Gold nanoclusters (AuNCs) with fluorescence in the Near Infrared (NIR) by both one- and two-photon electronic excitation were incorporated in mesoporous silica nanoparticles (MSNs) using a novel one-pot synthesis procedure where the condensation polymerization of alkoxysilane monomers in the presence of the AuNCs and a surfactant produce hybrid MSNs of 49 nm diameter. This method was further developed to prepare 30 nm diameter nanocomposite particles with simultaneous NIR fluorescence and superparamagnetic properties, with a core composed of superparamagnetic manganese ferrite nanoparticles (MnFe2O4) coated with a thin silica layer, and a shell of mesoporous silica decorated with AuNCs. The nanocomposite particles feature NIR-photoluminescence with 0.6% quantum yield and large Stokes shift (290 nm), and superparamagnetic response at 300 K, with a saturation magnetization of 13.4 emu g-1. The conjugation of NIR photoluminescence and superparamagnetic properties in the biocompatible nanocomposite has high potential for application in multimodal bioimaging.

Drought stress has been considered a major problem in coffee crops, and the higher occurrence of unpredictable environmental events has highlighted the vulnerability of agricultural systems. Several reports have indicated selenium (Se) as a plant biostimulant against environmental stress, including drought. The effects of Se in plants are related to the modulation of enzymatic activity, energetics and osmoprotectants plant content, and nutrient balance in plants. However, investi-gating the effective time of Se application is crucial for better understanding its effects on coffee plants, a drought-sensitive crop. This study aimed to investigate the role of Se supply in improving drought tolerance in coffee seedlings while also evaluating the best timing for Se application. Five times of Se foliar application were assessed during induced drought stress by PEG-6000 using the day of imposing stress as a default, plus two control treatments: i) with osmotic stress and without Se; ii) without osmotic stress and Se. The treatments were compared with both control treatments. Results demonstrated that the osmotic stress (OS) promoted mild stress in the coffee plants, as ex-pected. Plants under stress showed reduced GR and SOD activity compared with the non-stressed ones, and the OS induces starch degradation, which is potentialized by Se foliar supply, mainly when Se is applied before inducing the stress. The decline in the starch content might be considered a strategy to provide energy to coffee seedlings. The seedlings that received foliar Se application 8 days before the stress exhibited higher CAT, APX, and SOD than those that did not receive OS nor Se application. The results obtained in this study suggest that the previous Se foliar spray is more effective than the Se supply after OS to overcome the adverse condition. On the other hand, the post-stress application seems to impose extra stress on the plants, leading them to reduce the water potential.