Lanthanide-DTPA grafted silica nanoparticles as bimodal-imaging contrast agents

Abstract: The design and synthesis of a combined MRI-optical probe for bio-imaging are reported. The materials studied join the properties of lanthanide (Ln3+) complexes and nanoparticles (NPs), offering an excellent solution for bimodal imaging. The hybrid SiO2@APS/DTPA:Gd:Ln (Ln = Eu3+ or Tb3+) (APS: 3-aminopropyltriethoxysilane, DTPA: diethylenetriamine pentaacetic acid) system increases the payload of the active magnetic centre (Gd3+) and introduces a Ln3+ long-life excited state (Eu3+: 0.35 ± 0.02 ms, Tb3+: 1.87 ± 0.02 ms), with resistance to photobleaching and sharp emission bands. The Eu3+ ions reside in a single low-symmetry site. Although the photoluminescence emission is not influenced by the simultaneous presence of Gd3+ and Eu3+, a moderate r1 increase and a larger enhancement of r2 are observed, particularly at high fields, due to susceptibility effects on r2. The presence of Tb3+ instead of Eu3+ further raises r1 but decreases r2. These values are constant over a wide (5–13) pH range, indicating the paramagnetic NPs stability and absence of leaching. The uptake of NPs by living cells is fast and results in an intensity increase in the T 1-weighted MRI images. The optical properties of the NPs in cellular pellets are also studied, confirming their potential as bimodal imaging agents. [Copyright &y& Elsevier]