Arif E. Cetin

Seeing protein monolayers with naked eye through plasmonic Fano resonances

We introduce an ultrasensitive label-free detection technique based on asymmetric Fano resonances in plasmonic nanoholes with far reaching implications for point-of-care diagnostics. By exploiting extraordinary light transmission phenomena through high-quality factor (Qsolution ∼ 200) subradiant dark modes, we experimentally demonstrate record high figures of merits (FOMs as high as 162) for intrinsic detection limits surpassing that of the gold standard prism coupled surface-plasmon sensors (Kretschmann configuration). Our experimental record high sensitivities are attributed to the nearly complete suppression of the radiative losses that are made possible by the high structural quality of the fabricated devices as well as the subradiant nature of the resonances. Steep dispersion of the plasmonic Fano resonance profiles in high-quality plasmonic sensors exhibit dramatic light intensity changes to the slightest perturbations within their local environment. As a spectacular demonstration of the extraordinary sensitivity and the quality of the fabricated biosensors, we show direct detection of a single monolayer of biomolecules with naked eye using these Fano resonances and the associated Wood’s anomalies. To fabricate high optical-quality sensors, we introduce a high-throughput lift-off free evaporation fabrication technique with extremely uniform and precisely controlled nanofeatures over large areas, leading to resonance line-widths comparable to that of the ideally uniform structures as confirmed by our time-domain simulations. The demonstrated label-free sensing platform offers unique opportunities for point-of-care diagnostics in resource poor settings by eliminating the need for fluorescent labeling and optical detection instrumentation (camera, spectrometer, etc.) as well as mechanical and light isolation.

Fano Resonant Ring/Disk Plasmonic Nanocavities on Conducting Substrates for Advanced Biosensing

By introducing a conducting metal layer underneath a Fano resonant asymmetric ring/disk plasmonic nanocavity system, we demonstrate that electromagnetic fields can be strongly enhanced. These large electromagnetic fields extending deep into the medium are highly accessible and increase the interaction volume of analytes and optical fields. As a result, we demonstrate high refractive index sensitivities as large as 648 nm/RIU. By exciting Fano resonances with much sharper spectral features, as narrow as 9 nm, we experimentally show high figure of merits as large as 72 and reliable detection of protein mono- and bilayers. Furthermore, the conducting substrate enables strong interaction between fundamental and higher order modes of the system by minor structural asymmetries. This is very advantageous for experimental realization of systems supporting resonances with well-defined Fano-like line shape without requiring challenging fabrication resolution. Exploiting conducting metallic substrates and the associated propagating surface plasmons at their interface could be extended to other Fano resonant cavity geometries for improved biosensing performance.

Lensfree optofluidic plasmonic sensor for real-time and label-free monitoring of molecular binding events over a wide field-of-view

We demonstrate a high-throughput biosensing device that utilizes microfluidics based plasmonic microarrays incorporated with dual-color on-chip imaging toward real-time and label-free monitoring of biomolecular interactions over a wide field-of-view of >20 mm2. Weighing 40 grams with 8.8 cm in height, this biosensor utilizes an opto-electronic imager chip to record the diffraction patterns of plasmonic nanoapertures embedded within microfluidic channels, enabling real-time analyte exchange. This plasmonic chip is simultaneously illuminated by two different light-emitting-diodes that are spectrally located at the right and left sides of the plasmonic resonance mode, yielding two different diffraction patterns for each nanoaperture array. Refractive index changes of the medium surrounding the near-field of the nanostructures, e.g., due to molecular binding events, induce a frequency shift in the plasmonic modes of the nanoaperture array, causing a signal enhancement in one of the diffraction patterns while suppressing the other. Based on ratiometric analysis of these diffraction images acquired at the detector-array, we demonstrate the proof-of-concept of this biosensor by monitoring in real-time biomolecular interactions of protein A/G with immunoglobulin G (IgG) antibody. For high-throughput on-chip fabrication of these biosensors, we also introduce a deep ultra-violet lithography technique to simultaneously pattern thousands of plasmonic arrays in a cost-effective manner.

Monopole antenna arrays for optical trapping, spectroscopy, and sensing

We introduce a nanoplasmonic platform merging multiple modalities for optical trapping, nanospectroscopy, and biosensing applications. Our platform is based on surface plasmon polariton driven monopole antenna arrays combining complementary strengths of localized and extended surface plasmons. Tailoring of spectrally narrow resonances lead to large index sensitivities (S∼675 nm/RIU) with record high figure of merits (FOM∼112.5). These monopole antennas supporting strong light localization with easily accessible near-field enhanced hotspots are suitable for vibrational nanospectroscopy and optical trapping. Strong optical forces (350 pN/W/μm2) are shown at these hotspots enabling directional control with incident light polarization.

Plasmon induced transparency in cascaded π-shaped metamaterials

We experimentally and numerically demonstrate a planar metamaterial consisting of two asymmetrically positioned π-structures in a single unit that exhibits plasmonic analogue of electromagnetically induced transparency (EIT). Through the coupling of the constituent nanorod elements, the proposed structure enables fine spectral tuning of the EIT-like behavior and controlling the location of near field enhancement. Originated from the asymmetric cascaded π-structures, we introduce a more compact system which possesses the EIT-like characteristics and as well as much smaller mode volumes. Due to these properties, the proposed metamaterials can be utilized for a wide range of applications including bio-chemical sensors, optical filters and modulators and enhancement of non-linear processes.

Plasmonic Nanohole Arrays on Hybrid Substrate For Highly Sensitive Label-Free Biosensing

A biosensor device including a metal layer, a transparent substrate layer, and a dielectric layer, wherein the metal layer includes a plurality of sub-wavelength apertures, and wherein the dielectric layer is located between the metal layer and the transparent substrate layer to form a spectrally isolated and well-defined optical transmission resonance through the extraordinary optical transmission (EOT) phenomenon.

Multi-resonant metamaterials based on UT-shaped nano-aperture antennas

We demonstrate a compact multi-resonant metamaterial structure based on integrated U- and T-shaped nano-aperture antennas. We investigate the physical origin of the multi-resonant behavior and determine the parameter dependence of the nano-aperture antennas both experimentally and numerically. We also show enhanced field distribution in the apertures at the corresponding resonance wavelengths. Both multi-spectral response and enhanced near field distributions can open up exciting new opportunities in applications ranging from subwavelength optics and optoelectronics to chemical and biosensing.

Nanoparticle-Based Metamaterials as Multiband Plasmonic Resonator Antennas

Plasmonic metamaterials based on metal-dielectric nanostructures exhibit unique optical properties such as high near-field enhancement, negative refractive indexing, and optical cloaking. In this paper, we present a plasmonic multiband metamaterial based on UT shaped nanoparticles. In order to understand the multispectral response, we analyze the near-field distributions at the corresponding resonance frequencies. In addition, we both numerically and experimentally, show the dependence of the spectral response on the geometrical parameters of the structure. By embedding the system in a dielectric cladding medium, we show strong sensitivities of the resonant behavior to the refractive index and thickness of the dielectric load. Due to its tunable multiband spectral characteristics, the proposed metamaterial antenna can be used for wide range of applications, such as wavelength-tunable active filters, optical modulators, ultrafast switching devices, and biosensing.

Actively transporting virus like analytes with optofluidics for rapid and ultrasensitive biodetection

Effective analyte delivery is essential to achieve rapid and sensitive biodetection systems. In this article, we present an actively controlled fluidic system integrated with a suspended plasmonic nanohole sensor to achieve superior analyte delivery efficiency and ultrafast sensor response, as compared to conventional fluidic systems. 70 nm sized virus like analyte solution is used to experimentally demonstrate the system performance improvements. Sensor response time is reduced by one order of magnitude as compared to the conventional methods. A seven orders of magnitude dynamic concentration range from 10(3) to 10(9) particles mL(-1) is quantified, corresponding to a concentration window relevant to clinical diagnosis and drug screening. Our non-destructive detection system, by enabling efficient analyte delivery, fast sensing response and minimal sample volume, opens up opportunities for sensitive, rapid and real-time virus detection in infectious disease control and point-of-care applications.

Field-effect active plasmonics for ultracompact electro-optic switching

Merging of electronics and photonics at subwavelength dimensions could potentially allow development of ultracompact electro-optic modulators and active optical interconnects. Here, we introduce a field-effect active plasmonic modulator where the metallic ring serves as both a photonic resonator and a field electrode. By exploiting the simultaneous electronic and photonic functionalities of our plasmonic device, we show devices offering significantly improved modulation depths (as high as ∼10.85 dB) compared to active dielectric micro-ring resonators. Device concepts introduced in this work are applicable in realization of various integrated components and could play an important role in development of active plasmonic circuits.