Photoacoustic Detection of Superoxide Using Oxoporphyrinogen and Porphyrin

Sensing Reactive Oxygen Species with Photoacoustic Imaging Using Conjugation-Extended BODIPYs

Short-lived reactive intermediates such as reactive oxygen species (ROS) regulate many physiological processes, but overproduction can also lead to severe tissue dysfunction. Thus, there is a high demand for noninvasive detection of reactive molecules, which, however, is challenging. Herein, we report photoacoustic detection of ROS using conjugated BODIPY probes (ROS-BODIPYs). The ROS reaction with conjugated BODIPYs induced a redshift in absorption by ∼100 nm into the near infrared (from ∼700 to ∼800 nm), quenched fluorescence, and generated strong photoacoustic (PA) signals. Thus, the ROS-activated and ROS-nonactivated states of ROS-BODIPYs can be detected in vivo by PA and fluorescence imaging. Interestingly, ROS activation is reversible, in the presence of excess reducing agents, e.g., citric acid, converted back to its original state, suggesting that ROS-BODIPYs can be useful for the detection of over production of ROS but not physiological amounts. This makes the imaging independent of accumulation of the activated probe with the physiological ROS amounts and thus strongly improves applicability and highlights the translational potential of ROS-BODIPYs for detecting overexpression of ROS in vivo by optical and photoacoustic imaging methods.

Thienylpiperidine Donor NIR Xanthene-Based Dye for Photoacoustic Imaging

Few xanthene-based near-infrared (NIR) photoacoustic (PA) dyes with absorbance >800 nm exist. As accessibility to these dyes requires long and tedious synthetic steps, we designed a NIR dye (XanthCR-880) with thienylpiperidine donors and a xanthene acceptor that is accessible in 3-4 synthetic steps. The dye boasts a strong PA signal at 880 nm with good biological compatibility and photostability, yields multiplexed imaging with an aza-BODIPY reference dye, and is detected at a depth of 4 cm.

Expanded porphyrins: functional photoacoustic imaging agents that operate in the NIR-II region

Photoacoustic imaging (PAI) relies on the use of contrast agents with high molar absorptivity in the NIR-I/NIR-II region. Expanded porphyrins, synthetic analogues of natural tetrapyrrolic pigments (e.g. heme and chlorophyll), constitute as potentially attractive platforms due to their NIR-II absorptivity and their ability to respond to stimuli. Here, we evaluate two expanded porphyrins, naphthorosarin (1) and octaphyrin (4), as stimuli responsive PA contrast agents for functional PAI. Both undergo proton-coupled electron transfer to produce species that absorb well in the NIR-II region. Octaphyrin (4) was successfully encapsulated into 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-poly(ethylene glycol) (DSPE-PEG₂₀₀₀) nanoparticles to afford OctaNPs. In combination with PAI, OctaNPs allowed changes in the acidic environment of the stomach to be visualized and cancerous versus healthy tissues to be discriminated.

Recent development of near-infrared photoacoustic probes based on small-molecule organic dye

Photoacoustic imaging (PAI), which integrates the higher spatial resolution of optical imaging and the deeper penetration depth of ultrasound imaging, has attracted great attention. Various photoacoustic probes including inorganic and organic agents have been well fabricated in last decades. Among them, small-molecule based agents are most promising candidates for preclinical/clinical applications due to their favorite in vivo features and facile functionalization. In recent years, PAI, in the near-infrared region (NIR, 700-1700 nm) has developed rapidly and has made remarkable achievements in the biomedical field. Compared with the visible light region (400-700 nm), it can significantly reduce light scattering and meanwhile provide deeper tissue penetration. In this review, we discuss the recent developments of near-infrared photoacoustic probes based on small molecule dyes, which focus on their "always on" and "activatable" form in biomedicine. Further, we also suggest current challenges and perspectives.

Leucomethylene blue probe detects a broad spectrum of reactive oxygen and nitrogen species

A broad spectrum ROS/RNS sensing butylated phenol tethered leucomethylene blue is presented. This probe detects a variety of ROS/RNS, with up to 100-fold gain in fluorescence in the red range, is suitable for microscopic and macroscopic in vivo fluorescence imaging.

Photoacoustic imaging with fiber optic technology: A review

Photoacoustic imaging (PAI) has achieved remarkable growth in the past few decades since it takes advantage of both optical and ultrasound (US) imaging. In order to better promote the wide clinical applications of PAI, many miniaturized and portable PAI systems have recently been proposed. Most of these systems utilize fiber optic technologies. Here, we overview the fiber optic technologies used in PAI. This paper discusses three different fiber optic technologies: fiber optic light transmission, fiber optic US transmission, and fiber optic US detection. These fiber optic technologies are analyzed in different PAI modalities including photoacoustic microscopy (PAM), photoacoustic computed tomography (PACT), and minimally invasive photoacoustic imaging (MIPAI).

Photoacoustic Imaging Probes Based on Tetrapyrroles and Related Compounds

Photoacoustic imaging (PAI) is a rapidly evolving field in molecular imaging that enables imaging in the depths of ultrasound and with the sensitivity of optical modalities. PAI bases on the photoexcitation of a chromophore, which converts the absorbed light into thermal energy, causing an acoustic pressure wave that can be captured with ultrasound transducers, in generating an image. For in vivo imaging, chromophores strongly absorbing in the near-infrared range (NIR; > 680 nm) are required. As tetrapyrroles have a long history in biomedical applications, novel tetrapyrroles and inspired mimics have been pursued as potentially suitable contrast agents for PAI. The goal of this review is to summarize the current state of the art in PAI applications using tetrapyrroles and related macrocycles inspired by it, highlighting those compounds exhibiting strong NIR-absorption. Furthermore, we discuss the current developments of other absorbers for in vivo photoacoustic (PA) applications.

Reply to Comment on "Water-Soluble Fluorescent Probe with Dual Mitochondria/Lysosome Targetability Superoxide Detection in Live Cells and in Zebrafish Embryos"

Recently, we published a paper on the detection of superoxide (O₂^•-) with a water-soluble fluorescent probe (ACS Sens. 2018, 3, 59-64), and Francesco Tampieri et al. provided comments on our publication, mostly on the detection medium (deionized water) we used. Herein we present our responses to the addressed questions to explain that although KO₂ decomposes in aqueous environment, the results we obtained did not affect the general trend, since evidence from the literature afforded the correlation between KO₂ in aqueous media as a surrogate of superoxide and enzymatically produced O₂^•- for the probes wherein the deprotection pathway operated. Moreover, fluorescence imaging on cells and zebrafish embryos under PMA stimulation confirmed the effectiveness of our probe to detect superoxide using KO₂ as a convenient source. The detailed studies from Francesco Tampieri and coauthors are scientifically meaningful for the reliable evaluation of fluorescent probes using KO₂ as a surrogate of superoxide.