Selim Unlu

Screening of Excitons in Single, Suspended Carbon Nanotubes

Resonant Raman spectroscopy of single carbon nanotubes suspended across trenches displays red-shifts of up to 30 meV of the electronic transition energies as a function of the surrounding dielectric environment. We develop a simple scaling relationship between the exciton binding energy and the external dielectric function and thus quantify the effect of screening. Our results imply that the underlying particle interaction energies change by hundreds of meV.

InGaAs-based high-performance p-i-n photodiodes

We have designed, fabricated, and characterized high-speed and high-efficiency InGaAs-based p-i-n photodetectors with a resonant cavity enhanced structure. The devices were fabricated by a microwave-compatible process. By using a postprocess recess etch, we tuned the resonance wavelength from 1605 to 1558 nm while keeping the peak efficiencies above 60%. The maximum quantum efficiency was 66% at 1572 nm which was in good agreement with our theoretical calculations. The photodiode had a linear response up to 6-mW optical power, where we obtained 5-mA photocurrent at 3-V reverse bias. The photodetector had a temporal response of 16 ps at 7-V bias. After system response deconvolution, the 3-dB bandwidth of the device was 31 GHz, which corresponds to a bandwidth-efficiency product of 20 GHz.

Allergen microarrays on high-sensitivity silicon slides

We have recently introduced a silicon substrate for high-sensitivity microarrays, coated with a functional polymer named copoly(DMA-NAS-MAPS). The silicon dioxide thickness has been optimized to produce a fluorescence intensification due to the optical constructive interference between the incident and reflected lights of the fluorescent radiation. The polymeric coating efficiently suppresses aspecific interaction, making the low background a distinctive feature of these slides. Here, we used the new silicon microarray substrate for allergy diagnosis, in the detection of specific IgE in serum samples of subjects with sensitizations to inhalant allergens. We compared the performance of silicon versus glass substrates. Reproducibility data were measured. Moreover, receiver-operating characteristic (ROC) curves were plotted to discriminate between the allergy and no allergy status in 30 well-characterized serum samples. We found that reproducibility of the microarray on glass supports was not different from available data on allergen arrays, whereas the reproducibility on the silicon substrate was consistently better than on glass. Moreover, silicon significantly enhanced the performance of the allergen microarray as compared to glass in accurately identifying allergic patients spanning a wide range of specific IgE titers to the considered allergens.

High-speed GaAs-based resonant-cavity-enhanced 1.3 μm photodetector

We report GaAs-based high-speed, resonant-cavity-enhanced, Schottky barrier internal photoemission photodiodes operating at 1.3 μm. The devices were fabricated by using a microwave-compatible fabrication process. Resonance of the cavity was tuned to 1.3 μm and a nine-fold enhancement was achieved in quantum efficiency. The photodiode had an experimental setup limited temporal response of 16 ps, corresponding to a 3 dB bandwidth of 20 GHz.

Aberration compensation in aplanatic solid immersion lens microscopy

The imaging quality of an aplanatic SIL microscope is shown to be significantly degraded by aberrations, especially when the samples have thicknesses that are more than a few micrometers thicker or thinner than the design thickness. Aberration due to the sample thickness error is modeled and compared with measurements obtained in a high numerical aperture (NA ~3.5) microscope. A technique to recover near-ideal imaging quality by compensating aberrations using a MEMS deformable mirror is described and demonstrated.

Intra-cavity fiber laser technique for high accuracy birefringence measurement

When a device under test (DUT) with birefringence is placed within a laser cavity two distinct sets of orthogonally polarized longitudinal modes will result. If the output of the laser is sent through a 45(o) linear polarizer, polarization mode beating (PMB) between these two sets of longitudinal modes can be detected. We demonstrate the relation between PMB and the birefringence of the DUT and show that by tracking the PMB it provides a sensitive measurement of the birefringence of the device. We first examined the birefringence of a Newport PM fiber and then measured the birefringence of a 3M (Austin, TX) Chirped grating 1.0 m in length. For comparison, birefringence measurements were performed using a Hewlett-Packard Polarization Analyzer (HP 8509B).

Interferometric Reflectance Imaging Sensor for point-of-care viral identification

We show single virus detection using Interferometric Reflectance Imaging Sensor (IRIS) can be a sensitive and affective virus detector. Also we demonstrate how size and shape filtering affects sensitivity of the sensor.

Integrating microfluidic sample concentrator with Interferometric Reflectance Imaging Sensor for point-of-care viral identification

We integrated a portable, disposable, simple to fabricate, and highly effective polymeric microfluidic viral sample concentration device to the Interferometric Reflectance Imaging Sensor (IRIS) to increase infectious disease diagnostic speed and sensitivity at the point-of-care.

Multiplexed, rapid, point of care device to quantify allergen-specific IgE

Allergy is a disorder of the immune system characterized by a maladaptive immune response to harmless environmental antigens (“allergens”). Allergy affects nearly 40–50 million people in the US, with total estimated costs attributable to asthma care at

Widefield Subsurface Microscopy of Integrated Circuits

19.7B [1,2]. Phadia AB is the market leader in allergy in vitro diagnostics with the ImmunoCAP ISAC chip (not current FDA approved in the US). We have identified two specific shortcomings with this IVD technology. First, the ISAC “biochip is a solid substrate built from a glass plate” which reduces the fluorescence yield of the labels used in sensing, whereas significant signal enhancement is readily available by utilizing simple and inexpensive layered surfaces. The missed opportunity of increasing the signal by more than an order of magnitude results in requiring sophisticated fluorescent readers. Second, the measurements are not quantitative — the allergen spots are not calibrated and have very high variability in mass of spotted protein, which affects specific IgE capture and quantization. Thus, a need exists for a calibrated, sensitive allergy microarray platform that is combined with enhanced detection techniques for a rapid, point-of-care instrument.