Digital microfluidics (DMFs) show great potential in the fields of lab-on-a-chip applications for electro-chemical as well as biochemical sensing for decades. Various types of DMF devices have been demonstrated to improve their capabilities such as smaller device size for portability, higher reliability, and multi-purpose applications, etc. Among them, the electrowetting on dielectric (EWOD) is one of the most widely used mechanisms to manipulate droplets due to its good flexibility. On the other hand, the high-voltage application that required for EWOD-type DMF also limits the portability and dimension of the whole system. In this review, we discuss the DMFs which are powered by alternative sources other than electrical sources and evaluate their potential for future portable biochemical assays. Then, the demonstrations reported with the possibility beyond high voltage are discussed starting from lowering voltage requirement for EWODs to the unique methods using mechanical, optical, and energy harvesting to power DMF devices. Finally, the practical applications and prospective on the integrated multi-functional lab-on-a-chip applications are tackled.

Beyond high voltage in the digital microfluidic devices for an integrated portable sensing system

In order to get rid of the dependence on expensive photolithography technology and related facilities, an economic and simple design and fabrication technology for digital microfluidics (DMF) is proposed. The electrodes pattern was generated by inkjet printing nanosilver conductive ink on the flexible Polyethylene terephthalate (PET) substrate with a 3D circuit board printer, food wrap film was attached to the electrode array to act as the dielectric layer and Teflon® AF was sprayed to form a hydrophobic layer. The PET substrate and food wrap film are low cost and accessible to general users. The proposed flexible DMF chips can be reused for a long time by replacing the dielectric film coated with hydrophobic layer. The resolution and conductivity of silver traces and the contact angle and velocity of the droplets were evaluated to demonstrate that the proposed technology is comparable to the traditional DMF fabrication process. As far as the rapid prototyping of DMF is concerned, this technology has shown very attractive advantages in many aspects, such as fabrication cost, fabrication time, material selection and mass production capacity, without sacrificing the performance of DMF. The flexible DMF chips have successfully implemented basic droplet operations on a square and hexagon electrode array.

https://www.mdpi.com/2072-666X/11/12/1113/pdf

Electrowetting-on-Dielectric Based Economical Digital Microfluidic Chip on Flexible Substrate by Inkjet Printing

On the complexity of design tasks for Digital Microfluidic Biochips

Digital Microfluidic Biochips (DMFBs) are an emerging technology promising a high degree of automation in laboratory procedures by means of manipulating small discretized amounts of fluids. A crucial part in conducting experiments on biochips is the routing of discretized droplets. While doing so, droplets must not enter each others' interference region to avoid unintended mixing. This leads to cells in the proximity of the droplet being impassable for others. For different cell shapes, the effect of these temporary blockages varies as the adjacency of cells changes with their shapes. Yet, no evaluation with respect to routability in relation to cell shapes has been conducted so far. This paper analyses and compares various tessellations for the field of cells. Routing benchmarks are mapped to these and the results are compared in order to determine if and how cell shapes affect the performance of DMFBs, showing that certain cell shapes are superior to others.

Effects of cell shapes on the routability of Digital Microfluidic Biochips

Recent emergence of micro-electrode-dot array (MEDA) based digital microfluidic biochips has facilitated major improvement in microfluidic operations for conventional lab-on-chip devices. MEDA based digital microfluidic biochips typically consist of a 2D planar array of cells of square sized microelectrodes. One of the most critical issues in the biochip layout design is the droplet transportation within the 2D layout. MEDA allows for dynamic routing with variable shaped and sized droplets. Microelectrode cells are dynamically group together to form configured microelectrode array (CMA) for variable shaped and sized droplets. This existing square shaped CMA is highly suitable for the droplets that needs exactly rectangular or square area but may not be as effective for rhombus or hexagonal shaped areas occupied by droplets. This is because the occupied additional area may be useful for other droplets to accommodate their corresponding minimum shortest path. In this paper, we present some MEDA layout design of 2D planar array of cells using triangle shaped microelectrodes by arranging them in a regular way. This allows for better convenience towards formation of different droplet shapes more efficiently, specifically for rhombus or hexagonal sized droplets. MEDA routing operations has been conducted on this newly proposed MEDA layout (using variable shaped electrodes) followed by analysis and comparison with existing MEDA layout design. Finally droplet transportation with standard bench marks are mapped in order to demonstrate how well the proposed designs can improve the performance of bioassay execution in MEDA based DMFB layout.

Micro-electrode-dot Array Based Biochips : Advantages of Using Different Shaped CMAs

Digital Microfluidic Biochip (DMFB) is a ground-breaking invention in many areas of Microelectronics, Biochemistry, and Biomedical sciences. It is also known as ‘Lab-on-a-Chip’ for its performance as an alternative for laboratory experiments. Various types of diagnosis procedures are performed on it through a sequence of modular operations like sample preparation, mixing, and detection. Mixing is the most important operation of DMFB as the outcome of the experiment is almost dominated by mixing. A good mixing of corresponding sample and reagent gives proper result while an improper mixing leads to erroneous result, which may be the reason to discard the assay. So, our objective is the betterment of mixing operation. In this paper, we have proposed a design using equilateral triangular electrodes instead of square electrodes, maintaining all the constraints required to ensure safe droplet movement and other modular operations, while improvement of the mixing operation is the key design issue.

http://ieeexplore.ieee.org/iel7/7008821/7026810/07026907.pdf

A technology shift towards triangular electrodes from square electrodes in design of Digital Microfluidic Biochip

A Design of Digital Microfluidic Biochip along with Structural and Behavioural Features in Triangular Electrode Based Array

Microfluidic biochip is a lab-on-a-chip system that replaces conventional laboratory experiments. Digital Microfluidic Biochip (DMFB) handles liquids as discrete droplets, and offers highly reconfigurable and scalable technology. DMFB combines electronics with biology opening the new application areas of Microelectronics, Biochemistry, and Biomedical sciences. A new application area of DMFB using equilateral triangular electrodes instead of square electrodes has been proposed, considering the design issues and the fluidic constraints while performing all the modular operations. The improvement of sample-reagent mixing procedure is a key challenge issue in bioassay implementation as mixing is the most dominating operation in DMFB; hence, the Triangular DMFB (TEDMB) system leads over the existing DMFB system. In this paper, we have presented a study of TEDMB mixers and developed mixing library for TEDMB synthesis.

Enhancement of mixing operation through new movement strategies in digital microfluidic biochips

In recent times, digital microfluidic biochips have received an appreciable recognition as one of the most promising platforms for lab-on-a-chip attainment. Such a compound system can replace most of the laboratory experiments by controlling nano-litre or micro-litre volume of droplets and yield more accurate and faster results depending upon electrowetting on dielectric (EWOD) principle. Being aware of the fact about the progress of traditional square electrode biochips in the digital microfluidic realm, here in this paper, we present two-dimensional regular hexagonal digital microfluidic electrode (HDMFB) array. A hexagonal chip array offers numerous advantages over a square array like droplet movement, mixing operation, speed, etc. To cope with this new design technique care should be taken for fluidic constraints and electrode constraints to ensure safe droplet routing. Here, we propose an algorithm for efficient control pin assignment on the chip such that no droplet interference on the chip array occurs during an assay operation. Moreover, a multiplexed assay operation is performed by a scheduling algorithm, and the result is compared with a previous work conducted on the conventional square electrode array. Finally, a comparative study is done on the proposed architecture and the existing one on some relevant issues.

Structural and Behavioural Facets of Digital Microfluidic Biochips with Hexagonal-Electrode-Based Array

Digital microfluidic biochips skilfully manoeuvre a significant assignment in the realm of biochips by supervising droplets of nano-or micro-litre volume. Enhancement of reliable and precise outcomes of digital microfluidic biochips open a new era in environmental as well as biological science. Being concerned about various advancements and considering all design specifications along with the decisive factors like fluidic and pin constraints, we have structured the hexagonal electrode based digital microfluidic biochip system over traditional square electrodes, and also implemented the most significant modular operation, i.e. droplet routing regarding its behavioural natures. Finally, we have devised an improved safe droplet routing algorithm on the hexagonal cell array without any droplet interference and incorporated a comparative study between this new architecture and the existing square one.

Riya Majumder

Papers

A technology shift towards triangular electrodes from square electrodes in design of Digital Microfluidic Biochip

A Design of Digital Microfluidic Biochip along with Structural and Behavioural Features in Triangular Electrode Based Array

Enhancement of mixing operation through new movement strategies in digital microfluidic biochips

Structural and Behavioural Facets of Digital Microfluidic Biochips with Hexagonal-Electrode-Based Array

Structural Modelling, Design Automation, and a Generalized Routing Technique for Digital Microfluidic Biochips with Hexagonal Electrodes