Transmission Electron Microscopy and Time Resolved Optical Spectroscopy Study of the Electronic and Structural Interactions of ZnO Nanorods with Bovine Serum Albumin

Abstract

The adsorption behavior and electronic interactions of bovine serum albumin (BSA) with ZnO nanorod surfaces were investigated using high-resolution transmission electron microscopy as well as stationary and time-resolved optical spectroscopy techniques. Transmission electron microscopy shows that ZnO nanorod surfaces are surrounded by a homogeneous amorphous BSA film with thicknesses between ~2.5 and 5.0 nm. The electronic structure and adsorption geometry of BSA were examined using high-angle annular dark field scanning transmission electron microscopy combined with electron energy loss spectroscopy. The adsorption process was observed to result into an unfolded conformation of BSA becoming predominantly bound in the side-on orientation at the ZnO surface. This adsorption mode of the BSA molecules allows for a strong interaction with surface states of the ZnO nanorods. This is obvious from its efficient quenching of the defect-center photoluminescence of ZnO. Complementary information of electronic interactions across the ZnO nanorod interface was obtained from femtosecond transient absorption spectroscopy experiments. The rise dynamics of the measured transients revealed altered hole trapping dynamics and, thus, indicated to heterogeneous charge transfer as emerging from adsorbed BSA molecules to defect centers of the ZnO interface.

Optical biosensors based on ZnO nanostructures: advantages and perspectives. A review

“…Klaumunzer et al reported on BSA adsorption on the ZnO nanostructures. Investigation of the structure properties with Transmission Electron Microscopy (TEM) showed the formation of an amorphous phase of BSA over well crystalline ZnO structure [82]. The study of the fundamental properties of ZnO nanostructures dipped into buffer solution with pH 7-7.3, showed a positive value of Z-potential for ZnO [83].…”

“…Due to their high surface/volume ratio, surface tailoring ability, novel electron transport properties and electronic conductance multifunctionality it is possible to successfully immobilize various types of biomolecules. Mostly nanorods (NRs) [36,38,40,43,45,47,48,53,56,74,82,86] and nanowires (NWs) [29,33,42,46,49,75,77,94] were used as a biosensor platform. Nanoparticles (NPs) [35,37,50,83,84,97,98], quantum dots [34,44], other low-dimentional structures [30,32,39,52,70,71,76,79,80,81,85,89,93,95,99] and thin films [31,51,72,73] ...…”

“…In particular, electrostatic interactions between carboxylate anions of BSA and monovalent oxygen vacancies in the ZnO surface should induce the formation of doubly positively charged oxygen vacancies. It results in the reduction of the intensity of the green defect-center emission in ZnO [82].…”

ZnO superstructures via oriented aggregation initiated in a block copolymer melt

“…26 The green PL emission around 560 nm is attributed to radiative recombination of a shallowly trapped electron and a deeply trapped hole. 27,28 The latter is ascribed to a doubly positively charged oxygen vacancy formed by hole trapping through a monovalent, positively charged oxygen vacancy at the surface of ZnO. [26][27][28] The orange emission (660 nm) of ZnO nanostructures may involve bulk defects associated with excess oxygen occupying interstitial lattice sites.…”

“…27,28 The latter is ascribed to a doubly positively charged oxygen vacancy formed by hole trapping through a monovalent, positively charged oxygen vacancy at the surface of ZnO. [26][27][28] The orange emission (660 nm) of ZnO nanostructures may involve bulk defects associated with excess oxygen occupying interstitial lattice sites. 29 In any case, the bulk emission (393 nm, 660 nm) to surface emission (560 nm) intensity ratio is expected to crucially depend on both the size and morphology (surface to bulk ratio) and the surface coating of the ZnO mesocrystals.…”