Two-photon imaging of a magneto-fluorescent indicator for 3D optical magnetometry

Mechanism of Giant Magnetic Field Effect in a Red Fluorescent Protein

Several fluorescent proteins, when expressed in E. coli, are sensitive to weak magnetic fields. We found that mScarlet3 fluorescence in E. coli reversibly decreased by 21% in the presence of a 60 mT magnetic field, the largest magnetic field effect (MFE) reported in any fluorescent protein. Purified mScarlet3 did not show an MFE, but the addition of flavin mononucleotide (FMN) and simultaneous illumination with blue and yellow light restored the MFE. Through extensive photophysical experiments, we developed a quantitative model of the giant MFE in mScarlet3-FMN mixtures. The key reaction step involved electron transfer from fully reduced FMNH2 to triplet-state mScarlet3 to form a triplet spin-correlated radical pair. The magnetic field then controlled the branching ratio between singlet recombination vs triplet separation. Our quantitative model of the mScarlet3-FMN photocycle provides a framework for the design and optimization of magnetic-field-sensitive proteins, opening possibilities in fluorescent protein-based magnetometry, magnetic imaging, and magnetogenetic control.

Comprehensive Insights into Exciplex Behavior in Nonpolar Media: Revisiting Weller's Framework with Molecular Conformation

Exciplexes are pivotal in organic light-emitting diodes and photovoltaics. However, their formation and emission in nonpolar solvents remain unclear. Revisiting Weller's works on photoinduced electron transfer (PET) rates and exciplex emission based on electrochemical redox potentials, we investigate exciplex behavior in cyclohexane using anthracene (Ant) as an acceptor and N,N-dimethylaniline (DMA) derivatives as donors. Employing steady-state and time-resolved spectroscopy, electrochemistry, and density functional theory (DFT) calculations, we demonstrate that electrochemical redox potentials alone inadequately explain the exciplex behavior in nonpolar environments. Our DFT analysis reveals that the C-N rotational angle of the dimethylamine group of a donor influences the highest occupied molecular orbital (HOMO) energy levels, affecting quenching processes. Furthermore, time-dependent DFT simulations accurately reproduce experimental exciplex emission spectra, linking emission intensity to donor contribution in the exciplex HOMO. These findings deepen the understanding of exciplex behavior in nonpolar media and provide insights for designing and interpreting exciplex-based optoelectronic materials.

Enhanced Deoxygenation of Solvents via an Improved Inert Gas Bubbling Method with a Ventilation Pathway

We introduce an improved inert gas bubbling method for solvent deoxygenation, featuring a ventilation path alongside the inert gas inlet to enhance the efficiency and reproducibility. While essential for life, oxygen's reactivity can disrupt scientific and industrial processes by forming unwanted intermediates and deactivating catalysts, necessitating efficient deoxygenation methods. Traditional methods like freeze-pump-thaw (FPT) are effective but time-consuming, require stringent safety measures, and have potential limitations for use with aqueous and biological samples. Our enhanced inert gas bubbling method retains the simplicity and safety of conventional bubbling while achieving FPT-like deoxygenation efficiency, demonstrated by photoluminescence intensity and lifetime measurements in acetonitrile (ACN) and toluene (TOL). Simulations using a simplified kinetic model and the Stern-Volmer equation reveal that the added ventilation pathway reduces oxygen contamination in Ar gas bubbles, improving the deoxygenation efficiency. This method is widely applicable in academic and industrial fields, requiring consistent and efficient solvent deoxygenation.

Peptoid-Conjugated Magnetic Field-Sensitive Exciplex System at High and Low Solvent Polarities

The magnetic field effect (MFE) in exciplex emission (ExE) has been studied for decades, but it has been observed to occur only in solvents with a limited range of polarity. This limitation is mainly due to the reversible interconversion collapse between two quenching products of the photoinduced electron transfer, the exciplex and magnetic field-sensitive radical ion pair (RIP) beyond that polarity range. In a nonpolar solvent, the formation of RIPs is suppressed, whereas in a polar solvent, the probability of their re-encounter forming the exciplexes decreases. In this study, we developed new exciplex-forming (phenyl-phenanthrene)-(phenyl-N,N-dimethylaniline)-peptoid conjugates (PhD-PCs) to overcome this limitation. The well-defined peptoid structure allows precise control of the distance and the relative orientation between two conjugated moieties. Steady-state and time-resolved spectroscopic data indicate that the PhD-PCs can maintain the reversibility, which allows MFEs in ExE regardless of the solvent polarity. Subtle differences between the ExEs of the PhD-PCs were observed and explained by their exciplex geometries obtained through time-dependent density functional theory (TD-DFT) calculations.

Quantitative imaging of magnetic field distribution using a pyrene-based magnetosensing exciplex fluorophore

Quantitative imaging of magnetic field distribution was carried out using a pyrene-based magnetosensing exciplex fluorophore, pyrene-(CH₂)₁₂-O-(CH₂)₂-N,N-dimethylaniline (Py-12-O-2-DMA), on a conventional fluorescence microscope with an off-the-shelf LED lamp. No continuous sample supply was required for the process. The solvent system (anisole : DMF, 50 : 50 (v/v)) was carefully selected for monitoring the extent of modulation caused by the external magnetic field. The emission from Py-12-O-2-DMA increased by ca. 1.5 times under an external magnetic field of 50 mT. The pyrene-based reporter was ca. 24.7 times brighter than a previously reported phenanthrene-based complex when excited by using the widely available 355 nm excitation. Moreover, the maximum wavelength up to which Py-12-O-2-DMA could be excited (up to 380 nm) was longer than the wavelength up to which Phen-12-O-2-DMA could be excited. The combined advantages allowed the capture of magnetic field images with a high S/N ratio under milder conditions such as low illumination power, reduced sample concentration, and simpler optical setup. The system was also found to be feasible for 3D magnetic field distribution imaging by two-photon fluorescence microscopy.

Comment on “Magnetic-field-enabled resolution enhancement in super-resolution imaging” by M. Zhang et al., Phys. Chem. Chem. Phys., 2015, 17, 6722–6727

Spectral fluorimetry demonstrates that common organic fluorophores such as Alexa 647 exhibit no magnetic field enhanced fluorescence in the absence/presence of a strong magnet.

A simple approach to spectrally resolved fluorescence and bright field microscopy over select regions of interest

A standard wide field inverted microscope was converted to a spatially selective spectrally resolved microscope through the addition of a polarizing beam splitter, a pair of polarizers, an amplitude-mode liquid crystal-spatial light modulator, and a USB spectrometer. The instrument is capable of simultaneously imaging and acquiring spectra over user defined regions of interest. The microscope can also be operated in a bright-field mode to acquire absorption spectra of micron scale objects. The utility of the instrument is demonstrated on three different samples. First, the instrument is used to resolve three differently labeled fluorescent beads in vitro. Second, the instrument is used to recover time dependent bleaching dynamics that have distinct spectral changes in the cyanobacteria, Synechococcus leopoliensis UTEX 625. Lastly, the technique is used to acquire the absorption spectra of CH3NH3PbBr3 perovskites and measure differences between nanocrystal films and micron scale crystals.