Abstract:
The development of microscale devices or “Lab-on-a-Chip” has intrigued
widespread interest due to its possible analytical applications in the field of medical,
environmental, and material science. For example, microscale flow cells exhibit great
surface-to-volume ratio and therefore provide a high sensitivity even from a weak surface
interaction. Furthermore, different configurations of flow cells deliver their specific
electrochemical properties used for analyzing the electroactive species. The detection of
redox species is commonly practiced and comprehended however, the separation by
electrochemical field is not well understood. In order to better understand the separation
phenomenon with the microfluidic channel, a simple wall jet flow cell has been tested.
Then, the results obtained from these experiments were used to design experiments where
separation and detection can be done on the same platform. The electrochemical potential
modulated microchannel (EPMM) is the device capable of separating and detecting
electroactive species on the same platform. Both EPMM and wall jet flow cell were used
in this research to determine the area of the electrodes, diffusion properties, time
constant, and other electrochemical analysis with K3Fe(CN)6 and metal ions. Various
analytical parameters such as scan rate, flow rate, and concentrations also helped on
characterizing the system. As a result, 2.5mM K3Fe(CN)6 flowing at 4μL/min to the
system and scanned at different rates determined the area of an electrode and the
diffusion coefficient to be (1.00±0.05) x 10-3cm2 and (8.05±0.3) x 10-6cm2/s, respectively.
Several plots were constructed with the observed electrochemical parameters and
confirmed the system is quasireversible. The plots also determined the detection limits as
0.1mM for concentration and 0.14nA for current. Furthermore, the electron transfer rate
constant was found to be (5.52±0.04) x 10-3cm/s. Besides the basic voltammetric
properties of the cell and the redox couple, the detection of metal ions was attempted at a
ppb level using the EPMM device in addition with the AC modulation voltage and
frequency. In effect of electrolysis on detecting the metal ions with AC modulation of
1.0V and 1.0MHz, there were at least seven distinctive peaks correspondent to the metal
ions with respect to their retention order. The detection limit of 0.20 - 1.15ppb and the
sensitivity level of 50 - 250nA/ppb showed possibilities of enhancement.
