New highly fluorescent pH indicator for ratiometric RGB imaging of pCO2

Tailoring the interaction between a gold nanocluster and a fluorescent dye by cluster size: creating a toolbox of range-adjustable pH sensors

We present a novel strategy for tailoring the fluorescent azadioxatriangulenium (KU) dye-based pH sensor to the target pH range by regulating the pK _a value of the gold nanoclusters. Based on the correlation between the pK _a and surface curvature of ligand-protected nanoparticles, the pK _a value of the gold nanoclusters was controlled by size. In particular, three different-sized para-mercaptobenzoic acid (p-MBA) protected gold nanoclusters, Au₂₅(p-MBA)₁₈, Au₁₀₂(p-MBA)₄₄, and Au_210-230(p-MBA)_70-80 were used as the regulator for the pH range of the KU response. The negatively charged gold nanoclusters enabled the positively charged KU to bind to the surface, forming a complex and quenching the fluorescence of the KU by the energy transfer process. The fluorescence was restored after adjusting the surface charge of the gold nanocluster by controlling the solution pH. In addition, the KU exhibited a significantly different pH response behaviour for each gold nanocluster. Au_210-230(p-MBA)_70-80 showed a higher pH response range than Au₁₀₂(p-MBA)_44, which was intuitive. However, Au₂₅(p-MBA)₁₈ showed an unexpectedly high pH response behaviour. pK _a titration measurement, molecular dynamics simulations, and essential dynamics analysis showed that small nanoclusters do not follow the scaling between the curvature and the pK _a value. Instead, the behaviour is governed by the distribution and interaction of p-MBA ligands on the nanocluster surface. This work presents an effective design strategy for fabricating a range adjustable pH sensor by understanding the protonation behaviour of the ultrasmall gold nanoclusters in an atomic range.

Solid state structure and properties of phenyl diketopyrrolopyrrole derivatives

Crystal structures of the title compounds show diverse packing by interactions of auxochromes giving materials with varied optoelectronic properties.

Visualizing NH3 emission and the local O2 and pH microenvironment of soil upon manure application using optical sensors

The application of fertilizers and manure on fields is the largest source of ammonia (NH₃) in the atmosphere.·NH₃ emission from agriculture has negative environmental consequences and is largely controlled by the chemical microenvironment and the respective biological activity of the soil. While gas phase and bulk measurements can describe the emission on a large scale, those measurements fail to unravel the local processes and spatial heterogeneity at the soil air interface. We report a two dimensional (2D) imaging approach capable of visualizing three of the most important chemical parameters associated with NH₃ emission from soil. Besides the released NH₃ itself also O₂ and pH microenvironments are imaged using reversible optodes in real-time with a spatial resolution of <100 µm. This combined optode approach utilizes a specifically developed NH₃ optode with a limit of detection of 2.11 ppm and a large working range (0-1800 ppm) ideally suited for studying NH₃ volatilization from soil. This NH₃ optode will contribute to a better understanding of the driving factors for NH₃ emission on a microscale and has the potential to become a valuable tool in studying NH₃ dynamics.