Biomedical Engineering Reference
In-Depth Information
However, it is not possible to immobilize biomolecules directly because the deposited fi lms are
hydrophobic and chemically inert, so surface modifi cation is necessary.
A variety of strategies have been developed for surface functionalization of the diamond thin
fi lms; one of them is the direct chemical or photochemical functionalization of the hydrogen-
terminated surface [361-367]. In this approach, the hydrophobic hydrogen-terminated surfaces
were functionalized either photochemically by UV excitation of halogen gases [362-364] or alkenes
[361,367], thereby introducing chloro-, fl uoro- or aminoalkyl groups, or chemically by reacting
with the radical species generated from benzoyl peroxide [366]. Another commonly used approach
is the application of pretreatment methods to introduce chemically reactive groups onto the fi lms
[368-372]. Some special techniques such as oxygen plasma treatment, anodic polarization, and the
use of strong oxidizing acid are employed to introduce oxygen-containing functional groups onto
the diamond fi lm.
Tethering biomolecules is another important procedure for the whole biosensor fabrication.
Yang et al. [361] described the attachment of DNA to nanocrystalline diamond (NCD) fi lms using
UV illumination (0.35 mW cm
−
2
, 254 nm). In their approach, vinyl groups of organic molecules
were UV-linked to the hydrogen-terminated diamond surface. Applying a sulfosuccinimidyl
4-
N
-maleimidomethyl cyclohexane-1-carboxylate (SSMCC) cross-linker, thiol-modifi ed DNA was
subsequently tethered to hydrogen-terminated NCD fi lms.
Enzymes such as GOD can also be immobilized onto conducting diamond fi lms to form stable and
sensitive biosensors. In the works of Wang et al. [373], GOD was attached to the ultrananocrystalline
diamond (UNCD) surface by tethered aminophenyl functional moieties that were previously grafted to
UNCD surface by electrochemical reduction of aryl diazonium salt. It causes less microstructure dam-
age to diamond surface and has more stable C-C linkage at the interface compared with the surface
oxidation approach in which the diamond surface is exposed to oxygen or other reactive gas plasmas.
Recent research shows that when diamond surfaces are covalently bonded to DNA or anti-
bodies, the resulting biologically modifi ed surfaces exhibit unusual chemical stability and perfect
specifi city in biomolecular recognition studies [374-376]. When bonded to enzymes such as redox
enzymes, the whole system can exhibit excellent biocatalytic activity to analyte [373,377].
REFERENCES
1. Clark, L.C., Monitor and control of blood and tissue oxygen tensions,
Trans. Am. Soc. Artif. Intern.
Organs
, 2, 41, 1956.
2. Stephen, A.W. and John, P.H., Chemically modifi ed, carbon-based electrodes and their application as
electrochemical sensors for the analysis of biologically important compounds: a review,
Analyst
, 117,
1215, 1992.
3. Updike, S.J. and Hicks, G.P., The enzyme electrode,
Nature
, 214, 986, 1967.
4. Swoboda, B.E.P. and Massey, V., Purifi cation and properties of the glucose oxidase from
Aspergillus
niger
,
J. Biol. Chem
., 240, 2209, 1965.
5. Jones, M.N., Manley, P., and Wilkinson, A., The dissociation of glucose oxidase by sodium-
n
-dodecyl
sulphate,
Biochem. J.
, 203, 285, 1982.
6. Leskovac, V. et al., Glucose oxidase from
Aspergillus niger
: the mechanism of action with molecular
oxygen, quinones, and one-electron acceptors,
Int. J. Biochem. Cell. B
., 37, 731, 2005.
7. Weibel, M. and Bright, H., The glucose oxidase mechanism,
J. Biol. Chem
., 246, 2734, 1971.
8. Clark, L.C., The hydrogen peroxide sensing platinum anode as an analytical enzyme electrode,
Method.
Enzymol
., 56, 448, 1979.
9. Ianniello, R.M. and Yacynych, A.M., Immobilized enzyme chemically modifi e d ele ct rode as a n a mp ero -
metric sensor,
Anal. Chem
., 53, 2090, 1981.
10. Marcos, S. et al., An optical glucose biosensor based on derived glucose oxidase immobilised onto a
sol-gel matrix,
Sensor. Actuator. B Chem
., 57, 227, 1999.
11. Fortier, G., Brassard, E., and Bélanger, D., Optimization of a polypyrrole glucose oxidase biosensor,
Biosens. Bioelectron
., 5, 473, 1990.
