Nanocomposite based biosensors and related methods

1. A biosensor comprising:

an electrode having a surface;

a nanocomposite on the surface of the electrode, the nanocomposite comprising magnetic nanoparticles dispersed on an outer surface of each member of a population of carbon nanotubes,

wherein the magnetic nanoparticles comprise core-shell magnetic nanoparticles comprising a core comprising a ferromagnetic metal or compound thereof, and a shell comprising silicon dioxide; and

one or more biomolecules over the surface of the electrode, wherein the biomolecules are configured to undergo a redox reaction with a target molecule;

wherein the outer surface of the carbon nanotubes comprise one or more functional groups covalently bonded to the outer surface.

2. The biosensor of claim 1 , wherein the magnetic nanoparticles comprise iron, nickel, cobalt, or a compound of iron, nickel, or cobalt.

3. The biosensor of claim 1 , wherein the magnetic nanoparticles comprise nickel or cobalt, or a compound of nickel or cobalt.

4. The biosensor of claim 1 , wherein the magnetic nanoparticles comprise cobalt, cobalt oxide, nickel, nickel oxide, or cobalt-iron oxide.

5. The biosensor of claim 1 , wherein the magnetic nanoparticles comprise iron or a compound thereof.

6. The biosensor of claim 1 , wherein the magnetic nanoparticles comprise iron oxide.

7. The biosensor of claim 1 , wherein the magnetic nanoparticles comprise Fe 3 O 4 , cobalt, cobalt oxide, nickel, nickel oxide, or cobalt-iron oxide.

8. The biosensor of claim 1 , wherein the carbon nanotubes comprise multiwalled carbon nanotubes.

9. The biosensor of claim 1 , wherein the carbon nanotubes have an average outer diameter of about 30 nm to about 50 nm.

10. The biosensor of claim 1 , wherein the functional groups comprise COOH, OH, NH, NH 2 , F, COX, or SH, wherein X is F, Cl, Br, or I.

11. The biosensor of claim 1 , wherein the biomolecules comprise cholesterol oxidase, DNA, or a cancer drug.

12. The biosensor of claim 1 , wherein the biomolecules comprise glucose oxidase and the target molecule comprises glucose.

13. The biosensor of claim 12 , wherein the biosensor exhibits a detection limit for glucose of about 800 nM or less.

14. The biosensor of claim 12 , wherein the biosensor exhibits a linear response for glucose from about 1 μM to about 30 mM.

15. The biosensor of claim 1 , wherein the magnetic nanoparticles comprise core-shell magnetic nanoparticles and the core comprises Fe 3 O 4 , further wherein the carbon nanotubes comprise multiwalled carbon nanotubes, and further wherein the biomolecules comprise glucose oxidase and the target molecule comprises glucose.

16. A nanocomposite comprising:

a population of carbon nanotubes; and

a population of magnetic nanoparticles dispersed on the outer surface of each member of the population of carbon nanotubes;

wherein:

the magnetic nanoparticles comprise core-shell magnetic nanoparticles; and

the core comprises a ferromagnetic metal or a compound thereof;

wherein the outer surface of the carbon nanotubes comprise one or more functional groups covalently bonded to the outer surface, wherein the one or more functional groups are selected from the group consisting of COOH, OH, NH, NH 2 , F, COX, or SH, wherein X is F, Cl, Br, or I.

17. The nanocomposite of claim 16 , wherein the shell comprises silicon dioxide.

18. The nanocomposite of claim 16 , wherein the magnetic nanoparticles comprise iron, nickel, or cobalt.

19. A method for determining a concentration of a target molecule in a sample, the method comprising:

exposing the sample to a biosensor, the biosensor comprising an electrode;

a nanocomposite on the surface of the electrode, the nanocomposite comprising magnetic nanoparticles dispersed on an outer surface of each member of a population of carbon nanotubes,

wherein the magnetic nanoparticles comprise core-shell magnetic nanoparticles comprising a core comprising a ferromagnetic metal or compound thereof, and a shell comprising silicon dioxide; and

one or more biomolecules over the surface of the electrode, wherein the biomolecules are configured to undergo a redox reaction with a target molecule, wherein the outer surface of the carbon nanotubes comprise one or more functional groups covalently bonded to the outer surface, and

detecting a signal from the biosensor, wherein the signal is correlated to the concentration of the target molecule in the sample.