In the last decade, among the various cerebral ischemia biomarkers, microRNAs (miRNAs, MW 7-10 kDa) have recently attracted the attention of researchers. These are short endogenous biomolecules of noncoding ribonucleic acids that negatively regulate gene expression. The presence of miRNAs in blood and the ability to measure their level in a non-invasive way, the so-called liquid biopsy approach, has opened new doors in the search for peripheral biomarkers for the diagnosis and prognosis of diseases such as hemorrhagic stroke. In order to perform liquid biopsy, Bloch surface waves supported by one dimensional photonic crystals are exploited to enhance and redirect the fluorescence arising from a sandwiched miRNA recognition assay. Besides, the sensing elements consist of disposable and low-cost plastic biochips coated with a 1DPC. The assay format consists of a first partial hybridization of an oligonucleotidic probe, immobilized onto the 1DPC surface in five regions, with the miRNA target (miR-16-5p, hemorrhagic stroke biomarker) to be revealed in a complex biological medium. The protocol is then completed with a second partial hybridization of the miRNA target with a second synthetic oligonucleotide conjugated with an organic dye. This last step permits to specifically introduce fluorescence where the sandwich assay is accomplished. Thanks to the present technique, we are able to detect miRNA target solutions with a limit of detection of 32 ng/mL in less than 60 minutes. In conclusion, since the recommended therapeutic window is very limited, biomarkers for cerebral ischemia/hemorrhage have the potential to speed-up diagnosis and the assignment of treatments.
The study of the interaction of fibronectin and phosphorylcholine molecules with surfaces is of high relevance to understand the biological performance of bioactive coatings. To accomplish this task, one-dimensional photonic crystals supporting Bloch surface waves were interrogated in label-free and enhanced fluorescence operation modes. In particular, the enhanced fluorescence mode offers the possibility to confirm the presence of proteins with a sharp improvement of the resolution. Bioactive coatings based on fibronectin/ phosphorylcholine have thus the potential to not only enhance the body acceptance of implanted devices, but also extend the lifetime of such devices.
Human epidermal growth factor receptor 2 (HER2) over-expression occurs in 15–20% of breast cancers and it is generally associated with a dismal prognosis. In this work, we report on the use of one-dimensional photonic crystal biochips to detect clinically relevant concentrations of HER2 in human plasma samples. To this aim, we optimized an optical read-out system, combining both label-free and fluorescence detection, which makes use of biochips tailored with specific proteins for specific biological recognition. Our biochips were used to discriminate HER2 positive/negative human plasma samples providing a solid and reliable tool for clinical diagnostics.
The combination of fiber-optic–based platforms for biosensing with nanotechnologies is opening up the chance for the development of in situ, portable, lightweight, versatile, reliable and high-performance optical sensing devices. The route consists of the generation of lossy mode resonances (LMRs) by means of the deposition of nm-thick absorbing metaloxide films on special geometric-modified fibers. This allows measuring precisely and accurately the changes in surface refractive index due to the binding interaction between a biological recognition element and the analyte, with very high sensitivity compared to other optical technology platforms, such as fiber gratings or surface plasmon resonance. The proposed methodology, mixed with the use of specialty fiber structures such as D-shaped fibers, allows improving the light-matter interaction in a strong way. The shift of the LMR has been used to monitor in real-time the biomolecule interactions thanks to a conventional wavelength-interrogation system and an ad-hoc developed microfluidics. A big leap in performance has been attained by detecting femtomolar concentrations in real samples of human serum. The biosensor regeneration has been also studied by using a solution of sodium dodecyl sulphate (SDS), proving the device reusability. Therefore, this technology possibly represents a paradigm shift in the development of a simple, high-specificity and label-free biosensing platform, which can be applied to speed up diagnostic healthcare processes of different diseases toward an early diagnostic and personalized treatment system.
We report on the development of a biosensing platform that combines label-free and fluorescence based detection on disposable Bloch surface wave biochips. This system is applied to the detection of the HER2-neu/ErbB2 clinical biomarker related to breast cancer development. We first describe the design and fabrication of the BSW biochips as well as the principle of operation of the optical reading instrument. Then, the approaches for surface functionalization and immobilization of proteins for specific detection on the biochips are discussed. Finally, experimental results on a sandwich immunoassay for ErbB2 detection in cell lysates are presented.
A 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.
The increasing demand for early detection of diseases drives the efforts to develop more and more sensitive techniques to detect biomarkers in extremely low concentrations. Electromagnetic modes at the surface of one dimensional photonic crystals, usually called Bloch surface waves, were demonstrated to enhance the resolution and constitute an attractive alternative to surface plasmon polariton optical biosensors. We report on the development of Bloch surface wave biochips operating in both label-free and fluorescence modes and demonstrate their use in ovalbumin recognition assays.
Bloch surface waves (BSW) propagating at the boundary of truncated photonic crystals (1D-PC) have emerged as an attractive approach for label-free sensing in plasmon-like sensor configurations. Due to the very low losses in such dielectric thin film stacks, BSW feature very low angular resonance widths compared to the surface plasmon resonance (SPR) case. Besides label-free operation, the large field enhancement and the absence of quenching allow utilizing BSW coupled fluorescence detection to additionally sense the presence of fluorescent labels. This approach can be adapted to the case of angularly resolved resonance detection, thus giving rise to a combined label-free / labelled biosensor platform. It features a parallel analysis of multiple spots arranged as a one-dimensional array inside a microfluidic channel of a disposable chip. Application of such a combined biosensing approach to the detection of the Angiopoietin-2 cancer biomarker in buffer solutions is reported.
Bloch 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.
Optical 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.
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