Catechin tuned magnetism of Gd-doped orthovanadate through morphology as T1-T2 MRI contrast agents

Abstract

Tetragonal (t)-LaVO₄ has turned out to be a potential host for luminescent materials. Synthesis of t-LaVO₄ till date has been based on chelating effect of EDTA making it not ideal for bioimaging applications. An alternative was proposed by us through the use of catechin. In recent times there is interest for new MRI contrast agents that can through appropriate doping function both as MRI contrast and optical/upconversion materials. It is generally believed that under appropriate doping, t-LaVO₄ would be a better upconversion material than monoclinic (m)-LaVO₄. Based on these postulations, this work explores the use of gadolinium doped t-LaVO₄ as an MRI contrast agent. From literature, gadolinium oxide is a good T₁ contrast agent. Through this work, using catechin as a template for the synthesis of Gd doped t-LaVO₄, we demonstrate the possible use as a T₁ contrast agent. Interestingly, as the catechin concentration changes, morphology changes from nanorods to square nanoplates and spheres. In this process, a switch from T₁ to T₂ contrast agent was also observed. Under optimal concentration of catechin, with a rod shaped Gd doped t-LaVO₄ an r₂/r₁ value of 21.30 was observed. Similarly, with a spherical shape had an r₂/r₁ value of 1.48 was observed.

Figure 1

XRD pattern of GL nanoparticles (A) without cat (a) and cat (b, [cat⁴⁺]/[La³⁺] = 1:0.05) (Experimental conditions: T = 210 °C, t = 4 h, pH = 7), (B) [cat⁴⁺]/[La³⁺] = 1:0.01(c), [cat⁴⁺]/[La³⁺] = 1:0.05(d) and [cat⁴⁺]/[La³⁺] = 1:1 (e) (Experimental conditions: T = 180 °C, t = 24 h) and (C) Corresponding W-H plot.

Figure 2. Depicts the formation of GL nanoparticles using catechin hydrate.

Figure 3. Final Rietveld XRD data plot of GL nanoparticles with the values of agreement factors and χ² (red, observed; green, calculated; black, vertical bars – positions of the Bragg reflections; pink, difference between observed and calculated intensities).

Figure 4

TEM Image for MGL (a), TGL (b), 01GL (c), 5GL (e) and 1GL (g) and HRTEM images of 01GL (d), 5GL (f) and 1GL (h) nanoparticles [Inset represents the corresponding SAED pattern].

Figure 5

FTIR spectrum (A) and TGA (B) for (a) MGL, (b) TGL, (c) 01GL, (d) 5GL and (e) 1GL nanoparticles.

Figure 6

DLS (1) and Zeta potential (2) for (a) MGL, (b) TGL, (c) 01GL, (d) 5GL, and (e) 1GL nanoparticles.

Figure 7

Zeta potential at various pH values for (A) 01GL (a), 5GL (b) and 1GL (c) and EDAX spectrum (B) nanoparticles.

Figure 8

Absorption (Black line) and luminescence spectra (Blue line) for Gd doped t-LaVO₄ nanoparticles.

Figure 9

Magnetization curves of GL nanoparticles at 300 K 1) without cat (a) and cat (b, [cat4−]/[La3 +] = 1:0.05) (Experimental conditions: T = 210 °C, t = 4 h, pH = 7), 2) [cat4−]/[La3+] = 1:0.01 (c), [cat4−]/[La3+] = 1:0.05 (d) and [cat4−]/[La3+] = 1:1 (e) (Experimental conditions: T = 180 °C, t = 24 h).

Figure 10

Linear fit plot employed for the calculation of r₁ and r₂: T₁- and T₂-weighted phantom images of GL nanoparticles with different concentrations where (a) MGL and (b) TGL. Subscript 1 and 2 represents T₁ and T₂ relaxivity.

Figure 11

Linear fit plot employed for the calculation of r₁ and r₂: T₁- and T₂-weighted phantom images of GL nanoparticles with different concentrations where (a) 01GL, (b) 5GL and (c) 1GL. Subscript 1 and 2 represents T₁ and T₂ relaxivity.