NANOSTRUCTURED METAL OXIDE-BASED BIOSENSORS

BIOSENSOR

It is based on a biochemical reaction that occurs between an analyte and a biocatalyst

Immobilized on a suitable substrate.

Interaction between biocatalyst and a biomolecule is effected by

• Surface area, surface charge, energy, roughness

• And porosity, valence/conductance states, functional groups, physical

• States and hygroscopic nature all affect the formation of a biointerface.

NPG ASIA MATERIALS | VOL 3 | JANUARY 2011 | www.natureasia.com/asia-materials

The enzymatic reaction can be electrochemically monitored either by the decreased oxygen content in the solution or detection

formed hydrogen peroxide

The main immobilizing approaches adopted for cholesterol biosensor

• Self assembled monolayers

• Lipid bilayer memberane

• Anodic porous alumina

• Graphite-Teflon composite

• Prussian blue/poly pyrrole composite

• Direct adsorption Chitosan film

• Sol-gel composite film

Metal oxide matrix for enzyme immobilization has become attractive due to

• high ratio surface area

• uniform open pore structure

• chemical and thermal stability

Cobalt nanoparticles possess many good properties such as

• Low cost

• Biocompatibility

• Uniform film-forming ability

• No toxicity

Immobilization of ChOx onto a GC Electrode

Repetitive potential cycling (30 cycles at 100 mV s1 at potential range between 1.2 and1.1 V) in phosphate

buffer solution pH 7, containing 1 mM cobalt-chloride was used for electrodeposition of the cobalt oxihydroxide film

on the surface of the GC electrode.

{Electrophoretic deposition is that colloidal particles suspended in a liquid medium migrate under the influence of an electric

field (electrophoresis) and are deposited onto an electrode.}

After the deposition of cobalt oxihydroxide nanoparticles onto GC electrode, the electrode was immersed in fresh phosphate

solution containing 5 mg mL1 ChOx and the potential was repetitively cycled (20 scans) from 1.2 to

1.0 Vat scan rate 50 mV s1 for immobilization of ChOx.

Finally, the modified electrode was removed from ChOx solution, washed with double distilled water and stored at

refrigerator (4 °C) before being used in experiments

SEM image

Electrodeposited film exhibits uniform and porous cobalt-oxide

nanostructure containing nanowires with average diameter

ranging from 40 to 70 nm.

XRD imageNo peaks corresponding to cobalt oxide were observed.

AFM images• CoOx distributed uniformly on the electrode surface• After immobilization of Cholesterol oxidase enzyme,

the surface morphology was changed and AFM image, with more

aggregated appearance was observed .

Voltammetric Response of the Biosensor to Cholesterol• Determination of H2O2 which produced during enzymatic

oxidation of cholesterol is a strategy for cholesterol detection.• We confirmed that CoOx nanoparticles are excellent electron transfer mediator

for H2O2 oxidation

Result and discussion

Characterizations of CoOx Nanomaterials

• The cyclic voltammogram, SEM image and XRD spectra

• The electrodeposited CoOx nanoparticles were taken

Cyclic Voltameter

• Formation of CoOx layer on the surface of electrode was checked by recording

cyclic voltammograms of the modified electrode in alkaline solution (pH 12) without

cobalt ions.

• Three oxidation peaks were observed at 0.1, 0.22 and 0.55 V during the

positive potential scan.

• These results can be attributed to the conversion between four different

cobalt oxidation phases of Co(OH)2, Co3O4, CoOOH and CoO2 which are stable

at alkaline pH.

• During the cathodic scan, two reduction peaks at 0.54 and 0.2 V were

observed, corresponding to the reduction of the various CoOx species formed

during the positive sweep.

Conclusion

• Cholesterol biosensor was made based on immobilizing ChOx onto CoOx nanoparticles without adding

any electron transfer mediator.

• The experimental results show that the ChOx enzyme remains active upon immobilization onto CoOx nanostructures.

• Determination of cholesterol was done by detection of generated hydrogen peroxide in the enzymatic reaction.