Bulk Cs 3 Bi 2 I 9 exhibits zero-dimensional (0-D) perovskite crystal structure at the molecular level, providing scopes for novel optical properties compared to three-dimensional perovskite structures. Here, 0-D refers to the crystal structure irrespective of the size of the crystal. We have prepared colloidal Cs 3 Bi 2 I 9 nanocrystals and elucidated the unique optical properties arising from their 0-D crystal structure. Absorption spectrum at 10 K confirms that the electronic band gap of Cs 3 Bi 2 I 9 nanocrystals is at 2.86 eV, along with a sharp excitonic peak at 2.56 eV, resulting in a very high excitonic binding energy, E b X = 300 meV. Interestingly, we observe two peaks in the photoluminescence spectra at room temperature on both sides of the excitonic absorption energy. Because E b X (300 meV) ≫ effective phonon energy (36 meV), the phonon-mediated relaxation of carriers from conduction band minimum to the excitonic state is suppressed to an extent. Consequently, two photoluminescence peaks related to both the bulk band edge and the excitonic transitions are observed. Furthermore, Rb 3 Bi 2 I 9 nanocrystals have also been synthesized, but they exhibit two-dimensional layered structure, unlike the 0-D structure of Cs 3 Bi 2 I 9 .

Herein we report the colloidal synthesis of Cs 3 Sb 2 I 9 and Rb 3 Sb 2 I 9 perovskite nanocrystals,a nd explore their potential for optoelectronic applications.D ifferent morphologies,s uch as nanoplatelets and nanorods of Cs 3 Sb 2 I 9 ,a nd spherical Rb 3 Sb 2 I 9 nanocrystals were prepared. All these samples show band-edge emissions in the yellow-red region. Exciton many-body interactions studied by femtosecond transient absorption spectroscopyofCs 3 Sb 2 I 9 nanorods reveals characteristic second-derivative-type spectral features,suggesting red-shifted excitons by as much as 79 meV.Ah igh absorption cross-section of ca. 10 À15 cm 2 was estimated. The results suggest that colloidal Cs 3 Sb 2 I 9 and Rb 3 Sb 2 I 9 nanocrystals are potential candidates for optical and optoelectronic applications in the visible region, though ab etter control of defect chemistry is required for efficient applications. Figure 1. a) Schematic representation of the relationship among the perovskitec rystal structures of i) 3D CsMI 3 (M = Pb 2+ /Sn 2+ ), ii)2D Cs 3 Sb 2 I 9 ,and iii)0DCs 2 SnI 6 .b)Schematic representation of the synthesis of Cs 3 Sb 2 I 9 NPLs and Cs 3 Sb 2 I 9 NRs. ODE = 1-octadecene, OnA = octanoic acid, OAm = oleylamine.[*] J. Pal, S. Manna, [+] A. Nag

Optical coherence tomography (OCT) is a powerful tool in ophthalmology that provides in vivo morphology of the retinal layers and their light scattering properties. The directional (angular) reflectivity of the retinal layers was investigated with focus on the scattering from retinal pigment epithelium (RPE). The directional scattering of the RPE was studied in three mice strains with three distinct melanin concentrations: albino (BALB/c), agouti (129S1/SvlmJ), and strongly pigmented (C57BL/6J). The backscattering signal strength was measured with a directional OCT system in which the pupil entry position of the narrow OCT beam can be varied across the dilated pupil of the eyes of the mice. The directional reflectivity of other retinal melanin-free layers, including the internal and external limiting membranes, and Bruch's membrane (albinos) were also measured and compared between the strains. The intensity of light backscattered from these layers was found highly sensitive to the angle of illumination, whereas the inner/outer segment (IS/OS) junctions showed a reduced sensitivity. The reflections from the RPE are largely insensitive in highly pigmented mice. The differences in directional scattering between strains shows that directionality decreases with an increase in melanin concentrations in RPE, suggesting increasing contribution of Mie scattering by melanosomes.

It has been recently demonstrated that structures corresponding to the cell bodies of highly transparent cells in the retinal ganglion cell layer could be visualized noninvasively in the living human eye by optical coherence tomography (OCT) via temporal averaging. Inspired by this development, we explored the application of volumetric temporal averaging in mice, which are important models for studying human retinal diseases and therapeutic interventions. A general framework of temporal speckle-averaging (TSA) of OCT and optical coherence tomography angiography (OCTA) is presented and applied to mouse retinal volumetric data. Based on the image analysis, the eyes of mice under anesthesia exhibit only minor motions, corresponding to lateral displacements of a few micrometers and rotations of a fraction of 1 deg. Moreover, due to reduced eye movements under anesthesia, there is a negligible amount of motion artifacts within the volumes that need to be corrected to achieve volume coregistration. In addition, the relatively good optical quality of the mouse ocular media allows for cellular-resolution imaging without adaptive optics (AO), greatly simplifying the experimental system, making the proposed framework feasible for large studies. The TSA OCT and TSA OCTA results provide rich information about new structures previously not visualized in living mice with non-AO-OCT. The mechanism of TSA relies on improving signal-to-noise ratio as well as efficient suppression of speckle contrast due to temporal decorrelation of the speckle patterns, enabling full utilization of the high volumetric resolution offered by OCT and OCTA. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

The efficacy of therapeutics for brain tumors is seriously hampered by multiple barriers to drug delivery, including severe destabilizing effects in the blood circulation, the blood–brain barrier/blood–brain tumor barrier (BBB/BBTB), and limited tumor uptake. Here, a sequential targeting in crosslinking (STICK) nanodelivery strategy is presented to circumvent these important physiological barriers to improve drug delivery to brain tumors. STICK nanoparticles (STICK‐NPs) can sequentially target BBB/BBTB and brain tumor cells with surface maltobionic acid (MA) and 4‐carboxyphenylboronic acid (CBA), respectively, and simultaneously enhance nanoparticle stability with pH‐responsive crosslinkages formed by MA and CBA in situ. STICK‐NPs exhibit prolonged circulation time (17‐fold higher area under curve) than the free agent, allowing increased opportunities to transpass the BBB/BBTB via glucose‐transporter‐mediated transcytosis by MA. The tumor acidic environment then triggers the transformation of the STICK‐NPs into smaller nanoparticles and reveals a secondary CBA targeting moiety for deep tumor penetration and enhanced uptake in tumor cells. STICK‐NPs significantly inhibit tumor growth and prolong the survival time with limited toxicity in mice with aggressive and chemoresistant diffuse intrinsic pontine glioma. This formulation tackles multiple physiological barriers on‐demand with a simple and smart STICK design. Therefore, these features allow STICK‐NPs to unleash the potential of brain tumor therapeutics to improve their treatment efficacy.