Impedimetric array in polymer microfluidic cartridge for low cost point-of-care diagnostics.

Deep Vein Thrombosis and pulmonary embolism (DVT/PE) is one of the most common causes of unexpected death for hospital in-patients. D-dimer is used as a biomarker within blood for the diagnosis of DVT/PE. We report a low-cost microfluidic device with a conveniently biofunctionalised interdigitated electrode (IDE) array and a portable impedimetric reader as a point-of-care (POC) device for the detection of D-dimer to aid diagnosis of DVT/PE. The IDE array elements, fabricated on a polyethylenenaphtalate (PEN) substrate, are biofunctionalised in situ after assembly of the microfluidic device by electropolymerisation of a copolymer of polypyrrole to which is immobilised a histidine tag anti-D-Dimer antibody. The most consistent copolymer films were produced using chronopotentiometry with an applied current of 5µA for a period of 50 s using a two-electrode system. The quality of the biofunctionalisation was monitored using optical microscopy, chronopotentiometry curves and impedimetric analysis. Measurement of clinical plasma sample with a D-dimer at concentration of 437 ng/mL with 15 biofunctionalised IDE array electrodes gave a ratiometric percentage of sample reading against the blank with an average value of 124 ±â€¯15 at 95% confidence. We have demonstrated the concept of a low cost disposable microfluidic device with a receptor functionalised on the IDE array for impedimetric detection towards POC diagnostics. Changing the receptor on the IDE array would allow this approach to be used for the direct detection of a wide range of analytes in a low cost manner.

Determination of the isomeric forms proportion of fluorogenic naphthalene-2,3-dicarboxaldehyde in a binary mixture of water:methanol using electrochemical methods.

The electrochemical response of the fluorogenic label naphthalene-2,3-dicarboxyaldehyde (NDA) in a binary mixture of water/methanol was characterized with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) electrochemical techniques. Naphthalene-2,3-dicarboxyaldehyde does exist in three isomeric forms in aqueous solution: the unhydrated dialdehyde (DA), the acyclic monohydrated (MA) and the cyclic hemiacetal (HAC). The study underlines that the proportion of each of them varies according to the working pH. At low and high pH, the dialdehyde form is in larger proportion than the acyclic monohydrated form. Conversely at intermediate pH, the concentration of the acyclic form is in greater proportion than the dialdehyde form. These results allowed us to determine the optimal pH of 9 for which the labeling of biomolecules could be more efficient due to the base catalyzed regeneration of the unhydrated form. At this pH, the data processing from the analysis of measured currents and estimation of diffusion coefficients of each form according to the semi-empirical models of Wilke-Chang, Scheibel, Reddy-Doraiswamy and Lusis-Ratcliff allowed us to obtain the concentration of dialdehyde (0.28 mM), acyclic monohydrated (0.57 mM) and cyclic hemiacetal monohydrated (0.15 mM) forms starting from 1mM naphthalene-2,3-dicarboxyaldehyde.

Study of Surface Charge Instabilities by EOF Measurements on a Chip: A Real-Time Hysteresis and Peptide Adsorption Based Methodology.

This paper describes the measurement of the electroosmotic mobility (EOF) in a Wheatstone fluidic bridge (µFWB) as a direct probe of the surface instability. The variation of EOF known as one major contribution of the electrokinetic migration has been determined with a real-time measurement platform after different conditionings on chips. We also scan the pH of the background electrolytes with three different ionic strengths to evaluate the dependencies of the EOF as a function of the pH. A hysteresis methodology has been developed for probing the surface charge instabilities. EOF mobility has been recorded during on-a-chip electrophoresis to estimate the effect of such instability on the analytical performance. As expected, our experimental curves show that a decrease in the ionic strength increases the surface charge stability of the hybrid microchip. This result demonstrates that ionic exchanges between the surface and the fluid are clearly involved in the stability of the surface charge. With this original method based on real-time EOF measurement, the surface state can be characterized after hydrodynamic and electrophoresis sequences to mimic any liquid conditioning and separation steps. Finally, as a demonstrative application, isotherms of the adsorption of insulin have been recorded showing the change in surface charge by unspecific adsorption of this biomolecule onto the microfluidic channel's wall. These methodologies and findings could be particularly relevant to investigating various analytical pathways and to understanding the molecular mechanisms at solid/liquid interfaces.

Improved electrochemical detection of a transthyretin synthetic peptide in the nanomolar range with a two-electrode system integrated in a glass/PDMS microchip.

An alternative to a three-electrode set-up for electrochemical detection and analysis in microfluidic chips is described here. The design of the electrochemical sensor consists of the surface of the glass substrate covered with a PDMS block which bears the microfluidic channels. A band microelectrode which acts as a working electrode surrounded by a large counter electrode is obtained at the micrometric level to propose a simple and efficient sensing area for on-a-chip analysis. The counter-electrode with a surface area about 22-fold greater than the working-microelectrode can also be considered as a pseudo reference since its current density is low and thus limits the potential variations around the rest potential. To this purpose, the [Fe(III)(CN)6]³â»/[Fe(II)(CN)6]4⁻ redox couple was used in order to set a reference potential at 0 V since both electrodes were platinum. The electrochemical microchip performance was characterized using differential pulse voltammetric (DPV) detection and quantification of the optically multi-labelled transthyretin synthetic peptide mimicking a tryptic fragment of interest for the diagnosis of familial transthyretin amyloidosis (ATTR). The limit of detection of the peptide by the working microelectrode was 25 nM, a value 100-fold lower than the one reported with conventional capillary electrophoresis coupled with laser-induced fluorescence under the same analytical conditions.