Pyrene nanoparticles as a novel FRET probe for detection of rhodamine 6G: spectroscopic ruler for textile effluent

Abstract

An aqueous suspension of pyrene nanoparticles (PyNPs) stabilized by sodium lauryl sulfate exhibit red shifted aggregation induced enhanced emission (AIEE) in the spectral region where Rhodamine 6G (R6G) absorbs strongly. Dynamic light scattering results of the aqueous suspension show a narrow particle size distribution with an average size of 38 nm and the zeta potential of −22 mV predicted a high degree of stability and surface charge modification of the nanoparticles. The negative zeta potential allowed cationic R6G to adsorb on the oppositely charged surface of the nanoparticles and both the molecules bind within the close distance required for efficient fluorescence resonance energy transfer (FRET) to take place from PyNPs to R6G. Systematic FRET experiments performed by measuring quenching of fluorescence of PyNPs with successive addition of R6G solution exploited the use of the PyNPs as a novel probe first time for the detection and estimation of R6G from textile effluents with a Limit of Detection (LOD) equal to 8.905 × 10⁻⁶ mol L⁻¹ by fluorimetric measurements. The quenching results obtained at different constant temperatures were found to fit the well-known Stern–Volmer relation and were used further to estimate photokinetic and thermodynamic parameters such as quenching rate constant, enthalpy change (ΔH), Gibbs free energy change (ΔG) and entropy change (ΔS). The mechanism of binding and quenching of fluorescence of PyNPs by R6G is proposed based on the thermodynamic parameter, the energy transfer efficiency, critical energy transfer distance (R₀) and distance of approach between donor–acceptor molecules (r). The fluorescence quenching results are used further to develop analytical methods for estimation of R6G from industrial textile effluents.