Chemistry Department Seminar


Presented by Pradyumma S. Singh, Delft University of Technology

Friday, October 8, 2010, 11:00 am — Chemistry Bldg. 555, Room 300

Electrochemical experiments in small confined volumes presents an interesting avenue to explore fundamental questions regarding the behavior of ions and redox-active molecules in solution in the vicinity of an electrode. These studies are also vitally important for development of lab-on-a-chip type applications which rely on electro-chemical detection.
Using microfabrication methods we have developed electrochemical devices that con¬sist of two plane-parallel electrodes that are embedded in a nanofluidic channel. The electrode spacings can be reliably adjusted during the fabrication process to be ∼ 50 nm. The volume enclosed by the active area of the device is ca. 1 femtoliter (10−15 L). Redox-active molecules are capable of freely diffusing in and out of the nanochan¬nel. When the electrodes are suitably biased, the molecules can repeatedly shuttle multiple electrons between the electrode, leading to an amplification in the measured electrical current.
Because of the small volume of the detection area, statistical fluctuations in the number of molecules in it give rise to corresponding fluctuations in the measured current which can be readily observed as electrical noise. As the absolute number of molecules decreases with decreasing detection volume, these fluctuations become an increasingly prominent feature in nanoscale devices. We recently introduced a new technique called Electrochemical Correlation Spectroscopy (ECS). Much like its optical counterpart, Fluoresence Correlation Spectroscopy (FCS), ECS relies on an autocorrelation analysis of these fluctuations. This yields new information about ad¬sorption dynamics of molecules in the channel, hitherto unavailable through other electrochemical means -a direct consequence of performing electrochemical experi¬ments in such small volumes.
Recently, we have also been able to detect fluctuations corresponding to th

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