We report the fine-tuning of the relaxometry of gamma-Fe2O3@SiO2 core-shell nanoparticles by adjusting the thickness of the coated silica layer. It is clear that the coating thickness of Fe2O3@SiO2 nanoparticles has a significant impact on the r(1) (at low B0 fields), r(2), and r(2)* relaxivities of their aqueous suspensions. These studies clearly indicate that the silica layer is heterogeneous and has regions that are porous to water and others-that are not. It is also shown, that the viability and the mitochondrial dehydrogenase expression of the microglial cells do not appear to be sensitive to the vesicular load with these core-shell nanoparticles. The adequate silica-shell thickness can therefore be tuned to allow for both a sufficiently high response as contrast agent, and-adequate grafting of targeted biomolecules.

The first hyperpolarizability of aqueous suspensions of polyphosphate stabilized CdS nanocrystals of different mean sizes and of Cd x Zn1 - x S nanocrystals (x = 0, 0.25, 0.75, 1) was determined by the hyper-Rayleigh scattering technique. We report the first experimental observation that the first hyperpolarizability decreases as the band gap energy increases. This is ascribed to the decrease of the resonance enhancement. The surface modification of 9 nm CdS nanocrystals with OH- increases the first hyperpolarizability by a factor 1.7. This is explained in terms of the higher polarizability of the surface terminating groups after the OH- modification. Finally, we have also established the size dependence of the first hyperpolarizability for CdS nanocrystals. Although it increases with the particle size, its values normalized per CdS pair increase with decreasing of size, leading to an enhancement by 1 order of magnitude for 2 nm particles in comparison with bulk. This is explained by assuming the enhancement of both the bulk contribution from the noncentrosymmetric nanocrystal core and the surface contribution. The enhancement of the bulk contribution is ascribed to quantum confinement effects on the normalized oscillator strengths. The surface contribution becomes more relevant as the size decreases and may be enhanced by several effects, especially surface polarization. A two-level model can explain both the band-gap and the size dependences.

Aqueous suspensions of paramagnetic lanthanide oxide nanoparticles have been studied by NMR relaxometry. The observed R 2 * relaxivities are explained by the static dephasing regime (SDR) theory. The corresponding R 2 relaxivities are considerably smaller and are strongly dependent on the interval between the two refocusing pulses. The experimental data are rationalized by assuming the value of the diffusion correlation time, τ D , to be very long in a layer with adsorbed xanthan on the particle's surface. In this layer, the refocusing pulses are fully effective and R 2 ≈ 0. Outside this layer, the diffusion model for weakly magnetized particles was applied. From the fit of the experimental relaxation data with this model, both the particle radii (r p ) and the radii of the spheres, within which the refocusing pulses are fully effective (r diff ), were estimated. The values of r p obtained are in agreement with those determined by dynamic light scattering. Because the value of r diff depends on the external magnetic field B and on the magnetic moment of the lanthanide of interest (µ eff 2 ), the R 2 relaxivity was found to be proportional to B and to µ eff 2 .

, were synthesized with the aim of exploring the influence of the second hydration sphere on the relaxivity of Gd III complexes.

Aqueous suspensions of metal organic frameworks (MOF) containing different Ln(3+) ions, consisting of a series of layered Ln(3+) networks formulated as [Ln(H(2)cmp)(H(2)O)] (where H(5)cmp is (carboxymethyl)iminodi(methylphosphonic acid), with a relatively wide size distribution (400 nm to 1 microm) were studied by relaxometry. The water (1)H longitudinal (r(1)) and transverse (r(2)) relaxivities were obtained for aqueous suspensions of these materials with different lanthanide ions. The values of r(1) are very small and varied only slightly with the effective magnetic moment (mu(eff)) of the lanthanide ions, while r(2) values are larger and proportional to the value of mu(eff)(2). The dependence of R(2) on tau(CP) (the time interval between two consecutive refocusing pulses in the train of 180 degrees pulses applied in a CPMG pulse sequence) was evaluated. The value of R(2) initially increases with tau(CP) and then saturates at higher tau(CP) at a value that is about 3 to 5 times lower than R(2p)*. This can be explained by the static dephasing regime (SDR) theory, in which the diffusion effect is taken into account and where the condition tau(D) > Delta omega(r(p))(-1) holds (tau(D) = r(p)(2)/D, where D is the diffusion coefficient, r(p) is the radius of the particle, and Delta omega(r(p)) is the Larmor frequency shift at the particle's surface). Separation of the particles into two fractions with different particle sizes led to a significant enhancement of the r(2) relaxivity of the smaller particles with a narrow size distribution. Magnetometric measurements performed with the particles containing Dy(III), Ho(III), and Gd(III) showed a typical paramagnetic behavior from 4 to 100 K, used to determine the Curie constants.

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Complexes of 4,10-bis(phosphonomethyl)-1,4,7,10-tetraazacyclododecane-1,7-diacetic acid (trans-H(6)do2a2p, H(6)L) with transition metal and lanthanide(III) ions were investigated. The stability constant values of the divalent and trivalent metal-ion complexes are between the corresponding values of H(4)dota and H(8)dotp complexes, as a consequence of the ligand basicity. The solid-state structures of the ligand and of nine lanthanide(III) complexes were determined by X-ray diffraction. All the complexes are present as twisted-square-antiprismatic isomers and their structures can be divided into two series. The first one involves nona-coordinated complexes of the large lanthanide(III) ions (Ce, Nd, Sm) with a coordinated water molecule. In the series of Sm, Eu, Tb, Dy, Er, Yb, the complexes are octa-coordinated only by the ligand donor atoms and their coordination cages are more irregular. The formation kinetics and the acid-assisted dissociation of several Ln(III)-H(6)L complexes were investigated at different temperatures and compared with analogous data for complexes of other dota-like ligands. The [Ce(L)(H(2)O)](3-) complex is the most kinetically inert among complexes of the investigated lanthanide(III) ions (Ce, Eu, Gd, Yb). Among mixed phosphonate-acetate dota analogues, kinetic inertness of the cerium(III) complexes is increased with a higher number of phosphonate arms in the ligand, whereas the opposite is true for europium(III) complexes. According to the (1)H NMR spectroscopic pseudo-contact shifts for the Ce-Eu and Tb-Yb series, the solution structures of the complexes reflect the structures of the [Ce(HL)(H(2)O)](2-) and [Yb(HL)](2-) anions, respectively, found in the solid state. However, these solution NMR spectroscopic studies showed that there is no unambiguous relation between (31)P/(1)H lanthanide-induced shift (LIS) values and coordination of water in the complexes; the values rather express a relative position of the central ions between the N(4) and O(4) planes.

Quantum dots (QDs) are semiconductor nanocrystals, which present unique photophysical properties, enabling their application as new fluorescent platforms for biomedical sciences. Colloidal QDs are end-capped with organic or inorganic compounds, not only to prevent their agglomeration but also to provide reaction sites for the attachment of targeting (bio)molecules, nanoparticles or other interfaces, for specific biological purposes. The (bio)conjugation can involve non-covalent or covalent interactions, which can be accomplished through different strategies. The final assembly needs to maintain its chemical and optical stability and biochemical functionality. Although a relative good comprehension of the experimental procedures has been established, the bioconjugation process is still a challenge. The present manuscript aims to review the main (bio)conjugation strategies successfully applied to QDs, describing the steps necessary to prepare stable targeting fluorescent nanoplatforms, as well as some usual methods used to evaluate and optimize this process.