Naturally Occurring Proteins Direct Chiral Nanorod Aggregation

Abstract

Serum albumin can template gold nanorods into chiral assemblies, but the aggregation mechanism is not entirely understood. We used circular dichroism spectroscopy and scanning electron microscopy to investigate the role of protein identity/ shape, protein/nanorod ratio, and surfactants on chiral protein− nanorod aggregation. Three globular proteinsserum albumin, immunoglobulin, and transferrinproduced similarly sized chiral protein−nanorod aggregates. In solution these aggregates exhibited circular dichroism at the plasmon resonance that switched direction at specific protein/nanorod concentration ratios. Our explanation is that the extent of protein crowding influences protein conformation and therefore protein−protein interactions, which in turn direct nanorod aggregation into preferentially left-or right-handed structures. The fibrous proteins fibrinogen and fibrillar serum albumin also produced chiral nanorod aggregates but did not exhibit a ratio-dependent switch in the circular dichroism direction. In addition, cetyltrimethylammonium bromide micelles prevented all aggregation, providing compelling evidence that protein−protein interactions are crucial for chiral protein−nanorod aggregate formation. The protein-dependent variations in circular dichroism and aggregation reported here present opportunities for future chiral nanostructure engineering and biosensing applications.

Chiral Au Nanorods: Synthesis, Chirality Origin, and Applications

“…Chiral templates, such as amino acids, ,, peptides or proteins, − DNA or DNA origami, ,− and cellulose nanocrystals (CNCs), , polymers, − and silica helices, − serve as soft templates providing the chirality origin of 3D helical ac-Au NRs (Figure a). On one hand, the designed chiral templates with active sites are adsorbed on the surface of Au NRs through electrostatic forces or chemical bonds (thiols, DNA complementary pairing, or others).…”

Thermoplasmonics Enable the Coupling of Light into the Solvent-Mediated Self-Assembly of Gold Nanoparticles

“…and physical (light, magnetic or electric field, temperature, sound waves, etc.) triggers have been used to achieve stimuli-responsive self-assembly processes in NPs. − It is worth mentioning that most of the dynamic self-assembly processes in NPs have been achieved either with chemical or physical stimuli. Design of NP building blocks that are responsive to multiple triggers has been the target in recent years to expand the scope and complexity of the stimuli-responsive self-assembly process.…”

Chiral Plasmonic Pinwheels Exhibit Orientation-Independent Linear Differential Scattering under Asymmetric Illumination

“…Chirality is a geometric property possessed by almost all biomolecules and describes the lack of inversion or mirror symmetry in a structure. Traditionally, chirality is characterized through far-field spectroscopies, but recently, chiral plasmonic substrates have gained interest for enhanced chirality sensing. − Chiral plasmonic substrates amplify molecular chirality through a variety of mechanisms, including Coulombic interactions, providing enhanced local optical chirality, − and employing molecular analytes to template plasmonic nanoparticles into chiral arrangements. , Aside from the interest in chirality sensing platforms, chiral plasmonics has also emerged as a tool for achieving superior optical activity , and negative refraction − and is expected to lead to on-chip nanoantennas for telecommunications applications. − As plasmonic chirality is many orders of magnitude larger than molecular chirality, it is now fairly routine to probe the chirality of single nanoparticles through circular differential scattering (CDS). ,− Single-particle CDS affords high sensitivity for resolving enantiomeric purity and paves the way to the ultrasensitive detection of molecular chirality …”

“… 1 − 7 Chiral plasmonic substrates amplify molecular chirality through a variety of mechanisms, including Coulombic interactions, 8 providing enhanced local optical chirality, 9 − 13 and employing molecular analytes to template plasmonic nanoparticles into chiral arrangements. 14 , 15 Aside from the interest in chirality sensing platforms, chiral plasmonics has also emerged as a tool for achieving superior optical activity 16 , 17 and negative refraction 18 − 24 and is expected to lead to on-chip nanoantennas for telecommunications applications. 25 − 28 As plasmonic chirality is many orders of magnitude larger than molecular chirality, it is now fairly routine to probe the chirality of single nanoparticles through circular differential scattering (CDS).…”