It depends on the chemistry of the ligand and the substrate.

The FTIR of the drug would provide you with the bonds that are present in the drug, but may not provide you with the 3D structure of it, so that you may not know which part is open for interaction with outside

If you want to have an interaction between your nanoparticles and drug, then you should derive it from the structure of the drug. For example if it is a negatively charged chemical, then you nanoparticle should be positiely charged, so that they would have an interaction (like DNA and cationic polymer interactions).

If you want to check whether they are interacting, firstly you should consider modelling. Since it is a cheaper method and it provides you with the required information. This would give you some ideas about how your drug may interact with the excipient. And after that, to check the possibility, you should change the parts of drug that you think are interacting (for example, if interaction is from PO4 residues, remove them from the formulation, or provide two irrelevant drugs, one with PO4 and one without PO4).

That is a short summary for understanding the interaction of the excipient and drug during nanoparticle formulation.

If you have more question please ask.

I hope it helped.

Wish you luck.

It depends on the chemistry of the ligand and the substrate.

The FTIR of the drug would provide you with the bonds that are present in the drug, but may not provide you with the 3D structure of it, so that you may not know which part is open for interaction with outside

If you want to have an interaction between your nanoparticles and drug, then you should derive it from the structure of the drug. For example if it is a negatively charged chemical, then you nanoparticle should be positiely charged, so that they would have an interaction (like DNA and cationic polymer interactions).

If you want to check whether they are interacting, firstly you should consider modelling. Since it is a cheaper method and it provides you with the required information. This would give you some ideas about how your drug may interact with the excipient. And after that, to check the possibility, you should change the parts of drug that you think are interacting (for example, if interaction is from PO4 residues, remove them from the formulation, or provide two irrelevant drugs, one with PO4 and one without PO4).

That is a short summary for understanding the interaction of the excipient and drug during nanoparticle formulation.

If you have more question please ask.

I hope it helped.

Wish you luck.

If you can, you can use ITC to detect the dynamic index of the interaction

By comparing FTIR of pristine particles and drug loaded particles. If any new peak arises (except drug and polymers) that is because of chemical interaction between drug and polymer

You can also check if there are some shifts (more than 5-10 cm-1) in the signals of both nanoparticles and drugs. Just pay attention on the method, sometimes some interactions are erroneously assigned to differences in the spectra of samples acquired by different methods, for instance ATR- FTIR/transmission in KBr pellets..... Another common mistake is looking for interactions in optical artifacts derived from the samples itself.

On FT-IR spectra, some changes can be seen on peaks positions and peaks shapes. Some changes are related to bonding between API and excipients but some others can be due to a change in physical state; for example, the API can be crystalline before formulation (in that case, the IR peaks related to API are relatively sharper) but the formulation can induce some changes in the form of the API toward a more amorphous form (broader IR peaks); the same for some of the excipients. I would recommend to run IR spectra with the best resolution! (Worth keeping in mind that any physical stress on the samples may in some cases induce some physical changes too).