(157c) Electrochemical Detection in Nanofluidic Channels

As experiments involving micro- and nanofluidic devices become commonplace, the need for detection at these scales becomes increasingly important. Many current microfluidic sensing techniques employ optical methods. While they can be incredibly sensitive, optical techniques are often complicated and difficult to incorporate with the rest of the microfluidic device fabrication process. A promising alternative to optical sensors involves the use of electrical elements incorporated into fluidic systems. Electrical sensors can be less demanding in space, less expensive, and easier to integrate than their optical counterparts.

We have developed a nanofluidic detection scheme that specifically exploits these small dimensions. The device consists of two parallel electrodes in a nanofluidic channel with openings at either end that allows for very sensitive detection of electrochemically active species. Electrochemically active molecules that enter the cavity transfer charge between the electrodes when a potential difference is applied. Since these molecules are capable of repetitively undergoing oxidation and reduction, each molecule can transfer, on average, thousands of electrons by repeatedly traveling between the electrodes before escaping back out into the bulk.

The fabrication process involves a combination of lithographic patterning and evaporation to form the electrodes and nanocavity. We have shown the benefits of such an approach for measuring molecular fluctuations [1], absorption [2] and electron-transfer kinetics [3]. We have also demonstrated the utility of such an arrangement for sensor applications, where catechol [4] and acetaminophen [5] were detected in the presence of ascorbic acid. This presentation will focus on the fabrication, design rules, and ongoing efforts to integrate these sensors in complex microfluidic systems.

REFERENCES:

[1] M.A.G. Zevenbergen, D. Krapf, M.R. Zuiddam, S.G. Lemay, Nano Letters, 8, 497 (2007).

[2] M. A. G. Zevenbergen, P.S. Singh, E.D. Goluch, B.L. Wolfrum, S.G. Lemay, Analytical Chemistry, 81, 8203 (2009).

[3] M. A. G. Zevenbergen, B.L. Wolfrum, E.D. Goluch, P.S. Singh, S.G. Lemay, Journal of the American Chemical Society, 394, 447 (2009).

[4] B.L. Wolfrum, M.A.G. Zevenbergen, S.G. Lemay, Analytical Chemistry, 36, 3342 (2008).

[5] E.D. Goluch, B.L. Wolfrum, P.S. Singh, M.A.G. Zevenbergen, S.G. Lemay, Analytical and Bioanalytical Chemistry, 22, 1036 (2009).