We report what we believe to be the first evidence of localized nanoscale photonic jets generated at the shadow-side surfaces of micronscale, circular dielectric cylinders illuminated by a plane wave. These photonic nanojets have waists smaller than the diffraction limit and propagate over several optical wavelengths without significant diffraction. We have found that such nanojets can enhance the backscattering of visible light by nanometer-scale dielectric particles located within the nanojets by several orders of magnitude. Not involving evanescent fields and not requiring mechanical scanning, photonic nanojets may provide a new means to detect and image nanoparticles of size well below the diffraction limit. This could yield a potential novel ultramicroscopy technique using visible light for detecting proteins, viral particles, and even single molecules; and monitoring molecular synthesis and aggregation processes of importance in many areas of biology, chemistry, material sciences, and tissue engineering.

Diffuse reflectance spectra were collected from adenomatous colon polyps (cancer precursors) and normal colonic mucosa of patients undergoing colonoscopy. We analyzed the data by using an analytical light diffusion model, which was tested and validated on a physical tissue model composed of polystyrene beads and hemoglobin. Four parameters were obtained: hemoglobin concentration, hemoglobin oxygen saturation, effective scatterer density, and effective scatterer size. Normal and adenomatous tissue sites exhibited differences in hemoglobin concentration and, on average, in effective scatterer size, which were in general agreement with other studies that employ standard methods. These results suggest that diffuse reflectance can be used to obtain tissue information about tissue structure and composition in vivo.

We report observation of a fine structure component in backscattered light from mucosal tissue which is periodic in wavelength. This structure is ordinarily masked by a diffusive background. We have identified the origin of this component as being due to light which is Mie scattered by surface epithelial cell nuclei. By analyzing the amplitude and frequency of the fine structure, the density and size distribution of these nuclei can be extracted. These quantities are important indicators of neoplastic precancerous changes in biological tissue. [S0031-9007(97)05049-7]

Chromatin decompaction via increasing euchromatin or decreasing heterochromatin results in a softer nucleus and abnormal nuclear blebbing, independent of lamin perturbations. Conversely, increasing heterochromatin stiffens the nucleus and rescues nuclear morphology in lamin-perturbed cells that present abnormal nuclear morphology.

No abstract

We report an in situ method of probing the structure of living epithelial cells, based on light scattering spectroscopy with polarized light. The method makes it possible to distinguish between single backscattering from uppermost epithelial cells and multiply scattered light. The spectrum of the single backscattering component can be further analyzed to provide histological information about the epithelial cells such as the size distribution of the cell nuclei and their refractive index. These are valuable quantities to detect and diagnose precancerous changes in human tissues.

No abstract

This paper reviews the substantial body of literature emerging since 2004 concerning photonic nanojets. The photonic nanojet is a narrow, high-intensity, non-evanescent light beam that can propagate over a distance longer than the wavelength λ after emerging from the shadow-side surface of an illuminated lossless dielectric microcylinder or microsphere of diameter larger than λ. The nanojet’s minimum beamwidth can be smaller than the classical diffraction limit, in fact as small as ~λ/3 for microspheres. It is a nonresonant phenomenon appearing for a wide range of diameters of the microcylinder or microsphere if the refractive index contrast relative to the background is less than about 2:1. Importantly, inserting within a nanojet a nanoparticle of diameter dν perturbs the far-field backscattered power of the illuminated microsphere by an amount that varies as dν3 for a fixed λ. This perturbation is much slower than the dν6 dependence of Rayleigh scattering for the same nanoparticle, if isolated. This leads to a situation where, for example, the measured far-field backscattered power of a 3-μm diameter microsphere could double if a 30-nm diameter nanoparticle were inserted into the nanojet emerging from the microsphere, despite the nanoparticle having only 1/10,000th the cross-section area of the microsphere. In effect, the nanojet serves to project the presence of the nanoparticle to the far field. These properties combine to afford potentially important applications of photonic nanojets for detecting and manipulating nanoscale objects, subdiffraction-resolution nanopatterning and nanolithography, low-loss waveguiding, and ultrahigh-density optical storage.