Olga Ordeig

On-Chip Electric Field Driven Electrochemical Detection Using a Poly(dimethylsiloxane) Microchannel with Gold Microband Electrodes

An external electric field driven in-channel detection technique for on-chip electrochemical detection in micro fabricated devices is described based on a microfluidic system containing an array of 20 microband electrodes. It is shown that an external electric field induces a potential difference between two gold microband electrodes in a poly(dimethylsiloxane) (PDMS) microchannel, and that this enables the electrochemical detection of electroactive species such as ascorbic acid and Fe(CN) 6 (4-). The results, which are supported by simulations of the behavior of the microband electrodes in the microfluidic system, show that the induced potential difference between the electrodes can be controlled by altering the external electric field or by using different microbands in the microband array. As the obtained currents depend on the concentrations of electroactive species in the flowing solution and the detection can be carried out anywhere within the channel without interference of the external electric field, the present approach significantly facilitates electrochemical detection in capillary electrophoresis. This approach consequently holds great promise for application in inexpensive portable chip-based capillary electrophoresis (CE) devices.

Dual photonic-electrochemical lab on a chip for online simultaneous absorbance and amperometric measurements.

A dual lab on a chip (DLOC) approach that enables simultaneous optical and electrochemical detection working in a continuous flow regime is presented. Both detection modes are integrated for the first time into a single detection volume and operate simultaneously with no evidence of cross-talk. The electrochemical cell was characterized amperometrically by measuring the current in ferrocyanide solutions at +0.4 V vs gold pseudoreference electrode, at a flow rate of 200 μL min(-1). The experimental results for ferrocyanide concentrations ranging from 0.005 to 2 mM were in good agreement with the values predicted by the Levich equation for a microelectrode inside a rectangular channel, with a sensitivity of 2.059 ± 0.004 μA mM(-1) and a limit of detection (LoD) of (2.303 ± 0.004) × 10(-3) mM. Besides, optical detection was evaluated by measuring the absorbance of ferricyanide solutions at 420 nm. The results obtained therein coincide with those predicted by the Beer-Lambert law for a range of ferricyanide concentrations from 0.005 to 0.3 mM and showed an estimated LoD of (0.553 ± 0.001) × 10(-3) mM. The DLOC was finally applied to the analysis of L-lactate via a bienzymatic reaction involving lactate oxidase (LOX) and horseradish peroxidase (HRP). Here, the consumption of the reagent of the reaction (ferrocyanide) was continuously monitored by amperometry whereas the product of the reaction (ferricyanide) was recorded by absorbance. The DLOC presented good performance in terms of sensitivity and limit of detection, comparable to other fluidic systems found in the literature. Additionally, the ability to simultaneously quantify enzymatic reagent consumption and product generation confers the DLOC a self-verifying capability which in turn enhances its robustness and reliability.

Diffusional protection of electrode surfaces using regular arrays of immobilised droplets: overcoming interferences in electroanalysis

Regular arrays of ca. micron sized droplets on a gold electrode surface can block diffusion to the electrode surface of one metal ion (which binds with the material in the droplet) whilst having no significant effect on another (which does not), so allowing interference effects in electroanalysis to be eliminated.

Dual photonic electrochemical lab on a chip for lactate detection in continuous flow mode

An integrated lab on a chip that enables simultaneous optical and electrochemical analysis working in continuous flow mode is presented. Both transducers are integrated into a single detection cell and operated simultaneously with no evidences of cross-talk and in agreement with theoretical predictions by Levich equation (electrochemical) and by Lambert-Beer law (absorbance). Their performance is demonstrated by continuous detection of lactate via a double enzymatic reaction with lactate oxidase (LOX) and horseradish peroxidase (HRP). The consumption of the enzymatic reaction mediator (ferrocyanide, [Fe(CN)6]4−) is recorded by amperometry, while the product (ferricyanide, [Fe(CN)6]3−) is quantified by absorbance. The ability to quantify reagent and product simultaneously increases the robustness of the system by making it self-verifying, in addition to the inherent advantages of microfluidic devices.