Unraveling the Nano-Bio Interface Interactions of a Lipase Adsorbed on Gold Nanoparticles under Laser Excitation.

The complex nature and structure of biomolecules and nanoparticles and their interactions make it challenging to achieve a deeper understanding of the dynamics at the nano-bio interface of enzymes and plasmonic nanoparticles subjected to light excitation. In this study, circular dichroism (CD) and Raman spectroscopic experiments and molecular dynamics (MD) simulations were used to investigate the potential changes at the nano-bio interface upon plasmonic excitation. Our data showed that photothermal and thermal heating induced distinct changes in the secondary structure of a model nanobioconjugate composed of lipase fromCandida antarcticafraction B (CALB) and gold nanoparticles (AuNPs). The use of a green laser led to a substantial decrease in the α-helix content of the lipase from 66% to 13% and an increase in the ß-sheet content from 5% to 31% compared to the initial conformation of the nanobioconjugate. In contrast, the differences under similar thermal heating conditions were only 55% and 11%, respectively. This study revealed important differences related to the enzyme secondary structure, enzyme-nanoparticle interactions, and the stability of the enzyme catalytic triad (Ser105-Asp187-His224), influenced by the instantaneous local temperature increase generated from photothermal heating compared to the slower rate of thermal heating of the bulk. These results provide valuable insights into the interactions between biomolecules and plasmonic nanoparticles induced by photothermal heating, advancing plasmonic biocatalysis and related fields.

Light-Driven Catalytic Regulation of Enzymes at the Interface with Plasmonic Nanomaterials.

Regulation of enzymes is highly relevant toward orchestrating cell-free and stepwise biotransformations, thereby maximizing their overall performance. Plasmonic nanomaterials offer a great opportunity to tune the functionality of enzymes through their remarkable optical properties. Localized surface plasmon resonances (LSPR) can be used to modify chemical transformations at the nanomaterial's surface, upon light irradiation. Incident light can promote energetic processes, which may be related to an increase of local temperature (photothermal effects) but also to effects triggered by generated hotspots or hot electrons (photoelectronic effects). As a consequence, light irradiation of the protein-nanomaterial interface affects enzyme functionality. To harness these effects to finely and remotely regulate enzyme activity, the physicochemical features of the nanomaterial, properties of the incident light, and parameters governing molecular interactions must be optimized. In this Perspective, we discuss relevant examples that illustrate the use of plasmonic nanoparticles to control enzyme function through LSPR excitation. Finally, we also highlight the importance of expanding the use of plasmonic nanomaterials to the immobilization of multienzyme systems for light-driven regulation of cell-free biosynthetic pathways. Although this concept is living its infancy, we encourage the scientific community to advance in the development of novel light-controlled biocatalytic plasmonic nanoconjugates and explore their application in biosensing, applied biocatalysis, and biomedicine.

Surface interactions of gold nanorods and polysaccharides: From clusters to individual nanoparticles.

Gold nanorods (AuNRs) are suitable for constructing self-assembled structures for the development of biosensing devices and are usually obtained in the presence of cetyltrimethylammonium bromide (CTAB). Here, a sulfated chitosan (ChiS) and gum arabic (GA) were employed to encapsulate CTAB/AuNRs with the purpose of studying the interactions of the polysaccharides with CTAB, which is cytotoxic and is responsible for the instability of nanoparticles in buffer solutions. The presence of a variety of functional groups such as the sulfate groups in ChiS and the carboxylic groups in GA, led to efficient interactions with CTAB/AuNRs as evidenced through UV-vis and FTIR spectroscopies. Electron microscopies (HR-SEM and TEM) revealed that nanoparticle clusters were formed in the GA-AuNRs sample, whereas individual AuNRs, surrounded by a dense layer of polysaccharides, were observed in the ChiS-AuNRs sample. Therefore, the presented work contributes to the understanding of the driving forces that control the surface interactions of the studied materials, providing useful information in the building-up of gold self-assembled nanostructures.