A droplet-based microfluidic electrochemical sensor using platinum-black microelectrode and its application in high sensitive glucose sensing.

We describe a droplet-based microfluidic electrochemical sensor using platinum-black (Pt-black) microelectrode. Pt-black microelectrode was generated by electrodeposition of Pt nanoparticles on bare Pt microelectrode. Scanning electron microscope (SEM) image displays a flower-like microstructure of Pt nanoparticels. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) indicate that the Pt-black efficiently decreased the charge transfer resistance and improved the electrocatalytic activity towards oxidation of hydrogen peroxide (H2O2). Compared with bare Pt microelectrode, the current response on Pt-black microelectrode increased 10.2 folds. The effect of applied potential and electrodeposition time has been investigated in detail. The proposed sensor was validated by performing enzyme activity assay in flowing droplets. For demonstration, glucose oxidase (GOx) is chosen as the model enzyme, which catalyzes the oxidation of ß-D-glucose to the product H2O2. The enzyme activity of GOx was evaluated by measuring the electrochemical current responding to various glucose concentrations. And the results indicate that this microfluidic sensor holds great potential in fabricating novel glucose sensors with linear response up to 43.5mM. The analytical applications of the droplet-based microfluidic sensor were tested by using human blood serum samples. Reproducibility, interferences, and long-term stability of the modified electrode were also investigated. The present approach shows the feasibility and great potentials in constructing highly sensitive and low-consumption sensors in the field of droplet microfluidics.

Droplet-based microfluidics for dose-response assay of enzyme inhibitors by electrochemical method.

A simple but robust droplet-based microfluidic system was developed for dose-response enzyme inhibition assay by combining concentration gradient generation method with electrochemical detection method. A slotted-vials array and a tapered tip capillary were used for reagents introduction and concentration gradient generation, and a polydimethylsiloxane (PDMS) microfluidic chip integrated with microelectrodes was used for droplet generation and electrochemical detection. Effects of oil flow rate and surfactant on electrochemical sensing were investigated. This system was validated by measuring dose-response curves of three types of acetylcholinesterase (AChE) inhibitors, including carbamate pesticide, organophosphorus pesticide, and therapeutic drugs regulating Alzheimer's disease. Carbaryl, chlorpyrifos, and tacrine were used as model analytes, respectively, and their IC50 (half maximal inhibitory concentration) values were determined. A whole enzyme inhibition assay was completed in 6 min, and the total consumption of reagents was less than 5 µL. This microfluidic system is applicable to many biochemical reactions, such as drug screening and kinetic studies, as long as one of the reactants or products is electrochemically active.