Make Conjugation Simple: A Facile Approach to Integrated Nanostructures

We report a facile approach to the conjugation of protein-encapsulated gold fluorescent nanoclusters to the iron oxide nanoparticles through catechol reaction. This method eliminates the use of chemical linkers and can be readily extended to the conjugation of biological molecules and other nanomaterials onto nanoparticle surfaces. The key to the success was producing water-soluble iron oxide nanoparticles with active catechol groups. Further, advanced electron microscopy analysis of the integrated gold nanoclusters and iron oxide nanoparticles provided direct evidence of the presence of a single fluorescent nanocluster per protein template. Interestingly, the integrated nanoparticles exhibited enhanced fluorescent emission in biological media. These studies will provide significantly practical value in chemical conjugation, the development of multifunctional nanostructures, and exploration of multifunctional nanoparticles for biological applications

MALDI MS In-Source Decay of Glycans Using a Glutathione-Capped Iron Oxide Nanoparticle Matrix

A new matrix-assisted laser desorption ionization (MALDI) mass spectrometry matrix is proposed for molecular mass and structural determination of glycans. This matrix contains an iron oxide nanoparticle (NP) core with gluthathione (GSH) molecules covalently bound to the surface. As demonstrated for the monosaccharide glucose and several larger glycans, the mass spectra exhibit good analyte ion intensities and signal-to-noise ratios, as well as an exceptionally clean background in the low mass-to-charge (<i>m</i>/<i>z</i>) region. In addition, abundant in-source decay (ISD) occurs when the laser power is increased above the ionization threshold; this indicates that the matrix provides strong energy transfer to the sample. For five model glycans, ISD produced extensive glycosidic and cross-ring cleavages in the positive ion mode from singly charged precursor ions with bound sodium ions. Linear, branched, and cyclic glycans were employed, and all were found to undergo abundant fragmentation by ISD. ¹⁸O labeling was used to clarify <i>m</i>/<i>z</i> assignment ambiguities and showed that the majority of the fragmentation originates from the nonreducing ends of the glycans. Studies with a peracetylated glycan indicated that abundant ISD fragmentation occurs even in the absence of hydroxyl groups. The ISD product ions generated using this new matrix should prove useful in the sequencing of glycans