Kaidi Zhang

Chemiluminescence detector based on a single planar transparent digital microfluidic device

We report on a compact and portable prototype of chemiluminescence detector based on a single planar single polar transparent electrowetting-on-dielectrics (EWOD) device. The coupling ground model was proposed to build the EWOD device, which could be driven under a single polar voltage. Such a design not only simplified the chip construction and control circuit, but also had the potential for the ball-like droplet to focus the fluorescence and enhance the detection sensitivity. Simulations and experiments both confirmed that the greater the contact angle, the stronger the detected optical signal, and thus the higher the sensitivity. The sensitivity of the prototype detector to H2O2 was 5.45 mV (mmol L(-1))(-1) and the detection limit was 0.01 mmol L(-1) when the contact angle of the EWOD surface was 120°. To further increase the sensitivity and decrease the detection limit, the contact angle of the EWOD device could be increased and the dark current of the photomultiplier decreased. The prototype shows potential applications as highly sensitive, cost effective and portable immuno-detectors, especially as a blood glucose monitor.

Portable Electrowetting Digital Microfluidics Analysis Platform for Chemiluminescence Sensing

A prototype of low-cost compact digital microfluidics analysis platform controlled by a smartphone was built. Controlled by a DIY-built application (App) with self-calibration, the smartphone was applied not only as the controller that manipulated droplets on an electro-wetting-on-dielectric microfluidic device through our home-made circuits, but also as the reader that quantified chemiluminescence signals through its camera. In order to deal with the non-uniformity of the chemiluminescence images acquired by the smartphone, we proposed a customize image process scheme. The results showed linear responses to H2O2 from 1 to 20 mM in the luminol-HRP-H2O2 chemiluminescence system.

Recoverable electrowetting-on-dielectric device in chemiluminescence enzymatic detector

Hydrophobic failure is a major obstacle faced in the application of electrowetting-on-dielectric (EWOD) for bio-detections. In this paper we study the failure mechanism of EWOD-based chemiluminescence detectors and propose a recovery method. The X-ray photoelectron spectroscopy (XPS) analysis reveals that the C–F bond breakage and C–O bond formation after the chemiluminescence reaction makes the Teflon surface hydrophilic. We design a recoverable EWOD device with an integrated heater. An experimental analysis confirms the recovery of the hydrophobic surface by heating the surface over 900 mW for 5 min.

Biocompatible/Biodegradable Electrowetting on Dielectric Microfluidic Chips with Fluorinated CTA/PLGA

One of the major hurdles in the development of biocompatible/biodegradable EWOD (Electrowetting-on-dielectric) devices is the biocompatibility of the dielectric and hydrophobic layers. In this study, we address this problem by using reactive ion etching (RIE) to prepare a super-hydrophobic film combining fluorinated cellulose triacetate (CTA) and poly (lactic-co-glycolic acid) (PLGA). The contact angle (CA) of water droplets on the proposed material is about 160°. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) characterizations indicate that a slight increase in the surface roughness and the formation of CFx (C-F or CF2) bonds are responsible for the super-hydrophobic nature of the film. Alternating Current (AC) static electrowetting and droplet transportation experiments evidence that contact angle hysteresis and contact line pinning are greatly reduced by impregnating the CTA/PLGA film with silicon oil. Therefore, this improved film could provide a biocompatible alternative to the typical Teflon® or Cytop® films as a dielectric and hydrophobic layer.

Application of cellulose triacetate as biocompatible/biodegradable dielectrics in EWOD devices

As a biocompatible/biodegradable material, cellulose triacetate (CTA) is used as dielectric layers in EWOD (electrowetting-on-dielectrics) devices. The CTA has a dielectric constant of 10 by spin-coating and annealing at 100°C in electrothermal drying oven for 30min. The porosity, unevenness and stability of electrowetting of CTA are studied. The results show its good property of film deposition and negative-potential sensitive electroewetting. An EWOD device with 1.2 μm thick CTA layer has been tested, demonstrating that water droplets can be driven and mixed successfully.

Smartphone-controlled electro-wetting on dielectric microfluidics

A prototype of low-cost compact digital microfluidics analysis platform controlled by a smartphone has been built. With customized circuits, the platform takes the advantages of portability and easy-application with a friendly user interface. It can manipulate droplet moving, merging and mixing through an application (App) on android smartphone. The system makes the microfluidics-based analytical system low cost and easy to use, which is suitable for onsite analysis and self detection at home.

Teflon wetting and dewetting on EWOD device for chemiluminescence detector

A hydrophobicity recoverable EWOD (electrowetting-on-dielectric) based chemiluminescence detector with an integrated signal and heater electrode was developed. X-ray-photoelectron-spectroscopy (XPS) was used to reveal the wetting and dewetting mechanism of Teflon on the EWOD device. It was found that the C-O bond formed on the surface of Teflon after the chemiluminescence reaction leaded to the surface permanent wetting. To recover the contact angle of the Teflon surface, the recovery threshold time and heating temperature were proposed experimentally for dewetting to release C-O bond.

Compact and portable chemiluminescence detector for glucose

A compact chemiluminescence detector for glucose measurement based on a single planar transparent EWOD (electrowetting-on-dielectrics) device is designed and manufactured. Its sensitivity can be as high as 0.12V/μM, and it has a large detection range from 1μM to 20mM, and a low detection limit of 1μM. Such a detector demonstrates its potential as a portable immuno-detector with prompt response and low cost measurement compared with expensive and bulky traditional instruments.