Fluorescent labels have been paramount in the advancement of molecular biology and related fields, for they unveil Nature's unknowns. Numerous labels have been developed that can be attached to most biomolecules via various labeling chemistries. Practitioners are expected to navigate through the growing libraries of fluorescent probes to select the best one for their target application. It is precisely this vast collection of labels that makes the selection process challenging, often leading to non‐ideal choices. Here, we present a meta‐analysis of fluorescent labels data with the intention of facilitating the selection process. We classify tags into molecular (dyes), macromolecular (proteins), and nanoparticles. Groups are then organised into subgroups by chemical structure. Entries were structured based on cost, absorption and emission wavelengths, Stokes shifts, molar extinction coefficients, quantum yields, lifetimes, and brightness. We correlate chemical composition to available photophysical properties of the fluorophores in their bound‐whenever possible‐and unbound states. The limited access to complete, comparable, and meaningful photophysical data for fluorescent labels and to reliable fluorescence standards, where calibration is still challenging and benchmarks are still ill‐defined, are highlighted to raise critical awareness of the current issues hampering further development of the field.

Whatman No. 1 chromatography paper is widely used as a substrate for cellulose-based immunoassays. The immobilized proteins are used to capture target biomarkers for detection. However, alternative paper substrates may facilitate mass production of immunoassays as diagnostic tests. Here, we assessed the physical characteristics and protein immobilization capabilities of different commercial papers. Some substrates fulfilled our design criteria, including adequate flow rate and sufficient protein immobilization for efficient target capture. This study demonstrates that a variety of paper substrates can be bioactivated and used to capture target biomarkers, enabling development of affordable diagnostic tests from a range of starting materials.

Invited for this month‘s cover is the group of Prof. Alan Aguirre‐Soto, head of the Macromolecular and Photo‐sciences Lab at Tecnologico de Monterrey, Mexico. The cover picture shows a set of molecular, macromolecular and nanoparticle fluorescent tags through space alluding to the expanding repertoire of fluorescent probes for which photophysical data is currently limited. More information can be found in the Review by D. Cavazos‐Elizondo and A. Aguirre‐Soto.

Photosensitized crosslinking of proteins in tissues has many medical applications including sealing wounds, strengthening tissues, and beneficially altering tissue properties. Rose Bengal (RB) is used most frequently as the photosensitizer but is not as efficient as would be desired for broad utilization in medicine. Aggregation of RB, at the high concentrations used for medical treatments, decreases the yield of singlet oxygen, which mediates protein crosslinking. We hypothesized that nanocages that sequester RB would inhibit self-association, increasing photosensitization efficiency. We tested cucurbituril and cyclodextrin nanocages, demonstrating that hydroxypropyl-functionalized cyclodextrins are most effective in inhibiting RB aggregation. For these RB/cyclodextrin solutions, we investigated the effect of nanocaging on the photobleaching and oxygen consumption kinetics under 530 nm LED light in aqueous phosphate-buffered solutions. At 100 μM RB, the initial oxygen consumption rates increased by 58% and 80% compared with uncaged RB for the β and γ (2-hydroxypropyl) cyclodextrins, respectively. For 1 mM RB, the enhancement in these rates was much greater, about 200% and 300%, respectively. In addition, at 1 mM RB these two cyclodextrins increased the RB photobleaching rate by ~20% and ~75%. These results suggest that nanocages can minimize RB aggregation and may lead to higher-efficiency photo-medical therapies.

Expanding Universe of Fluorescent Labels: The front cover picture represents the expanding repertoire of fluorescent probes, which have been of paramount importance in numerous fields. This meta‐analysis presents a compendium of the photophysical properties—both in the bound and unbound states—of fluorescent dyes, proteins, and nanoparticles, to aid in the application‐driven label selection amidst the sliver of available complete, comparable, and meaningful data. Also discussed are the barriers that are slowing down the development of this analysis & sensing toolbox. Cover designed by Daniela Cavazos‐Elizondo and Alan Aguirre‐Soto with support from Mariel Aguirre and Eric Butron. More information can be found in the Review by D. Cavazos‐Elizondo and A. Aguirre‐Soto.