120 research outputs found
Limit of detection comparison for surface wave biosensors
No full textBloch surface waves (BSW) propagating at the surface of truncated, one-dimensional crystals are valid candidates to improve sensors based on surface plasmon polaritons, usually referred to as surface plasmon resonance (SPR). The low losses introduced by the dielectric BSW stacks enable to achieve resonance widths much below the ones of SPR, thus proposing improved sensing results. A simplified, bi-linear model of the resonance intensity distribution is applied to estimate the effect of the resonance properties onto the measurement noise. This yields a limit of detection (LoD) that is used to optimize a BSW supporting thin film stack and to quantitatively compare SPR and BSW sensors. The results indicate that an order of magnitude reduction of the LoD is within reach when sufficient sampling of narrow BSW resonances is achieved. © 2014 SPIE
Sensitive label-free and fluorescence cancer biomarker detection using one dimensional photonic crystal biochips
No full textBiological and biochemical processes play a very important role in living organisms and their understanding is particularly important in medicine, biology and biotechnology. Optical biosensors hold great promise for solving challenging molecular recognition issues, such as the detection of biomolecules at very low concentration. In this framework, a direct measurement of the binding of analytes to a target molecule in biological samples is an essential step in diagnosis and in understanding how biomolecules interact under physiological conditions.
In this thesis, I contributed to the development of an optical platform that combines label-free and fluorescence detection modes. Such a platform makes use of one-dimensional photonic crystals (1DPC) sustaining Bloch surface waves (BSW) to detect relevant cancer biomarkers in body fluids.
BSWs are surface electromagnetic waves that propagate along the truncation interface between a 1DPC and an external medium (the analyte) and can be strongly confined with a significantly enhanced field at the surface. By exploiting such features, 1DPC sustaining BSW (BSW biochips) are used as optical transducers that convert refractive index changes and fluorescence emission at their surface into a measurable optical signal.
After discussing the results of the platform development, I report on the use I made of BSW biochips to detect clinically relevant concentrations of Angiopoietin 2 and ERBB2 in different biological matrices. The aim of such a research endeavour is clear: to reveal cancer by means of integrated optofluidic structures before cancer reveals itself. In the case of breast cancer, for example, it is a fact that ERBB2 is a pivotal biomarker and targetable oncogenic driver associated
with several different aggressive subtypes. To quantitate Angiopoietin 2 and soluble ERBB2, I developed and implemented specific sandwich detection assays in which the BSW biochips’ sensitive surface is tailored with monoclonal antibodies for highly specific biological recognition.
In a second step, a second antibody quantitatively detects the bound analytes. The strategy of the present approach takes advantage of the combination of both label-free and fluorescence techniques, making bio-recognition more robust and sensitive. In the fluorescence operation mode, the platform can attain the limit of detection 0.3 ng/mL (1.5 pM) for ERBB2 in cell lysates, which is the most complex biological matrix studied in the present work. Such a resolution meets the international guidelines and recommendations (15 ng/mL) for diagnostic ERBB2 assays that in the future may help to assign more precisely therapies counteracting cancer cell proliferation and metastatic spread
A nonlinear dynamics perspective on some aspects of towing operations relevant to safety and energy efficiency
No full textScheduled and emergency towing operations are carried out daily, both at sea and in restricted waters, as a means of transporting goods, aiding ships during berthing and casting-off or rescuing units in distress. Even in mild weather conditions, such activities can pose serious threats to the safety of the personnel and units involved and to the environment. This study investigates the dynamics of a tug-tow system, where towing is carried out by means of a single elastic towing line. A simplified model is used, in which the tug is modelled as a point-particle with a prescribed motion, while the dynamics of the towed object is modelled as a 3-DOF (surge/sway/yaw) nonlinear dynamical system. Equilibria of the system are analysed through a bifurcation analysis technique, supplemented by time-domain simulations, if/when necessary. An example application is reported for the case of towing of a barge-like hull, showing the effects of several parameters: ship speed, towline length, water depth and wind. The performed calculations confirm that, depending on the configuration parameters, multiple stable/unstable steady-state towing positions may exist. It is also clarified in this study that, in the absence of stable equilibria, the potentially dangerous oscillating phenomenon called “fishtailing” takes place
Design rules for combined label-free and fluorescence Bloch surface wave biosensors
No full textWe report on the fabrication and physical characterization of optical biosensors implementing simultaneous label-free and fluorescence detection and taking advantage of the excitation of Bloch surface waves at a photonic crystal’s truncation interface. Two types of purposely-designed one dimensional photonic crystals on molded organic substrates with micro-optics were fabricated. These feature either high or low finesse of the Bloch surface wave resonances and were tested on the same optical readout system. The experimental results show that designing biochips with a large resonance quality factor does not necessarily lead in the real case to an improvement of the biosensor performance. Conditions for optimal biochips’ design and operation of the complete bio-sensing platform are established
Multilayer coatings for Bloch surface wave optical biosensors
No full textSensors using surface plasmon resonance (SPR) are established as themethod of choice in label-free optical biosensing.
Their sensitivity for small refractive index changes at the surface originates from the enhanced evanescent
field at the surface of a thin metal layer. However, the small number of well-suited metals (Ag, Au) with
fixed optical constants limits a further refinement of the SPR performance in terms of dispersion and resonance
width. An alternative can be found in Bloch SurfaceWaves (BSW) sustained at specially designed dielectricmultilayer
stacks with low absorption losses. Due to the low losses an enormous narrowing of the resonance is obtained,
promising the reduction of the detection limit for such a label-free sensor. In order to deposit these
multilayers on plastic sensor chips, plasma ion assisted vacuum evaporation (PIAD) was applied as deposition
method. SiO2, TiO2, and Ta2O5 single layer properties were balanced in terms of absorption losses, stability in
aqueous environment and film stress. Dielectricmultilayer stacks could be designed in away, that resonance performance
is optimal and the total stack thickness as low as possible. Optimized Bloch stacks were successfully
coated on a large number of polymer chips. The application could be demonstrated by the detection of cancer biomarkers
using an analytical instrument that was developed with the BSWchips as core element
Roll motion of a ship with low metacentric height in bi-chromatic beam waves
No full textThis study investigates the roll motion of a ship with low metacentric height and significantly nonlinear restoring when the excitation is given by bi-chromatic and mono-chromatic beam waves. Experiments and simulations have been performed. Simulations are carried out by means of two different 1-DOF models, where roll restoring is modelled either using an absolute or a relative angle approach, and by means of a 6-DOF blended code. Large amplitude sub-harmonic rolling has been identified in experiments and by some of the numerical models. The capability of the mathematical models of reproducing the experimental behaviour is discussed
Probing losses of dielectric multilayers by means of Bloch surface waves
No full textWe exploit the excitation of electromagnetic surface waves on high-quality dielectric multilayers to measure the very low extinction coefficient of the structures, with a resolution down to 4.10(-7) and in a simple optical configuration. The effect of exposition to a rhodamine 6G solution in water and ethanol is also reported, including dye adsorption in the layers and bleaching upon resonant excitation. (C) 2013 Optical Society of Americ
Exploiting the phase properties of Bloch surface waves on photonic crystals for efficient optical sensing
No full textOptical sensors exploiting Bloch surface waves at the truncation edge of one dimensional photonic crystals are used here as a valid alternative to surface plasmon resonance operating in the Kretschmann-Raether configuration, and commonly adopted for label-free optical biosensing. In order to reduce the Bloch surface waves resonance width and increase the resolution it is desirable to work with one dimensional photonic crystals with as small losses as possible. However this makes that the resonances observed in a single polarization reflection scheme are shallow and difficult to track in a sensing experiment. Here we report on the practical implementation of an angularly resolved ellipsometric optical sensing scheme based on Bloch surface waves sustained by tantalia/silica multilayers. The angular resolution is obtained by a focused illumination at fixed wavelength and detecting the angular reflectance spectrum by means of a CMOS array detector. The experimental results, obtained by using one tantalia/silica multilayer with a defined structure, show that the limit of detection can be pushed below 2.1x10-7RIU/Hz1/2. © 2014 SPIE
Combined label-free/fluorescence platform based on Bloch surface waves biochips for cancer biomarker detection
No full textA biosensor platform based on Bloch Surface Waves and operating in angular interrogation mode is applied to the detection of a clinical biomarker (HER2-neu/ERBB2) related to breast cancer initiation/progression. Preparing regions for specific recognition of different proteins as well as a reference on the biochip enables to correct the signal for nonspecific effects. Additionally, label-free analysis and surface wave enhanced fluorescence detection can be applied and compared directly on the platform. Cell lysates with high and low expression levels of ERBB2 are analyzed. Comparing the signals of such ERBB2 positive and negative samples estimates the limit of detection at 1.7 ng/mL. This is well below the threshold of 15 ng/mL set by the FDA for clinically useful ERBB2 detection in human serum, demonstrating that 1DPC-based biochips are attractive candidates for breast cancer detection/monitoring
A novel technique based on Bloch surface waves sustained by one-dimensional photonic crystals to probe mass transport in a microfluidic channel
No full textWe report on the use of an optical sensing platform based on Bloch surface waves sustained by one-dimensional photonic crystals as a novel optical tool to probe in real time the fluid flow at a boundarywall of a microfluidic channel under dynamic conditions. Understanding how fluid flow interacts withwall surfaces is crucial for a broad range of biological processes and engineering applications, such as sur-face wave biosensing. The proposed platform provides nanometric resolution with respect to the distancefrom the boundary wall sensor’s surface. Here, for the first time, we report on the experimental inves-tigation on the temporal evolution of the interface between two fluids with different refractive indicesunder convective and diffusive conditions. The temporal evolution of the fluids interface in proximity ofthe wall is recovered. From the data analysis, the diffusion coefficients of glucose and glycerol in waterare measured and found in good agreement with the literature. Tuning the one-dimensional photoniccrystals geometry and the Bloch surface wave’s dispersion has the potential to probe the fluid flow in anextremely wide range of distances from the microfluidic channel wall
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