title: Evidence of Energy Transfer from Tryptophan to BSA/HSA Protected Gold Nanoclusters.
abstract: This work reports on the chromophores interactions within protein-protected gold nanoclusters. We conducted spectroscopic studies of fluorescence emissions originated from gold nanoclusters and intrinsic tryptophan (Trp) in BSA or HSA proteins. Both, steady state fluorescence and lifetime measurements show a significant Forster resonance energy transfer (FRET) from Trp to the gold nanocluster. Tryptophan lifetimes in the case of protein-protected gold nanoclusters are 2.6ns and 2.3ns for BSA and HSA Au clusters while 5.8ns for native BSA and 5.6 for native HSA. The apparent distances from Trp to gold nanocluster emission center, we estimated as 24.75A0for BSA and 23.80A0for HSA. We also studied a potassium iodide (KI) quenching of protein-protected gold nanoclusters and compared with the quenching of BSA and HAS alone. The rates of Trp quenching were smaller in BSA-Au and HSA-Au nanoclusters than in the case of free proteins, which is consistent with shorter lifetime of quenched Trp(s) and lower accessibility for KI. While Trp residues were quenched by KI, the emissions originated from nanoclusters were practically unquenched. In summary, for BSA and HSA Au clusters, we found 55% and 59% energy transfer efficiency respectively from tryoptophan to gold clusters. We believe this interaction can be used to our advantage in terms of developing resonance energy transfer based sensing applications.
authors.affiliation: Center for Fluorescence Technologies and Nanomedicine, Department of Cell Biology and immunology, University of North Texas Health Science Center, 3500 Camp Bowie Blvd. Fort Worth, Texas, USA, 76107.
authors.forename: Sangram
authors.initials: S
authors.lastname: Raut
authors.affiliation: Center for Fluorescence Technologies and Nanomedicine, Department of Cell Biology and immunology, University of North Texas Health Science Center, 3500 Camp Bowie Blvd. Fort Worth, Texas, USA, 76107.
authors.forename: Rahul
authors.initials: R
authors.lastname: Chib
authors.affiliation: Center for Fluorescence Technologies and Nanomedicine, Department of Cell Biology and immunology, University of North Texas Health Science Center, 3500 Camp Bowie Blvd. Fort Worth, Texas, USA, 76107.
authors.forename: Susan
authors.initials: S
authors.lastname: Butler
authors.affiliation: Center for Fluorescence Technologies and Nanomedicine, Department of Cell Biology and immunology, University of North Texas Health Science Center, 3500 Camp Bowie Blvd. Fort Worth, Texas, USA, 76107.
authors.forename: Julian
authors.initials: J
authors.lastname: Borejdo
authors.affiliation: Department of Physics. Texas Christian University, 2800 S. University Dr., Fort Worth, Texas, USA, 76129.
authors.forename: Zygmunt
authors.initials: Z
authors.lastname: Gryczynski
authors.affiliation: Department of Cell Biology and Anatomy, University of North Texas Health Science Center. 3500 Camp Bowie Blvd. Fort Worth, Texas, USA, 76107.
authors.forename: Ignacy
authors.initials: I
authors.lastname: Gryczynski