Near infrared fluorescence-magnetic resonance dual-modal imaging with Cy5-labeled, Gd–Al co-doped mesoporous silica nanoparticles

Abstract

To obtain comprehensive information and to compensate the limits of individual modalities in molecular imaging, the research on dual-modal imaging probes (DMIPs) attracts much interest. Here, we report a reliable and facile procedure to prepare near infrared fluorescence (NIRF)-magnetic resonance (MR) DMIPs using Cy5-labeled, Gd–Al co-doped mesoporous silica nanoparticles (MSNs). Amine-modified, Gd–Al co-doped MSNs were first synthesized through one-step co-condensation. A Cy5-NHS ester was then coupled to the amino groups to produce the DMIPs, which were denoted as Gd–Al@MSNs-Cy5. High intensity NIRF and a relaxation rate (17.7 mM⁻¹ s⁻¹) were observed. Featuring the lower background and the deeper penetration depth, the cutting-edge NIRF imaging was achieved. Moreover, the larger surface area of MSNs could be modified with more NIRF probes, Cy5, for improved NIRF. Following the Solomon–Bloembergen–Morgan theory, enhanced MR performance was illustrated by the relaxation rate because MSNs have a porous structure that enables access of water into the interior, and co-doping with Al in the MSNs promotes the doped amount of Gd. The exchange rate of water is much more accelerated through doping Gd and Al since a disordered pore arrangement is found in Gd–Al co-doped MSNs. The DMIPs in saline were injected into mice through the tail vein for imaging and basic pharmacokinetics studies. They were excreted by the stomach and intestine in 3 h, a circulation time long enough for imaging. Thus, Gd–Al@MSNs-Cy5 are attractive for clinical NIRF-MR dual-modal imaging by integrating the biocompatibility of MSNs, the NIRF of Cy5, and the high MR response of Gd.