Superoxide electrochemical sensors and biosensors: principles, development and applications - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 155

TABLE 6.1
Electrochemical parameters of Cu, Zn-SOD promoted by COOH-terminated SAMs

E 0

Γ modifi er Γ SOD

(10 10 mol cm 2 ) (10 11 mol cm 2 ) k s (s 1 )

Molecules (mV vs Ag/AgCl) α c

Cysteine 6.71 0.21 1.31 0.21 65 3 0.61 0.02 1.2 0.1

D,L-Homo-cysteine 4.09 0.78 0.51 0.09 135 3 0.38 0.02 0.4 0.1

Mercapto-succinic acid 5.65 0.60 1.23 0.35 205 3 0.44 0.02 0.8 0.1

N-Acetyle-L-cysteine 4.42 0.38 1.02 0.14 197 3 0.46 0.02 0.9 0.1

Thiolactic acid 9.04 0.38 0.53 0.05 195 3 0.74 0.02 0.1

Mercapto-acetic acid 13.2 1.2 1.45 0.36 202 2 0.59 0.02 1.3 0.1

3-Mercapto-propionic acid 8.11 0.32 1.26 0.42 175 3 0.61 0.02 1.1 0.1

Dimercapto-succinic acid 6.63 0.56 0.55 0.08 201 2 0.69 0.02 0.1

L-Cystine 5.41 0.24 1.42 0.32 40 3 0.52 0.02 2.1 0.1

E p c )/2 in the cyclic voltammograms obtained with the SAM-modifi ed Au electrodes in phosphate
buffer at 100 mVs 1 . E p a and E p c are anodic and cathodic peak potentials of the Cu, Zn-SOD, respectively. (Reprinted from Y.
Tian, T. Ariga, N. Takashima, T. Okajima, L. Mao, and T. Ohsaka, Electrochem. Commun . 6 (2004) 609-614, with permission
from Elsevier.)

E 0 was estimated as ( E p a

TABLE 6.2
SAMs unable to facilitate the electron transfer of Cu, Zn-SOD

Γ modifi er Γ modifi er

(10 10 mol cm 2 ) (10 10 mol cm 2 ) Molecules Molecules

2-Amino ethanthiol 8.97 0.52 4-Aminothiophenol 4.12 0.41

Cystamine 5.25 0.53 4-Hydroxythiophenol 3.81 0.36

1-Ethanethiol 8.54 0.65 1-Butanethiol 9.86 0.96

1-Decanethiol 11.2 1.8 MESA 12.4 2.8

4-Mercaptopyridine 3.68 0.23 2-Mercaptopyridine 0.62 0.06

Diphenyl disufi de 3.42 0.25 4,4 -Dithiodipyridine 1.23 0.14

MESA: 2-Mercaptoethanesulfonic acid (sodium salt).

function to bond the Cu, Zn-SOD on the COOH-terminated SAMs. These inter-
actions could be relatively favorable for the orientation of the Cu, Zn-SOD on the SAM-
modifi ed Au electrodes and further for facilitating the observed electron transfer.
While more evidence is still needed to understand the interactions between the SAMs
and the Cu, Zn-SOD, the above demonstrations may primarily conclude that the inter-
actions between ˆ COOH groups of the SAMs and the Cu, Zn-SOD are probably the
determinative interactions, which are mainly responsible for the observed promoted
electron transfer between the Cu, Zn-SOD and the Au electrode.