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.
Label-free optical sensors are considered ideal for biomedical analysis since they provide the advantages of multiplex
and real-time detection. They still suffer; however, from lower sensitivity and/or more sophisticated equipment as
compared to indirect detection methods. Here, we propose a label-free sensor based on White Light Reflectance
Spectroscopy that overcomes the limitation of high cost and low detection sensitivity. The optical setup consists of a
VIS-NIR light source, a spectrometer and a reflection probe. The sensor is Si with 1-μm thick thermal SiO2 and
functionalized with antibodies. The incident light is directed vertically to sensor surface and the reflected interference
spectrum is recorded through the spectrometer. The evolution of the biomolecular reactions are monitored in real-time
by monitoring the shifts in the interference spectrum. Up to seven different reactions sites have been created onto the
same sensing surface allowing for multi-analyte determinations. The analytical capabilities of the proposed sensor were
demonstrated through the development of a sensitive immunoassay for the detection of C-Reactive Protein (CRP) in
human serum samples. CRP, a biomarker related to acute inflammatory incidents, it has attracted particular interest as a
marker of inflammation associated with cardiovascular diseases. The lowest CRP concentration detected was 10 ng/mL,
and the dynamic range of the assay was extended up to 500 ng/mL. Regeneration of antibody coated sensing areas for up
to 20 times without loss of immobilized antibody reactivity is also presented. In conclusion, the proposed sensing system
is characterized by low cost, high assay sensitivity and, reliability.
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.
Cell behavior (i.e. attachment, proliferation, etc.) on nanostructured surfaces is currently a hot topic throughout the scientific community. However, studies often show diverging results due to differences in cells, local surface chemistry, and nanotopography fabrication methods. In this study, we use Oxygen plasma etching to both randomly nanotexture a PMMA surface and change its surface chemistry. We find that 3T3 cells behave quite differently on flat PMMA surfaces as compared to nanotextured ones, showing an on-off attachment behavior. Work is under progress to exploit this effect allowing selective cell capturing, and creation of cell arrays in adjacent plasma-nanotextured/smooth areas using a stencil mask during etching.
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.
A new class of miniaturized monolithic silicon optoelectronic transducers properly functionalized to biosensors is outlined. The devices are based on biofunctionalized optocoupler arrays made on silicon by employing mainstream silicon integrated circuit technology. The optocouplers consist of silicon avalanche diodes operating as light emitting devices self aligned to thin silicon nitride waveguides and silicon detectors. Bioanalytical results that demonstrate the efficiency of the device are provided and include protein and DNA detection. Label free determinations are also demonstrated. The optical microdevices are suitable for multianalyte portable bioanalytical microsystems and present unique advantages due to their monolithic optical detection and small size.
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