Electrochemical nanofluidics: The mesoscopic limit

Nano Letters

We report the electrochemical detection of individual redox-active molecules as they freely diffuse in solution. Our approach is based on microfabricated nanofluidic devices, wherein repeated reduction and oxidation at two closely spaced electrodes yields a giant sensitivity gain. Single molecules entering and leaving the cavity are revealed as anticorrelated steps in the faradaic current measured simultaneously through the two electrodes. Cross-correlation analysis provides unequivocal evidence of single molecule sensitivity. We further find agreement with numerical simulations of the stochastic signals and analytical results for the distribution of residence times. This new detection capability can serve as a powerful alternative when fluorescent labeling is invasive or impossible. It further enables new fundamental (bio)electrochemical experiments, for example, localized detection of neurotransmitter release, studies of enzymes with redox-active products, and single-cell electroc...

Analytical …, 2009

We introduce both theoretically and experimentally a new electrochemical technique based on measuring the fluctuations of the faradaic current during redox cycling. By analogy with fluorescence correlation spectroscopy (FCS), we refer to this technique as electrochemical correlation spectroscopy (ECS). We first derive an analytical expression of the power spectral density for the fluctuations in a thin-layer-cell geometry. We then show agreement with measurements using ferrocenedimethanol, Fc(MeOH) 2 , in water and in acetonitrile in microfabricated thinlayer cells with a ∼70 nm electrode spacing. The fluctuation spectra provide detailed information about the adsorption dynamics of Fc(MeOH) 2 , which cause an apparent slowing of Brownian motion. We furthermore observe high-frequency fluctuations from which we estimate the rates of adsorption and desorption.

Sensors and Actuators B: Chemical, 2013

We developed the versatile microfluidic device for on-chip electrochemical analysis in a single integrated platform. Gold nanostructures were fabricated at defined positions within microchannels by electrochemical deposition, and used as electrocatalytic materials for glucose detection and suitable sensing surfaces for ultratrace arsenic(III) detection. The continuous streaming solution in microfluidic devices allowed for enhanced mass transport to the electrodes and elimination of fouling effects, resulting in increased currents and high sensitivities. As a result, the current response showed a strong linear dependence (R 2 = 0.995) in the glucose concentration range of 0.1-9 mM with an excellent sensitivity of 1.10 ± 0.07 mA cm −2 mM −1. Furthermore, in ultratrace arsenic(III) analysis, the calibration plot corresponding to peak current shows good linearity (R 2 = 0.998) up to the concentration of 30 ppb and remarkable sensitivity of 4.49 ± 1.01 A cm −2 ppb −1 in a short accumulation time of 60 s. We believe that the proposed device is a promising approach for various microfluidic applications with the extensibility of functional nanostructures and possibility of biomolecule self-assembly.

Trends in Analytical Chemistry, 2006

This overview covers important aspects of microfluidic chip platforms as new materials for electrochemical (EC) sensing. It describes important trends in constructing detectors and their electronics on microfluidic chip platforms, the importance of selecting appropriate detector materials, and the different detection modes in on-chip amperometry, conductometry and potentiometry. We pay particular attention to the latest developments and to the fundamental issues of on-chip EC detection. We also discuss important applications of microfluidic chip platforms in genomic, security and environmental applications. ª

Microfluidics and Nanofluidics, 2014

Electrochemical techniques are widely used in microfluidic and nanofluidic devices because they are suitable for miniaturization, have better sensitivity compared to optical detection techniques, and their components can be reliably microfabricated. In addition to the detection and quantification of analytes, electrochemical techniques can be used to monitor processes such as biological cell death and protein/DNA separations/purifications. Such techniques are combined with micro-and nanofluidic devices with point-of-care (POC) applications in mind, where cost, footprint, ease of use, and independence from peripheral equipment are critical for a viable design. A large variety of electrode materials and device configurations have been employed to meet these requirements. This review introduces the reader to the major electrochemical techniques, materials, and fabrication methods for working and reference electrodes, and to surface modifications of electrodes to facilitate electrochemical measurements, in the context of micro-and nanofluidic devices. The continuing development of these techniques holds promise for the next-generation lab-on-a-chip devices, which can realize the goals of this technology such as POC clinical analysis.