diff --git a/internal-dev/npo-ext.owl b/internal-dev/npo-ext.owl
index c268b506..7a950298 100644
--- a/internal-dev/npo-ext.owl
+++ b/internal-dev/npo-ext.owl
@@ -3133,6 +3133,13 @@
         <rdfs:label xml:lang="en">CeZrO2 nanoparticle</rdfs:label>
     </owl:Class>
 
+    <!-- http://purl.enanomapper.net/onto/ENM_3733911 -->
+
+    <owl:Class rdf:about="http://purl.enanomapper.net/onto/ENM_3733911">
+        <rdfs:subClassOf rdf:resource="http://purl.bioontology.org/ontology/npo#NPO_1367"/>
+        <obo:IAO_0000115> Silica coating.</obo:IAO_0000115>
+        <rdfs:label xml:lang="en">Nanoparticle material part consisting of a silica coat</rdfs:label>
+    </owl:Class>
 
 </rdf:RDF>