silver conductive paint, making a 9-pole comb electrode. Lastly, we evaluate the separation efficiency of our device by introducing a mixture of 3 μm and 10 μm polystyrene particles and tracking their progression. Our device is able to efficiently separate these particles when the electrodes are energized with ±12 V at 75 kHz. Overall, our method allows the fabrication of cheap and effective dielectrophoretic microfluidic devices using commercial off-the-shelf equipment.

Label-free microfluidic cell sorting and detection for rapid blood analysis

Blood tests are considered as standard clinical procedures to screen for markers of diseases and health conditions. However, the complex cellular background (>99.9% RBCs) and biomolecular composition often pose significant technical challenges for accurate blood analysis. An emerging approach for point-of-care blood diagnostics is utilizing "label-free" microfluidic technologies that rely on intrinsic cell properties for blood fractionation and disease detection without any antibody binding. A growing body of clinical evidence has also reported that cellular dysfunction and their biophysical phenotypes are complementary to standard hematoanalyzer analysis (complete blood count) and can provide a more comprehensive health profiling. In this review, we will summarize recent advances in microfluidic label-free separation of different blood cell components including circulating tumor cells, leukocytes, platelets and nanoscale extracellular vesicles. Label-free single cell analysis of intrinsic cell morphology, spectrochemical properties, dielectric parameters and biophysical characteristics as novel blood-based biomarkers will also be presented. Next, we will highlight research efforts that combine label-free microfluidics with machine learning approaches to enhance detection sensitivity and specificity in clinical studies, as well as innovative microfluidic solutions which are capable of fully integrated and label-free blood cell sorting and analysis. Lastly, we will envisage the current challenges and future outlook of label-free microfluidics platforms for high throughput multi-dimensional blood cell analysis to identify non-traditional circulating biomarkers for clinical diagnostics.

Fabrication and Separation of EGaIn Microparticles from Human Blood Based on Dielectrophoresis Force and a W-Type Electrode

Harmful particles such as heavy metal particles in the human body can cause many problems such as kidney stones, gallstones, and cerebrovascular diseases. Therefore, it is critical to separate them from the blood and perform a systematic analysis as early as possible. Here, we apply eutectic gallium indium (EGaIn) microparticles as a model to study the separation of particles from blood, thanks to their properties of low toxicity, excellent degradability, and negligible vapor pressure. In particular, the dielectrophoresis (DEP) separation method is employed to separate EGaIn of different sizes and characteristics in blood. First, the screen-printing method is used to create EGaIn microparticles with diameters of 15, 23, 18, and 11 μm. According to the lifetime test, these microparticles can last more than 1 month, as evidenced by their surface oxidation characteristics. Moreover, a DEP platform with W-type electrodes is developed to sort EGaIn particles from whole human blood. The results show that a sorting efficiency of 95% can be attained, which is similar to the separation efficiency of 98% achieved by finite element analysis (FEA) using COMSOL software based on the orthogonal array experiment method. The proposed study successfully validates the use of the DEP method to separate particles from human blood, providing insights into heavy metal particle separating, drug screening, and cell sorting and potentially broadening the applications in environmental analysis, food engineering, and bioengineering.

Impact of buffer composition on biochemical, morphological and mechanical parameters: A tare before dielectrophoretic cell separation and isolation

Dielectrophoresis (DEP) represents an electrokinetic approach for discriminating and separating suspended cells based on their intrinsic dielectric characteristics without the need for labeling procedure. A good practice, beyond the physical and engineering components, is the selection of a buffer that does not hinder cellular and biochemical parameters as well as cell recovery. In the present work the impact of four buffers on biochemical, morphological, and mechanical parameters was evaluated in two different cancer cell lines (Caco-2 and K562). Specifically, MTT ([3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide]) assay along with flow cytometry analysis were used to evaluate the occurring changes in terms of cell viability, morphology, and granulocyte stress formation, all factors directly influencing DEP sorting capability. Quantitative real-time PCR (qRT-PCR) was instead employed to evaluate the gene expression levels of interleukin-6 (IL-6) and inducible nitric oxide synthase (iNOS), two well-known markers of inflammation and oxidative stress, respectively. An additional marker representing an index of cellular metabolic status, i.e. the expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene, was also evaluated. Among the four buffers considered, two resulted satisfactory in terms of cell viability and growth recovery (24 h), with no significant changes in cell morphology for up to 1 h in suspension. Of note, gene expression analysis showed that in both cell lines the apparently non-cytotoxic buffers significantly modulated IL-6, iNOS, and GAPDH markers, underlining the importance to deeply investigate the molecular and biochemical changes occurring during the analysis, even at apparently non-toxic conditions. The selection of a useful buffer for the separation and analysis of cells without labeling procedures, preserving cell status, represents a key factor for DEP analysis, giving the opportunity to further use cells for additional analysis.

Dielectrophoresis: An Approach to Increase Sensitivity, Reduce Response Time and to Suppress Nonspecific Binding in Biosensors?

The performance of receptor-based biosensors is often limited by either diffusion of the analyte causing unreasonable long assay times or a lack of specificity limiting the sensitivity due to the noise of nonspecific binding. Alternating current (AC) electrokinetics and its effect on biosensing is an increasing field of research dedicated to address this issue and can improve mass transfer of the analyte by electrothermal effects, electroosmosis, or dielectrophoresis (DEP). Accordingly, several works have shown improved sensitivity and lowered assay times by order of magnitude thanks to the improved mass transfer with these techniques. To realize high sensitivity in real samples with realistic sample matrix avoiding nonspecific binding is critical and the improved mass transfer should ideally be specific to the target analyte. In this paper we cover recent approaches to combine biosensors with DEP, which is the AC kinetic approach with the highest selectivity. We conclude that while associated with many challenges, for several applications the approach could be beneficial, especially if more work is dedicated to minimizing nonspecific bindings, for which DEP offers interesting perspectives.