You might want to try to see if, after electrospinning, the nano CuS is coated by the TPU. If so, then biomolecules won't be able to adsorb on the nano CuS that you have, so the bandgap for the nano-CuS won't change (it'll be whatever it is when TPU is coating it all around), so you won't expect to see any change with or without biomolecules in your medium (e.g. water, air) - I'm assuming you're active observing fluorescence to try to detect sensing of biomolecules.

(My understanding is, the color that you can get from nano-CuS changes depending on how the local environment, including for example the biomolecule adsorption, changes the bandgap of the CuS).

You can try to make PU hydrophilic that may result in better blending with CuS. In turn, PU/nano-CuS may enhance the absorption of biomolecules. I mean you can modify PU surface.

In addition, if you wish to enhance PU conductivity since it is a very low conducting plastic, you can try to make PU-nanocomposite by adding high conducting nano-materials such as CNTs or graphene.

Also, you may like to explore other thermoplastics such as polyethylene or PVC as compared to PU since PU is a toxic material. It is composed of toxic isocyanates.

thank you @ Kaoru Aou for your valuable inputs. I am using CV curves to detect biomolecules and i have observed that pure CuS is able to detect Biomolecules, but when the same is deposited on PU fibres it fails to sense. any insights you would like to provide me?

Thanks a lot Manisha Chhikara for suggesting modifications and alternatives. but i have to wind up the project soon and also now i cannot change my substrate. moreover since i am still an undergraduate i have difficulty in getting CNTs.

Since you first mentioned that you "electrospun Pu by blending nano CuS" then I would expect that that PU is coated around the CuS, and that the PU gets in the way of CuS sensing. One thing you can do to convince yourself is to try to electrospin PU without CuS, and then coat the PU with CuS later. Probably that will be able to sense biomolecules - that is my speculation.

>> observed that pure CuS is able to detect Biomolecules, but when the same is deposited on PU fibres it fails to sense. any insights you would like to provide me?

Look at this article, it may help

Fabrication, characterization and sensor application of electrospun polyurethane nanofibers filled with carbon nanotubes and silver nanoparticles