You could try fluorescence imaging. Check for fluorescence emission from the drugs loaded in nanoparticles if the nanoparticles are non-fluorescent. In the absence of fluorescence from nanoparticles, the fluorescence has to come from the drug present in the nanoparticles.

But there are other methods such as infrared spectroscopy. You could identify unique characteristic IR bands of the drug molecule and check their presence in the sample confirming the presence of drug inside the nanoparticle.

Hi Varun,. Depending on the excitation you could use NTA (nanoparticle tracking analysis). For example the NanoSight NS500 device can visualise particles up to 1000 nm and has excitation of ~405 nm. It has a long-pass filter so you can detect any emission (as long as it can excite at 405 nm such as QTracker nanoparticles).

I have been using one recently and it is pretty good. Not sure of the price but I think it is