1. Chemical Stimuli: These include changes in pH, ionic strength, or the presence of specific molecules. For instance, pH-sensitive nanoparticles can release drugs in acidic environments, typical of many tumor sites.
2. Physical Stimuli: These encompass temperature, light, and magnetic fields. Thermo-responsive polymers can gel or liquefy at different temperatures. Similarly, magnetic nanoparticles can be guided to a specific location using an external magnetic field.
3. Biological Stimuli: These involve enzymatic reactions or the presence of specific biomolecules. Nanomaterials can be designed to respond to enzymes that are overexpressed in certain diseases, providing a highly specific and localized response.
