Surface Sensing of Quantum Dots by Electron Spins

Abstract

The nanoscale design of quantum dots (QDs) requires advanced analytical techniques. However, those that are commonly used do not have sufficient sensitivity or spatial resolution. Here, we use magnetic resonance techniques combined with paramagnetic Mn impurities in PbS QDs for sensitive probing of the QD surface and environment. In particular, we reveal inequivalent proton spin relaxations of the capping ligands and solvent molecules, strengths and anisotropies of the Mn nuclear spin interactions, and Mn nuclei distances with ∼1 Å sensitivity. These findings demonstrate the potential of magnetically doped QDs as sensitive magnetic nanoprobes and the use of electron spins for surface sensing.

Synthesis of folic acid functionalized gold nanoclusters for targeting folate receptor-positive cells

“…In our NMR studies, we observed significant shortening of the longitudinal relaxation time, T 1 , for protons in the capping ligands of Au NCs compared to that for protons in the ligand only. We note that the biggest difference is observed for the protons in the immediate proximity of the NC core (T 1 decreases from 1.61 to 0.64 s), as was shown previously for paramagnetic quantum dots [26] (see also supplementary information, S1). The observation of magnetism in AuNCs is of potential interest for their application in magnetic resonance imaging.…”

Realization of Universal Quantum Gates with Spin‐Qudits in Colloidal Quantum Dots

“…However, the separation between the peaks in the SQ (≈43 MHz) and DQ (≈84 MHz) doublets are larger than the expected values, 2ν I and 4ν I , respectively, revealing the contribution of second order hyperfine interactions For B = 1213 mT, A ≡ A iso = 267 MHz, ν 0 = 34 GHz, S = 5/2, and m s = 1/2, we find that 2ν I ≈ 43 MHz and 4ν I ≈ 86 MHz, in agreement with the experimental data. Finally, the peak at Δν ≈ 51 MHz is assigned to hydrogen‐atoms on the QD capping ligands weakly coupled to Mn spins …”

“…Synthesis of the Materials and Samples Preparation : The Mn‐doped PbS QDs were synthesized in aqueous solution with an Mn weight content of 0.05%, which corresponds to a nominal average number of Mn ions per QD of 0.5. The surface of the QDs was passivated with thiolglycerol (TGL) molecules enabling the realization of nanostructures that are stable and optically active . The core of the QDs has the cubic rocksalt crystal structure of PbS and an average diameter d = 4.5 ± 1.2 nm (Figure a).…”

“…Mn) with concentration down to a single impurity per QD17c,20 and flexibility in the manipulation of the QD surface and environment enable the minimization of the major sources of Mn spin qubit decoherence (i.e. Mn–Mn spin interactions, protons of the QD surface capping ligands and nuclear spins) and to observe long quantum coherence near room temperature 18,21,17a. Furthermore, these narrow band gap nanocrystals offer opportunities for optical control of exciton‐Mn entangled states by ultrafast optical pulses and integration with other low‐dimensional semiconductors, such as graphene, to construct new hybrid functional devices …”

Developing Mn-doped lead sulfide quantum dots for MRI labels

“…On the other hand, the broadening of the NMR lines and the non-linear decrease of T 1 and T 2 with increasing Mn-content indicate much stronger effects at low Mn content (Mn o 1%), thus suggesting the preferential location of Mn close to the periphery of the nanocrystal. 31 Self-purification mechanisms 4 can lead to impurity out-diffusion resulting in greater impurity content in the proximity of the QD surface compared to the centre. 32 The greater Mn-dependent reduction of T 1 and T 2 times at low Mn compared to higher Mn content indicates a saturation of the concentration of Mn-ions close to the QD surface.…”