Enhancing MRI Relaxivity of the Gd³⁺ Ions Coordinated to Carboxylated Highly Water-Soluble Graphene Nanoribbons

Magnetic resonance imaging (MRI) is a powerful tool for diagnostic medicine.1 One of applications of MRI is the ability to track cells and nanoconstucts in vivo. For this purpose chemical contrast agents (CAs) need to be internalized into cells to exhibit both safe cell internalization and enhanced proton relaxivity per Gd3+ion, so that the amount of internalized CA is as minimal as possible. In this work, we report that Gd3+ ions coordinated to carboxylated surfactant-free highly water-soluble graphene nanoribbons2 (GNRs) result in Gd/GNRs (as shown in Figure 1a-d) to produce enhanced r1 and r2 relaxivities, which are up to 20 times higher when compared to the commercially-available MRI CA, magnevist. Here we also show that the new Gd/GNR CAs can be used for T1 and T2 weighted MRI imaging (Figure 1e,f). Also, taking into account the lipophilic nature of the Gd/GNRs, they possible can be used for cell internalization as has been previously shown for other honeycomb carbon-based nanostructures such as gadonanotubes3 and gadofullerenes.4Available results will be reported. ACKNOWLEDGEMENTS A. Gizzatov, V. K., A. Guven, and L. J. W. acknowledge The Welch Foundation (C-0627) for partial support of this work, while A. M. D. and J. M. T. acknowledge the ONR (#00006766, N00014-09-1-1066), the AFOSR MURI (FA9550-12-1-0035), and the AFOSR (FA9550-09-1-0581). REFERENCES 1. P. Caravan, J. J. Ellison, T. J. McMurry, R. B. Lauffer, Chem. Rev. 99, 2293 (1999). 2. A. Gizzatov, A. Dimiev, Y. Mackeyev, J. M. Tour, L. J. Wilson, Chem. Commun. 48, 5602 (2012). 3. L. A. Tran, R. Krishnamurthy, R. Muthupillai, M. G. Cabreira-Hansen, J. T. Willerson, E. C. Perin, L. J. Wilson, Biomaterials 31, 9482 (2010). 4. B. Sitharaman, L. A. Tran, Q. P. Pham, R. D. Bolskar, R. Muthupillai, S. D. Flamm, A. G. Mikos, L. J. Wilson, Contrast Media Mol. Imaging 2, 139 (2007). Figure 1. TEM images of a) Gd/GNRs and b) GNRs. Electron dispersion spectroscopy - TEM mapping for Gd3+c) Gd/GNRs and d) GNRs. (scale bars = 600 nm). MRI images of e) T1-weighted MRI inversion recovery phantom images acquired at different inversion times (TI) for the GNR, Gd/GNR samples in aqueous solutions and H2O at 1.5 T and f) T2-weighted MRI spin-echo phantom images acquired at different echo times (TE) for the GNR, Gd/GNR samples in aqueous solutions and H2O at 1.5 T.