Abdulkadir Yurt

High-throughput detection and sizing of individual low-index nanoparticles and viruses for pathogen identification.

Rapid, chip-scale, and cost-effective single particle detection of biological agents is of great importance to human health and national security. We report real-time, high-throughput detection and sizing of individual, low-index polystyrene nanoparticles and H1N1 virus. Our widefield, common path interferometer detects nanoparticles and viruses over a very large sensing area, orders of magnitude larger than competing techniques. We demonstrate nanoparticle detection and sizing down to 70 nm in diameter. We clearly size discriminate nanoparticles with diameters of 70, 100, 150, and 200 nm. We also demonstrate detection and size characterization of hundreds of individual H1N1 viruses in a single experiment.

Single nanoparticle detectors for biological applications

Nanoparticle research has become increasingly important in the context of bioscience and biotechnology. Practical use of nanoparticles in biology has significantly advanced our understanding about biological processes in the nanoscale as well as led to many novel diagnostic and therapeutic applications. Besides, synthetic and natural nanoparticles are of concern for their potential adverse effect on human health. Development of novel detection and characterization tools for nanoparticles will impact a broad range of disciplines in biological research from nanomedicine to nanotoxicology. In this article, we discuss the recent progress and future directions in the area of single nanoparticle detectors with an emphasis on their biological applications. A brief critical overview of electrical and mechanical detection techniques is given and a more in-depth discussion of label-free optical detection techniques is presented.

Label-Free Optical Biosensors for Virus Detection and Characterization

Label-free optical biosensors have shown promise in rapid and sensitive detection of viruses. Recently, we have demonstrated a technique termed interferometric reflectance imaging sensor (IRIS) capable of detecting viral antigens and single viruses in a high-throughput, quantitative, and label-free fashion. In this paper, we briefly review the current label-free optical methods that have demonstrated virus detection through ensemble measurements of viral antigen and emerging techniques that are capable of detecting individual viruses captured by the sensor. We then present the principle of single nanoparticle detection using IRIS and show proof-of-principle results on specific detection and shape analysis of individual viruses captured on the IRIS platform.

Chromatic and spherical aberration correction for silicon aplanatic solid immersion lens for fault isolation and photon emission microscopy of integrated circuits

Current state-of-the-art in backside fault isolation and logic analysis utilizes solid immersion lens (SIL) imaging in the central configuration. An attractive advancement is the development and integration of an aplanatic SIL, which allows significant improvement in resolution, signal acquisition and isolation capabilities, especially for the 22 nm node and beyond. However, aplanatic SIL configurations introduce both chromatic and spherical aberrations. We have developed backing objective designs capable of correcting for chromatic aberrations allowing application in photon emission microscopy, as well as deformable mirror designs and experiments that eliminate spherical aberrations of aplanatic SILs to account for variations in substrate thickness and off-axis imaging.

Effect of vector asymmetry of radially polarized beams in solid immersion microscopy

We theoretically and experimentally investigate the effect of imperfect vector symmetry on radially polarized beams focused by an aplanatic solid immersion lens at a numerical aperture of 3.3. We experimentally achieve circularly symmetric focused spot with a full-width-half-maximum of ~λ0/5.7 at λ0 = 1,310 nm, free-space wavelength. The tight spatial confinement and overall circular symmetry of the focused radially polarized beam are found to be sensitive to perturbations of its cylindrical polarization symmetry. The addition of a liquid crystal based variable retarder to the optical path can effectively ensure the vector symmetry and achieve circularly symmetric focused spots at such high numerical aperture conditions.

Evanescent waves in high numerical aperture aplanatic solid immersion microscopy: Effects of forbidden light on subsurface imaging

The collection of light at very high numerical aperture allows detection of evanescent waves above the critical angle of total internal reflection in solid immersion lens microscopy. We investigate the effect of such evanescent modes, so-called forbidden light, on the far-field imaging properties of an aplanatic solid immersion microscope by developing a dyadic Greens function formalism in the context of subsurface semiconductor integrated circuit imaging. We demonstrate that the collection of forbidden light allows for sub-diffraction spatial resolution and substantial enhancement of photon collection efficiency albeit inducing wave-front discontinuities and aberrations.

Spherical aberration correction in aplanatic solid immersion lens imaging using a MEMS deformable mirror

Aplanatic solid immersion lens (SIL) microscopy is required to achieve the highest possible resolution for next generation silicon IC backside inspection and failure analysis. However, aplanatic SILs are very susceptible to spherical aberrations introduced by substrate thickness mismatch. We correct this aberration using a MEMS deformable mirror. Good agreement between theory and experiment is achieved and spot intensity increases by a factor of two to three are demonstrated.

Coherent light scattering from a buried dipole in a high-aperture optical system

We develop a theoretical formulation to calculate the absolute and differential transmission of a focused laser beam through a high-aperture optical system. The focused field interacts with a point dipole that is buried in a high-index material, and is situated at the Gaussian focus of the focusing and collection two-lens system. The derived expressions account for the vectorial nature of the focused electromagnetic field and the inhomogeneous focal region environment. The results obtained are in agreement with recent resonant light-scattering experiments where the buried emitter is an indium arsenide semiconductor quantum dot in gallium arsenide.

Widefield interferometric detection and size determination of dielectric nanoparticles

We propose an interferometric technique to detect and size low-index nanoparticles with radius smaller than 100nm. The method offers sensitive detection and identification of pathogens such as viruses based on the size information.

High-throughput size determination of nearly spherical gold nanoparticles

This paper demonstrates a wide-field interferometric imaging technique for determining the size of nearly spherical gold particles. Investigation of interferometric response as a function of polarization angle of illumination reveals the absolute dimensions and lateral orientation angle of the nanoparticles immobilized on a precisely designed reflective layered substrate. We demonstrate the sensitivity, precision and multiplexing capability of the method by studying a solution of gold nanoparticles with 45nm in diameter. The technique is promising for applications that require sensitive morphology characterization of nearly spherical nanoparticles.