Characterization of Nitrazine Yellow as a Photoacoustically Active pH Reporter Molecule

Portable Photoacoustic Analytical System Combined with Wearable Hydrogel Patch for pH Monitoring in Chronic Wounds

Timely diagnosis, monitoring, and management of chronic wounds play crucial roles in improving patients' quality of life, but clinical evaluation of chronic wounds is still ambiguous and relies heavily on the experience of clinician, resulting in increased social and financial burden and delay of optimal treatment. During the different stages of the healing process, specific and dynamic changes of pH values in the wound exudate can be used as biomarkers to reflect the wound status. Herein, a pH-responsive agent with well-behaved photoacoustic (PA) properties, nitrazine yellow (NY), was incorporated in poly(vinyl alcohol)/sucrose (PVA/Suc) hydrogel to construct a wearable pH-sensing patch (PVA/Suc/NY hydrogel) for monitoring of pH values during chronic wound healing. According to Rosencwaig-Gersho theory and the combination of 3D printing technology, the PA chamber volume and chopping frequency were systematically optimized to improve the sensitivity of the PA analytical system. The prepared PVA/Suc/NY hydrogel patch had excellent mechanical properties and flexibility and could maintain conformal contact with skin. Moreover, combined with the miniaturized PA analytical device, it had the potential to detect pH values (5.0-9.0) free from the color interference of blood and therapeutic drugs, which provides a valuable strategy for wound pH value monitoring by PA quantitation. This strategy of combining the wearable hydrogel patch with portable PA analysis offers broad new prospects for the treatment and management of chronic wounds due to its features of simple operation, time savings, and anti-interference.

Microfluidic paper-based analytical device for the speciation of inorganic nitrogen species

A microfluidic paper-based analytical device (μPAD) utilizing gas-diffusion separation and solid-phase reduction was developed for the first time for the determination of both ammonium and nitrate, which are the dominant inorganic nitrogen species in environmental waters. The device consists of 3 filter paper layers accommodating the sample, reagent and detection zones. The reagent zone is separated from the detection zone by a semipermeable hydrophobic membrane and acts as a solid-phase reactor where nitrate is reduced to ammonia by Devarda's alloy microparticles, integrated into a μPAD for the first time. The detection zone incorporates the acid-base indicators bromothymol blue (BTB) or nitrazine yellow (NY) and changes colour in two steps. Initially the colour change is caused by ammonia generated by the reaction of ammonium and sodium hydroxide in the sample zone. This colour change is followed by a subsequent colour change as a result of the ammonia produced by the reduction of nitrate by the Devarda's alloy microparticles. The corresponding reflectance value changes are used for the quantification of the two inorganic nitrogen species in the ranges 6.5-100.0 or 2.1-15.0 mg N L-1 for ammonium and 18.2-100.0 or 4.2-15.0 mg N L-1 for nitrate when BTB or NY are used, respectively. Under optimal conditions the limits of quantification of ammonium and nitrate in the case of BTB were determined as 6.5 and 18.2 mg N L-1, respectively, while the corresponding values in the case of NY were found to be 2.1 and 4.2 mg N L-1. The newly developed μPAD was stable for 62 days when stored in a freezer and 1 day at ambient temperature. It was validated with a certified reference material and successfully applied to the determination of ammonium and nitrate in spiked environmental water samples and soil extracts.

Multiplexed whole-animal imaging with reversibly switchable optoacoustic proteins

We introduce two photochromic proteins for cell-specific in vivo optoacoustic (OA) imaging with signal unmixing in the temporal domain. We show highly sensitive, multiplexed visualization of T lymphocytes, bacteria, and tumors in the mouse body and brain. We developed machine learning-based software for commercial imaging systems for temporal unmixed OA imaging, enabling its routine use in life sciences.

Subsequent radical fragmentation reactions of N, N-diethylamino-substituted azobenzene derivatives in a Fourier transform ion cyclotron resonance mass spectrometer using collision-induced dissociation and photodissociation

The fragmentation behavior of N, N-diethylamino-substituted azobenzene derivatives is investigated by high-resolving mass spectrometry using a Fourier transform ion cyclotron resonance mass spectrometer. Former investigations by photodissociation as well as collision-induced dissociation experiments used to induce a loss of C₃H₈ from the diethylamino group. The position of the additional proton in [M + H]⁺ ions is important due to the sequences of radical fragmentation reactions. Two possibilities arise. First, a charge is located at the azo group leading to a methyl radical loss. The second possibility is that the charge has been located on the aniline nitrogen of the molecule resulting in an ethyl radical loss. Only o-ethyl red has shown the overall loss of C₃H₈ in a two-step radical reaction mechanism. Nevertheless, p-ethyl red and ethyl yellow have shown systematic fragmentation reactions as well. Loss of C₃H₈ has not been likely regarding both these molecules. All experimental findings together with quantum chemical calculations as well as kinetic calculations support the proposed fragmentation mechanisms of the three azo dyes.

A Self-Assembled Albumin-Based Nanoprobe for In Vivo Ratiometric Photoacoustic pH Imaging

A photoacoustic nanoprobe is self-assembled from human serum albumin and two types of dye molecules, one is inert to pH and the other is pH sensitive. This probe and the quantitative ratiometric photoacoustic pH imaging method are shown to have high safety, be easy-to-operate, and have depth-independent accuracy for real-time in vivo pH imaging of entire tumors. These features make them promising for future cancer prognosis and therapeutic planning.