Neus Godino

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.

Improved bacteria detection by coupling magneto-immunocapture and amperometry at flow-channel microband electrodes

This paper describes the first immunosensing system reported for the detection of bacteria combining immunomagnetic capture and amperometric detection in a one-step sandwich format, and in a microfluidic environment. Detection is based on the electrochemical monitoring of the activity of horseradish peroxidase (HRP), an enzyme label, through its catalysis of hydrogen peroxide (H(2)O(2)) in the presence of the mediator hydroquinone (HQ). The enzymatic reaction takes place in an incubation micro-chamber where the magnetic particles (MPs) are confined, upstream from the working electrode. The enzyme product is then pumped along a microchannel, where it is amperometrically detected by a set of microelectrodes. This design avoids direct contact of the biocomponents with the electrode, which lowers the risk of electrode fouling. The whole assay can be completed in 1h. The experiments performed with Escherichia coli evidenced a linear response for concentrations ranging 10(2)-10(8) cell ml(-1), with a limit of detection of 55 cells ml(-1) in PBS, without pre-enrichment steps. Furthermore, 100 cells ml(-1) could be detected in milk, and with negligible interference by non-target bacteria such as Pseudomonas.

Impedance-Based Biosensors for Pathogen Detection

Electrochemical impedance spectroscopy (EIS) is an important detection technique for biosensors. In the field of immunosensors, and particularly pathogen detection, it is one of the preferred electrochemical techniques because it does away with the use of enzyme labels or redox mediators. This chapter provides an introduction to the fundamentals of EIS and basic data analysis, with an emphasis on the most common features found in immunosensors and possible experimental limitations.

Integration of a zero dead-volume PDMS rotary switch valve in a miniaturised (bio)electroanalytical system

This work features the design, fabrication and characterisation of a miniaturised electroanalytical lab on a chip that allows the performance of a complete bioassay, from the capture of magnetic particles through their functionalisation and sample incubation to the detection of electroactive reaction products. The system is built using mainly polymeric materials such as PMMA and PDMS and fast prototyping techniques such as milling and moulding. The system also includes a set of microelectrodes, photo-lithographed on a silicon chip. The novelty lies in the design of the rotary microvalve, which contains a microreactor so that various reaction and incubation steps can be carried out in isolation from the detection event with zero dead volume. This avoids contamination and fouling of the electrodes by proteins or other organic matter, and extends the useful lifetime of the detector. The system operation is demonstrated by a model example, consisting in the functionalisation of streptavidin-coated magnetic particles with biotinylated beta-galactosidase over periods ranging from 5 to 15 min, at which point the particles saturate. Although the system is intended for the development of enzyme-based electrochemical bioassays, the concept of its rotary microreactor can be applied more broadly.