Smart design of exquisite multidimensional multilayered sand-clock-like upconversion nanostructures with ultrabright luminescence as efficient luminescence probes for bioimaging application.

A facile scalable approach is presented for the rational design of multidimensional, multilayered sand-clock-like UCNPs (denoted as UCCKs) bounded with high index facets, with a tunable Nd3+ content, and without a template or multiple complicated reaction steps. This was achieved using the seed-mediated growth and subsequent longitudinal direction epitaxial growth with the assistance of oleic acid and NH4F. The as-formed UCCKs composed of an inner layer (NaYF4:Yb,Er,Ca), an intermediate layer (NaYF4:Yb,Ca), and an outer layer (NaNdF4:Yb,Ca). The outer shell, enriched with Nd3+ sensitizer, augmented the near-infrared (NIR) photon absorption, whereas the intermediate shell, enriched with Yb3+, acted as a bridge for energy transfer from Nd3+ to Er3+ emitter in the inner core alongside with precluding any deleterious energy back-transfer from Er3+ or quenching effect from Nd3+. These unique structural and compositional properties of UCCKs endowed the UCL intensity of UCCKs by 22 and 10 times higher than that of hexagonal UCNP core (NaYF4:Yb,Er,Ca) and hexagonal UCNP core-shell (NaYF4:Yb,Er,Ca@NaYF4:Yb,Ca), respectively. Intriguingly, the UCL intensity increased significantly with increasing the content of Nd3+ in the outer shell. The silica-coated UCCKs were used as excellent long-term luminescence probes for the in vitro bioimaging without any noteworthy cytotoxicity. The presented approach may pave the road for controlling the synthesis of multidimensional UCCKs for various applications. Graphical abstract We developed novel multidimensional multilayered sand-clock-like upconversion nanostructures composed of a spherical inner core (NaYF4:Yb,Er,Ca), hexagonal intermediate shell (NaYF4:Yb,Ca) and two up-down outer shell (NaNdF4:Yb,Ca) with controllable Nd3+ as an efficient and safe probe for bioimaging applications without any quenching effect.

Ferric-bipyridine assay: A novel spectrophotometric method for measurement of antioxidant capacity.

Measurement of the antioxidant potential using in vitro assays is paramount in the assessment of various food products and nutraceuticals. Researchers always attempt to develop more accurate assays which can be performed in unsophisticated conditions. This novel method, Ferric-Bipyridine reducing capacity of total antioxidants (FBRC) is a very simple, accurate assay performed based on the reduction of Fe (III) to Fe (II) by antioxidants with the formation of a colored complex with bipyridine (Bp) i.e, Fe(II)-Bp. The FBRC method thus developed was assessed under carefully adjusted parameters of oxidant concentration, pH, temperature, solvent, light and time in order to fix the optimum conditions for the assay. The spectrophotometric monitoring of Fe(II)-Bp complex was noted by the formation of an intense pink color at room temperature with absorption maxima at 535 nm, pH 4. The analytical performance of this method was fully validated, and the obtained results were satisfactory. It was successfully applied to measure the total antioxidant capacity of standard compounds such as gallic acid, ascorbic acid and butylated hydroxy toluene (BHT), in addition to some plant extracts and oils. The FBRC method is inexpensive, reproducible and simple to perform. In addition, the antioxidant activity of the tested compounds compared to common reference methods showed that the novel FBRC method is superior to the Ferric reducing antioxidant power (FRAP) with regard to its use of realistic pH and faster kinetics. Thus, the FBRC method is convenient for the estimation of total antioxidant in plants extracts, natural products, essential oils and food stuff.