Toby D. M. Bell

Divalent europium formamidinates [Eu(DFForm) ₂ (py) ₃ ] and [Eu(DippForm) ₂ (py) ₃ ]·3py were synthesized by the direct reaction of europium metal with N , N ′-bis(2,6-difluorophenyl)formamidine or N , N ′-bis(2,6-diisopropylphenyl)formamidine in pyridine.

Photoacoustic imaging coupled with molecularly responsive sensors is emerging as an attractive alternative to traditional fluorescence sensors in the deep-tissue quantification of specific molecular analytes. The range of fluorophore/quencher pairs suitable for this approach remains limited. In response, here we have systematically evaluated a set of near-infrared fluorophores for their ability to support photoacoustic imaging coupled with molecularly responsive sensors. Specifically, we have used a DNA molecular ruler to precisely vary the fluorophore-quencher distance while monitoring the absorbance, fluorescence, and photoacoustic spectra of five near-infrared fluorophores. Our results confirm previous findings identifying IRDye 800CW as a strong candidate and further establish ICG and IRDye 800 as highly promising fluorophores for responsive photoacoustic applications. We also demonstrated robust tissue penetration and preserved distance-dependent behavior under biologically relevant conditions, with ICG achieving the highest signal-to-noise ratio and the most predictable quenching response. These findings expand the palette of near-infrared probes and provide a clear framework for designing next-generation photoacoustic molecular sensors for in vivo imaging.

Fluorescence lifetime offers a powerful approach to probe chemical microenvironments in biological systems, yet suitable fluorophores remain limited. Here, we report the synthesis and photophysical characterisation of a library of fifteen 4‐amino‐substituted 1,8‐naphthalimides, incorporating diverse aliphatic and aromatic amines. These compounds exhibit strong solvatochromism and varied fluorescence lifetimes in response to polarity and viscosity. Notably, compound 13 demonstrates high brightness and pronounced fluorescence lifetime sensitivity to polarity, while compound 17 shows strong viscosity‐dependent lifetime changes. We apply compound 13 to rat serum samples, revealing significant differences in fluorescence lifetime between healthy and acute pancreatitis conditions, consistent with polarity changes. In contrast, compound 17 showed no lifetime variation, suggesting limited viscosity changes in serum. These findings highlight the potential of 4‐amino‐1,8‐naphthalimides as environment‐sensitive probes, particularly for polarity sensing in complex biological samples. More generally, this work expands the photophysical understanding of naphthalimide derivatives and supports their application in fluorescence lifetime‐based sensing of disease‐related microenvironmental changes.

Hydroboration is considered as one of the most widely used reactions for reduction of various unsaturated fragments/functional groups such as carbonyls, imines, and alkynes. However, this transformation is rarely used for the preparation of boron-containing materials as the boron fragment, which is used in reductions, is normally sacrificed during the isolation step(s). In this work, we examine the use of hydroboration of imines, which contain an acetylene moiety, to prepare several conjugated polymers that contain a boron-nitrogen fragment along the main polymer chain. The polymeric materials were characterized via several analytical techniques.

The mechanism of new mechanofluorochromic is resolved using established and unexplored techniques, including electron diffraction and fluorescence lifetime mapping. Driving factors posited include conformational flexibility and partial amorphisation.

Semiconductor nanocrystals are promising optoelectronic materials. Understanding their anisotropic photoluminescence is fundamental for developing quantum-dot-based devices such as light-emitting diodes, solar cells, and polarized single-photon sources. In this study, we experimentally and theoretically investigate the photoluminescence anisotropy of CdSe semiconductor nanocrystals with various shapes, including plates, rods, and spheres, with either wurtzite or zincblende structures. We use defocused wide-field microscopy to visualize the emission dipole orientation and find that spheres, rods, and plates exhibit the optical properties of 2D, 1D, and 2D emission dipoles, respectively. We rationalize the seemingly counterintuitive observation that despite having similar aspect ratios (width/length), rods and long nanoplatelets exhibit different defocused emission patterns by considering valence band structures calculated using multiband effective mass theory and the dielectric effect. The principles are extended to provide general relationships that can be used to tune the emission dipole orientation for different materials, crystalline structures, and shapes.

"Reagentless" immunosensors are emergingto addressthe challenge of practical and sensitive detection of important biomarkersin real biological samples without the need for multistep assays anduser intervention, with applications ranging from research tools topoint-of-care diagnostics. Selective target binding to an affinityreagent is detected and reported in one step without the need forwashing or additional reporters. In this study, we used a structure-guidedapproach to identify a mutation site in an antibody fragment for thepolarity-dependent fluorophore, Anap, such that upon binding of theprotein target cardiac troponin I, the Anap-labeled antibody wouldproduce a detectable and dose-dependent shift in emission wavelength.We observed a significant emission wavelength shift of the Anap-labeledanti-cTnI mutant, with a blue shift of up to 37 nm, upon binding tothe cTnI protein. Key differences in the resulting emission spectrabetween target peptides in comparison to whole proteins were alsofound; however, the affinity and binding characteristics remainedunaffected when compared to the wild-type antibody. We also highlightedthe potential flexibility of the approach by incorporating a near-infrareddye, IRDye800CW, into the same mutation site, which also resultedin a dose-dependent wavelength shift upon target incubation. Thesereagents can be used in experiments and devices to create simplerand more efficient biosensors across a range of research, medicallaboratory, and point-of-care platforms.

Standard optical imaging is diffraction-limited and lacks the resolving power to visualize many of the organelles and proteins found within the cell. The advent of super-resolution techniques overcame this barrier, enabling observation of subcellular structures down to tens of nanometers in size; however these techniques require or are typically applied to fixed samples. This raises the question of how well a fixed-cell image represents the system prior to fixation. Here we present the addition of live-cell Super-Resolution Optical Fluctuation Imaging (SOFI) to a previously reported correlative process using Single Molecule Localization Microscopy (SMLM) and Atomic Force Microscopy (AFM). SOFI was used with fluorescent proteins and low laser power to observe cellular ultrastructure in live COS-7 cells. SOFI-SMLM-AFM of microtubules showed minimal changes to the microtubule network in the 20 min between live-cell SOFI and fixation. Microtubule diameters were also analyzed through all microscopies; SOFI found diameters of 249 ± 68 nm and SMLM was 71 ± 33 nm. AFM height measurements found microtubules to protrude 26 ± 13 nm above the surrounding cellular material. The correlation of SMLM and AFM was extended to two-color SMLM to image both microtubules and actin. Two target SOFI was performed with various fluorescent protein combinations. rsGreen1-rsKAME, rsGreen1-Dronpa, and ffDronpaF-rsKAME fluorescent protein combinations were determined to be suitable for two target SOFI imaging. This correlative application of super-resolution live-cell and fixed-cell imaging revealed minimal artifacts created for the imaged target structures through the sample preparation procedure and emphasizes the power of correlative microscopy.

Correlative imaging methods can provide greater information for investigations of cellular ultra-structure, with separate analysis methods complementing each other's strengths and covering for deficiencies. Here we present a method for correlative applications of super resolution and atomic force microscopies, optimising the sample preparation for correlative imaging of the cellular cytoskeleton in COS-7 cells. This optimisation determined the order of permeabilisation and fixation, the concentration of Triton X-100 surfactant used and time required for sufficient removal of the cellular membrane while maintaining the microtubule network. Correlative SMLM/AFM imaging revealed the different information that can be obtained through each microscopy. The widths of microtubules and microtubule clusters were determined from both AFM height measurements and Gaussian fitting of SMLM intensity cross sections, these were then compared to determine the orientation of microtubules within larger microtubule bundles. The ordering of microtubules at intersections was determined from the AFM height profiles as each microtubule crosses the other. The combination of both microtubule diameter measurements enabled greater information on their structure to be found than either measurement could individually.

Single molecule (SM) super-resolution microscopies bypass the diffraction limit of conventional optical techniques and provide excellent spatial resolutions in the tens of nanometers without overly complex microscope hardware. SM imaging using optical astigmatism is an efficient strategy for visualizing subcellular features in 3D with a z-range of up to ∼1 µm per acquisition. This approach however, places high demands on fluorophore brightness and photoswitching resilience meaning that imaging entire cell volumes in 3D using SM super-resolution remains challenging. Here we employ SM astigmatism together with multiplane acquisition to visualize the whole nuclear lamina of COS-7 and T cells in 3D. Nuclear lamina provides structural support to the nuclear envelope and participates in vital nuclear functions including internuclear transport, chromatin organization and gene regulation. Its position at the periphery of the nucleus provides a visible reference of the nuclear boundary and can be used to quantify the spatial distribution of intranuclear components such as histone modifications and transcription factors. We found Alexa Fluor 647, a popular photoswitchable fluorophore, remained viable for over an hour of continuous high laser power exposure, and provided sufficient brightness detectable up to 8 µm deep into a cell, allowing us to capture the entire nuclear lamina in 3D. Our approach provides sufficient super-resolution detail of nuclear lamina morphology to enable quantification of overall nuclear dimensions and local membrane features.