Measuring the Accessible Surface Area within the Nanoparticle Corona Using Molecular Probe Adsorption

Abstract

The corona phase-the adsorbed layer of polymer, surfactant or stabilizer molecules around a nanoparticle-is typically utilized to disperse nanoparticles into a solution or solid phase. However, this phase also controls molecular access to the nanoparticle surface, a property important for catalytic activity and sensor applications. Unfortunately, few methods can directly probe the structure of this corona phase, which is subcategorized as either a hard, immobile corona or a soft, transient corona in exchange with components in the bulk solution. In this work, we introduce a Molecular Probe Adsorption (MPA) method for measuring the accessible nanoparticle surface area using a titration of a quenchable fluorescent molecule. For example, riboflavin is utilized to measure the surface area of gold nanoparticle standards, as well as corona phases on dispersed single walled carbon nanotubes and graphene sheets. A material balance on the titration yields certain surface coverage parameters, including the ratio of the surface area to dissociation constant of the fluorophore, q K D as well as K D itself. Uncertainty, precision, and the correlation of these parameters across different experimental systems, preparations, and modalities are all discussed. Using MPA across a series of corona phases, we find that the Gibbs free energy of probe binding scales inversely with the cube root of surface area, q. In this way, MPA is the only technique to date capable of discerning critical structure-property relationships for such nanoparticle surface phases. Hence, MPA is a rapid quantitative technique that should prove useful for elucidating corona structure for nanoparticles across different systems.

A synthetic mimic of phosphodiesterase type 5 based on corona phase molecular recognition of single-walled carbon nanotubes

“…We arrived at similar conclusions about the surface coverage by quantifying the hydrophobic dye adsorption to the exposed surface of SWNTs, using a technique recently developed in our laboratory (49). More specifically, as riboflavin is titrated with a SWNT colloidal solution, it adsorbs onto the exposed SWNT surface as a result of hydrophobic interactions, quenching the fluorescence of riboflavin.…”

Solution NMR methods for structural and thermodynamic investigation of nanoparticle adsorption equilibria

“…For example, the Molecular Probe Adsorption (MPA) method demonstrated the convenience of fluorescence spectroscopy for estimating the available adsorption surface in NPs containing a corona phase. 53 …”

Antibody-Free Rapid Detection of SARS-CoV-2 Proteins Using Corona Phase Molecular Recognition to Accelerate Development Time

“… 41 The accessible surface area of the PEG-phospholipid-wrapped SWCNT was measured using the molecular probe adsorption technique. 32 Fluorescence emission (510–560 nm) intensity of riboflavin was measured using a Thermo Varioskan plate, with excitation at 460 nm. Deflections of the riboflavin fluorescence were taken in the presence of nanosensor suspensions with an SWCNT concentration of 10 mg/L.…”