Reversible switching of photoluminescence (PL) of carbon nanoparticles (CNP) can be achieved with counterionic macromolecular caging and decaging at the nanoscale. A negatively charged uncoated, "bare" CNP with high luminescence loses its PL when positively charged macromolecules are wrapped around its surface. Prepared caged carbons could regain their emission only through interaction with anionic surfactant molecules, representing anionic amphiphiles of endocytic membranes. This process could be verified by gel electrophoresis, spectroscopically and in vitro confocal imaging studies. Results indicated for the first time that luminescence switchable CNPs can be synthesized for efficient intracellular tracking. This study further supports the origin of photoluminescence in CNP as a surface phenomenon correlated a function of characteristic charged macromolecules.
Photoacoustic imaging has emerged as a promising imaging platform with a high tissue penetration depth. However, biodegradable nanoparticles, especially those for photoacoustic imaging, are rare and limited to a few polymeric agents. The development of such nanoparticles holds great promise for clinically translatable diagnostic imaging with high biocompatibility. Metabolically digestible and inherently photoacoustic imaging probes can be developed from nanoprecipitation of biliverdin, a naturally occurring heme-based pigment. The synthesis of nanoparticles composed of a biliverdin network, cross-linked with a bifunctional amine linker, is achieved where spectral tuning relies on the choice of reaction media. Nanoparticles synthesized in water or water containing sodium chloride exhibit higher absorbance and lower fluorescence compared to nanoparticles synthesized in 2-(N-morpholino) ethanesulfonic acid buffer. All nanoparticles display high absorbance at 365 and 680 nm. Excitation at near-infrared wavelengths leads to a strong photoacoustic signal, while excitation with ultraviolet wavelengths results in fluorescence emission. In vivo photoacoustic imaging experiments in mice demonstrated that the *
The early detection of bone microdamages is crucial to make informed decisions about the therapy and taking precautionary treatments to avoid catastrophic fractures. Conventional computed tomography (CT) imaging faces obstacles in detecting bone microdamages due to the strong self‐attenuation of photons from bone and poor spatial resolution. Recent advances in CT technology as well as novel imaging probes can address this problem effectively. Herein, the bone microdamage imaging is demonstrated using ligand‐directed nanoparticles in conjunction with photon counting spectral CT. For the first time, Gram‐scale synthesis of hafnia (HfO2) nanoparticles is reported with surface modification by a chelator moiety. The feasibility of delineating these nanoparticles from bone and soft tissue of muscle is demonstrated with photon counting spectral CT equipped with advanced detector technology. The ex vivo and in vivo studies point to the accumulation of hafnia nanoparticles at microdamage site featuring distinct spectral signal. Due to their small sub‐5 nm size, hafnia nanoparticles are excreted through reticuloendothelial system organs without noticeable aggregation while not triggering any adverse side effects based on histological and liver enzyme function assessments. These preclinical studies highlight the potential of HfO2‐based nanoparticle contrast agents for skeletal system diseases due to their well‐placed K‐edge binding energy.
Phosphonated compounds, in particular, bisanalogs are widely applied in clinical settings for the treatment of severe bone turnovers and recently as imaging probes when conjugated with organic fluorophores. Herein, we introduce a bone seeking luminescent probe that shows a high binding affinity toward bone minerals based on monophosphonated carbon dots (CDs). Spheroidal CDs tethered with PEG monophosphates are synthesized in a one-pot hydrothermal method and are physicochemically characterized, where the retention of phosphonates is confirmed by P NMR and X-ray photoelectron spectroscopy. Interestingly, the high abundance of multiple monodentate phosphonates exhibited strong binding to hydroxyapatite, the main bone mineral constituent. The remarkable optophysical properties of monophosphonated CDs were confirmed in an ex vivo model of the bovine cortical bone where the imaging feasibility of microcracks, which are calcium-rich regions, was demonstrated. The in vivo studies specified the potential application of monophosphonated CDs for imaging when injected intramuscularly. The biodigestible nature and cytocompatibility of the probe presented here obviate the demand for a secondary fluorophore, while offering a nanoscale strategy for bone targeting and can eventually be employed for potential bone therapy in the future.
Proline, a stress marker, is routinely quantified by a protocol that essentially uses hazardous toluene. Negative impacts of toluene on human health prompted us to develop a reliable alternate protocol for proline quantification. Absorbance of the proline-ninhydrin condensation product formed by reaction of proline with ninhydrin at 100 °C in the reaction mixture was significantly higher than that recorded after its transfer to toluene, revealing that toluene lowers sensitivity of this assay. λ of the proline-ninhydrin complex in the reaction mixture and toluene were 508 and 513 nm, respectively. Ninhydrin in glacial acetic acid yielded higher quantity of the proline-ninhydrin condensation product compared to ninhydrin in mixture of glacial acetic acid and HPO, indicating negative impact of HPO on proline quantification. Further, maximum yield of the proline-ninhydrin complex with ninhydrin in glacial acetic acid and ninhydrin in mixture of glacial acetic acid and HPO was achieved within 30 and 60 min, respectively. This revealed that HPO has negative impact on the reaction rate and quantity of the proline-ninhydrin complex formed. In brief, our proline quantification protocol involves reaction of a 1-ml proline sample with 2 ml of 1.25 % ninhydrin in glacial acetic acid at 100 °C for 30 min, followed by recording absorbance of the proline-ninhydrin condensation product in the reaction mixture itself at 508 nm. Amongst proline quantification protocols known till date, our protocol is the most simple, rapid, reliable, cost-effective, and eco-friendlier.
Surface abundant oxidize‐able functionalities at the nanoscale of carbon dots are prone to undergo sequential aerial oxidation leading to polarity‐driven wavelength tuning of their photoluminescence and consequently boost their quantum yields. With the progression of time, aerial oxidation is gradually increased from 1 to 6 h; consequently, a remarkable shift in the emission peak is observed, likely due to a gradual decrease in their respective band gaps leading to red shift of their photoluminescence. These bands are found to be dependent on the time of hydrothermal treatment of the model small molecules, i.e., benzophenone imine, and not on the size of the carbon core, as is the typical case for semiconductor quantum dots. Due to their high quantum yield (≈31%), it is demonstrated that these wavelength‐tuned carbon nanoparticles can be efficiently used for multiscale bioimaging, i.e., intracellular, deep tissue ex vivo and in vivo fluorescence bioimaging.
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