A generalized model on the effects of nanoparticles on fluorophore fluorescence in solution

Authors: ZHANG, DONGMAO - Mississippi State University; NETTLES, CHARLES - Mississippi State University

Submitted to: Journal of Physical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2015
Publication Date: 3/18/2015
Citation: Zhang, D., Nettles, C.B. 2015. A generalized model on the effects of nanoparticles on fluorophore fluorescence in solution. Journal of Physical Chemistry. 119:7941-7948.

Interpretive Summary: A generalized model was developed for conceptual understanding of the effect of NPs on fluorophore fluorescence in solution. This model explicitly considered the NP- and fluorophore-imposed fluorescence inner filter effect. An example application of this generalized model is demonstrated with bovine serum albumin protein adsorbed onto AuNPs. The fact that AuNP binding only attenuates, but does not eliminate, the protein tryptophan fluorescence undermines the reliability of using the Stern-Volmer equation to study the protein/AuNP binding constant and dynamic quenching kinetics. The methodology and insights provided in this work should be of general importance for nanoscience research given the popularity of fluorescence spectroscopy in studying the NP interfacial phenomena. This research will help to develop rapid and sensitive methods in the future for detection of food-borne pathogens in fish and other foods. This study was cosponsored by National Science Foundation and USDA-ARS.

Technical Abstract: Nanoparticles (NP) can modify fluorophore fluorescence in solution through multiple pathways that include fluorescence inner filter effect (IFE), dynamic and static quenching, surface enhancement, and fluorophore quantum yield variation associated with structural and conformational modifications induced by NP binding. The combined contribution of the latter three effects is termed the collective near-field effect because (1) they affect only fluorophore fluorescence in molecules close to the NPs, and (2) it is impossible to differentiate these effects with steady-state fluorescence measurements. A generalized model (F0corr/FNPcorr = (1 + K[NP])/(1 + K[NP]S) was developed for the determination of the NP collective near-field effect S on the fluorophore fluorescence in the surface-adsorbed molecules. The popular Stern–Volmer equation (F0corr/FNPcorr = (1 + K[NP]) used in current fluorescence studies of NP interfacial interactions is a special case of this generalized model, valid only under situations in which the surface-bound molecules are completely fluorescence inactive (S = 0). In addition, we excluded the possibility of NPs inducing significant dynamic fluorescence quenching under realistic experimental conditions on the basis of a simple back-of-the-envelope calculation. Furthermore, using an external reference fluorescence IFE correction method developed in this work, we demonstrated that gold nanoparticles (AuNPs) only slightly attenuate, but do not completely quench the fluorescence signal of the protein, bovine serum albumin (BSA), on AuNP. This result undermines the reliability of the BSA/AuNP binding constants calculated using the Stern–Volmer equation in earlier studies of BSA/AuNP interfacial interactions. The methodology and insights provided in this work should be of general importance for fluorescence study of nanoparticle interfacial interactions.