Integrated optic/nanofluidic detection device with plasmonic readout

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references.Integrated lab-on-a-chip devices provide the promise of many benefits in many application areas. A low noise, high resolution, high sensitivity integrated optical microfluidic device would not only improve the capabilities of existing procedures but also enable new applications. This thesis presents an architecture and fabrication process for such a device. Previously, the possibilities for such integrated systems were limited by existing fabrication technologies. An integrated fabrication process including glass nanofluidics, diffused waveguides and metal structures was developed. To enable this process a voltage-assisted polymer bond procedure was developed. This bond process enables high strength, robust, optically clear, low temperature bonding of glass - a capability that was not possible before. Bond strength was compared with a glass-to-glass anodic type bond using various materials and a polymer bond using two polymers: Cytop and PMMA. Bond strength was far superior to standard polymer bonding procedures. Design considerations to minimize background noise are presented, analyzed and implemented. Using Cytop as an index-matched polymer layer reduces scattered light in the device. Plasmonic devices driven via evanescent fields were designed, simulated, fabricated, and tested in isolation as well as in the integrated system. A sample device was made to demonstrate applicability of this process to direct linear analysis of DNA. The device was shown to provide enhanced and confined electromagnetic excitation as well as the capability to excite submicron particles. A demonstrated excitation spot of 200nm is the best we have seen in this type of device. Further work is suggested that can improve this resolution further.by Jonathan S. Varsanik.Ph.D

Development of nanostencil lithography and its applications for plasmonics and vibrational biospectroscopy

Thesis (Ph.D.)--Boston UniversityDevelopment of low cost nanolithography tools for precisely creating a variety of nanostructure shapes and arrangements in a high-throughput fashion is crucial for next generation biophotonic technologies. Although existing lithography techniques offer tremendous design flexibility, they have major drawbacks such as low-throughput and fabrication complexity. In addition the demand for the systematic fabrication of sub-100 nm structures on flexible, stretchable, non-planar nanoelectronic/photonic systems and multi-functional materials has fueled the research for innovative fabrication methods in recent years. This thesis research investigates a novel lithography approach for fabrication of engineered plasmonic nanostructures and metamaterials operating at visible and infrared wavelengths: The technique is called Nanostencil Lithography (NSL) and relies on direct deposition of materials through nanoapertures on a stencil. NSL enables high throughput fabrication of engineered antenna arrays with optical qualities similar to the ones fabricated by standard electron beam lithography. Moreover, nanostencils can be reused multiple times to fabricate series of plasmonic nanoantenna arrays with identical optical responses enabling high throughput manufacturing. Using nanostencils, very precise nanostructures could be fabricated with 10 nm accuracy. Furthermore, this technique has flexibility and resolution to create complex plasmonic nanostructure arrays on the substrates that are difficult to work with e-beam and ion beam lithography tools. Combining plasmonics with polymeric materials, biocompatible surfaces or curvilinear and non-planar objects enable unique optical applications since they can preserve normal device operation under large strain. In this work, mechanically tunable flexible optical materials and spectroscopy probes integrated on fiber surfaces that could be used for a wide range of applications are demonstrated. Finally, the first application of NSL fabricated low cost infrared nanoantenna arrays for plasmonically enhanced vibrational biospectroscopy is presented. Detection of immunologically important protein monolayers with thickness as small as 3 nm, and antibody assays are demonstrated using nanoantenna arrays fabricated with reusable nanostencils. The results presented indicate that nanostencillithography is a promising method for reducing the nano manufacturing cost while enhancing the performance of biospectroscopy tools for biology and medicine. As a single step and low cost nanofabrication technique, NSL could facilitate the manufacturing of biophotonic technologies for real-world applications

Microfluidics and Nanofluidics Handbook

The Microfluidics and Nanofluidics Handbook: Two-Volume Set comprehensively captures the cross-disciplinary breadth of the fields of micro- and nanofluidics, which encompass the biological sciences, chemistry, physics and engineering applications. To fill the knowledge gap between engineering and the basic sciences, the editors pulled together key individuals, well known in their respective areas, to author chapters that help graduate students, scientists, and practicing engineers understand the overall area of microfluidics and nanofluidics. Topics covered include Finite Volume Method for Numerical Simulation Lattice Boltzmann Method and Its Applications in Microfluidics Microparticle and Nanoparticle Manipulation Methane Solubility Enhancement in Water Confined to Nanoscale Pores Volume Two: Fabrication, Implementation, and Applications focuses on topics related to experimental and numerical methods. It also covers fabrication and applications in a variety of areas, from aerospace to biological systems. Reflecting the inherent nature of microfluidics and nanofluidics, the book includes as much interdisciplinary knowledge as possible. It provides the fundamental science background for newcomers and advanced techniques and concepts for experienced researchers and professionals

Excitation of resonant plasmonic cavities by integrated waveguides for sensing applications

Optical sensors represent a large growing market which is nowadays focusing onto advancement in mobile technology. Innovations in the field of optical sensors are mostly driven by the technological advancements in the domain of micro & nanofabrication. One key to the miniaturization of optical sensors is their integration onto small chips having their own light sources and detectors. This thesis shows two separate applications of integrated optical sensors which benefit from the implementation of optical nano-structures. A first study investigates a biosensor based on a plasmonic slot waveguide cavity for the detection of changes in refractive index in femto-liter volumes. By integrating the biosensor onto a silicon-on-insulator platform, we could confine the light excitation of the cavity into a single-mode silicon strip waveguide. In a first step realized by simulation, we showed the efficient coupling of the fundamental quasi-transverse electric mode of the waveguide to the plasmonic slot waveguide cavity. We showed that the strong light confinement into the slot is an intrinsic property of the plasmonic slot waveguide which is based on the excitation of a guided wave at a metal-insulator-metal interface. We investigated the surface sensitivity of this biosensor which revealed its potential to detect single-molecules at high concentrations. Moreover, we reported a high bulk sensitivity of up to 600nm per refractive index units. In a second step, we developed a multi-step process based on electron beam lithography to fabricate the sensor. In a third step, we characterized the propagation properties of the fabricated waveguides. Finally, we measured the transmission properties of the integrated sensor has well as the far-field scattering of the plasmonic cavity. A second study focused on a new architecture of a standing-wave integrated Fourier transform spectrometer. This type of spectrometer uses nano-samplers (metallic nano-structures) to probe the intensity of a standing wave generated inside a single-mode waveguide terminated by a mirror. To enhance the well known bandwidth limitation of this type of spectrometer, we implemented a scanning mirror enabling the sub-sampling of the interferogram between each fixed nano-sampler. We fabricated a chip containing a 1D array of low delta n single-mode waveguides made out of epoxy-based "EpoCore" polymer. Equidistant metallic nano-samplers were patterned on top of the waveguides thanks to electron beam lithography. Micro-lenses were fabricated, aligned and glued to the facet of the chip to enable the free space coupling of the waveguides. We implemented a mechanical setup which included a closed-loop piezo actuated mirror to induce an additional phase shift to the interferogram. The realization of an optical setup taking care of the readout of the interferogram showed a 2D multiplexing potential of the spectrometer by realizing the simultaneous detection of independent waveguides. We also investigated the calibration procedures to overcome the fabrication uncertainties by an adapted post-processing step

Plasmonic Waveguide Lithography for Patterning Nanostructures with High Aspect-Ratio and Large-Area Uniformity

The rapid development of the semiconductor industry in the past decades has driven advances in nano-manufacturing technologies towards higher resolution, higher throughput, better large-area uniformity, and lower manufacturing cost. Along with these advancements, as the size of the devices approaches tens of nanometers, challenges in patterning technology due to limitations in physics, equipment and cost have quickly arisen. To solve these problems, unconventional lithography systems have attracted considerable interest as promising candidates to overcome the diffraction limit. One recently evolved technology, plasmonic lithography, can generate subwavelength features utilizing surface plasmon polaritons (SPPs). Evanescent waves generated by the subwavelength features can be transmitted to the photoresist (PR) using plasmonic materials. Another approach of plasmonic lithography involves the use of hyperbolic metamaterial (HMM) structures, which have been studied intensively because of their unique electromagnetic properties. Specifically, epsilon near zero (ENZ) HMMs offer the potential to produce extremely small features due to their high optical anisotropy. Despite the advancements in plasmonic lithography, several key issues impede progress towards more practical application, which includes shallow pattern depth (due to the evanescent nature of SPPs), non-uniformity over a large area (due to the interference of multiple diffraction orders) and high sensitivity of the roughness on the films and defects on the mask. The light intensity in the PR is very weak which results in an extremely long exposure time. To this end, this dissertation is dedicated to plasmonic lithography systems based on SPP waveguides and ENZ HMMs for patterning nanostructures with high aspect-ratio and large-area uniformity. New schemes are exploited in this thesis to address these challenges. Lithography systems based on a specially designed waveguide and an ENZ HMM are demonstrated. By employing the spatial filtering properties of the waveguide and the ENZ HMM, the period, linewidth and height of the patterns can be well controlled according to various design purposes. Periodic structures were achieved in both systems with a half-pitch of approximately 50 ~ 60 nm, which is 1/6 of the exposure wavelength of 405 nm. The thickness of the PR layer is around 100 ~ 250 nm, which gives an aspect-ratio higher than 2:1. The subwavelength patterns are uniform in cm2 areas. In addition to the design principle, various numerical simulations, fabrication conditions and corresponding results are discussed. The design principle can be generalized to other materials, structures and wavelengths. The real-world performance of the lithography system considering non-idealities such as line edge roughness and single point defect is analyzed. Comparisons between the plasmonic systems based on different design rules are also carried out, and the advantages of the spatial frequency selection principle is verified. The plasmonic waveguide lithography systems developed in this dissertation provide a technique to make deep subwavelength features with high aspect-ratio, large-area uniformity, high light intensity distribution, and low line-edge-roughness for practical applications. Compared with the previously reported results, the performance of plasmonic lithography is drastically improved. A plasmonic roller system combining the photo-roller system and plasmonic lithography is also developed. This plasmonic roller system can support a continuous patterning with a high throughput for cost sensitive applications. Several potential applications of the plasmonic materials including near field spin Hall effects and a particle based Lidar design are explored. Other advances towards plasmonic functional devices including silicon (Si) nanowire (NW) arrays, light-thermal converters and plasmonic lasers are also reported.PHDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144126/1/sxichen_1.pd

Design, fabrication and characterization of resonant waveguide grating based optical biosensors

The absence of rapid, low cost and highly sensitive biodetection platform has hindered the implementation of next generation cheap and early stage clinical or home based point-of-care diagnostics. Label-free optical biosensing with high sensitivity, throughput, compactness, and low cost, plays an important role to resolve these diagnostic challenges and pushes the detection limit down to single molecule. Optical nanostructures, specifically the resonant waveguide grating (RWG) and nano-ribbon cavity based biodetection are promising in this context. The main element of this dissertation is design, fabrication and characterization of RWG sensors for different spectral regions (e.g. visible, near infrared) for use in label-free optical biosensing and also to explore different RWG parameters to maximize sensitivity and increase detection accuracy. Design and fabrication of the waveguide embedded resonant nano-cavity are also studied. Multi-parametric analyses were done using customized optical simulator to understand the operational principle of these sensors and more important the relationship between the physical design parameters and sensor sensitivities. Silicon nitride (SixNy) is a useful waveguide material because of its wide transparency across the whole infrared, visible and part of UV spectrum, and comparatively higher refractive index than glass substrate. SixNy based RWGs on glass substrate are designed and fabricated applying both electron beam lithography and low cost nano-imprint lithography techniques. A Chromium hard mask aided nano-fabrication technique is developed for making very high aspect ratio optical nano-structure on glass substrate. An aspect ratio of 10 for very narrow (~60 nm wide) grating lines is achieved which is the highest presented so far. The fabricated RWG sensors are characterized for both bulk (183.3 nm/RIU) and surface sensitivity (0.21nm/nm-layer), and then used for successful detection of Immunoglobulin-G (IgG) antibodies and antigen (~1μg/ml) both in buffer and serum. Widely used optical biosensors like surface plasmon resonance and optical microcavities are limited in the separation of bulk response from the surface binding events which is crucial for ultralow biosensing application with thermal or other perturbations. A RWG based dual resonance approach is proposed and verified by controlled experiments for separating the response of bulk and surface sensitivity. The dual resonance approach gives sensitivity ratio of 9.4 whereas the competitive polarization based approach can offer only 2.5. The improved performance of the dual resonance approach would help reducing probability of false reading in precise bio-assay experiments where thermal variations are probable like portable diagnostics

Multispectral plasmon enhanced quantum dots in a well infrared photodetectors

Infrared detectors in 3-5 μm and 8-12 μm regions are extensively used for applications in remote sensing, target detection and medical diagnostics. Detectors using intersubband transitions in the quantum dots in a well (DWELL) system for infrared detection have gained prominence recently, owing to their ability to detect normally incident light, bicolor detection and use of mature III-V technology. In this dissertation, two aspects of DWELL detectors that make them suitable for third generation infrared systems are discussed: 1) High temperature operation, 2) Multispectral detection. There are two parts to this dissertation. In the first part, an alternate structure with an improved operating temperature and thicker active region is presented. Traditionally, DWELL detectors use InAs quantum dots embedded in In0.15Ga0.85As wells with GaAs barriers. Intersubband transitions in the conduction band of this system result in infrared detection. InAs quantum dots are grown using self assembly on a GaAs substrate for this system. The strain of the quantum dots and the In0.15Ga0.85As well limits the thickness of the active region. An improved design that minimizes the strain in growth of DWELL active region is discussed. By minimizing the amount of In0.15Ga0.85As in the quantum well, a lower strain per DWELL active region stack is achieved. This design consists of InAs dots in In0.15Ga0.85As/GaAs wells, forming dots-in-a-double-well (DDWELL) is presented. Optimization using PL and AFM is discussed. Detectors fabricated using DDWELL design show an operating temperature of 140 K and a background limited performance at 77 K. A peak detectivity of 6.7x1010 cm.Hz/W was observed for a wavelength of 8.7 μm. In the second part of this dissertation, multispectral and polarization detectors using DWELL absorbers are discussed. Integration of a subwavelength metallic pattern with the detector results in coupling of surface plasmons excited at the metal- semiconductor interface with DWELL active regions. Simulations indicate the presence of several modes of absorption, which can be tuned by changing the pitch of the pattern. Enhancement of absorption is predicted for the detector. Experimental demonstration show spectral tuning in MWIR and LWIR regions and a peak absorption enhancement of 4.9x. By breaking the symmetry of the fabricated pattern, we can extract a polarization dependent response, as shown from device measurements. The technique used is detector agnostic, simple and can easily be transferred to focal plane arrays (FPA). Integrating plasmonic structures on detectors using low noise DDWELL active regions can provide a higher operating temperature and high absorption. The origin of resonant peaks in multispectral DWELL detectors is examined. Use of surface patterns that selectively excite different types of modes, with absorbers of different thicknesses, show the presence of enhancement mechanisms in these devices. A 2.2x enhancement is measured from waveguide modes and 4.9x enhancement is observed from plasmon modes. Finally, a pathway of integration with FPA and integration with other infrared technologies is discussed

Design, Fabrication, and Testing of a Chitosan Based Optical Biosensor

This work presents the design, fabrication, and testing of an original concept for an optical biosensor device intended for use in a microfluidic network. The device uses planar waveguides intersecting a microfludic channel with biofunctionalized patterned sidewalls to detect biomolecules via fluorescent labeling. The optical-biological interface is provided through chitosan, a natural biopolymer. Chitosan is electrodepositable, and this material platform was developed to enable spatially selective and temporally selective assembly of biospecies in the sensor using electrical signals. The unique fabrication process flow integrates waveguides and microfluidic channels which are fabricated in a single step with a thick polymer layer on a Pyrex substrate. Key to the success of the device was the development of a process to pattern indium tin oxide on the sidewalls of deep (130 um) fluid channels. The device was tested in several modes of operation and the proof of concept was shown

Silicon Neural Probes for Stimulation of Neurons and the Excitation and Detection of Proteins in the Brain

This thesis describes the development of a number of novel microfabricated neural probes for a variety of specific neuroscience applications. These devices rely on single mode waveguides and grating couplers constructed from silicon nitride thin films, which allows the use of planar lightwave circuits to create advanced device geometries and functions. These probes utilize array waveguide gratings to select an individual emitter from a large array of emitters using the wavelength of incoming light, allowing for spatial multiplexing of optical stimulation. These devices were tested in the laboratory and in living tissue to verify their efficacy. This technology was then modified to create steerable beam forming for stimulation of neurons using optical phase arrays. This technology was also tested for use in fluoresence lifetime imaging microscopy and the first application of pulsed light through the photonic circuits. Finally, this technology was again modified to create laminar illumination patterns for light sheet fluorescence microscopy applications. These devices were further improved by adding embedded microfluidics to the probes. The process of creating embedded microfluidic channels by the dig and seal method is described in detail, including modifications to the procedure that were added to address potential pitfalls in the fabrication process. Next, two projects which combine microfluidics with the optical devices described in the previous chapter are detailed. One project involves combining the use of optical emitters with microfluidic injections containing caged neurotransmitters to stimulate neurons is described. The other project involves microfluidic sampling of the extracellular space for neuropeptides which are detected using ring resonator biosensors. The sensitivity of these biosensors was analyzed in detail, determining both the physical limit of detection and the effect of biological noise due to non-specific binding on the sensors