The extension of in vivo optical imaging for disease screening and image-guided surgical interventions requires brightly-emitting, tissue-specific materials that optically transmit through living tissue and can be imaged with portable systems that display data in real-time. Recent work suggests that a new window across the short wavelength infrared region can improve in vivo imaging sensitivity over near infrared light. Here we report on the first evidence of multispectral, real-time short wavelength infrared imaging offering anatomical resolution using brightly-emitting rare-earth nanomaterials and demonstrate their applicability toward disease-targeted imaging. Inorganic-protein nanocomposites of rare-earth nanomaterials with human serum albumin facilitated systemic biodistribution of the rare-earth nanomaterials resulting in the increased accumulation and retention in tumor tissue that was visualized by the localized enhancement of infrared signal intensity. Our findings lay the groundwork for a new generation of versatile, biomedical nanomaterials that can advance disease monitoring based on a pioneering infrared imaging technique.

In this paper, we study the perturbative aspects of a twisted version of the two-dimensional (0, 2) heterotic sigma model on a holomorphic gauge bundle E over a complex, hermitian manifold X. We show that the model can be naturally described in terms of the mathematical theory of "Chiral Differential Operators". In particular, the physical anomalies of the sigma model can be reinterpreted in terms of an obstruction to a global definition of the associated sheaf of vertex superalgebras derived from the free conformal field theory describing the model locally on X. One can also obtain a novel understanding of the sigma model 1-loop beta-function solely in terms of holomorphic data. At the (2, 2) locus, where the obstruction vanishes for any smooth manifold X, we obtain a purely mathematical description of the half-twisted variant of the topological A-model and (if c 1 (X) = 0) its elliptic genus. By studying e-print archive: http://lanl.arXiv.org/abs/0604179v3 760 MENG-CHWAN TANthe half-twisted (2, 2) model on X = CP 1 , one can show that a subset of the infinite-dimensional space of physical operators generates an underlying superaffine Lie algebra. Furthermore, on a non-Kähler, parallelized, group manifold with torsion, we uncover a direct relationship between the modulus of the corresponding sheaves of chiral de Rham complex and the level of the underlying WZW theory.

Monodisperse β-NaYF4:Yb,Er nanocrystals with mean sizes of 11, 40, and 110 nm were synthesized by a thermal decomposition solvothermal process to better understand the relationship between particle size and optical properties. A systematic study of luminescence intensity versus size revealed that both visible upconversion and infrared downconversion emission intensities decrease with decreasing nanocrystal size. The intrinsic quantum efficiency of the infrared 4 I 13/2 → 4 I 15/2 downconversion transition was studied in great detail since this specific transition allows us to quantify the contribution of nonradiative losses more easily than the observed upconversion transitions. The intrinsic quantum efficiency of the 4 I 13/2→4 I 15/2 transition decreased from 50% (110 nm) to 15% (11 nm). Multiphonon relaxation and −OH quenching was studied in these materials by measuring the vibrational characteristics of β-NaYF4:Yb,Er nanospheres. While multiphonon relaxation exhibited increased contribution to nonradiative decay, −OH quenching rates were calculated to be ∼4 orders of magnitude higher than that of the multiphonon relaxation. Therefore, surface −OH quenching effects were concluded to be primarily responsible for the observed dependence of emission intensity versus particle size.