Monovalent maleimide functionalization of gold nanoparticles via copper-free click chemistry

Site-Specific Functionalization of Recombinant Spider Silk Janus Fibers

Biotechnological production is a powerful tool to design materials with customized properties. The aim of this work was to apply designed spider silk proteins to produce Janus fibers with two different functional sides. First, functionalization was established through a cysteine‐modified silk protein, ntag^CyseADF4(κ16). After fiber spinning, gold nanoparticles (AuNPs) were coupled via thiol‐ene click chemistry. Significantly reduced electrical resistivity indicated sufficient loading density of AuNPs on such fiber surfaces. Then, Janus fibers were electrospun in a side‐by‐side arrangement, with “non‐functional” eADF4(C16) on the one and “functional” ntag^CyseADF4(κ16) on the other side. Post‐treatment was established to render silk fibers insoluble in water. Subsequent AuNP binding was highly selective on the ntag^CyseADF4(κ16) side demonstrating the potential of such silk‐based systems to realize complex bifunctional structures with spatial resolutions in the nano scale.

Valence-controlled protein conjugation on nanoparticles via re-arrangeable multivalent interactions of tandem repeat protein chains

Tandem repeat protein chains were wrapped around nanoparticles via re-arrangeable multivalent interactions for valence controlled protein conjugation.

Surface-enhanced Raman scattering (SERS)-based immunosystem for ultrasensitive detection of the 90K biomarker

The research and the individuation of tumour markers in biological fluids are currently one of the main tools to support diagnosis, prognosis, and monitoring of the therapeutic response in oncology. Although the identification of tumour markers in asymptomatic patients is crucial for early diagnosis, its application is still limited by the relatively low sensitivity and the complexity of existing methods (i.e. ELISA, mass spectrometry). We developed an easy, fast, and ultrasensitive surface-enhanced Raman scattering (SERS)-based system, for the detection and quantitation of the LGALS3BP (90K) biomarker that was used as a model, based on the development of antibody-functionalized nanostructured gold surfaces. The detection system was effective for the ultrasensitive detection and characterization of samples of different biochemical compositions. In conclusion, this work could provide the foundation for the development of a medical diagnostic device with the highest predictive power when compared with the methods currently used in cancer diagnostics.

Enhanced inhibition of influenza virus infection by peptide-noble-metal nanoparticle conjugates

The influenza ("flu") type-A virus is a major medical and veterinary health concern and causes global pandemics. The peptide "FluPep" is an established inhibitor of influenza virus infectivity in model systems. We have explored the potential for noble-metal nanoparticle conjugates of FluPep to enhance its antiviral activity and to determine their potential as a delivery platform for FluPep. FluPep ligand is FluPep extended at its N-terminus with the sequence CVVVTAAA, to allow for its incorporation into a mixed-matrix ligand shell of a peptidol and an alkanethiol ethylene glycol consisting of 70% CVVVTol and 30% HS(CH2)11(OC2H4)4OH (mol/mol). Gold and silver nanoparticles (ca. 10 nm diameter) with up to 5% (mol/mol) FluPep ligand remained as stable as the control of mixed-matrix-passivated nanoparticles in a variety of tests, including ligand exchange with dithiothreitol. The free FluPep ligand peptide was found to inhibit viral plaque formation in canine MDCK cells (IC50 = 2.1 nM), but was less potent than FluPep itself (IC50 = 140 pM). Nanoparticles functionalised with FluPep ligand showed enhanced antiviral activity compared to the free peptides. The IC50 value of the FluPep-functionalised nanoparticles decreased as the grafting density of FluPep ligand increased from 0.03% to 5% (both mol/mol), with IC50 values down to about 10% of that of the corresponding free peptide. The data demonstrate that conjugation of FluPep to gold and silver nanoparticles enhances its antiviral potency; the antimicrobial activity of silver ions may enable the design of even more potent antimicrobial inhibitors, capable of targeting both influenza and bacterial co-infections.

Surface-Anchored Thiol-Reactive Soft Interfaces: Engineering Effective Platforms for Biomolecular Immobilization and Sensing

Fabrication of antibiofouling, specifically reactive polymeric coatings that undergo facile functionalization with thiol-bearing small molecules and ligands, yields effective platforms for biomolecular immobilization and sensing. Poly(ethylene glycol) (PEG)-based copolymers containing alkoxysilyl groups to enable surface-anchoring and furan-protected maleimide groups as latent thiol-reactive moieties as side-chains were synthesized. Reactive interfaces were obtained by coating these copolymers onto Si/SiO₂ or glass surfaces and activating the maleimide groups to their thiol-reactive forms via thermal treatment. A series of surfaces modified with copolymers containing varying amounts of maleimide groups were synthesized. Effectiveness of surface modification was probed using Fourier transform infrared spectroscopy, contact angle goniometry, ellipsometry and X-ray photoelectron spectroscopy. Facile surface modification through thiol-maleimide conjugation was established by attachment of a thiol-containing fluorescent dye, namely BODIPY-SH. It was demonstrated that these surfaces allow spatially localized modification through microcontact printing. Importantly, the extent of surface modification could be tuned by varying the initial composition of the copolymer used for coating. Using fluorescence microscopy, it was observed that increasing amount of fluorescent dye was attached onto surfaces fabricated with copolymers with increasing amount of masked maleimide groups. Thereafter, the thiol-maleimide conjugation was utilized to decorate these surfaces with biotin, a protein-binding ligand. It was observed that though these biotinylated surfaces were able to bind Streptavidin effectively, some nonspecific binding was observed on places that were not in conformal contact with the stamp during microcontact printing. This nonspecific binding was eliminated upon neutralizing the residual maleimide units on the printed surface using thiol-containing PEG. Notably, fluorescence analysis of Streptavidin immobilized onto biotinylated surfaces fabricated using varying amounts of maleimide demonstrated that the amount of immobilized protein could be tuned by varying surface composition. It can be envisioned that facile fabrication of these maleimide-containing polymeric surfaces, their effective functionalization in a tunable manner to engineer interfaces for effective immobilization or sensing of biomolecules in a spatially controlled manner would make them attractive candidates for various biotechnological applications.

Ligand Layer Engineering To Control Stability and Interfacial Properties of Nanoparticles

The use of mixed ligand layers including poly(ethylene glycol)-based ligands for the functionalization of nanoparticles is a very popular strategy in the context of nanomedicine. However, it is challenging to control the composition of the ligand layer and maintain high colloidal and chemical stability of the conjugates. A high level of control and stability are crucial for reproducibility, upscaling, and safe application. In this study, gold nanoparticles with well-defined mixed ligand layers of α-methoxypoly(ethylene glycol)-ω-(11-mercaptoundecanoate) (PEGMUA) and 11-mercaptoundecanoic acid (MUA) were synthesized and characterized by ATR-FTIR spectroscopy and gel electrophoresis. The colloidal and chemical stability of the conjugates was tested by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and UV/vis spectroscopy based experiments, and their interactions with cells were analyzed by elemental analysis. We demonstrate that the alkylene spacer in PEGMUA is the key feature for the controlled synthesis of mixed layer conjugates with very high colloidal and chemical stability and that a controlled synthesis is not possible using regular PEG ligands without the alkylene spacer. With the results of our stability tests, the molecular structure of the ligands can be clearly linked to the colloidal and chemical stabilization. We expect that the underlying design principle can be generalized to improve the level of control in nanoparticle surface chemistry.

Photothermal raster image correlation spectroscopy of gold nanoparticles in solution and on live cells

Raster image correlation spectroscopy (RICS) measures the diffusion of fluorescently labelled molecules from stacks of confocal microscopy images by analysing correlations within the image. RICS enables the observation of a greater and, thus, more representative area of a biological system as compared to other single molecule approaches. Photothermal microscopy of gold nanoparticles allows long-term imaging of the same labelled molecules without photobleaching. Here, we implement RICS analysis on a photothermal microscope. The imaging of single gold nanoparticles at pixel dwell times short enough for RICS (60 μs) with a piezo-driven photothermal heterodyne microscope is demonstrated (photothermal raster image correlation spectroscopy, PhRICS). As a proof of principle, PhRICS is used to measure the diffusion coefficient of gold nanoparticles in glycerol : water solutions. The diffusion coefficients of the nanoparticles measured by PhRICS are consistent with their size, determined by transmission electron microscopy. PhRICS was then used to probe the diffusion speed of gold nanoparticle-labelled fibroblast growth factor 2 (FGF2) bound to heparan sulfate in the pericellular matrix of live fibroblast cells. The data are consistent with previous single nanoparticle tracking studies of the diffusion of FGF2 on these cells. Importantly, the data reveal faster FGF2 movement, previously inaccessible by photothermal tracking, and suggest that inhomogeneity in the distribution of bound FGF2 is dynamic.