Label-free, nucleotide-mediated dispersion of magnetic nanoparticles for "non-sandwich type" MRI-based quantification of enzyme

Adsorption mechanism of rhein-coated Fe3O4 as magnetic adsorbent based on low-field NMR

In the present study, a magnetic adsorbent, rhein-coated magnetic Fe₃O₄ nanoparticle (RMNP), for Pb²⁺ and Mg²⁺ had been developed, and adsorption mechanism was studied via low-field NMR. RMNP was characterized by TEM, FTIR, and XRD. RMNP could adsorb and remove Pb²⁺ and Mg²⁺ from water and was successfully applied to remove Pb²⁺ and Mg²⁺ from wastewater, with satisfactory recovery rates and high adsorption capacities. The calculated maximum adsorption capacity for Mg²⁺ and Pb²⁺ was approximately 69.3 and 64.9 mg g^-1 of RMNP, respectively, which was better than some results reported. Low-field NMR results showed that Pb²⁺ or Mg²⁺ enhanced the T₂ relaxation time of RMNP, which suggested that RMNP selectively coordinated with Pb²⁺ or Mg²⁺ and led to the aggregation of RMNP, furthermore removal of Pb²⁺ or Mg²⁺ from water. The standard curves for △T₂-cation concentration exhibited good line correlation. The linear ranges were from 4.2 × 10^-6 to 2.0 × 10^-4 mol L^-1 for Pb²⁺ and from 5.0 × 10^-6 mol L^-1 to 1.0 × 10^-4 mol L^-1 for Mg²⁺, respectively. The limits of detection were 1.4 × 10^-6 mol L^-1 for Pb²⁺ and 2.1 × 10^-6 mol L^-1 for Mg²⁺, respectively. In short, low-field NMR could clearly display the interaction between RMNP and Pb²⁺ or Mg²⁺, even be used to detect Pb²⁺ or Mg²⁺ in suitable condition. Besides, this method could be expanded to study the interaction between other magnetic adsorbents and analytes.

Aggregation effects on the magnetic properties of iron oxide colloids

Magnetic nanoparticles (MNPs), and in particular iron oxide nanoparticles (mainly magnetite and maghemite), are being widely used in the form of aqueous colloids for biomedical applications. In such colloids, nanoparticles tend to form assemblies, either aggregates, if the union is permanent, or agglomerates, if it is reversible. These clustering processes have a strong impact on the MNPs' properties that are often not well understood. In this review, the causes and consequences of MNPs aggregation/agglomeration are reviewed and discussed. Special attention has been paid to the impact of the MNPs aggregation/agglomeration on their magnetic properties and heating properties, when exposed to an alternating magnetic field in the frame of magnetic hyperthermia. In addition, a model system with MNPs of two different sizes coated with three different molecules oleic acid, meso-2, 3-dimercaptosuccinic acid and poly(maleic anhydride-alt-1-octadecene) has been characterized and the results used to support the ideas reviewed.

Selective and sensitive detection of MiRNA-21 based on gold-nanorod functionalized polydiacetylene microtube waveguide

Development of rapid, highly selective and sensitive miRNA detection in a complex biological environment has attracted considerable attention. Herein, we describe a novel two step method to construct gold-nanorod functionalized polydiacetylene (PDA) microtube for miRNA detection. In PDA microtube, with a one-dimensional (1D) waveguide nature, the excitation position and emission out-coupling position are far apart, thus helpful in reducing contribution of auto-fluorescence from biological sample. The use of specially designed toehold-mediated strand displacement reaction enables the reliable and selective discrimination of miRNA sequences with high sequence homology. Based on the condensing enrichment effect, the detection limit of the proposed PDA microtube system is as low as 0.01nM, and it can be applied directly to detect disease-specific miRNA targets in human serum. This PDA microtube waveguide system can be further integrated into the chip for the potential applications in minimally invasive, portable clinical diagnostic equipment.

Lanthanide-doped upconversion nano-bioprobes: electronic structures, optical properties, and biodetection

The latest advances in lanthanide-doped upconversion nanoparticles were comprehensively reviewed, which covers from their fundamental photophysics to biodetection.