Optical biosensors have emerged in the past decade as the most promising candidates for portable, highly-sensitive bioanalytical systems that can be employed for in-situ measurements. In this work, a miniaturized optoelectronic system for rapid, quantitative, label-free detection of harmful species in food is presented. The proposed system has four distinctive features that can render to a powerful tool for the next generation of Point-of-Need applications, namely it accommodates the light sources and ten interferometric biosensors on a single silicon chip of a less-than-40mm2 footprint, each sensor can be individually functionalized for a specific target analyte, the encapsulation can be performed at the wafer-scale, and finally it exploits a new operation principle, Broad-band Mach-Zehnder Interferometry to ameliorate its analytical capabilities. Multi-analyte evaluation schemes for the simultaneous detection of harmful contaminants, such as mycotoxins, allergens and pesticides, proved that the proposed system is capable of detecting within short time these substances at concentrations below the limits imposed by regulatory authorities, rendering it to a novel tool for the near-future food safety applications.
In this work, interferometric silicon chips with monolithically-integrated light-emitting devices coupled to co-integrated monomodal waveguides shaped as Young interferometers through mainstream silicon technology, are presented. Although the light sources are broad-band emitters, Young interferometry is possible through filtering. Chips with arrays of ten multiplexed interferometers have been employed for the label-free determination of pesticides in drinking water currently achieving detection limits in the ng/ml range.
The existing technological approaches employed in the realization of optical sensors still face two major challenges: the
inherent inability of most sensors to integrate the optical source in the transducer chip, and the need to specifically
design the optical transducer per application. We have introduced a unique Optoelectronic chip that consists of a series
of light emitting diodes (LEDs) coupled to silicon nitride waveguides allowing for multi-analyte detection. Each
optocoupler is structured as Broad-Band Mach-Zehnder Interferometer and has its own excitation source and can either
have its own detector or the entire array can share a common detector. The light emitting devices (LEDs) are silicon
avalanche diodes which when biased beyond their breakdown voltage emit in the VIS-NIR part of the spectrum. The
optoelectronic chip is fabricated by standard silicon technology allowing for potential mass production in silicon
foundries. The integrated nature of the optoelectronic chip and the ability to functionalize each transducer independently
allows for the development of miniaturized optical transducers tailored towards multi-analyte tests. The platform has
been successfully applied in bioassays and binding assays monitoring in a real-time and label-free format and is
currently being applied to ultra-sensitive food safety applications.
ZnO nanostructures were explored as templates for the development of topography-mediated neuronal cultures. Nanostructures of varying features were produced on 4” Si substrates via a rapid, facile and low-cost technique that allows the systematic investigation of nanotopographically-mediated formation of neuronal cultures. The developed ZnO-nanowire based templates were seeded with Neuro-2A mouse neuroblastoma cells and their viability over the course of 1 to 4 days was assessed. Our studies demonstrate that the ZnO-templates can support neuronal cell growth and proliferation suggesting that ZnO substrate can be used for the development of neuronal cell-based platform technologies.
Despite the advances in optical biosensors, the existing technological approaches still face two major challenges: the inherent inability of most sensors to integrate the optical source in the transducer chip, and the need to specifically design the optical transducer per application. In this work, the development of a radical optoelectronic platform is demonstrated based on a monolithic optocoupler array fabricated by standard Si-technology and suitable for multi-analyte detection. The platform has been specifically designed biochemical sensing. In the all-silicon array of transducers, each optocoupler has its own excitation source, while the entire array share a common detector. The light emitting devices (LEDs) are silicon avalanche diodes biased beyond their breakdown voltage and emit in the VIS-NIR part of the spectrum. The LEDs are coupled to individually functionalized optical transducers that converge to a single detector for multiplexed operation. The integrated nature of the basic biosensor scheme and the ability to functionalize each transducer independently allows for the development of miniaturized optical transducers tailored towards multi-analyte tests. The monolithic arrays can be used for a plethora of bio/chemical interactions becoming thus a versatile analytical tool. The platform has been successfully applied in bioassays and binding in a real-time and label-free format and is currently being applied to ultra-sensitive food safety applications.
Miniaturized bioanalytical devices find wide applications ranging from blood tests to environmental monitoring. Such
devices in the form of hand held personal laboratories can transform point-of-care monitoring provided miniaturization,
multianalyte detection and sensitivity issues are successfully resolved. Optical detection in biosensors is superior in
many respects to other types of sensing based on alternative signal transduction techniques, especially when both
sensitivity and label free detection is sought. The main drawback of optical biosensing transducers relates to the
unresolved manufacturability issues encountered when attempting monolithic integration of the light source. If the
mature silicon processing technology could be used to monolithically integrate optical components, including light
emitting devices, into complete photonic sensors, then the lab on a chip concept would materialize into a robust and
affordable way. Here, we describe and demonstrate a bioanalytical device consisting of a monolithic silicon optocoupler
properly engineered as a planar interferometric microchip. The optical microchip monolithically integrates silicon light
emitting diodes and detectors optically coupled through silicon nitride waveguides designed to form Mach-Zehnder
interferometers. Label free detection of proteins is demonstrated down to pM sensitivities.
ZnO nanostructures, especially in the form of dense arrays of nanorods or belts have the ability to efficiently convert
mechanical energy to electrical energy. One of the drawbacks though for the exploitation of nanorod technology for
commercial devices is the ability to make the electrical contacts to these nanostructured piezoelectric converting
elements. Although technologies have been developed that provide solutions for electrical contact issues, metal contact
on uniform thin films are much simpler, and can readily be implemented to commercial mass-produced applications. At
the same time it is known that high piezoelectric coefficients ZnO uniform films with columnar grains having their c-axis
perpendicular to the substrate are required.
In this work, we investigate the growth of uniform ZnO films, using a low temperature, low cost hydrothermal process
typically used for the fabrication of ZnO nanorods. Under appropriate conditions coalescence of the nanorods occur
resulting in uniform films with a columnar structure. The study focuses on understanding the role of the growth factors in
order to be able to fully control the proposed process. Moreover, the hydrothermal method is further exploited for the
fabrication of uniform ZnO nanostructures on patterned substrates with Au interdigitated electrodes (IDE) using standard
lithography as a proof-of-concept of the applicability of the method to standard microfabrication techniques. The
piezoelectric films with the IDEs are electrically characterized in order to assess the electrical properties of the grown
films. From this analysis, process conditions have been identified for the growth of uniform nanostructured ZnO films,
suitable for piezoelectric microgenerators.
A low-temperature hydrothermal process for the growth of ZnO nanostructures on patterned Si substrates was
investigated with the aim of their future exploitation as functional cores of nanopiezotronic applications. The study
focused on understanding the role of the growth factors in order to better control the suggested process and to introduce
it as a low-cost, repeatable and reliable method for large-scale ZnO nanorod production. The parameters that were
examined were: (a) the role of the substrate, and (b) the concentration of the metal precursor in conjunction with the
growth temperature and time.
Microelectromechanical systems (MEMS) have found several applications in various fields from homeland security to personalized health care. However, rendering MEMS into autonomous wireless systems operating in any given environment requires the integration of energy harvesters into the MEMS structures, ensuring thus the self-powering of the devices. In this work, we investigated the mechanical and magnetic properties of Samarium Cobalt (SmCo) thin films, with the goal to implement them into electromagnetic energy harvesters. The films were deposited by sputtering on suspended silicon cantilevers fabricated with a front-side micromachining process. The magnetic films, grown under various pressures and thermally annealed at several temperatures and ambient conditions, were studied in terms of their mechanical and magnetic properties. Depending on the fabrication parameters, the stresses that developed in the magnetic material, deposited on top of the cantilevers, are altered from compressive (downward deflection of the cantilevers) to tensile (upward deflection), indicating that it is possible to control not only the magnetic properties of the films, but also the mechanical properties of the complete structure. Our results suggest that SmCo magnetic films are suitable candidates for integration in suspended structures for the development of electromagnetic micro-generators.
We report on high output power from the quaternary AlGaInN multiple quantum well (MQW) ultraviolet light emitting diodes (UV LEDs) in the 340 nm and 280 nm wavelength range. The output power up to 1.5 mW from a 100 μm diameter device with bare-chip configuration was measured under room temperature cw operation. The internal quantum efficiency was estimated to be between 7 and 10%. In addition, the output power and external quantum efficiency for fully packaged 1x1mm2 large area device were as high as 54.6 mW and 1.45%, respectively, at the injection current of 200 A/cm2 under pulsed operation. The devices were incorporated into prototype system for fluorescence based bio-sensing. We also report the performance of 285 nm UV LEDs.
We have demonstrated hole injection through a tunnel junction embedded in the GaN-based light emitting diode structure. The tunnel junction consists of 30 nm GaN:Si++ and 15 nm InGaN:Mg++ grown on a GaN-InGaN quantum well heterostructure. The forward voltage of the light emitting diode, included the voltage drop across the reverse-biased tunnel junction, is 4.1 V at 50 Z/cm$_2), while that of a standard light emitting diode with a conventional contact structure is 3.5 V. The light output of the diode with the tunnel junction is comparable to that of the standard device. We then employed the tunnel junction in vertical cavity surface emitting laser structures and dual-wavelength light emitters. In the vertical cavity structure, a good lateral current spreading was accomplished, resulting in uniform emission pattern. The dual-wavelength light emitter has been operated as a three- terminal device with independent electrical control of each LEDs to a nsec time scale.
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