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Control over supramolecular recognition between proteins and nanoparticles (NPs) is of fundamental importance in therapeutic applications and sensor development. Most NP-protein binding approaches use 'tags' such as biotin or His-tags to provide high affinity; protein surface recognition provides a versatile alternative strategy. Generating high affinity NP-protein interactions is challenging however, due to dielectric screening at physiological ionic strengths. We report here the co-engineering of nanoparticles and protein to provide high affinity binding. In this strategy, 'supercharged' proteins provide enhanced interfacial electrostatic interactions with complementarily charged nanoparticles, generating high affinity complexes. Significantly, the co-engineered protein-nanoparticle assemblies feature high binding affinity even at physiologically relevant ionic strength conditions. Computational studies identify both hydrophobic and electrostatic interactions as drivers for these high affinity NP-protein complexes.

The delivery of proteins into cells is a potential game changer for a wide array of therapeutic purposes, including cancer therapy, immunomodulation and treatment of inherited diseases. In this review, we present recently developed nanoassemblies for protein delivery that utilize strategies that range from direct assembly, encapsulation and composite formation. We will discuss factors that affect the efficacy of nanoassemblies for delivery from the perspective of both nanoparticles and proteins. Challenges in the field, particularly achieving effective cytosolar protein delivery through endosomal escape or evasion are discussed.

The demand for eco-friendly synthetic methods of metal nanoparticles is on the rise. We hereby present a green approach for a one pot synthesis of nontoxic gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) using water soluble, naturally-derived luteolin tetraphosphate (LTP). LTP was used as the reducing and capping agent using water as the solvent excluding the use of other capping agents. The synthesis was achieved by varying the concentrations of the metal precursor and the reducing agent to form spherical and cuboidal AuNPs and spherical & quasi spherical AgNPs, respectively. The AgNPs and AuNPs were characterized by UV-vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive absorption spectroscopy (EDS) and high resolution transmission electron microscopy (HR-TEM). TEM images showed that the resulting AuNPs exhibited cuboidal characteristics with average particle sizes ranging from 16 to 23 nm, whereas those of the spherical nanoparticles of the synthesized AuNPs ranged from 8 nm to 11 nm. However, the average edge length of truncated AuNCs ranged from 372 nm to 509 nm. The average particle size for the spherical AgNPs ranged from 12 to 13 nm, whereas that of the larger quasi-spherical AgNPs ranged from 10 nm to 100 nm, respectively. Additional quantitative metrics assessing the properties of the nanomaterials made by our water-based, greener synthesis method and those made by other methods include lattice constant values of gold nanocubes (AuNCs) with TEM images, XRD data and 3-D models of the fcc structure using the Vesta software. The TEM images of AuNCs exhibited slightly truncated edges which are in agreement with AuNCs synthesized using organic solvents. Furthermore, the lattice constant of the SAED pattern of the AuNCs was calculated to be 4.052 A which is in agreement with that for fcc gold of 4.078 A (JCPDS 04-0784) and comparable to that for AuNCs in the literature of 4.068 A. This confirms that the synthesized AuNCs were achieved at room temperature without using organic reducing solvents and toxic capping agents. The synthesized LTP derived AuNPs were found to maintain stability for a period of 8 months compared to those synthesized using luteolin alone which showed stability for only 336 hours.

We hereby present a novel approach for the synthesis of gold nanoparticles (AuNPs) using water soluble, naturally-derived flavonoids. Quercetin pentaphosphate (QPP), quercetin sulfonic acid (QSA) and apigenin triphosphate (ATRP) were utilized as reducing agents and stabilizers for the gold nanoparticle synthesis. Synthesis was achieved at room temperature using water as a solvent and it requires no capping agents. The AuNPs were characterized using UV-vis, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive absorption spectroscopy (EDS), high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED). The resulting AuNPs were spherical, triangular, cubicle, hexagonal and rectangular in shape. The average particle sizes of 4.85 nm, 9.56 nm and 13.54 nm were obtained for the nanoparticles derived from QPP, ATRP and QSA respectively. The surface plasmon resonance peak of the AuNPs derived from QSA, ATRP and QPP was observed at 541 nm, 544 nm and 547 nm respectively. The AuNPs exhibited excellent antibacterial activities of 99.9%, 100% and 99.9% growth inhibition for Escherichia coli ATCC® 25922™, Staphylococcus epidermidis ATCC® 12228™ and Citrobacter freundii ATCC® 8090 at 104 cfu inoculations. The AuNPs were observed to retain stability after 150 days compared to those reported using conventional approaches of 30 days. This work also provides insights into the mechanism of flavonoid-based nanoparticle synthesis while eliminating the use of hazardous and toxic organic solvents and adopting the use of water as a solvent.