ACS Sensors最新文献

Mapping of O₂ with luminescent sensors within intact animals is challenging due to attenuation of excitation and emission light caused by tissue absorption and scattering as well as interfering background fluorescence. Here we show the application of luminescent O₂ sensor nanoparticles (∼50-70 nm) composed of the O₂ indicator platinum(II) tetra(4-fluoro)phenyltetrabenzoporphyrin (PtTPTBPF) immobilized in poly(methyl methacrylate-co-methacrylic acid) (PMMA-MA). We injected the sensor nanoparticles into the gastrovascular system of intact colony fractions of reef-building tropical corals that harbor photosynthetic microalgae in their tissues. The sensor nanoparticles are excited by red LED light (617 nm) and emit in the near-infrared (780 nm), which enhances the transmission of excitation and emission light through biological materials. This enabled us to map the internal O₂ concentration via time-domain luminescence lifetime imaging through the outer tissue layers across several coral polyps in flowing seawater. After injection, nanoparticles dispersed within the coral tissue for several hours. While luminescence intensity imaging showed some local aggregation of sensor particles, lifetime imaging showed a more homogeneous O₂ distribution across a larger area of the coral colony. Local stimulation of symbiont photosynthesis in corals induced oxygenation of illuminated tissue areas and formation of lateral O₂ gradients toward surrounding respiring tissues, which were dissipated rapidly after the onset of darkness. Such measurements are key to improving our understanding of how corals regulate their internal chemical microenvironment and metabolic activity, and how they are affected by environmental stress such as ocean warming, acidification, and deoxygenation. Our experimental approach can also be adapted for in vivo O₂ imaging in other natural systems such as biofilms, plant and animal tissues, as well as in organoids and other cell constructs, where imaging internal O₂ conditions are relevant and challenging due to high optical density and background fluorescence.

Fluorescent protein-based pH biosensors enable the tracking of pH changes during protein trafficking and, in particular, exocytosis. The recent development of chemogenetic reporters combining synthetic fluorophores with self-labeling protein tags offers a versatile alternative to fluorescent proteins that combines the diversity of chemical probes and indicators with the selectivity of the genetic encoding. However, this hybrid protein labeling strategy does not avoid common drawbacks of organic fluorophores such as the risk of off-target signal due to unbound molecules. Here, we describe a novel fluorogenic and chemogenetic pH sensor based on a cell-permeable molecular pH indicator called pHluo-Halo-1, whose fluorescence can be locally activated in cells by reaction with HaloTag, ensuring excellent signal selectivity in wash-free imaging experiments. pHluo-Halo-1 was selected out of a series of four fluorogenic molecular rotor structures based on protein chromophore analogues. It displays good pH sensitivity with a pK_a of 6.3 well-suited to monitor pH variations during exocytosis and an excellent labeling selectivity in cells. It was applied to follow the secretion of CD63-HaloTag fusion proteins using TIRF microscopy. We anticipate that this strategy based on the combination of a tunable and chemically accessible fluorogenic probe with a well-established protein tag will open new possibilities for the development of versatile alternatives to fluorescent proteins for elucidating the dynamics and regulatory mechanisms of proteins in living cells.

Hydrogen (H₂) is a promising alternative energy source for Net-zero, but the risk of explosion requires accurate and rapid detection systems. As the use of H₂ energy expands, sensors require high performance in a variety of properties. Palladium (Pd) is an attractive material for H₂ detection due to its high H₂ affinity and catalytic properties. However, poor stability caused by volume changes and reliability due to environmental sensitivity remain obstacles. This study proposes a micropatterned thin film of PdAu with optimized composition (Pd_0.62Au_0.38) as a chemoresistive sensor to overcome these issues. At room temperature, the sensor has a wide detection range of 0.0002% to 5% and a fast response time of 9.5 s. Significantly, the sensor exhibits excellent durability for repeated operation (>35 h) in 5% H₂ and resistance to humidity and carbon monoxide. We also report a negative resistivity change in PdAu, which is opposite to that of Pd. Density functional theory (DFT) calculations were performed to investigate the resistance change. DFT analysis revealed that H₂ penetrates specific interstitial sites, causing partial lattice compression. The lattice compression causes a decrease in electrical resistance. This work is expected to contribute to the development of high-performance H₂ sensors using Pd-based alloys.