You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Potential for metal contamination by direct sonication of nanoparticle suspensions. While conducting toxicity tests with nano titanium dioxide, the authors found that test suspensions were being contaminated with aluminum and titanium from tip erosion during direct sonication. The contaminating alloy particles had a measurable size distribution and zeta potential using dynamic light scattering, which changed the measured characteristics of the suspensions. Caution should be used when employing direct sonication for preparing test suspensions due to potential interferences of these particles in toxicological assessments.
{"Chemical": ["aluminum", "titanium", "titanium dioxide"]}