The enhancement of upconversion luminescence (UCL) of rare earth doped upconversion nanoparticles (UCNPs) in aqueous solution is particularly important and urgently required for a broad range of biomedical applications. Herein, an effective approach to achieve highly enhanced UCL from NaYF4:Yb3+,Tm3+ UCNPs in aqueous solution is presented. We demonstrate that UCL of these UCNPs can be enhanced more than 104-fold by using a mesoporous silica low refractive index resonant waveguide grating (low-n RWG) in contact with aqueous solution, which makes it well-suited for biomedical applications. The structure parameters of the low-n RWG are tuned via rigorous coupled-wave analysis simulation to ensure strong local excitation field to form atop the TiO2 surface of the low-n RWG, where UCNPs are deposited. As the low-n RWG is excited by a near-infrared laser at 976 nm to match its guided mode resonance (GMR) condition, UCL emitted from UCNPs is greatly enhanced thanks to the strong interaction between excitation local field and UCNPs. UCL emission of UCNPs can be further enhanced about two to four times when the UCL emission condition (wavelength and angle) matches with the GMR condition. Furthermore, we show that the presence of biotin molecules atop of the low-n RWG can be easily detected through UCL emission generated from streptavidin-functionalized UCNPs with the help of the streptavidin–biotin specific binding. The results indicate that the low-n RWG has high potential for UCL biosensing and bioimaging applications.

Lanthanide (Ln3+)–doped upconversion nanoparticles (UCNPs) offer an ennormous future for a broad range of biological applications over the conventional downconversion fluorescent probes such as organic dyes or quantum dots. Unfortunately, the efficiency of the anti−Stokes upconversion luminescence (UCL) process is typically much weaker than that of the Stokes downconversion emission. Albeit recent development in the synthesis of UCNPs, it is still a major challenge to produce a high−efficiency UCL, meeting the urgent need for practical applications of enhanced markers in biology. The poor quantum yield efficiency of UCL of UCNPs is mainly due to the fol-lowing reasons: (i) the low absorption coefficient of Ln3+ dopants, the specific Ln3+ used here being ytterbium (Yb3+), (ii) UCL quenching by high−energy oscillators due to surface defects, impurities, ligands, and solvent molecules, and (iii) the insufficient local excitation intensity in broad-field il-lumination to generate a highly efficient UCL. In order to tackle the problem of low absorption cross-section of Ln3+ ions, we first incorporate a new type of neodymium (Nd3+) sensitizer into UCNPs to promote their absorption cross-section at 793 nm. To minimize the UCL quenching induced by surface defects and surface ligands, the Nd3+-sensitized UCNPs are then coated with an inactive shell of NaYF4. Finally, the excitation light intensity in the vicinity of UCNPs can be greatly enhanced using a waveguide grating structure thanks to the guided mode resonance. Through the synergy of these three approaches, we show that the UCL intensity of UCNPs can be boosted by a million−fold compared with conventional Yb3+–doped UCNPs.

We report a versatile strategy to exploit parafilm waste as a carbon precursor for fabrication of freestanding, hollow few-layer graphene fiber mesh (HFGM) structures without use of any gaseous carriers/promoters via an annealing route. The freestanding HFGMs possess good mechanical flexibility, tailorable transparency, and high electrical conductivity, consequently qualifying them as promising electrochemical electrodes. Because of the hollow spaces, electrolyte ions can easily access into and contact with interior surfaces of the graphene fibers, accordingly increasing electrode/electrolyte interfacial area. As expected, solid-state supercapacitors based on the HFGMs exhibit a considerable enhancement in specific capacitance (20-30 fold) as compared to those employing chemical vapor deposition compact graphene films. Moreover, the parafilm waste is found to be beneficial for one-step fabrication of nanocarbon/few-layer graphene composite meshes with superior electrochemical performance, outstanding superhydrophobic property, good self-cleaning ability, and great promise for oil spill cleanup.

Deep-level transient spectroscopy measurements in InAs quantum dots (QDs) grown in both n-GaAs and p-GaAs show that tunneling is an important mechanism of carrier escape from the dots. The doping level in the barrier strongly affects the tunneling emission rates, enabling or preventing the detection of a transient capacitance signal from a given QD level. The relative intensity of this signal acquired with different rate windows allows the estimation of tunneling emission energies.

2021) Gold nanorods conjugated upconversion nanoparticles nanocomposites for simultaneous bioimaging, local temperature sensing and photothermal therapy of OML-1 oral cancer cells,

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We introduce a compact array fluorescence sensor principle that takes advantage of the long luminescence lifetimes of upconversion nanoparticles (UCNPs) to deploy a filter-free, optics-less contact geometry, advantageous for modern biochemical assays of biomolecules, pollutants or cells. Based on technologically mature CMOS chips for ∼10 kHz technical/scientific imaging, we propose a contact geometry between assayed molecules or cells and a CMOS chip that makes use of only a faceplate or direct contact, employing time-window management to reject the 975 nm excitation light of highly efficient UCNPs. The chip surface is intended to implement, in future devices, a resonant waveguide grating (RWG) to enhance excitation efficiency, aiming at the improvement of upconversion luminescence emission intensity of UCNP deposited atop of such an RWG structure. Based on mock-up experiments that assess the actual chip rejection performance, we bracket the photometric figures of merit of such a promising chip principle and predict a limit of detection around 10-100 nanoparticles.

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