Superparamagnetic graphene quantum dot as a dual-modality contrast agent for confocal fluorescence microscopy and magnetomotive optical coherence tomography

NaYF4:Ho3+/Yb3+@NaGdF4 core@shell upconversion nanoparticles for contrast enhancement in bimodal in-vitro OCT imaging

Contrast enhancement is explored in optical coherence tomography images using core NaYF4:Ho3+/Yb3+ and core@shell NaYF4:Ho3+/Yb3+@NaGdF4 nanoparticles. Under 980 nm excitation, core@shell nanoparticles exhibited 2.8 and 3.3 times enhancement at 541 nm and 646 nm emission wavelengths of Ho3+ ions compared to core nanoparticles. Photo-thermal conversion efficiencies were 32% and 20% for core and core@shell nanoparticles. In swept-source optical coherence tomography (SSOCT), core@shell nanoparticles have shown superior contrast, while in photo-thermal optical coherence tomography (PTOCT) core nanoparticles have excelled due to their higher photo-thermal conversion efficiency. The enhancement in contrast to noise ratio obtained is 58 dB. Comparative assessments of scattering coefficients and contrast-to-noise ratios were conducted, providing insights into nanoparticle performance for contrast enhancement in optical coherence tomography.

Molecular Contrast Optical Coherence Tomography and Its Applications in Medicine

The growing need to understand the molecular mechanisms of diseases has prompted the revolution in molecular imaging techniques along with nanomedicine development. Conventional optical coherence tomography (OCT) is a low-cost in vivo imaging modality that provides unique high spatial and temporal resolution anatomic images but little molecular information. However, given the widespread adoption of OCT in research and clinical practice, its robust molecular imaging extensions are strongly desired to combine with anatomical images. A range of relevant approaches has been reported already. In this article, we review the recent advances of molecular contrast OCT imaging techniques, the corresponding contrast agents, especially the nanoparticle-based ones, and their applications. We also summarize the properties, design criteria, merit, and demerit of those contrast agents. In the end, the prospects and challenges for further research and development in this field are outlined.

Investigation of Gd2O3: Er3+/Yb3+ Upconversion Nanoparticles (UCNPs) as a Multi-model Contrast Agent for Functional Optical Coherence Tomography (fOCT)

Currently, upconversion nanoparticles (UCNPs) implanted as a contrast agent for optical coherence tomography (OCT) system due to its biocompatibility, anti-stock emission, narrow emission bandwidth non-photobleaching effects etc., but it was not used as multi model imaging probe. We synthesized multimodal imaging probe having upconversion property along with paramagnetic property and used as dual contrast agents for Photothermal Optical Coherence Tomography (PTOCT) and Magnetomotive Optical Coherence Tomography (MMOCT). The synthesized Gd₂O₃:Er³⁺/Yb³⁺ UCNPs shows the bright yellow upconversion emission, biocompatibility with hydrophilic property. A custom built SSOCT setup modified for PTOCT and MMOCT imaging along with custom MATLAB algorithm for signal extraction. A dynamic study was performed with synthesized UCNPs as an imaging probe and functional OCT system for targeted imaging. This shows the utility of the Gd₂O₃:Er³⁺/Yb³⁺ UCNPs as molecular probe for targeted imaging applications.

Optical coherence tomography and fluorescence microscopy dual-modality imaging for in vivo single-cell tracking with nanowire lasers

Emerging cell-based therapies such as stem cell therapy and immunotherapy have attracted broad attention in both biological research and clinical practice. However, a long-standing technical gap of cell-based therapies is the difficulty of directly assessing treatment efficacy via tracking therapeutically administered cells. Therefore, imaging techniques to follow the in vivo distribution and migration of cells are greatly needed. Optical coherence tomography (OCT) is a clinically available imaging technology with ultrahigh-resolution and excellent imaging depth. It also shows great potential for in vivo cellular imaging. However, due to the homogeneity of current OCT cell labeling contrast agents (such as gold and polymer nanoparticles), only the distribution of entire cell populations can be observed. Precise tracking of the trajectory of individual single cells is not possible with such conventional contrast agents. Microlasers may provide a route to track unique cell identifiers given their small size, high emission intensities, rich emission spectra, and narrow linewidths. Here, we demonstrate that nanowire lasers internalized by cells provide both OCT and fluorescence signal. In addition, cells can be individually identified by the unique lasing emission spectra of the nanowires that they carry. Furthermore, single cell migration trajectories can be monitored both in vitro and in vivo with OCT and fluorescence microscopy dual-modality imaging system. Our study demonstrates the feasibility of nanowire lasers combined with the dual-modality imaging system for in vivo single cell tracking with a high spatial resolution and identity verification, an approach with great utility for stem cell and immunomodulatory therapies.

Recent Advances on Graphene Quantum Dots for Bioimaging Applications

Being a zero-dimensional (0D) nanomaterial of the carbon family, graphene quantum dots (GQDs) showed promising biomedical applications owing to their ultra-small size, non-toxicity, biocompatibility, excellent photo stability, tunable fluorescence, and water solubility, etc., thus capturing a considerable attention in biomedical field. This review summarizes the recent advances made in the research field of GQDs and place special emphasis on their bioimaging applications. We briefly introduce the synthesis strategies of GQDs, including top-down and bottom-up strategies. The bioimaging applications of GQDs are also discussed in detail, including optical [fluorescence (FL)], two-photon FL, magnetic resonance imaging (MRI), and dual-modal imaging. In the end, the challenges and future prospects to advance the clinical bioimaging applications of GQDs have also been addressed.