<i>In Vivo</i> Evaluation of Liver Injury and Arthritis Enabled by a Nitroxyl-Activated Near-Infrared Fluorescence and Photoacoustic Dual-Modality Imaging Probe

Nitroxyl (HNO) is the transient form of nitric oxide (NO) and is highly reactive, which makes its <i>in vivo</i> study a significant challenge. We report here simultaneous fluorescence and photoacoustic imaging of HNO, enabled by a newly synthesized near-infrared, dual-modality fluorescence and photoacoustic (FPA) probe. The 2-(diphenylphosphonyl)-benzoate moiety in the FPA probe specifically recognized HNO. The photophysical properties of the probe were tuned, e.g., by substituting an oxygen atom in the hemicyanine moiety with sulfur, resulting in a 45 nm red-shift. The maximum absorption wavelength increased from 650 nm in the absence of HNO to 760 nm in the presence of HNO. We demonstrate an application of the HNO-activated FPA probe to <i>in vivo</i> evaluation of inflammatory disease progression in a mouse model. Treatment of mice with acetaminophen stimulated endogenous generation of HNO in their liver, which was successfully imaged using dual-modality near-infrared fluorescence and photoacoustic measurements. Fluorescence and photoacoustic imaging of the ankle site of an arthritis mouse model enabled a study of the onset of this inflammatory disease.