The gold interdigitated microelectrode sensor was fabricated
in-house on a glass chip (1737, Corning) by standard microelec-
tronic fabrication methods. Each chip contained four interdigi-
tated microelectrode sensors and measured 36 mm
15 mm as
depicted in supplemental information Fig. S1(left). Each gold
interdigitated microelectrode sensor consisted of a pair of 50-
finger electrodes with 8 mm of
finger width and spacing. The
fabrication process of the gold interdigitated microelectrode
sensor is illustrated in Fig. S1(right). Firstly, a standard positive
photoresist S1818 was coated on the glass chip (Fig. S1(a)). Then a
mask pattern of the interdigitated microelectrode was transferred
to the photoresist by exposing the photoresist to UV light (Fig. S1
(b)) and subsequently developing the exposed areas in MF-
319 developer (Shipley Far East Ltd., Tokyo, Japan) (Fig. S1(c)). The
chip was then rinsed in deionized water and dried by a stream of
nitrogen. Once the pattern was defined, 2 nm of chromium was
deposited by Q150T ES sputter-coater (Quorum Technologies Ltd.,
Laughton, UK) in order to improve the adherence of gold to the
glass surface (Fig. S1(d)). After the chromium deposition, 50 nm of
gold layer was sputtered to form the complete electrodes (Fig. S1
(e)). The excess metal on top of the unexposed photoresist was
lifted off by ultra-sonication in acetone (Fig. S1(f)). Fig. S2(a)
shows an optical microscopic image of a photoresist pattern
created using the photolithographic process and Fig. S2(b) shows
an optical microscopic image of a gold interdigitated microelec-
trode sensor.
90 J.-T. Liu et al. / Electrochimica Acta 182 (2015) 89–95