Nanozeolite‐LTL with Gd^III Deposited in the Large and Eu^III in the Small Cavities as a Magnetic Resonance Optical Imaging Probe

Abstract

The immense structural diversity of more than 200 known zeolites is the basis for the wide variety of applications of these fascinating materials ranging from catalysis and molecular filtration to agricultural uses. Despite this versatility, the potential of zeolites in medical imaging has not yet been much exploited. In this work a novel strategy is presented to selectively deposit different ions into distinct framework locations of zeolite-LTL (Linde type L) and it is demonstrated that the carefully ion-exchanged Gd/Eu-containing nanocrystals acquire exceptional magnetic properties in combination with enhanced luminescence. This smart exploitation of the framework structure yields the highest relaxivity density (13.7 s(-1) L g(-1) at 60 MHz and 25 °C) reported so far for alumosilicates, rendering these materials promising candidates for the design of dual magnetic resonance/optical imaging probes, as demonstrated in preliminary phantom studies.

Prototropic Exchange Governs T1 and T2 Relaxivities of a Potential MRI Contrast Agent Nanozeolite Gd−LTL with a High pH Responsiveness

“…The obtained best-fit parameters agree well with those previously reported. 14 The negligible |∆δ zeo | value obtained shows that the Fermi contact shift inside zeolite Gd-LTL is completely compensated by the BMS with opposite sign, which suggests that the particles are aligned in the magnetic field. If the particles were randomly rotating, the BMS would average out and a relatively large overall shift determined by the Fermi contact interaction would result.…”

“…40 Here, w is the number of free water molecules inside the zeolite per Gd 3+ -ion, q is the number of water molecules coordinated to Gd 3+ , P m is the molal fraction of Gd 3+ Table S1). Although the accuracy of these numbers is low due to the small magnitudes of the experimental data, they show that the exchange rate of (whole) water between the interior of the zeolite and that of bulk (τ zeo,O ≈ 7 µs at 298 K) is 3 orders of magnitude larger than the corresponding exchange rates of protons as evaluated from the 1 H NMRD profile (τ zeo ≈ 10 µs) 14 , which confirms that prototropic exchange is dominating the relaxivity of Gd-LTL. The 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 15 value for τ zeo,O is of the same order of magnitude as that determined for previously studied zeolitic Gd-Y and Gd-A systems (τ zeo ≈ 30 µs) 12 , where prototropic exchange was unimportant.…”

“…Simulations using eqs [10][11][12][13][14][15] show that the increase of electronic relaxation upon increase of the Gd 3+ -loading, observed by EPR would result in a minor decrease in relaxivity, whereas τ r is so large and τ zeo so small, that they do not limit the relaxivity. Therefore, changes of these parameters can also be excluded as reason for the decrease in relaxivity with the Gd 3+ -loading of Gd-LTL-L.…”

“…have fitted the inner-sphere longitudinal relaxivity of Gd-LTL-L with 5.2 % loading using a twostep mechanism, 14 in which first only the relaxivity inside the zeolite cavity is considered and treated as a concentrated solution of Gd 3+ -ions. 10 In the second step, the propagation of the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 9 relaxation enhancement from the interior water of zeolite to the bulk water outside was taken into account ( Figure 2).…”

Smart Supramolecular Nanosystems for Bioimaging and Drug Delivery

“…[1][2][3][4][5][6][7] Supramolecular self-assembled nanosystems used as diagnostic/therapeutic agents encompass a wide range of substances, such as liposomes, [8][9][10][11] polymer-based nanoparticles, [12][13][14][15][16][17] carbon nanomaterials, [18][19][20][21] metallic nanomaterials [22][23][24][25] and zeolites. [26][27][28][29] Supramolecular self-assembled nanosystems can provide clear signals such as fluorescent, magnetic, photoacoustic signals for imaging when acting on lesion location as bioprobes. Supramolecular self-assembled nanosystems as non-invasive diagnostic tools have the capacity to combine multiple modalities on one nanosystem, which shows an outstanding advantage in imparting higher sensitivity and deeper insight in vivo processes.…”