A Divide-and-Conquer Strategy for Quantification of Light Absorption, Scattering, and Emission Properties of Fluorescent Nanomaterials in Solutions

Abstract

Optical properties of fluorescent materials including their UV–vis absorption, scattering, and on-resonance fluorescence activities are strongly wavelength-dependent. Reported herein is a divide-and-conquer strategy for experimental quantification of fundamental optical constants of fluorescent nanomaterials including their UV–vis absorption, scattering, and on-resonance-fluorescence (ORF) cross-section spectra and ORF fluorescence and light scattering depolarization spectra. The fluorophore UV–vis extinction spectrum is first divided into a blue and a red wavelength region. The UV–vis extinction cross-section spectrum in the blue wavelength region is decomposed into its absorption and scattering extinction spectra straightforwardly using the established polarized resonance synchronous spectroscopic technique. In its red wavelength region, however, the fluorophores can be simultaneous photon absorbers, scatterers, and anti-Stokes-shifted, on-resonance, and Stokes-shifted fluorescence emitters under the resonance excitation and detection conditions. A polarized anti-Stokes’-shifted, on-resonance, and Stokes’-shifted spectroscopic method is developed for quantifying fluorophore absorption, scattering, one-resonance fluorescence (ORF) cross-section spectra, and scattering and ORF fluorescence depolarization spectra in this wavelength region. Example applications of the presented techniques were demonstrated with fluorescent polystyrene nanoparticles, fluorescent quantum dots, and molecular fluorophores Rhodamine 6G and Eosin Y.

Quantification of the Photon Absorption, Scattering, and On-Resonance Emission Properties of CdSe/CdS Core/Shell Quantum Dots: Effect of Shell Geometry and Volumes

“…In contrast, the PAOS VH spectra are dominated by the RQD fluorescence with relatively small light scattering contribution (Figure M–P). Using the method described in the PAOS publication, the RQD PRS2 VV and PRS2 VH spectra are decomposed into their respective ORF and light scattering component spectra. (Figure I–L, and R–U).…”

“…The UV–vis extinction spectra were measured with a Thermo Scientific Evoltion 300 UV–vis spectrometer, and the SSF, fluorescence excitation, PRS2, and PAOS spectra were acquired with a Horiba FluoroMax-4 spectrofluorometer equipped with excitation and detection linear polarizers. Detailed PRS2 and PAOS spectral acquisition and analysis has been demonstrated before . Unless indicated otherwise, all the spectrofluorometer-based spectra were acquired with an intergration time of 0.3 s, and a slit width of 2 nm for both the excitation and detection monochromators.…”

“…The quantification of the QD optical properties was performed using combination of UV–vis, fluorescence, and the recently developed polarized resonance synchronous spectroscopic (PRS2) techniques. , PRS2 is similar to the conventional resonance synchronous spectroscopic (RS2) method. Both PRS2 and RS2 spectra are acquired using spectrofluorometers by setting the excitation and detection wavelengths identical while scanned synchronously.…”

“…One drawback of the BV-PRS2 technique is tedious data analysis and processing. The third is the polarized anti-Stokes-shifted, on-resonance, and Stokes-shifted spectroscopic (PAOS) method that is also applicable to all samples . The key advantage of PAOS method is that it enables direct visualization and separation of the light scattering and fluorescence contribution to the signal detected under resonance excitation and detection conditions.…”

“…One complete PAOS spectrum is needed in order to extract the light scattering and fluorescence contribution to the resonance signal detected at each wavelength. The fourth method is the divide-and-conquer PRS2 technique that uses combination of the direct PRS2 and the PAOS methods . This approach combines high efficiency, general applicability, and easy understanding.…”