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: To confirm the pro - apoptotic effects , we performed flow cytometric detection , cardiac histology , transmission electron microscopy and terminal deoxynucleotidyl transferase - mediated dUTP - biotin nick end labeling assay .
### Output Text:
To confirm the pro - apoptotic effects , we performed flow cytometric detection , cardiac histology , transmission electron microscopy and terminal deoxynucleotidyl transferase - mediated <span class="chemical">dUTP</span> - <span class="chemical">biotin</span> nick end labeling assay . 