Environmental Engineering Reference
In-Depth Information
The 2
m
width. The external magnetic field was used to align probes toward the same direc-
tion. Glass/silicon composite electrode arrays, known as The Utah Electrode Array
(UEA), were developed with 100 silicon needle-type electrodes in a 10
×
3 probe array was fabricated with a 1.2 mm height and a 160
μ
×
10 array
[54]. The needles were 1.5 mm in length and 80
m in diameter. Glass was melted
to electrically isolate individual electrodes on the back side of a silicon substrate and
then the sawing process produced tall silicon columns, which were sharpened and
tapered using an acid etching procedure. However, all of these needle-type MEMS
electrodes have been designed for neural recording and can only measure potential
(e.g., neuronal activity). Consequently, development of MEMS needle-type sensors
capable of
electrochemical
measurements is still a necessity.
The proposed needle-type sensor system concept is illustrated in Fig. 6.2. The
sensor system is divided into two key components: (1) a multi-analyte microelec-
trode array (MEA) sensor for
in situ
electrochemical measurements; and (2) an IC
chip and circuitry for signal acquisition, processing, and transmission to a data
storage/display device. By intimately integrating the sensors and the electronics,
signal-to-noise ratio can be improved drastically. Such an integrated sensor sys-
tem will be ideally suited for on-site applications, capable of rapidly and accurately
sensing multiple analytes
in situ
for environmental applications.
This chapter describes development of the needle-type multi-analyte MEA sen-
sor. More specifically, research work to miniaturize and characterize individual
sensors for measurements of the oxidation reduction potential (ORP) [55, 56],
dissolved oxygen (DO) [57, 58], and phosphate [59, 60] is described. These sen-
sors were integrated into a single sensor array to demonstrate a proof-of-concept
multi-analyte MEA, which was then applied to
in situ
evaluation of biofilms.
Microelectrode miniaturization and integration was performed using MEMS tech-
nologies, which offer the advantages of accurate fabrication methods, reduced
complexity of the fabrication process, increased reliability and reproducibility,
reduced cost, and possibility of batch fabrication for large scale production. It
μ
Fig. 6.2
Concept of an
integrated multi-analyte
MEMS sensor array for
in
situ
monitoring in biofilms
and the environment [57]
