Avidin Decorated Core–Shell Nanoparticles for Biorecognition Studies by Elastic Light Scattering

Magnetic Nanoplatforms for Covalent Protein Immobilization Based on Spy Chemistry

Immobilization of proteins on magnetic nanoparticles (MNPs) is an effective approach to improve protein stability and facilitate separation of immobilized proteins for repeated use. Herein, we exploited the efficient SpyTag-SpyCatcher chemistry for conjugation of functional proteins onto MNPs and established a robust magnetic-responsive nanoparticle platform for protein immobilization. To maximize the loading capacity and achieve outstanding water dispersity, the SpyTag peptide was incorporated into the surface-charged polymers of MNPs, which provided abundant active sites for Spy chemistry while maintaining excellent colloidal stability in buffer solution. Conjugation between enhanced green fluorescence protein (EGFP)-SpyCatcher-fused proteins and SpyTag-functionalized MNPs was efficient at ambient conditions without adding enzymes or chemical cross-linkers. Benefiting from the excellent water dispersity and interface compatibility, the surface Spy reaction has fast kinetics, which is comparable to that of the solution Spy reaction. No activity loss was observed on EGFP after conjugation due to the site-selective nature of Spy chemistry. The immobilization process of EGFP on MNPs was highly specific and robust, which was not affected by the presence of other proteins and detergents, such as bovine serum albumin and Tween 20. The MNP platform was demonstrated to be protective to the conjugated EGFP and significantly improved the shelf life of immobilized proteins. In addition, experiments confirmed the retained magnetophoresis of the MNP after protein loading, demonstrating fast MNP recovery under an external magnetic field. This MNP is expected to provide a versatile and modular platform to achieve effective and specific immobilization of other functional proteins, enabling easy reuse and storage.

Specific On-site Assembly of Multifunctional Magnetic Nanocargos Based on Highly Efficient and Parallelized Bioconjugation: Toward Personalized Cancer Targeting Therapy

The rational design of particle-based cancer theranostic agents, combining diagnostic and therapeutic features in a single entity, has emerged as an effective approach toward personalized cancer therapy; however, creating a flexible assembly of specific targeting ligands with regard to a broad range of tumor tissues and cells is still challenging. Here, we present a convenient and highly variable on-site assembly strategy for the preparation of multifunctional doxorubicin (DOX)-loaded nanocargos with magnetic supraparticles (MSPs) as a core and redox-degradable poly(methylacrylic acid-co-N,N-bis(acryloyl) cystamine) (P(MAA-co-Cy) as the shell, which could be simultaneously modified with multiple targeting ligands through parallelized bioconjugation on the basis of a streptavidin-biotin (SA-BT) interaction. Under physiological conditions similar to those of the cytoplasm of tumor cells, DOX could be released in a controlled manner from these nanocargos to specific tumor sites, while dual-ligand modified nanocargos showed remarkable proliferation inhibition for the HeLa cells and the SK-OV-3 cells that overexpressed both folate as well as integrin receptors. The experimental results demonstrated that the on-site assembly strategy described herein opens access to highly efficient targeting drug delivery systems toward personalized cancer targeting therapy by incorporating functional diversity, which can be easily achieved through highly efficient and parallelized one-step bioconjugation.

Tuning gold nanoparticles interfaces by specific peptide interaction for surface enhanced Raman spectroscopy (SERS) and separation applications

Surface functionalization and control over nanostructured interfaces represents a key aspect in nanoscience and nanobiotechnology. Nanoplasmonic structures for analyte detection typically require sophisticated nanofabrication techniques, as well as bioactivated nanostructures that need multistep conjugations for chemical ligation. An alternative to such complex processes is to rely on specific biomolecules adsorption for decoration or self-assembly of nanoparticles at solid/liquid interface. In principle, small biomolecules with specific binding properties to nanostructures could control the assembly without modifying the nanoparticle chemistry, pH of the solution or salt concentration. Importantly, such an approach could be direct, robust, and reversible. In this work, we report about the use of a specific peptide for direct and reversible adsorption on gold nanoparticles with tuned interfacial properties just by simply adjusting the ratio between the numbers of peptide molecules to the number of gold nanoparticles. This easy, direct and reversible assembly of gold nanoparticles mediated by the specific peptide makes this platform ideal for small-volume samples and low concentrations detection using surface enhanced Raman Spectroscopy, as well as for the capture or separation of biomolecules in complex mix.

A multidentate peptide for stabilization and facile bioconjugation of gold nanoparticles

Gold nanoparticles of two different sizes stabilized by a 15-mer peptide ligand specifically designed for this purpose have been prepared in aqueous solution and characterized by UV-vis spectroscopy and TEM. The presence of the ligand and its binding mode to the particles via its four cystein thiols is evidenced by FTIR and NMR spectroscopy. Biotinylation of the particles via binding to a freely accessible lysine residue is demonstrated.

In situ IR spectroscopic studies of the avidin-biotin bioconjugation reaction on CdS particle films

Avidin-biotin bioconjugation reactions have been carried out on CdS nanoparticle films in H2O and D2O and investigated using in situ ATR-IR spectroscopic techniques. The experimental procedure involved the sequential adsorption of mercaptoacetic acid, the protein avidin, and the subsequent binding of the ligand biotin. The IR spectra of the solution-phase species mercaptoacetic acid, avidin, and biotin, at pH=7.2 were generally found to be similar in both H2O and D2O, with some minor peak shifts due to solvation changes. The IR spectra of the adsorbed species suggested that avidin may have undergone a conformational change upon adsorption to the CdS surface. In general, adsorption-induced conformational changes for avidin are likely, but to our knowledge have not been previously reported. The conformation of adsorbed avidin appeared to change again upon the binding of biotin, with the spectral data suggesting partial reversion to its native solution conformation.