In polymer coated planar Inter Digitated Electrodes (IDEs), the gas sensing sensitivity is much lower than the sensitivity of parallel plate capacitors. Here, we introduce a simple patterning step for the modification of the geometry of the dielectric substrate of the planar IDEs, and increase of the contribution of the sensitive layer to the output signal. The proposed methodology is investigated through simulation and verified by experimental data. Polymer coated IDEs with different dimensions of spatial wavelength were studied experimentally upon exposure to analytes of varying polarity. The sensing performance of the fabricated structures compare very well with theoretically estimated values obtained through finite element simulations. The maximum performance gain is also calculated by simulation demonstrating the potential of the technology.

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.

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.

Laboratory evaluation of gas sensing systems is usually performed under well-controlled experimental conditions. However, in real applications, environmental parameters, such as temperature and humidity, are likely to be unstable. In this work, the effect of temperature variations ranging from 0.5-3 degrees C, on the signal of a chemocapacitor sensor array, equilibrated at different levels of relative humidity is studied. Accurate recording of temperature concurrently to the capacitance signal of the sensors enabled us to develop a temperature (Delta T)-capacitance (Delta C) calibration curve for each sensor. The linear Delta C-Delta T relations were found to depend on the specific polymeric sensing layer, and were then used to demonstrate the importance of the said correction in Volatile Organic Compounds (VOCs) sensing in humid environment and under relatively unstable temperature conditions. Additionally, the sensors response under static and under dynamic headspace conditions was compared.

Arrays of monolithically integrated Mach-Zehnder interferometers were fabricated by standard silicon technology and applied to the label-free real-time monitoring of biomolecular interactions. Chips accommodating 10 MZIs were functionalized with recognition biomolecules and encapsulated in wafer scale. Detection is based on Frequency-Resolved Mach-Zehnder Interferometry, a new concept that takes advantage of the broad-band input spectrum by monitoring the changes for every input frequency. The sensitivity of the device in terms of refractive index changes (Δn) was calculated using isopropanol/water solutions. A detection limit of Δn = 4×10 -6 was calculated. The bioanalytical capabilities of the device there demonstrated through model binding assays (biotin/streptavidin) as well as the detection of total prostate specific antigen in serum samples using devices coated with antigen-specific monoclonal antibody. Detection limits at the pM range were determined.

A solid-state optical biosensor integrated with a single layer flexible blue Polymer Light Emitting Diode (PLED) as the light source was demonstrated and used for the detection of biomolecules labeled with two different fluorescent dyes. An anti-rabbit IgG antibody labeled with the fluorescent dyes, that was adsorbed on the opposite side of a polyethylene tetraphthalate (PET) flexible substrate, was excited by light emitted from the PLED. Light is then absorbed by the dye-labeled antibody resulting in a red shift of the polymer emission spectrum. Emission originating from the dye is also observed. The emission spectral shift and its efficiency depend primarily on the concentration of the biomolecule solution, the overlap between the emission spectra of the polymer and the absorption spectra of the dye and the PLED emission characteristics. Biomolecules immobilized onto distinct areas of a plastic substrate might then selectively be detected with high sensitivity after reacting with fluorescently labeled counterpart molecules.

Photochemically induced emission tuning (PIET) for the definition of different color emitting areas in a single conducting polymeric layer is demonstrated. The commercially available poly(9-vinylcarbazole) (PVK), well known as a hole transporting layer in OLEDs technology, was used. The three primary colors emitting areas in a single layer of PVK film were defined using a suitable green emitter 1-[4-(dimethylamino)phenyl]-6-phenylhexa-1,3,5,-triene (DMA-DPH) along with the red emitter (4-dimethylamino-4'-nitrostilbene) (DANS). The selected emitters were dispersed in the PVK films in the presence of a photoacid generator (PAG). Various onium salts were tested as photoacid generators in order to select those, which could cause effectivily the photoinduced protonation and emission tuning of the probes molecules. Through proton induced bleaching of the red emitter and proton induced spectral shift of the green one, the definition of all three primary color emitting areas was possible. In this way the unexposed areas of the film remain red, the areas exposed with the intermediate dose become green and the fully exposed areas emit blue color. Intermediate colors and white light can also be obtained.