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Proteins provide versatile mediators for assembling nanoparticles into organized composites. Here, we demonstrate that a single protein spacer (lysozyme) can be used to direct the self-assembly of gold mixed monolayer protected clusters into controlled ensembles with varied functional response. This efficient self-assembly process provides nanocomposites featuring tunable interparticle spacings, as determined through small angle X-ray scattering, varied sample morphology, as observed by transmission electron microscopy, and modular collective optical behavior, as examined through UV−visible spectroscopic measurements.

Biomacromolecule surface recognition is an important factor in regulating cellular processes. Nanometer-scale mixed monolayer-protected clusters (MMPCs) provide scaffolds for creating receptors targeting biomacromolecular surfaces. Unique features of nanoparticles that make them particularly attractive resources for biomacromolecular recognition and their use in modification of structure and function of biomacromolecules are illustrated in this review.

The interaction of nanomaterials with cells and lipid bilayers is critical in many applications such as phototherapy, imaging, and drug/gene delivery. These applications require a firm control over nanoparticle-cell interactions, which are mainly dictated by surface properties of nanoparticles. This critical Review presents an understanding of how synthetic and natural chemical moieties on the nanoparticle surface (in addition to nanoparticle shape and size) impact their interaction with lipid bilayers and cells. Challenges for undertaking a systematic study to elucidate nanoparticle-cell interactions are also discussed.

Intracellular trafficking of nanoscale objects is regulated by cell membranes through interactions that are under intense investigation. These materials are typically internalized by cells into membrane-bounded endosomes and never gain access to the cell machinery located in the cytosol. While some bio-macromolecules can penetrate or fuse with cell membranes without overt membrane disruption, no synthetic material of comparable size has shown this property yet. Cationic nanoscale objects (mostly assisted by some degree of hydrophobicity) pass through cell membranes by generating transient holes, a process associated with cytotoxicity. To date, studies aimed at generating cell-penetrating nanomaterials have focused on the effect of size, shape, and composition. Here we compare membrane penetration by two nanoparticle ‘isomers’ with the same composition (same hydrophobic content), one coated with sub-nanometer striations of alternating anionic and hydrophobic groups, and the other coated with the same moieties but in a random distribution. We show that the former particles penetrate the plasma membrane without bilayer disruption while the latter were instead mostly trapped in endosomes. Our results highlight a new design rule for materials that interact with cells and offer a paradigm for analyzing the fundamental problem of cell membrane penetrating bio- and macro-molecules. We anticipate consequences for designing materials for biomedical applications and for understanding potential safety issues associated with synthetic nanomaterials.

alpha-Helices are important structural elements in proteins. To provide a scaffold for the facial recognition of peptides, we have explored the interaction of cationic mixed monolayer protected clusters (MMPCs) with a tetra-aspartate peptide in water. In these studies, substantial enhancement of peptide helicity was observed upon addition of the MMPC. Significantly, this stabilization increased with time, demonstrating templation of the monolayer to the peptide helix.

Thioalkyl and thioalkylated oligo(ethylene glycol) (OEG) ligands with chain-end functionality were used to fabricate water-soluble CdSe nanoparticle scaffolds. Surface recognition of chymotrypsin (ChT) was achieved using these functionalized nanoparticle scaffolds, with three levels of interaction demonstrated: no interaction (OEG terminated with hydroxyl group), inhibition with denaturation (carboxylate-terminated thioalkyl ligands), and inhibition with retention of structure (carboxylate-terminated OEG). The latter process was reversible upon an increase in ionic strength, with essentially complete restoration of enzymatic activity.

Anionically functionalized amphiphilic nanoparticles efficiently inhibit chymotrypsin through electrostatic binding followed by protein denaturation. We demonstrate the ability to disrupt this "irreversible" inhibition of chymotrypsin through modification of the nanoparticle surface using cationic surfactants. Up to 50% of original chymotrypsin activity is rescued upon long-chain surfactant addition. Dynamic light-scattering studies demonstrate that chymotrypsin is released from the nanoparticle surface. The conformation of the rescued chymotrypsin was characterized by fluorescence and fluorescence anisotropy, indicating that chymotrypsin regains a high degree of native structure upon surfactant addition.

Monolayer-protected nanoparticles feature tunable size, surface functionality and core material, providing scaffolds for targeting biomacromolecules. This review highlights recent advances in nanoparticle-biomacromolecule interactions, focusing on two key areas: (1) The modulation of structure and function of biomacromolecules through engineered interactions with nanoparticle surfaces; (2) The use of biomacromolecules as building blocks for nanostructured materials.

Nanoparticles present a versatile scaffold to target biomacromolecule surfaces via complementary interactions. This review highlights some unique features of nanoparticles that make them particularly attractive resources for biomacromolecular recognition, and displays their use in modulation of structure and function of biomacromolecules.

Highly water-soluble mixed monolayer protected "rippled'' gold nanoparticles were synthesized through a one step reaction with sodium 11-mercaptoundecanesulfonate and octanethiol ligands at various ratios.