In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Empty nanoparticles provided similar results to control ( saline - treated ) group of animals .
### Output Text:
Empty nanoparticles provided similar results to control ( saline - treated ) group of animals . 