Biosensors based on direct electron transfer of protein - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 568

the electron transfer of xanthine oxidase embedded on DNA. When hypoxanthine was
added to the pH 5.0 phosphate buffer solution, a catalytic peak appears at 0.500 V,

and the anodic peak at 0.420 V disappears by increasing hypoxanthine.

Ghamouss [263] developed a screen-printed carbon electrode modifi ed with both
HRP and LOD (SPCE-HRP/LOD) to determine l-lactate. The sensitivity of the opti-
mized SPCE-HRP/LOD to l-lactate was 0.84 nAL M 1 in a detection range between

µ

10 and 180 µ M.

17.4 CONCLUSIONS

The direct electron transfer of redox proteins and enzymes is very diffi cult on many bare
solid electrodes. Many methods and materials are used to immobilize the proteins and
enzymes in order to enhance the direct electron-transfer rate and provide a suitable micro-
environment for them. Proteins and enzymes prepared by these methods can retain their
catalytic activity and be used to make the mediator-free biosensors. These biosensors are
widely used in environmental, food, industrial, and other fi elds by detection of hydrogen
peroxide, glucose, NO, uric acid, xanthine, hypoxanthine, and so on. Because of the spe-
cifi city of proteins and enzymes these mediator-free biosensors have more selectivity than
those biosensors without enzymes. The absence of mediator can also simplify the prepara-
tion of the biosensor and reduce its charge. Many scientists work in this fi eld and achieve
much progress. However, only a few of the proteins and enzymes can achieve direct elec-
trochemistry. There is no common method to immobilize the proteins and enzymes to
achieve their direct electrochemistry. At the same time, we are not very clear about the
mechanism of direct electron transfer between proteins and electrodes. Future work will
focus on fi nding effi cient methods to achieve direct electron transfer of most proteins and
enzymes, pointing out the mechanism of the electron-transfer process in biologic systems,
and preparing excellent and steady enzyme-based mediator-free biosensors.

17.5 ACKNOWLEDGMENTS

We are grateful to all the authors and coworkers cited in the references for their efforts
in carrying out the work described in this chapter. We are also grateful to the National
Natural Science Foundation of China (Nos 60571042/30370397 and 60171023) and
the State Key Laboratory of Transducer Technology, Chinese Academy of Sciences,
for fi nancial support.

17.6 REFERENCES

1. L.C. Clark and C. Lyons, Electrode systems for continuous monitoring in cardiovascular surgery. Ann. N
Y. Acad. Sci. 102 , 29-45 (1962).
2. Y. Ikariyama, S. Yamauchi, T. Yukiashi, and H. Vshioda, One step fabrication of microbiosensor
prepared by the codeposition of enzyme and platinum particles. Anal. Lett. 20 , 1791-1801 (1987).