Absorbance spectroscopy of light scattering samples placed inside an integrating sphere for wide dynamic range absorbance measurement

Reddening of the Unicellular Green Alga Euglena gracilis by Dried Bonito Stock and Intense Red Light Irradiation

This study confirms for the first time that the significant red coloration of Euglena gracilis is induced by bonito stock (BS), a traditional Japanese food, and intense red light exposure (605~660 nm, 1000~1300 µmol photons/m2/s). Under the condition, excessive photosynthetic activity destroyed many chloroplasts, while carotenoids were maintained, resulting in the formation of reddened cells. The HPLC analysis revealed that diadinoxanthin was the primary carotenoid present in reddened cells. Additionally, an undefined xanthophyll, not produced under normal culture conditions, was synthesized and suggested to contain a C=O bond. While it has been reported that strong light stress can increase the total carotenoid content of cells, this study did not verify this claim, and it should be investigated further in future research. Under white light irradiation conditions (90 μmol photons/m2/s) in BS medium, no reddening of cells was observed, and good growth was achieved (over four times the cell density in CM medium on the seventh day). This cell suspension is considered to have a high nutritional value because it is composed of functional food, BS and E. gracilis. The fact that this method does not involve genetic modification suggests the possibility of industrial applications, including food use, even in reddened cells.

Advancing Evidence-Based Data Interpretation in UV-Vis and Fluorescence Analysis for Nanomaterials: An Analytical Chemistry Perspective

UV-vis spectrophotometry and spectrofluorometry are indispensable tools in education, research, and industrial process controls with widespread applications in nanoscience encompassing diverse nanomaterials and fields. Nevertheless, the prevailing spectroscopic interpretations and analyses often exhibit ambiguity and errors, particularly evident in the nanoscience literature. This analytical chemistry Perspective focuses on fostering evidence-based data interpretation in experimental studies of materials' UV-vis absorption, scattering, and fluorescence properties. We begin by outlining common issues observed in UV-vis and fluorescence analysis. Subsequently, we provide a summary of recent advances in commercial UV-vis spectrophotometric and spectrofluorometric instruments, emphasizing their potential to enhance scientific rigor in UV-vis and fluorescence analysis. Furthermore, we propose potential avenues for future developments in spectroscopic instrumentation and measurement strategies, aiming to further augment the utility of optical spectroscopy in nano research for samples where optical complexity surpasses existing tools. Through a targeted focus on the critical issues related to UV-vis and fluorescence properties of nanomaterials, this Perspective can serve as a valuable resource for researchers, educators, and practitioners.

Fluorescent Multifunctional Organic Nanoparticles for Drug Delivery and Bioimaging: A Tutorial Review

Fluorescent organic nanoparticles (FONs) are a large family of nanostructures constituted by organic components that emit light in different spectral regions upon excitation, due to the presence of organic fluorophores. FONs are of great interest for numerous biological and medical applications, due to their high tunability in terms of composition, morphology, surface functionalization, and optical properties. Multifunctional FONs combine several functionalities in a single nanostructure (emission of light, carriers for drug-delivery, functionalization with targeting ligands, etc.), opening the possibility of using the same nanoparticle for diagnosis and therapy. The preparation, characterization, and application of these multifunctional FONs require a multidisciplinary approach. In this review, we present FONs following a tutorial approach, with the aim of providing a general overview of the different aspects of the design, preparation, and characterization of FONs. The review encompasses the most common FONs developed to date, the description of the most important features of fluorophores that determine the optical properties of FONs, an overview of the preparation methods and of the optical characterization techniques, and the description of the theoretical approaches that are currently adopted for modeling FONs. The last part of the review is devoted to a non-exhaustive selection of some recent biomedical applications of FONs.

Integrating-Sphere-Assisted Resonance Synchronous Spectroscopy for the Quantification of Material Double-Beam UV-Vis Absorption and Scattering Extinction

Integrating spheres (IS) have been used extensively for the characterization of light absorption in turbid samples. However, converting the IS-based sample absorption coefficient to the UV-vis absorbance quantified with a double-beam UV-vis spectrophotometer is challenging. Herein, we report an integrating-sphere-assisted resonance synchronous (ISARS) spectroscopy method performed with conventional spectrofluorometers equipped with an integrating-sphere accessory. Mathematical models and experimental procedures for quantifying the sample, solvent, and instrument-baseline ISARS intensity spectra were provided. A three-parameter analytical model has been developed for correlating the ISARS-based UV-vis absorbance and the absorbance measured with double-beam instruments. This ISARS method enables the quantitative separation of light absorption and scattering contribution to the sample UV-vis extinction spectrum measured with double-beam UV-vis spectrophotometers. Example applications of this ISARS technique are demonstrated with a series of representative samples differing significantly in their optical complexities, from approximately pure absorbers, pure scatterers, to simultaneous light absorbers, scatterers, and emitters under resonance excitation and detection conditions.