Help to solve Non-specific binding in CNT FET

[1MK5]

Hi everyone,

Just wondering if anyone in the forum have any experience in carbon nanotube field-effect transistor biosensor?


I have a real head ache on how to overcome non-specific binding in this device.


And I am wondering if someone would be kind enough to give some suggestions how to overcome this problem.


I have tried several common blocking strategy, such as with PEG, tween20, triton-X, and BSA; but none of them give me satisfactory result.



Is there any other strategy out there that I do not know on how to block non-specific binding?


If there is, would you be so kind to share some suggestions with me?


Many thanks


- 1MK5 -

 

[chemisttree]

What have you done to the surface of the nanotube to ensure specific binding in the first place?

 

[1MK5]

Hi chemisttree,

Thanks for the reply.


I have done some standard carbodiimide linking chemistry (NHS+EDC) to attach the biomolecules to the CNT (my carbon nanotube has carboxylic functional group)



Cheers,


- 1MK5-

 

[chemisttree]

Yes, I see. Carboxylic acid functionalized stuff would definitely cause non-specific binding. Have you done any FTIR on your sample to look for unfunctionalized COOH or the diimide/carboxylate intermediate... even urea salts? If you go that way I would recommend a photoacoustic measurement since that works best on highly absorbing species like carbon black and probably carbon nanotubes. I don't know what the biomolecule is, so that might interfere, of course. I know that the reaction mechanism for diimide coupling is not very good with bulky alcohols although I have done it with t-BuOH in one case (10:1 excess of the alcohol and lots of DMAC catalyst... at least 1:1 with alcohol ). A big bulky biomolecule might be difficult to complex unless used in great excess and perhaps using a properly spaced amine spacer group. The spacing group will have to be optimized to get both maximum coverage and good ultimate signal from the nanofibre.

I'm thinking it would be neat to find a linkage spacer that was crystalline at RT and more open at mildly elevated temperature. That way you could do the coupling at elevated temperature (with the terminal amine unraveled and less bulky...more accessable) and then allow the thing to cool and have the (paraffinic?) spacer group coil up on itself and bring the biomolecule into more intimate and rigid contact with the nanofibre. That way you might get more effective coverage/blockage of unreacted carboxylated nanotube.

 

[1MK5]

Hi Chemistree,


Sorry for the late reply. Kinda busy with my experiments recently


Thanks for your help.


So, you think that unreacted carboxylic functional group might be the cause why I get so many non-specific binding (NSB)?


I was thinking more in the line of hydrophobic-hydrophobic interaction between the biomolecules and the CNT itself.


May I know your opinion on this possibility?

 

[chemisttree]

I couldn't say with that with certainty unless I knew more about the ligand. Is the ligand or the other non-specific binding species hydrophobic? I assume that they are dissolved in water...

What is the energy difference between hydrogen bonds and Van der Waals type interactions?