A solid-surface fluorescence study of Rhodamine B and fluorescein adsorbed onto a filter paper, and semi-quantitative determination using EEM data

Abstract

In this work, solid-surface fluorescence spectra of Rhodamine B (RhB) and fluorescein (FLU), two extensively used fluorophores, were studied and their concentrations were semi-quantitatively determined using the three-dimensional excitation–emission matrix (3D-EEM) data. In order to measure the solid fluorescence spectra, a trace amount of fluorophores was physically adsorbed on a piece of filter paper as a fluorescent paper, and the fluorescence spectra were recorded from the surface of the fluorescent paper instead of the inner parts of the solution. The spectral measurement was performed utilizing a routine spectrofluorimeter designed to measure the fluorescence of solution only by placing the fluorescent paper in a simple handmade holder at an adjusted incident angle of radiation. The results revealed a significant increase in the fluorescence intensity of the fluorescent paper strip compared to the solution phase. Moreover, in the RhB–FLU paper strip the forster resonance energy transfer was observed between FLU and RhB, similar to the observed phenomenon in the solution phase. For quantifying fluorophores, the EEM data were successfully resolved by applying multivariate partial least squares and parallel factor analysis (PARAFAC) modeling, and the results were compared with the univariate method. This study may provide a general guideline in further developing the solid fluorescence measurement of concentrated solutions or solid samples that have fluorescence measurement limitations such as high self-absorption and highly scattered spectra by using a conventional spectrofluorimeter, and also of biological samples where a trace amount of the analyte is available and high sensitivity is required.

Graphical abstract