Semiconducting Polymer Nanoprobe for In Vivo Imaging of Reactive Oxygen and Nitrogen Species

Abstract

Semiconducting polymer nanoparticles are utilized as a free-radical inert and light-harvesting nanoplatform for in vivo molecular imaging of reactive oxygen and nitrogen species (RONS). With its RONS-sensitive fluorescence, good biodistribution and passive targeting ability to leaky inflammatory vasculature, this nanoprobe permits detection of RONS in the microenvironment of spontaneous bacterial infection following systemic administration. Keywords semiconducting polymers; RONS; nanoparticles; biosensors; imaging agentsThe elevated generation of reactive oxygen and nitrogen species (RONS) is a hallmark of many pathological processes ranging from acute and chronic bacterial infections to chronic diseases such as cancer, cardiovascular disease, and arthritis. [1] Therefore, the ability to detect the generation of RONS as pathological chemical messengers is critical to both understanding the etiology of these diseases and optimizing therapeutic interventions against these potentially life-threatening conditions. The main effort in RONS sensing has been devoted to the construction of fluorescence probes because of the high sensitivity and nonionizing nature of fluorescence imaging. [2] Although small-molecule fluorophores, [3] genetically encoded proteins, [4] fluorescent single-walled carbon nanotubes (SWCNs), [5] quantum dots (QDs), [6] and dye-conjugated inorganic nanoparticles [7] have been developed for this purpose, probes applicable for in vivo imaging are still very limited. [2] In addition to near-infrared (NIR) fluorescence, one of the most important prerequisites for in vivo RONS imaging is the resistance of the reporter moiety of the probe to degradation by RONS. Failing to meet this requirement will likely result in a greatly reduced signal-to-noise ratio because persistent microenvironmental RONS in vivo will bleach the activated probe and lead to false negative signals. QDs and many small molecules dyes are not stable in the presence of highly oxidative RONS such as hypochlorite (ClO − ), [6,8] and thus are not ideal to serve as the signal output units in this application of imaging probes.Semiconducting polymer nanoparticles (SPNs) represent a new class of photostable fluorescent nanomaterials with excellent brightness that can be orders of magnitude higher than that of small-molecule fluorophores, and tens of times better than that of QDs. [9] As these nanoparticles are primarily composed of π-conjugated polymers, their utilization as fluorescent probes eliminates the possibility of heavy metal ion-induced toxicity to living organisms, potentially giving rise to good biocompatibility. [10] Despite theses advantages, exploration of SPNs in molecular imaging is still in its infancy with only a few in vivo studies reported. [11] Recently, we have developed a bioluminescence resonance energy transfer (BRET) and fluorescence resonance energy transfer (FRET) relay nanoprobe for lymph node mapping and tumor imaging by taking advantage of the efficient lightharvesting properties of SPNs. [12] ...

Mind your P's and Q's: the coming of age of semiconducting polymer dots and semiconductor quantum dots in biological applications

“…Interestingly, this group is also well-known for developing BRET-based self-illuminating QDs [90], and SLNM was one of the first proof-of-concept applications of NIR-emitting QDs [91]. Rao and coworkers have also developed CRET/FRET-based Pdot probes for oxidative and nitrosative stress [65,66 ], including measurement of peroxide and peroxynitrite in the liver of a mouse model with overdoses of acetaminophen and isoniazid ( Figure 4b) [66 ].…”

“…For example, doping Pdots with NIR fluorophores [63][64][65]66 ], QDs [67], or Eu(III) complexes [68 ] yields more spectrally narrow, redshifted emission, and, in the case of Eu(III), long-lived excited states to permit time-gated measurements with improved signal-to-background ratios. Alternatively, boron-dipyrromethene (BODIPY) fluorophores [53 ,54] and Eu(III) complexes [69] can be incorporated directly into the constituent polymer chains (Figure 4a).…”

Implantable Nanosensors: Toward Continuous Physiologic Monitoring

“…Recently, Pu et al developed a RONS nanosensor based on RONS-activated FRET between a semiconducting polymer and a NIR dye. Although it was not reversible, the nanosensor could image inflammatory microenvironments in vivo 17 . Another implantable nanosensor paired an oxygen-sensitive dye with an oxygen-consuming enzyme and demonstrated reversible in vivo detection of the small-molecule histamine (Figure 2) as a platform proof-of concept for nonsaccharides 18 .…”

“…Other semiconductor fluorophores like non-crystalline semiconducting polymer-dots (Pdots) 17 and upconverting nanocrystals have interesting optical properties for nanosensors 66 . Both fluorophores have been incorporated into ratiometric nanosensors 67 , and neither has raised acute toxicity concerns 94b, c, 95 although their biocompatibilities are not fully characterized 67b, 68 .…”

Upconversion nanoprobes for efficiently in vitro imaging reactive oxygen species and in vivo diagnosing rheumatoid arthritis

“…Here, we used RAW264.7, a murine macrophage cell line, as the model system. To mimic the inflammatory conditions, RAW264.7 cells were successively treated with lipopolysaccharide (LPS) and phorbol 12-myristate 13-acetate (PMA) to activate the generation of ROS such as O 2 À , OH, ONOO À , and ClO À [22,23]. As determined by laser-scanning upconversion luminescence microscopy (LSUCLM), control RAW264.7 cells incubated with HAR-UCNPs showed only a weak green UCL emission at 515e560 nm (Fig.…”