Jianfeng Chen

Parallel-plate lab-on-a-chip based on digital microfluidics for on-chip electrochemical analysis

This paper describes an electrowetting on dielectric (EWOD) digital microfluidic-based lab-on-a-chip (LOC) integrated with on-chip electrochemical microsensor by IC compatible fabrication process, and its application for the entire online biosensing process capable of fully automatic analysis for ferrocenemethanol (FcM) and dopamine (DA). In this work, we made full use of the parallel-plate structure of the EWOD digital microfluidic device to fabricate the microfluidic module on the bottom plate and the three-microelectrode-system-integrated electrochemical cell together with patterned ground electrode on the top plate. The proposed LOC possesses the multifunction of: (1) creating, merging and transporting of microliter-level sample droplets, (2) online biosensing, and (3) droplets recycling. The three-electrode-integrated microsensor not only reveals a sensitive electrochemical detection for FcM in a wide concentration range (10 µM–1.0 mM), but also shows good stability, selectivity and reproducibility for surface-controlled detection of DA. The calibration of DA was linear for concentration from 1.0 to 50.0 µM with a high sensitivity of 2145 nA µM−1 cm−2 (R2 = 0.9933) and estimated detection limit of 0.42 µM (signal/noise ratio of 3). This work shows the promise of state-of-the-art digital microfluidic biosensors for fully automatic online bioanalysis in a future LOC to perform on-chip biomedical protocols in vitro diagnostic assays.

Microfabrication of a digital microfluidic platform integrated with an on-chip electrochemical cell

We report on an IC compatible microfabrication process proposed for a novel monolithic lab-on-a-chip (LOC) with an electrochemical cell embedded in an electrowetting on dielectric (EWOD) digital microfluidic device. The optimized process focused on the surface modification of Teflon, selective exposure for the electrochemical module and recovery of surface properties by one-step annealing at low temperature. The optimum modification time and annealing temperature were 20 s and 210 °C, respectively. The experimental results from atomic force microscope and contact angle (CA) measurement revealed the effects of surface roughness and apparent CA on the wettability for different etch times. The multifunctionality of droplet creation, merger and transportation in the EWOD microfluidic module and sensitive electrochemical detection for the redox probe were realized simultaneously. The proposed microfabrication process has many advantages of remarkable simplicity, prominent repeatability, low cost and compatibility with standard IC processes. It shows great promise for the microsystem of the microfluidic unit and detecting cell, and gives a brilliant conception for the future fabrication of monolithic LOC integrated with functional detection.

Size-variable droplet actuation by interdigitated electrowetting electrode

We propose electrowetting on dielectric (EWOD) electrodes to actuate size-variable droplets. By using interdigitated fingers and maximizing them in optimized construction, we can control droplets in different sizes with the same electrode array automatically. We both do the theory calculation and experiment verification to study the electrode with rectangular fingers. It is found that the electrode with triangle fingers can actuate droplets as small as 1/36 of that actuated by conventional square electrode array. It can actuate large droplets more efficiently than rectangular fingers. This work provides an approach to achieve multifunctional EWOD devices in the future.

An electrode design for droplet dispensing with accurate volume in electro-wetting-based microfluidics

Electro-wetting-on-dielectric actuation enables droplets, the basic units of digital microfluidics, to be manipulated on a two-dimensional surface, providing a versatile platform for chemical assays or multi-step operations at micro- or nano-scale. In this paper, we carry out characterization experiments to demonstrate an electrode design to improve the reproducibility of on-chip droplet generation with no extra external apparatus. The overall reproducibility for a sequence of droplets dispensed consecutively from a non-refilling reservoir can be limited within ±0.5%. Results from the repetition of 1000 iterations offer the long-term reproducibility in the range of ±1%, indicating its validity in practical applications.

A monolithic lab-on-a-chip for electrochemical detection

This paper reports a novel monolithic lab-on-a-chip (LOC) with an electrochemical system embedded in an electrowetting on dielectric (EWOD) microfluidic device for the first time. The fabrication process is compatible with IC technology. This chip could not only merge and transport droplets successfully, but show good electrochemical responses of glucose and glucose oxidase with the sensitivity of 0.028mA/mM and the statistic adjust R-square of 0.9549.

Integrated electrochemical sensor based on electrowetting-on-dielectric microfluidic chip

In this work, we describe the design and study of a novel electrochemical microsensor integrated with electrowetting-on-dielectric (EWOD) microfluidic chip for automatic, rapid and microscale detection. The microsensor was based on the parallel plate EWOD chip. The pretreatment of microliter analyte including dispensing, transporting, mixing and colleting was realized mainly by EWOD electrodes on the bottom plate. The top plate consists of the ground wires for EWOD microfluidics and an on-chip electrochemical cell with gold three-electrode system. The structure and fabrication process were optimized to improve the reliability and stability of integrated chip. The chip can simultaneously realize multifunctional manipulation and online electrochemical detection for reagent droplets. It shows a wide linear range of 10.0 μM-1.0 mM ferrocenemethanol (FcM). The sensitivity of anodic and cathodic peak current was about 5.47 nA/μM (R2=0.99994) and 5.21 nA/μM (R2=0.99904), respectively. This work shows a great promise for microliter biosensing based on smart microfluidic unit and integrated electrochemical cell in the future.

Electrochemical dopamine biosensor using over-oxidized polypyrrole with assistance of graphene

This paper described a disposable overoxidized polypyrrole/graphene/gold (OPPy/GE/Au) microelectrode by two-step electrooxidation at a three-electrode-integrated electrochemical sensor, and its application for selective determination of dopamine (DA) without the interference of ascorbic acid (AA). Compared with the bare Au electrode, OPPy/GE/Au electrode exhibits much stronger electroactivity for DA, as well as intense electrostatic inhibition towards the oxidation of AA at the same time. Such a compatible with mass production and low-cost fabrication of on-chip DA sensor presented a sensitivity of 1.1 µA/μM with a correlation coefficient of 0.99. These properties make the prepared biosensor suitable for the analysis of trace detection of DA in most clinical preparations with a high sensitivity.

Droplet generating with accurate volume for EWOD digital microfluidics

Electrowetting-on-dielectric (EWOD) actuation enables digital microfluidics, typically droplets, to be manipulated on a two-dimensional surface, providing a new platform for manipulating chemicals for multi-step chemical synthesis or assays at the microscale. However, the deficiency of volume precision has long limited its applications in lab on chip (LOC) and micro total analysis systems (μ-TAS) where the accuracy of assays is largely determined by the fluid volume control of the reagent dosing. In this paper, we present a novel electrodes design which improves the reliability of on-chip droplets generating process and reproducibility significantly without any extra external apparatus.

Enzyme-free electroreduction of hydrogen peroxide at polypyrrole/graphene/au microelectrode based on three-electrode-system array

This work reported a one-step electrodeposition to fabricate a graphene nanosheets doped polypyrrole modified gold (PPy/GENS/Au) electrode at the on-chip three-electrode-system electrochemical sensor array. The PPy/GENS/Au electrode exhibited excellent electrochemical properties of large current response, good reproducibility and stability. When applied for the detection of hydrogen peroxide (H2O2), this proposed sensor carry out a rapid, direct and selective determination of H2O2 with the linear range from 1 to 10mM (R-square=0.9914) and a sensitivity of about 32 μA mM-1cm-2. The simple and low-cost construction of PPy/GENS/Au electrode shows a great promise to fabricate mass-produced nano-platform for potential application of biosensing analysis in a lab-on-a-chip system.

Evaluation of Cyanoethyl Pullulan material as the dielectric layer for EWOD devices

The excellent dielectric and electrowetting properties of Cyanoethyl Pullulan (CEP) material were evaluated in this paper. The CEP can obtained a dielectric constant of 18 (100 kHz) by spin-coating and annealing at 100°C in atmosphere. The asymmetry, reversibility and stability of electrowetting on CEP were studied, showing negative-potential sensitive and good electrowetting performance. Based on these results, an EWOD device with 1μm thick CEP dielectric layer has been fabricated and tested, demonstrating the successful manipulation of water droplets with drive voltage of 20 V. The easy fabrication and excellent performance of CEP make it a superior dielectric material in the future EWOD devices.