There is growing interest in the development of nanomaterials that facilitate the high-precision detection of cancer cells with the least possible invasion of the body. The association of drugs and contrast agents for concomitant therapy and diagnostic is extremely important to follow the evolution of treatment. However, cancer drugs can often cause collateral damage to non-cancer cells and a promising alternative to these treatments is plasmonic photothermal therapy (PTT) [1]. The use of silver nanoparticles (AgNPs) present advantages over other metals, as it combines good qualities in terms of plasmonic feature, synthesis with high control over size and morphology, and cost-effectiveness. AgNPs also have the versatility to modify their surface, providing higher specificity and/or even a signal for a diagnostic technique, like magnetic resonance imaging (MRI). MRI is a non-invasive diagnostic tool that allows the differentiation between healthy and tumoral tissues. However, this technique commonly requires the use of contrast agents (ACs) to enhance the image contrast. Gd³⁺ chelates are the systems most used clinically as ACs and their conjugation with NPs allows a greater concentration of paramagnetic ions, generating a greater contrast without increasing their dosage. Bifunctional nanosystems based on AgNPs and Gd³⁺ chelates present the promising possibility to achieve theranostic nanoplatforms, combining the photothermal property of AgNPs with the relaxometric efficiency of Gd³⁺ chelates. Thus, AgNPs, with good chemical and colloidal stability and a prismatic shape, and DOTA-Gd complexes containing a thiol group were prepared. The obtained bifunctional nanosystems maintained the optical properties of AgNPs and showed longitudinal relativities for Gd³⁺ similar to the AC used clinically (at 20 MHz and 37 °C) [2]. Therefore, the results are promising for the preparation of theranostic systems for MRI and PTT.