Microgreens have gained attention for their exceptional culinary characteristics and high nutritional value. The present study focused on a novel approach for investigating the easy extraction of plant samples and the utilization of immersible silicon photonic sensors to determine, on the spot, the nutrient content of microgreens and their optimum time of harvest. For the first time, it was examined how these novel sensors can capture time-shifting spectra caused by the molecules' dynamic adhesion onto the sensor surface. The experiment involved four types of microgreens (three types of basil and broccoli) grown in a do-it-yourself hydroponic installation. The sensors successfully distinguished between different plant types, showcasing their discriminative capabilities. To determine the optimum harvest time, this study compared the sensor data with results obtained through standard analytical methods. Specifically, the total phenolic content and antioxidant activity of two basil varieties were juxtaposed with the sensor data, and this study concluded that the ideal harvest time for basil microgreens was 14 days after planting. This finding highlights the potential of the immersible silicon photonic sensors for potentially replacing time-consuming analytical techniques. By concentrating on obtaining plant extracts, capturing time-shifting spectra, and assessing sensor reusability, this research paves the way for future advancements in urban farming.

Silicon photonic probes based on broad-band Mach-Zehnder interferometry are explored for the first time as directly immersible immunosensors alleviating the need for microfluidics and pumps. Each probe includes two U- shaped waveguides allowing light in- and out-coupling from the same chip side through a bifurcated fiber and a mechanical coupler. At the opposite chip side, two Mach-Zehnder interferometers (MZI) are located enabling real-time monitoring of binding reactions by immersion of this chip side into a sample. The sensing arm windows of the two MZIs have different length resulting in two distinct peaks in the Fourier domain, the phase shift of which can be monitored independently through Fast Fourier Transform of the output spectrum. The photonic probes analytical potential was demonstrated through detection of antibodies against SARS-CoV-2 in human serum samples. For this, one MZI was functionalized with the Receptor Binding Domain (RBD) of SARS-CoV-2 Spike 1 protein, and the other with bovine serum albumin to serve as reference. The biofunctionalized probes were immersed for 10 min in human serum sample and then for 5 min in goat anti-human IgG Fc specific antibody solution. Using a humanized rat antibody against SARS-CoV-2 RBD, a detection limit of 20 ng/mL was determined. Analysis of human serum samples indicated that the proposed sensor discriminated completely non- infected/non-vaccinated from vaccinated individuals, and the antibodies levels determined correlated well with those determined in the same samples by ELISA. These results demonstrated the potential of the proposed sensor to serve as an efficient tool for expeditious point-of-care testing

Despite the tremendous advances in micro- and nanoelectronics and the fast-pacing advances in photonic circuit designs, seamless monolithic integration of electronic and photonic components on single chips still remains elusive. In this work, a radically designed silicon-based chip that monolithically integrates in a 37 mm(2) footprint 10 interferometric optical sensors along with their respective optical sources, spectral analyzers, and photodetector arrays is presented. The chip is fabricated with mainstream CMOS-compatible fabrication techniques and employs optical devices operating in the visible/infrared spectrum and waveguides with a critical dimension of 1.0 mu m. In addition, it exploits the newly introduced detection principle of broad-band Mach Zehnder interferometry that surpasses the stringent requirement for external monochromatic sources and inherent limitations of traditional interferometry and introduces alternative designs of on-chip spectral analyzers and mode-filtering components, aspiring thus to become a novel lab-on-a-chip that can address the needs of next-generation analytical systems. Apart from the conceptual design, novel photonic features, fabrication steps, and out-of-the-box system development that circumvents the need for fluidic interfacing and employs only electrical interconnects, the present work tests the potential of the fully spectroscopic chip for analytical applications through real-time monitoring of immunochemical reactions and demonstrates limits of detection for antimouse IgG antibody and CRP of 60 and 8 pM, respectively.

A silicon microphotonic chip with ten monolithically integrated interferometers and an equal number of light sources is employed for the label-free and multiplexed detection of two proteins of the cytokine family. The chip implements broad-band Mach-Zehnder interferometry and is used for the detection of the IL-6 and IL-8 interleukins. The silicon transducer is made through mainstream silicon technology and integrates avalanche diode based white light LEDs and monomodal waveguides forming Mach-Zehnder interferometers. The light spectrum is modulated through the interferometer and the spectrally resolved interference fringes are monitored by a digital spectrometer. Biomolecular built-up on the sensing arm causes pattern shifts that are evaluated through Fourier Transform. The microsystem level set-up includes microfluidic components, direct contacting of the chip contact pads through spring loaded pins and alignment guides and a spectrometer. The dual polarization optics allows the simultaneous derivation of the TE and TM sensitivity plots and the calculation of the refractive indices of either protein. (C) 2017 Published by Elsevier B.V.

An interferometric detection principle, capable of label-free detection of biomolecules through the employment of broadband light and integrated optics, is presented and analyzed. Broadband Young interferometry (BB-YI) is demonstrated to outperform standard monochromatic Young interferometers through the emergence of two distinct packets of interference fringes, one for TE and one for TM polarization, on the imaging array resulting in the instantaneous and independent measurement of the phase signal for both polarizations over a wide range of wavelengths. This dual polarization aspect eliminates the need for additional external polarizers in order to de-convolute cover medium refractive index changes from biomolecular adlayer buildup and helps in bypassing the inherent limitation of phase ambiguity encountered by monochromatic YI. All these features, combined with the flexibility to employ cost-efficient broadband sources, render BB-YI as an alternative tool suitable for miniaturized bioanalytical systems. (C) 2017 Optical Society of America

An immunosensor for fast and accurate determination of C-reactive protein (CRP) in human serum samples based on an array of all-silicon broad-band Mach-Zehnder interferometers (BB-MZIs) is demonstrated. The detection was based on monitoring the spectral shifts during the binding of CRP on the antibody molecules that have been immobilized on the sensing arms of the BB-MZIs. By employing the reaction rate as the analytical signal the assay time was compressed to few minutes. The detection limit was 2.1 ng/mL, the quantification limit was 4.2 ng/mL and the linear dynamic range extended up to 100 ng/mL. The measurements performed in human serum samples with the developed immunosensor were characterized by high repeatability and accuracy as it was demonstrated by dilution linearity and recovery experiments. In addition, the concentration values determined were in excellent agreement with those determined for the same samples by a standard clinical laboratory method. The compact size of the chip makes the proposed immunosensor attractive for incorporation into miniaturized devices for the determination of clinical analytes at the point-of-need.

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.

An optical biosensor for label-free detection of ochratoxin A (OTA) in beer samples is presented. The biosensor consists of an array of ten Mach-Zehnder interferometers (MZIs) monolithically integrated along with their respective broad-band silicon light sources on the same Si chip (37mm2). The chip was transformed to biosensor by functionalizing the MZIs sensing arms with an OTA-ovalbumin conjugate. OTA determination was performed by pumping over the chip mixtures of calibrators or samples with anti-OTA antibody following a competitive immunoassay format. An external miniaturized spectrometer was employed to continuously record the transmission spectra of each interferometer. Spectral shifts obtained due to immunoreaction were transformed to phase shifts through Discrete Fourier Transform. The assay had a detection limit of 2.0ng/ml and a dynamic range 4.0-100ng/ml in beer samples, recoveries ranging from 90.6 to 116%, and intra- and inter-assay coefficients of variation of 9% and 14%, respectively. The results obtained with the sensor using OTA-spiked beer samples spiked were in good agreement with those obtained by an ELISA developed using the same antibody. The good analytical performance of the biosensor and the small size of the proposed chip provide for the development of a portable instrument for point-of-need determinations.

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.

The label-free detection of bovine milk in goat milk through a miniaturized optical biosensor is presented. The biosensor consists of ten planar silicon nitride waveguide Broad-Band Mach-Zehnder interferometers (BB-MZIs) monolithically integrated and self-aligned with their respective silicon LEDs on the same Si chip. The BB-MZIs were transformed to biosensing transducers by functionalizing their sensing arm with bovine k-casein. Measurements were performed by continuously recording the transmission spectra of each interferometer through an external spectrometer. The amount of bovine milk in goat milk was determined through a competitive immunoassay by passing over the sensor mixtures of anti-k-casein antibodies with the calibrators or the samples. The output spectra of each BB-MZI recorded during the reaction were subjected to Discrete Fourier Transform in order to convert the observed spectral shifts to phase shifts in the wavenumber domain. The method had a detection limit of 0.04 % (v/v) bovine milk in goat milk, dynamic range 0.1-1.0 % (v/v), recoveries 93-110 %, and intra- and inter-assay coefficients of variation less than 12 and 15 %, respectively. The proposed biosensor compared well in terms of analytical performance with a competitive ELISA developed using the same monoclonal antibodies. Nevertheless, the duration of the biosensor assay was 10 min whereas the ELISA required 2 h. Thus, the fast and sensitive determinations along with the small size of the sensor make it ideal for incorporation into portable devices for assessment of goat or ewe's milk adulteration with bovine milk at the point-of-need.

Protein detection and characterization based on Broad-band Mach-Zehnder Interferometry is analytically outlined and demonstrated through a monolithic silicon microphotonic transducer. Arrays of silicon light emitting diodes and monomodal silicon nitride waveguides forming Mach-Zehnder interferometers were integrated on a silicon chip. Broad-band light enters the interferometers and exits sinusoidally modulated with two distinct spectral frequencies characteristic of the two polarizations. Deconvolution in the Fourier transform domain makes possible the separation of the two polarizations and the simultaneous monitoring of the TE and the TM signals. The dual polarization analysis over a broad spectral band makes possible the refractive index calculation of the binding adlayers as well as the distinction of effective medium changes into cover medium or adlayer ones. At the same time, multi-analyte detection at concentrations in the pM range is demonstrated.

The increasing demand of enhanced sensitivity in the detection of various biochemical analytes paves the way for the development of a new generation of biosensors. Label free multianalyte immunosensing methods utilizing photonic probing have proven to result in better sensitivity and reliability than other types of biosensing methods. Here we described a monolithic silicon optoelectronic transducer capable of label-free and multianalyte determinations. The transducer includes ten Mach-Zehnder interferometers each of which is coupled to its own broad band light emitting device. The adlayers on the sensing arm cause spectral shifts detected at the output of the interferometers by coupling a portable spectrometer through an external fiber. Fourier transform techniques are employed to determine with a high degree of accuracy the shifts of the sinusoidal spectral outputs. The microphotonic chip was integrated with a microfluidic module and a model binding assay (mouse-antimouse) was run to demonstrate the operation.

Broad-band Mach-Zehnder interferometry is analytically described and experimentally demonstrated as an analytical tool capable of high accuracy refractive index measurements over a wide spectral range. Suitable photonic engineering of the interferometer sensing and reference waveguides result in sinusoidal TE and TM spectra with substantially different eigen-frequencies. This allows for the instantaneous deconvolution of multiplexed polarizations and enables large spectral shifts and noise reduction through filtering in the Fourier Transform domain. Due to enhanced sensitivity, optical systems can be designed that employ portable spectrum analyzers with nm range resolution without compromising the sensor analytical capability. Practical detection limits in the 10(-6)-10(-7) RIU range are achievable, including temperature effects. Finally, a proof of concept device is realized on a silicon microphotonic chip that monolithically integrates broad-band light sources and single mode silicon nitride waveguides. Refractive index detection limits rivaling that of ring resonators with externally coupled laser sources are demonstrated. Sensitivities of 20 μm/RIU and spectral shifts in the tens of a pm are obtained.

A complete Mach-Zehnder interferometer monolithically integrated on silicon is presented and employed as a refractive index and bio-chemical sensor. The device consists of broad-band light sources optically coupled to photodetectors through monomodal waveguides forming arrays of Mach-Zehnder interferometers, all components being monolithically integrated on silicon through mainstream silicon technology. The interferometer is photonically engineered in a way that the phase difference of light travelling through the sensing and reference arms is approximately wavelength independent. Consequently, upon effective medium changes, it becomes feasible even with a broad-band source to induce sinusoidal-type of detector photocurrents similar to the classical monochromatic counterparts. The device is completed with its fluidic and interconnect components so that on chip interferometric measurements can be performed. Examples of refractive index and protein sensing are presented to establish the potential of the proposed device for real-time in situ monitoring applications. This is the only silicon device that has achieved complete on-chip interferometry.

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.

An optical method is presented for in the situ monitoring of biomolecular films via reflection microscopy on patterned substrates. The method is based on measuring the reflection coefficient of a composite consisting of a substrate, a patterned optical layer, the thin film to be monitored and the cover medium. The optical layer is patterned so that an array of squares is surrounded by the bare substrate. The reflectance difference between the optical layer squares and the bare substrate is the observable, whose fractional changes reveal the thickness of the film through a simple analytical expression. The periodic image is recorded by a digital microscope, and through Fourier transform techniques, the normalized differential reflectance of the patterned optical composite is calculated as the contrast factor of two dimensional bit map. The method is demonstrated by measuring a protein binding assay inside a microfluidic module placed under a microscope.