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:

Enhancing Raman Scattering without Plasmons: Unprecedented Sensitivity Achieved by TiO2 Shell-Based Resonators. A remarkable enhancement of Raman scattering is achieved by TiO2 shell-based spherical resonators in the absence of plasmonic enhancers. This effect is ascribed to the synergistic combination of high refractive index of the shell layer, multiple light scattering through the spheres, and related geometrical factors and can be exploited to fabricate a new generation of self-diagnostic, recyclable SERS-active substrates.
{"Chemical": ["TiO2"]}