Antifouling coatings for optoelectronic tweezers

The application of an applied electrical potential to generate electrical fields and forces to enhance affinity biosensors

Affinity biosensors play a crucial role in clinical diagnosis, pharmaceuticals, immunology, and other areas of human health. Affinity biosensors rely on the specific binding between target analytes and biological ligands such as antibodies, nucleic acids, aptamers, or other receptors to primarily generate electrochemical or optical signals. Considerable effort has been put into improving the performance of the affinity technologies to make them more sensitive, efficient and reproducible, of the many approaches electrokinetic phenomena are a viable option. In this perspective, studies that combine electrokinetic phenomena with affinity biosensor are discussed about their promise for achieving higher sensitivity and lower detection limit.

Optoelectronic tweezers: a versatile toolbox for nano-/micro-manipulation

This review covers the fundamentals, recent progress and state-of-the-art applications of optoelectronic tweezers technology, and demonstrates that optoelectronic tweezers technology is a versatile and powerful toolbox for nano-/micro-manipulation.

Sulfonated Polyaniline as Zwitterionic and Conductive Interfaces for Anti-Biofouling on Open Electrode Surfaces in Electrodynamic Systems

Electrodynamic systems for bioanalytical applications constantly suffer from biofouling due to electrical field-induced nonspecific bioadsorption on electrode surfaces. To minimize this issue, surface modification using anti-biofouling and conductive materials is necessary to not only protect the electrode surface from nonspecific bioadsorption but also maintain desired electrodynamic properties for electrode operation. In this study, we designed and prepared a conductive, zwitterionic, and self-doped sulfonated polyaniline (SPANI) coating on Au electrode surfaces for anti-biofouling applications. The zwitterionic coating was fabricated by electrochemical polymerization of aniline on the Au electrode surface functionalized with cysteamine (HS-CH₂CH₂-NH₂) and then a post-polymerization treatment with fuming sulfuric acid. We found that the SPANI-coated electrodes exhibited an excellent anti-biofouling ability in dielectrophoresis (DEP) capturing-and-releasing processes, with a very low average residual mass rate of 1.44% for the SPANI-5s electrode, whereas electrodes modified with poly(ethylene glycol) (PEG) gave an average residual mass rate of 14.30%. Even under continuous operation for more than 1 h, the SPANI-5s electrode still showed stable anti-biofouling ability for an 11-cycle E. coli capturing-and-releasing DEP process, with the residual mass rate for all 11 cycles being kept at or below 2.18% to give an average residual mass rate of 1.62% with a standard deviation of 0.40%. This study demonstrates that electrodynamic systems with zwitterionic SPANI coated on open electrode surfaces can excellently function with decent conductance and anti-biofouling performance.

Optoelectrokinetics-based microfluidic platform for bioapplications: A review of recent advances

The introduction of optoelectrokinetics (OEK) into lab-on-a-chip systems has facilitated a new cutting-edge technique-the OEK-based micro/nanoscale manipulation, separation, and assembly processes-for the microfluidics community. This technique offers a variety of extraordinary advantages such as programmability, flexibility, high biocompatibility, low-cost mass production, ultralow optical power requirement, reconfigurability, rapidness, and ease of integration with other microfluidic units. This paper reviews the physical mechanisms that govern the manipulation of micro/nano-objects in microfluidic environments as well as applications related to OEK-based micro/nanoscale manipulation-applications that span from single-cell manipulation to single-molecular behavior determination. This paper wraps up with a discussion of the current challenges and future prospects for the OEK-based microfluidics technique. The conclusion is that this technique will allow more opportunities for biomedical and bioengineering researchers to improve lab-on-a-chip technologies and will have far-reaching implications for biorelated researches and applications in the future.

Extracellular-controlled breast cancer cell formation and growth using non-UV patterned hydrogels via optically-induced electrokinetics

The culturing of cancer cells on micropatterned substrates can provide insight into the factors of the extracellular environment that enable the control of cell growth. We report here a novel non-UV-based technique to quickly micropattern a poly-(ethylene) glycol diacrylate (PEGDA)-based hydrogel on top of modified glass substrates, which were then used to control the growth patterns of breast cancer cells. Previously, the fabrication of micropatterned substrates required relatively complicated steps, which made it impractical for researchers to rapidly and systematically investigate the effects of different cell growth patterns. The technique presented herein operates on the principle of optically-induced electrokinetics (OEKs) and uses computer-generated projection light patterns to dynamically pattern the hydrogel on a hydrogenated amorphous silicon (a-Si:H) thin-film, atop an indium tin oxide (ITO) glass substrate. This technique allows us to pattern lines, circles, pentagons, and more complex shapes in the hydrogel with line widths below 3 μm and thicknesses of up to 6 μm within 8 s by simply controlling the projected illumination pattern and applying an appropriate AC voltage between the two ITO glass substrates. After separating the glass substrates to expose the patterned hydrogel, we experimentally demonstrate that MCF-7 breast cancer cells will adhere to the bare a-Si:H surface, but not to the hydrogel patterned in various geometric shapes and sizes. Theoretical analysis and finite-element model simulations reveal that the dominant OEK forces in our technique are the dielectrophoresis (DEP) force and the electro-osmosis force, which enhance the photo-initiated cross-linking reaction in the hydrogel. Our preliminary cultures of breast cancer cells demonstrate that this reported technique could be applied to effectively confine the growth of cancer cells on a-Si:H surfaces and affect individual cell geometry during their growth.

Rapid and label-free separation of Burkitt's lymphoma cells from red blood cells by optically-induced electrokinetics

Early stage detection of lymphoma cells is invaluable for providing reliable prognosis to patients. However, the purity of lymphoma cells in extracted samples from human patients' marrow is typically low. To address this issue, we report here our work on using optically-induced dielectrophoresis (ODEP) force to rapidly purify Raji cells' (a type of Burkitt's lymphoma cell) sample from red blood cells (RBCs) with a label-free process. This method utilizes dynamically moving virtual electrodes to induce negative ODEP force of varying magnitudes on the Raji cells and RBCs in an optically-induced electrokinetics (OEK) chip. Polarization models for the two types of cells that reflect their discriminate electrical properties were established. Then, the cells' differential velocities caused by a specific ODEP force field were obtained by a finite element simulation model, thereby established the theoretical basis that the two types of cells could be separated using an ODEP force field. To ensure that the ODEP force dominated the separation process, a comparison of the ODEP force with other significant electrokinetics forces was conducted using numerical results. Furthermore, the performance of the ODEP-based approach for separating Raji cells from RBCs was experimentally investigated. The results showed that these two types of cells, with different concentration ratios, could be separated rapidly using externally-applied electrical field at a driven frequency of 50 kHz at 20 V_pp. In addition, we have found that in order to facilitate ODEP-based cell separation, Raji cells' adhesion to the OEK chip's substrate should be minimized. This paper also presents our experimental results of finding the appropriate bovine serum albumin concentration in an isotonic solution to reduce cell adhesion, while maintaining suitable medium conductivity for electrokinetics-based cell separation. In short, we have demonstrated that OEK technology could be a promising tool for efficient and effective purification of Raji cells from RBCs.

Microfluidic integrated optoelectronic tweezers for single-cell preparation and analysis

We report a novel microfluidic integrated optoelectronic tweezers (OET) platform for single-cell sample preparation and analysis. Integration of OET and microfluidics is achieved by embedding single-wall carbon nanotube (SWNT) electrodes into multilayer PDMS structures. This integrated platform allows users to selectively pick up individual cells from a population with light beams based on their optical signatures such as size, shape, and fluorescence, and transport them into isolated chambers using light induced dielectrophoretic forces. Isolated cells can be encapsulated into nanoliter liquid plugs and transported out of the platform for downstream molecule analysis using standard commercial instruments.

High-purity and label-free isolation of circulating tumor cells (CTCs) in a microfluidic platform by using optically-induced-dielectrophoretic (ODEP) force

Negative selection-based circulating tumor cell (CTC) isolation is believed valuable to harvest more native, and in particular all possible CTCs without biases relevant to the properties of surface antigens on the CTCs. Under such a cell isolation strategy, however, the CTC purity is normally compromised. To address this issue, this study reports the integration of optically-induced-dielectrophoretic (ODEP) force-based cell manipulation, and a laminar flow regime in a microfluidic platform for the isolation of untreated, and highly pure CTCs after conventional negative selection-based CTC isolation. In the design, six sections of moving light-bar screens were continuously and simultaneously exerted in two parallel laminar flows to concurrently separate the cancer cells from the leukocytes based on their size difference and electric properties. The separated cell populations were further partitioned, delivered, and collected through the two flows. With this approach, the cancer cells can be isolated in a continuous, effective, and efficient manner. In this study, the operating conditions of ODEP for the manipulation of prostate cancer (PC-3) and human oral cancer (OEC-M1) cells, and leukocytes with minor cell aggregation phenomenon were first characterized. Moreover, performances of the proposed method for the isolation of cancer cells were experimentally investigated. The results showed that the presented CTC isolation scheme was able to isolate PC-3 cells or OEC-M1 cells from a leukocyte background with high recovery rate (PC-3 cells: 76-83%, OEC-M1 cells: 61-68%), and high purity (PC-3 cells: 74-82%, OEC-M1 cells: 64-66%) (set flow rate: 0.1 μl min(-1) and sample volume: 1 μl). The latter is beyond what is currently possible in the conventional CTC isolations. Moreover, the viability of isolated cancer cells was evaluated to be as high as 94 ± 2%, and 95 ± 3% for the PC-3, and OEC-M1 cells, respectively. Furthermore, the isolated cancer cells were also shown to preserve their proliferative capability. As a whole, this study has presented an ODEP-based microfluidic platform that is capable of isolating CTCs in a continuous, label-free, cell-friendly, and particularly highly pure manner. All these traits are found particularly meaningful for exploiting the harvested CTCs for the subsequent cell-based, or biochemical assays.

Hybrid opto-electric manipulation in microfluidics-opportunities and challenges

Hybrid opto-electric manipulation in microfluidics/nanofluidics refers to a set of methodologies employing optical modulation of electrokinetic schemes to achieve particle or fluid manipulation at the micro- and nano-scale. Over the last decade, a set of methodologies, which differ in their modulation strategy and/or the length scale of operation, have emerged. These techniques offer new opportunities with their dynamic nature, and their ability for parallel operation has created novel applications and devices. Hybrid opto-electric techniques have been utilized to manipulate objects ranging in diversity from millimetre-sized droplets to nano-particles. This review article discusses the underlying principles, applications and future perspectives of various hybrid opto-electric techniques that have emerged over the last decade under a unified umbrella.

Microfluidic chips for point-of-care immunodiagnostics

We might be at the turning point where research in microfluidics undertaken in academia and industrial research laboratories, and substantially sponsored by public grants, may provide a range of portable and networked diagnostic devices. In this Progress Report, an overview on microfluidic devices that may become the next generation of point-of-care (POC) diagnostics is provided. First, we describe gaps and opportunities in medical diagnostics and how microfluidics can address these gaps using the example of immunodiagnostics. Next, we conceptualize how different technologies are converging into working microfluidic POC diagnostics devices. Technologies are explained from the perspective of sample interaction with components of a device. Specifically, we detail materials, surface treatment, sample processing, microfluidic elements (such as valves, pumps, and mixers), receptors, and analytes in the light of various biosensing concepts. Finally, we discuss the integration of components into accurate and reliable devices.

Optoelectrofluidic platforms for chemistry and biology

Extraordinary advances in lab on a chip systems have been made on the basis of the development of micro/nanofluidics and its fusion with other technologies based on electrokinetics and optics. Optoelectrofluidic technology, which has been recently introduced as a new manipulation scheme, allows programmable manipulation of particles or fluids in microenvironments based on optically induced electrokinetics. Herein, the behaviour of particles or fluids can be controlled by inducing or perturbing electric fields on demand in an optical manner, which includes photochemical, photoconductive, and photothermal effects. This elegant scheme of the optoelectrofluidic platform has attracted attention in various fields of science and engineering. A lot of research on optoelectrofluidic manipulation technologies has been reported and the field has advanced rapidly, although some technical hurdles still remain. This review describes recent developments and future perspectives of optoelectrofluidic platforms for chemical and biological applications.

Motile and non-motile sperm diagnostic manipulation using optoelectronic tweezers

Optoelectronic tweezers was used to manipulate human spermatozoa to determine whether their response to OET predicts sperm viability among non-motile sperm. We review the electro-physical basis for how live and dead human spermatozoa respond to OET. The maximal velocity that non-motile spermatozoa could be induced to move by attraction or repulsion to a moving OET field was measured. Viable sperm are attracted to OET fields and can be induced to move at an average maximal velocity of 8.8 ± 4.2 µm s(-1), while non-viable sperm are repelled to OET, and are induced to move at an average maximal velocity of -0.8 ± 1.0 µm s(-1). Manipulation of the sperm using OET does not appear to result in increased DNA fragmentation, making this a potential method by which to identify viable non-motile sperm for assisted reproductive technologies.