Fluorometric estimation of amino acids interaction with colloidal suspension of FITC functionalized graphene oxide nanoparticles

Abstract

A hydrosol approach developed to synthesize fluorescence quenched fluorescein isothiocyanate (FITC) functionalized colloidal suspension of graphene oxide nanoparticles (GONP). UV–vis spectroscopic measurements showed characteristic peak at 236nm and 300nm due to pi–pi* interaction in CC and n-pi* transition in CO bond of GONP, respectively. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra showed reduced intensity of 1429cm−1 IR band of GONP due to the electrostatic and pi–pi interactions of FITC with GONP in FITC-GONP. ATR-FTIR spectra of different amino acid co-functionalised FITC-GONP showed an increase in the FTIR band intensity at 1429cm−1 which was significantly reduced due to electrostatic/pi–pi interactions of FITC with GONP in the absence of the amino acids. A peak at 1084cm−1 in ATR-FTIR spectra appears which confirms the interaction between amine group of amino acids and COO− groups at GONP surface. The FITC interaction with GONP lead to fluorescence resonance energy transfers (FRET) and resulted in a liner decrease in the FITC fluorescence with an increase of GONP concentration. An increase in the reappearance of FITC fluorescence observed while the amino acid concentration was increased in co-functionalised FITC-GONP. The quantified amount of reappeared fluorescence of FITC in amino acid co-functionalised FITC-GONP depends on the concentration, polar and non-polar nature of amino acids. The reappearance of FITC from the surface of FITC-GONP with the addition of amino acid was found to be consistent with the organic substitute, size of amino acids and their functionalities. Therefore, FRET based method using FITC-GONP colloidal suspension may have potential application in determining the binding nature of biomolecules with GONP for biomedical applications.