An ECL-based microfluidic sensor
Recently, graduate student Wei Zhan and postdoc Dr. Julio Alvarez developed a versatile, microfluidics-based method for sensing redox-active molecules. One novel aspect of this sensor is that the redox molecule of interest is detected via electrochemical reduction, but its presence is reported by electrogenerated chemiluminescence (ECL) rather than by direct current measurement. The approach is shown schematically in Figure 1 for a two-electrode cell, but it also works using a one- or three-electrode microfluidic cell.
The
important finding of this research is that the ECL reporting reaction
is chemically decoupled from the electrochemical sensing reaction. That
is, the electrochemical sensing reaction does not participate directly
in the ECL process, but because electrochemical cells require charge balance,
the sensing and ECL reactions are electrically coupled. This provides
a convenient and sensitive means for direct photonic readout of electrochemical
reactions that do not directly participate in an ECL reaction and thus
broadens the spectrum of redox compounds that can be detected using ECL.
The
results indicate that the potential bias applied between the two electrodes,
using an external power source such as a battery, must be at least equal
to the difference in the formal potential of the two redox processes (Figure
2). The inset of Figure 2 shows that at ~1.4 V, the ECL process can be
turned on when it is coupled to the reduction of benzyl viologen (BV2+).
In contrast, a higher potential bias is required when BV2+ is absent.
This provides a means for detecting the presence of BV2+ by ECL, but without
BV2+ directly participating in the ECL reaction. In principle this same
approach can be used to detect the presence of other electrochemically
active analytes.
At present, we don't know what, if any, sensitivity enhancement this new
method will provide compared to direct current measurements, but those
studies are currently underway. If you would like to read more about these
results, the first research publication will be available as an ASAP article
in JACS (probably by the beginning of November, 2002).