Benefiting from near-infrared persistent luminescence, chromiumdoped zinc gallate nanoparticles have become appealing for background-free biomedical imaging applications, where autofluorescence from adjacent tissues no longer poses a problem. Nevertheless, the synthesis of persistent luminescent nanoparticles with controllable and biologically appropriate size, high luminescence intensity, and long persistent duration remains very challenging. Herein, we report a solvothermal synthetic route for preparing differently sized ZnGa 2 O 4 :Cr nanoparticles with a particle size tunable from 4 to 31 nm and afterglow duration longer than 20 h. The route involves lower reaction temperatures and involves no reworking of the particles postsynthesis, providing materials that have far fewer unwanted defects and much higher luminescence yields (up to 51%). It was found that methanol played a paramount role in obtaining the Cr 3+ -doped ZnGa 2 O 4 nanoparticles. The effects of methanol were discussed in combination with NMR spectroscopy studies and theoretical calculations, and the underlying alcoholmediated growth and doping mechanisms were elucidated, which will be beneficial for developing highly persistent luminescent nanoparticles.

To investigate the duration of humoral immune response in convalescent coronavirus disease 2019 (COVID-19) patients, we conduct a 12-month longitudinal study through collecting a total of 1,782 plasma samples from 869 convalescent plasma donors in Wuhan, China and test specific antibody responses. The results show that positive rate of IgG antibody against receptor-binding domain of spike protein (RBD-IgG) to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the COVID-19 convalescent plasma donors exceeded 70% for 12 months post diagnosis. The level of RBD-IgG decreases with time, with the titer stabilizing at 64.3% of the initial level by the 9th month. Moreover, male plasma donors produce more RBD-IgG than female, and age of the patients positively correlates with the RBD-IgG titer. A strong positive correlation between RBD-IgG and neutralizing antibody titers is also identified. These results facilitate our understanding of SARS-CoV-2-induced immune memory to promote vaccine and therapy development.

Physiological parameters in tumor microenvironments, including hypoxia, low extracellular pH, enzymes, reducing conditions, and so on, are closely associated with the proliferation, angiogenesis, invasion, and metastasis of cancer, and impact the therapeutic administrations. Therefore, monitoring the tumor microenvironment is significant for diagnosing tumors, predicting the invasion potential, evaluating therapeutic efficacy, planning the treatment, and cancer prognostics. Noninvasive molecular imaging technologies combined with novel "smart" nanoparticle-based activatable probes provide a feasible approach to visualize tumor-associated microenvironment factors. This review summarizes recent achievements in the designs of "smart" molecular imaging nanoprobes responding to the tumor microenvironment-related features, and highlights the state of the art in tumor heterogeneity imaging.

Ostwald ripening is the dominant particle growth mechanism in traditional routes to synthesize aqueous CdTe quantum dots (QDs), which results in a broadening of their size distribution and also their photoluminescence line width, in the case of prolonged reactions. We introduce a method to suppress the Ostwald ripening through the replenishment of precursors before size defocusing occurs in the aqueous synthetic system, which is realized through a programmed dropwise precursor (source) addition (denoted as PDPA) by a syringe pump arrangement that can control the precursor feed volume and rate. As a result, we have obtained a series of highly monodisperse CdTe QDs, with the emission full width at half-maximum in the red region (106 meV) being even narrower than that in the green region (160 meV). We monitored the conductivity of the reaction solution to follow the consumption of precursors, providing feedback as to whether the replenishment volume was matched. Correlations between the emission quantum yield and the fluorescence lifetime for different precursor source addition rates are provided. The influence of the respective sizes of the CdTe particles employed as precursors in PDPA on the growth rate, monodispersity, and emission characteristics of the resulting QDs is explored, and the underlying mechanisms are rationalized.

Near‐infrared lights have received increasing attention regarding imaging applications owing to their large tissue penetration depth, high spatial resolution, and outstanding signal‐to‐noise ratio, particularly those falling in the second near‐infrared window (NIR II) of biological tissues. Rare earth nanoparticles containing Er3+ ions are promising candidates to show up‐conversion luminescence in the first near‐infrared window (NIR I) and down‐conversion luminescence in NIR II as well. However, synthesizing particles with small size and high NIR II luminescence quantum yield (QY) remains challenging. Er3+ ions are herein innovatively combined with Yb3+ ions in a NaErF4@NaYbF4 core/shell manner instead of being codoped into NaLnF4 matrices, to maximize the concentration of Er3+ in the emitting core. After further surface coating, NaErF4@NaYbF4@NaYF4 core/shell/shell particles are obtained. Spectroscopy studies are carried out to show the synergistic impacts of the intermediate NaYbF4 layer and the outer NaYF4 shell. Finally, NaErF4@NaYbF4@NaYF4 nanoparticles of 30 nm with NIR II luminescence QY up to 18.7% at room temperature are obtained. After covalently attaching folic acid on the particle surface, tumor‐specific nanoprobes are obtained for simultaneously visualizing both subcutaneous and intraperitoneal tumor xenografts in vivo. The ultrahigh QY of down‐conversion emission also allows for visualization of the biodistribution of folate receptors.