A capillary electrophoresis (CE) microsystem, based on the combination of microphotolithographically fabricated separation chips and thick-film electrochemical detector strips, is described. The microsystem consists of a planar screen-printed carbon line electrode mounted perpendicular to the flow direction. Such coupling obviates the need for permanent attachment of the detector, to allow easy and fast replacement of the working electrode. Variables influencing the separation efficiency and amperometric response, including the channel-electrode spacing, separation voltage, or detection potential, are assessed and optimized. The versatility, simplicity, and low-cost advantages of the new design are coupled to an attractive performance, with submicromolar detection limits, and good precision. Applicability for assays of mixtures of nitroaromatic explosives or catecholamines is demonstrated. Such use of screen-printed detectors should also benefit conventional CE systems, particularly in applications requiring a frequent replacement of the working electrode.

Renewable graphite pencil electrodes are demonstrated to be excellent materials for adsorptive stripping measurements of trace nucleic acids. While displaying an attractive stripping performance, comparable to that of conventional carbon paste electrodes, the pencil electrode offers a convenient (mechanical) renewal, with each stripping potentiogram recorded at a fresh surface. Various pencil lead materials and lengths have been examined and experimental variables of the pretreatment and measurement procedures have been explored and optimized. The extremely low detection limits (e.g., 3 micrograms l-1 tRNA with 10 min accumulation) are coupled to a good surface-to-surface reproducibility (RSD of 6.4% for 14 repetitive measurements of 1 mg l-1 ssDNA).

An on-chip electrochemical detector for micromachined capillary electrophoresis (CE) systems, based on sputtering a gold working electrode directly onto the capillary outlet, is described. The new on-chip detector preparation requires no microfabrication or alignment procedures nor a decoupling mechanism. The attractive performance of the integrated electrophoresis chips/amperometric detection was demonstrated for the anodic detection of neurotransmitters. The response for dopamine was linear from 20 to 200 μM, with a LOD of 1.0 μM and a sensitivity of 52 pA/μM. Such intimate coupling of capillary electrophoresis chips and electrochemical detection facilitates the realization of complete integrated microanalytical devices.

We describe an on-chip microfluidic gradient-generating device that generates concentration gradients spanning nearly 5 orders of magnitude starting from a single concentration. The exiting stream of drugs held at different concentrations remains laminar in a recording chamber and can be presented as 24 discrete solutions to a cell-based sensor. The high-performance characteristics of the device are demonstrated by pharmacological screening of voltage-gated K+ channels (hERG) and ligand-gated GABA(A) receptors using scanning-probe patch-clamp measurements. Multiple data point dose-response curves and IC50 and EC50 values were rapidly obtained, typically in less than 30 min, through its combined functionality of gradient generation and open-volume laminar flow. The device facilitates rapid pharmacological profiling of ion channel and GPCR effectors and enables the acquisition of large numbers of data points with minute sample consumption and handling.

A new electrically heated carbon paste electrode has been developed for performing adsorptive stripping measurements of trace nucleic acids. Such coupling of electrochemistry at electrically heated electrodes with adsorptive constant-current stripping chronopotentiometry offers distinct advantages for trace measurements of nucleic acids. The application of increased temperatures during the deposition step results in dramatic (4-34-fold, depending on temperature applied) enhancement of the stripping signal. Such improvement is attributed to the accumulation step at the heated electrode. Forced thermal convection near the electrode surface facilitates the use of quiescent solutions and hence of ultrasmall volumes. Using an electrode temperature of 32 degrees C and a quiescent solution during the 1-min accumulation, the response is linear over the 1-8 mg/L range tested, with a detection limit of 0.5 mg/L. Such electrode heating technology offers great promise for various applications involving thermal manipulations of nucleic acids.