The Effect of Optically Induced Dielectrophoresis (ODEP)-Based Cell Manipulation in a Microfluidic System on the Properties of Biological Cells

The Utilization of Optically Induced Dielectrophoresis (ODEP)-Based Cell Manipulation in a Microfluidic System for the Purification and Sorting of Circulating Tumor Cells (CTCs) with Different Sizes

The analysis of circulating tumor cells (CTCs) at the molecular level holds great promise for several clinical applications. For this goal, the harvest of high-purity, size-sorted CTCs with different subtypes from a blood sample are important. For this purpose, a two-step CTC isolation protocol was proposed, by which the immunomagnetic beads-based cell separation was first utilized to remove the majority of blood cells. After that, an optically induced dielectrophoresis (ODEP) microfluidic system was developed to (1) purify the CTCs from the remaining magnetic microbeads-bound blood cells and to (2) sort and separate the CTCs with different sizes. In this study, the ODEP microfluidic system was designed and fabricated. Moreover, its optimum operation conditions and performance were explored. The results exhibited that the presented technique was able to purify and sort the cancer cells with two different sizes from a tested cell suspension in a high-purity (93.5% and 90.1% for the OECM 1 and HA22T cancer cells, respectively) manner. Overall, this study presented a technique for the purification and sorting of cancer cells with different sizes. Apart from this application, the technique is also useful for other applications in which the high-purity and label-free purification and sorting of cells with different sizes is required.

Recent Progress in Enhanced Cancer Diagnosis, Prognosis, and Monitoring Using a Combined Analysis of the Number of Circulating Tumor Cells (CTCs) and Other Clinical Parameters

Analysis of circulating tumor cells (CTCs) holds promise to diagnose cancer or monitor its development. Among the methods, counting CTC numbers in blood samples could be the simplest way to implement it. Nevertheless, its clinical utility has not yet been fully accepted. The reasons could be due to the rarity and heterogeneity of CTCs in blood samples that could lead to misleading results from assays only based on single CTC counts. To address this issue, a feasible direction is to combine the CTC counts with other clinical data for analysis. Recent studies have demonstrated the use of this new strategy for early detection and prognosis evaluation of cancers, or even for the distinguishment of cancers with different stages. Overall, this approach could pave a new path to improve the technical problems in the clinical applications of CTC counting techniques. In this review, the information relevant to CTCs, including their characteristics, clinical use of CTC counting, and technologies for CTC enrichment, were first introduced. This was followed by discussing the challenges and new perspectives of CTC counting techniques for clinical applications. Finally, the advantages and the recent progress in combining CTC counts with other clinical parameters for clinical applications have been discussed.

Development of an Optically Induced Dielectrophoresis (ODEP) Microfluidic System for High-Performance Isolation and Purification of Bacteria

For the rapid detection of bacteria in a blood sample, nucleic acid amplification-based assays are believed to be promising. Nevertheless, the nucleic acids released from the dead blood cells or bacteria could affect the assay performance. This highlights the importance of the isolation of live bacteria from blood samples. To address this issue, this study proposes a two-step process. First, a blood sample was treated with the immuno-magnetic microbeads-based separation to remove the majority of blood cells. Second, an optically induced dielectrophoresis (ODEP) microfluidic system with an integrated dynamic circular light image array was utilized to further isolate and purify the live bacteria from the remaining blood cells based on their size difference. In this work, the ODEP microfluidic system was developed. Its performance for the isolation and purification of bacteria was evaluated. The results revealed that the method was able to harvest the live bacteria in a high purity (90.5~99.2%) manner. Overall, the proposed method was proven to be capable of isolating and purifying high-purity live bacteria without causing damage to the co-existing cells. This technical feature was found to be valuable for the subsequent nucleic-acid-based bacteria detection, in which the interferences caused by the nontarget nucleic acids could be eliminated.

Microfluidic Bio-Sensors and Their Applications

Biosensors are a promising tool for a wide variety of target analyte detection and enable point-of-care diagnostics with reduced volume and space [...].

Label-free purification and characterization of optogenetically engineered cells using optically-induced dielectrophoresis

Optogenetically engineered cell population obtained by heterogeneous gene expression plays a vital role in life science, medicine, and biohybrid robotics, and purification and characterization are essential to enhance its application performance. However, the existing cell purification methods suffer from complex sample preparation or inevitable damage and pollution. The efficient and nondestructive label-free purification and characterization of the optogenetically engineered cells, HEK293-ChR2 cells, is provided here using an optically-induced dielectrophoresis (ODEP)-based approach. The distinctive crossover frequencies of the engineered cells and the unmodified cells enable effective separation due to the opposite DEP forces on them. The ODEP-based approach can greatly improve the purity of the separated cell population and especially, the ratio of the engineered cells in the separated cell population can be enhanced by 275% at a low transfection rate. The size and the membrane capacitance of the separated cell population decreases and increases, respectively, as the ratio of the engineered cells grows in the cell population, indicating that successful expression of ChR2 in a single HEK293 cell makes its size and membrane capacitance smaller and larger, respectively. The results of biohybrid imaging with the optogenetically engineered cells demonstrated that cell purification can improve the imaging quality. This work proves that the separation and purification of engineered cells are of great significance for their application in practice.

The Utilization of Tunable Transducer Elements Formed by the Manipulation of Magnetic Beads with Different Sizes via Optically Induced Dielectrophoresis (ODEP) for High Signal-to-Noise Ratios (SNRs) and Multiplex Fluorescence-Based Biosensing Applications

Magnetic beads improve biosensing performance by means of their small volume and controllability by magnetic force. In this study, a new technique composed of optically induced dielectrodphoresis (ODEP) manipulation and image processing was used to enhance the signal-to-noise ratio of the fluorescence for stained magnetic beads. According to natural advantages of size-dependent particle isolation by ODEP manipulation, biomarkers in clinical samples can be easily separated by different sizes of magnetic beads with corresponding captured antibodies, and rapidly distinguished by separated location of immunofluorescence. To verify the feasibility of the concept, magnetic beads with three different diameters, including 21.8, 8.7, and 4.2 μm, were easily separated and collected into specific patterns in the defined target zone treated as three dynamic transducer elements to evaluate fluorescence results. In magnetic beads with diameter of 4.2 μm, the lowest signal-to-noise ratio between stained and nonstained magnetic beads was 3.5. With the help of ODEP accumulation and detection threshold setting of 32, the signal-to-noise ratio was increased to 77.4, which makes this method more reliable. With the further optimization of specific antibodies immobilized on different-size magnetic beads in the future, this platform can be a potential candidate for a high-efficiency sensor array in clinical applications.

Dielectrophoretic separation of blood cells

Microfluidic dielectrophoretic (DEP) devices enable the label-free separation and isolation of cells based on differences in their electrophysiological properties. The technique can serve as a tool in clinical diagnostics and medical research as it facilitates the analysis of patient-specific blood composition and the detection and isolation of pathogenic cells like circulating tumor cells or malaria-infected erythrocytes. This review compares different microfluidic DEP devices to separate platelets, erythrocytes and leukocytes including their cellular subclasses. An overview and experimental setups of different microfluidic DEP devices for the separation, trapping and isolation or purification of blood cells are detailed with respect to their technical design, electrode configuration, sample preparation, applied voltage and frequency and created DEP field based and related to the separation efficiency. The technique holds the promise that results can quickly be attained in clinical and ambulant settings. In particular, point-of-care-testing scenarios are favored by the extensive miniaturization, which would be enabled by microelectronical integration of DEP devices.

Accurate Micromanipulation of Optically Induced Dielectrophoresis Based on a Data-Driven Kinematic Model

The precise control method plays a crucial role in improving the accuracy and efficiency of the micromanipulation of optically induced dielectrophoresis (ODEP). However, the unmeasurable nature of the ODEP force is a great challenge for the precise automatic manipulation of ODEP. Here, we propose a data-driven kinematic model to build an automatic control system for the precise manipulation of ODEP. The kinematic model is established by collecting the input displacement of the optical pattern and the output displacements of the manipulated object. Then, the control system based on the model was designed, and its feasibility and control precise were validated by numerical simulations and actual experiments on microsphere manipulation. In addition, the applications of ODEP manipulation in two typical scenarios further demonstrated the feasibility of the designed control system. This work proposes a new method to realize the precise manipulation of ODEP technology by establishing a kinematic model and a control system for micromanipulation, and it also provides a general approach for the improvement of the manipulation accuracy of other optoelectronic tweezers.

Improvement of Background Solution for Optically Induced Dielectrophoresis-Based Cell Manipulation in a Microfluidic System

Optically induced dielectrophoresis (ODEP) is effective for cell manipulation. However, its utilization has been limited by the requirement of solution with low conductivity. This issue has been ignored in ODEP-relevant studies. To address this issue, this study aims to investigate to what extent the cell viability and performance of ODEP-based cell manipulation are affected by low conductivity conditions. Additionally, this study aims to modify sucrose solutions to reduce the impacts caused by low-conductivity solutions. Results revealed the use of sucrose solution in ODEP operation could significantly reduce the viability of the manipulated cells by 9.1 and 38.5% after 2- and 4-h incubation, respectively. Prolonged operation time (e.g., 4 h) in sucrose solution could lead to significantly inferior performance of cell manipulation, including 47.2% reduction of ODEP manipulation velocity and 44.4% loss of the cells manipulatable by ODEP. The key finding of this study is that the use of bovine serum albumin (BSA)-supplemented sucrose solution (conductivity: 25–50 μS cm⁻¹) might significantly increase the cell viability by 10.9–14.8% compared with that in sucrose solution after 4 h incubation. Moreover, the ODEP manipulation velocity of cells in the BSA-supplemented sucrose solution (conductivity: 25 μS cm⁻¹) was comparable to that in sucrose solution during 4-h incubation. More importantly, compared with sucrose solution, the use of BSA-supplemented sucrose solution (conductivity: 25–50 μS cm⁻¹) contributed high percentage (80.4–93.5%) of the cells manipulatable by ODEP during 4-h incubation. Overall, this study has provided some fundamental information relevant to the improvement of background solutions for ODEP-based cell manipulation.

Label-free rapid isolation of saccharomyces cerevisiae with optically induced dielectrophoresis-based automatic micromanipulation

Saccharomyces cerevisiae is well-known in the baking and brewing industries and always used for the preparation of probiotics, especially its subtype, Saccharomyces boulardii, to prevent and treat various diarrhea and intestinal diseases. However, case reports on the side effects of a wide range of serious infections for the elderly, immunocompromised and critically ill patients after treatment with the S. cerevisiae have been increasing in recent years. The existing diagnose methods of the invasive S. cerevisiae infections in clinical, especially, the key step of the method-cell isolation, is time-consuming that always miss timey diagnose and early prevention. Here, we propose a new automatic micromanipulation method to label-free rapid isolation of S. cerevisiae based on the optically-induced dielectrophoresis (ODEP) technology, combining with image processing and recognition. S. cerevisiae is firstly identified by the image recognition method and then, automatically captured and moved to the target location by designing optical patterns. The results indicate the method can flexibly and automatically manipulate multiple S. cerevisiae cells simultaneously, such as, arranging S. cerevisiae cells, moving an array of the cells at any directions, aggregating the cells, and separating S. cerevisiae from the solution mixed with impurities. This work represents a step toward the use of automatic micromanipulation of ODEP technology to automatically and rapidly isolate S. cerevisiae for the detection of the invasive S. cerevisiae infections.

Methods of Generating Dielectrophoretic Force for Microfluidic Manipulation of Bioparticles

Manipulation of microscale bioparticles including living cells is of great significance to the broad bioengineering and biotechnology fields. Dielectrophoresis (DEP), which is defined as the interactions between dielectric particles and the electric field, is one of the most widely used techniques for the manipulation of bioparticles including cell separation, sorting, and trapping. Bioparticles experience a DEP force if they have a different polarization from the surrounding media in an electric field that is nonuniform in terms of the intensity and/or phase of the electric field. A comprehensive literature survey shows that the DEP-based microfluidic devices for manipulating bioparticles can be categorized according to the methods of creating the nonuniformity via patterned microchannels, electrodes, and media to generate the DEP force. These methods together with the theory of DEP force generation are described in this review, to provide a summary of the methods and materials that have been used to manipulate various bioparticles for various specific biological outcomes. Further developments of DEP-based technologies include identifying materials that better integrate with electrodes than current popular materials (silicone/glass) and improving the performance of DEP manipulation of bioparticles by combining it with other methods of handling bioparticles. Collectively, DEP-based microfluidic manipulation of bioparticles holds great potential for various biomedical applications.

An integrated actuating and sensing system for light-addressable potentiometric sensor (LAPS) and light-actuated AC electroosmosis (LACE) operation

To develop a lab on a chip (LOC) integrated with both sensor and actuator functions, a novel two-in-one system based on optical-driven manipulation and sensing in a microfluidics setup based on a hydrogenated amorphous silicon (a-Si:H) layer on an indium tin oxide/glass is first realized. A high-intensity discharge xenon lamp functioned as the light source, a chopper functioned as the modulated illumination for a certain frequency, and a self-designed optical path projected on the digital micromirror device controlled by the digital light processing module was established as the illumination input signal with the ability of dynamic movement of projected patterns. For light-addressable potentiometric sensor (LAPS) operation, alternating current (AC)-modulated illumination with a frequency of 800 Hz can be generated by the rotation speed of the chopper for photocurrent vs bias voltage characterization. The pH sensitivity, drift coefficient, and hysteresis width of the Si₃N₄ LAPS are 52.8 mV/pH, -3.2 mV/h, and 10.5 mV, respectively, which are comparable to the results from the conventional setup. With an identical two-in-one system, direct current illumination without chopper rotation and an AC bias voltage can be provided to an a-Si:H chip with a manipulation speed of 20 μm/s for magnetic beads with a diameter of 1 μm. The collection of magnetic beads by this light-actuated AC electroosmosis (LACE) operation at a frequency of 10 kHz can be easily realized. A fully customized design of an illumination path with less decay can be suggested to obtain a high efficiency of manipulation and a high signal-to-noise ratio of sensing. With this proposed setup, a potential LOC system based on LACE and LAPS is verified with the integration of a sensor and an actuator in a microfluidics setup for future point-of-care testing applications.