Grating-Coupled Surface Plasmon Resonance (GC-SPR) Optimization for Phase-Interrogation Biosensing in a Microfluidic Chamber.

Surface Plasmon Resonance (SPR)-based sensors have the advantage of being label-free, enzyme-free and real-time. However, their spreading in multidisciplinary research is still mostly limited to prism-coupled devices. Plasmonic gratings, combined with a simple and cost-effective instrumentation, have been poorly developed compared to prism-coupled system mainly due to their lower sensitivity. Here we describe the optimization and signal enhancement of a sensing platform based on phase-interrogation method, which entails the exploitation of a nanostructured sensor. This technique is particularly suitable for integration of the plasmonic sensor in a lab-on-a-chip platform and can be used in a microfluidic chamber to ease the sensing procedures and limit the injected volume. The careful optimization of most suitable experimental parameters by numerical simulations leads to a 30–50% enhancement of SPR response, opening new possibilities for applications in the biomedical research field while maintaining the ease and versatility of the configuration

Total angular momentum sorting in the telecom infrared with silicon Pancharatnam-Berry transformation optics

Parallel sorting of orbital angular momentum (OAM) and polarization has recently acquired paramount importance and interest in a wide range of fields ranging from telecommunications to high-dimensional quantum cryptography. Due to their inherently polarization-sensitive optical response, optical elements acting on the geometric phase prove to be useful for processing structured light beams with orthogonal polarization states by means of a single optical platform. In this work, we present the design, fabrication and test of a Pancharatnam-Berry optical element in silicon implementing a log-pol optical transformation at 1310 nm for the realization of an OAM sorter based on the conformal mapping between angular and linear momentum states. The metasurface is realized in the form of continuously-variant subwavelength gratings, providing high-resolution in the definition of the phase pattern. A hybrid device is fabricated assembling the metasurface for the geometric phase control with multi-level diffractive optics for the polarization-independent manipulation of the dynamic phase. The optical characterization confirms the capability to sort orbital angular momentum and circular polarization at the same time.Comment: 15 pages, 10 figure

Capacitance immunosensors for the early detection of circulating cancer biomarkers

I have been successful in improving and developing a homemade device based on a three-electrodes electrochemical redout setup thanks to it, we are able to perform measurements of DNA-hybridization, in real-time, from probe ssDNA-SAMs coupled to gold coated sensor surfaces. The measurements were carried out, in pure saline buffer solution, on a large range of concentrations of complementary-DNA strands (from 1 pM to 100 nM), monitoring the differential capacitance at the Working Electrode versus the incubation time. The studies on kinetics, modeled using the Langmuir adsorption model, not only give us important information on the kinetics itself but they allow us to detect eventual mismatches along the DNA-sequence target proving to be sensitive to the position of the mismatch with respect to the surface of the device or to define, in human extract and plasma, the unknown concentration of a specific miRNA-target connected to the heart failure taking into account the hindrances carried by the Argonaute proteins in which the miRNA are inglobed. This goal was achieved by performing a calibration curve on experiments of DNA/DNA hybridization performed in a simple saline buffer. The results were then confirmed using a real time qPCR by our partners in MD D. Cesselli's and MD A.P. Beltrami's group at University of Udine. Another strand of my PhD project concerns the detection of more complex components such as proteins or single-domain antibodies (e.g. VHH fragments)\u2013DNA conjugates, with the final purpose of the detection of circulating tumor cells (CTCs) not only in pure saline buffer but also in human serum. In particular, we have focused on the detection of the protein HER2 whose overexpression is connected to certain aggressive types of breast cancer. In addition, the systematic characterization of the device caught our attention, and it was developed by performing measurements of Self Assembled Monolayer (SAM) detection, carried out in different physiological buffers (KCl, NaCl, MgCl2, PBS, etc.), in different probe-density conditions and applying different potential in order to have a more comprehensive understanding of the phenomena occurring at the electrode/electrolyte interface. Studies that have led to the implementation of a theoretical model, able to provide an acceptable physical explanation of the biorecognition events of interest

Miniaturized Aptamer-Based Assays for Protein Detection

The availability of devices for cancer biomarker detection at early stages of the disease is one of the most critical issues in biomedicine. Towards this goal, to increase the assay sensitivity, device miniaturization strategies empowered by the employment of high affinity protein binders constitute a valuable approach. In this work we propose two different surface-based miniaturized platforms for biomarker detection in body fluids: the first platform is an atomic force microscopy (AFM)-based nanoarray, where AFM is used to generate functional nanoscale areas and to detect biorecognition through careful topographic measurements; the second platform consists of a miniaturized electrochemical cell to detect biomarkers through electrochemical impedance spectroscopy (EIS) analysis. Both devices rely on robust and highly-specific protein binders as aptamers, and were tested for thrombin detection. An active layer of DNA-aptamer conjugates was immobilized via DNA directed immobilization on complementary single-stranded DNA self-assembled monolayers confined on a nano/micro area of a gold surface. Results obtained with these devices were compared with the output of surface plasmon resonance (SPR) assays used as reference. We succeeded in capturing antigens in concentrations as low as a few nM.We put forward ideas to push the sensitivity further to the pM range, assuring low biosample volume (L range) assay conditions

Design, fabrication and characterization of Computer Generated Holograms for anti-counterfeiting applications using OAM beams as light decoders

In this paper, we present the design, fabrication and optical characterization of computer-generated holograms (CGH) encoding information for light beams carrying orbital angular momentum (OAM). Through the use of a numerical code, based on an iterative Fourier transform algorithm, a phase-only diffractive optical element (PH-DOE) specifically designed for OAM illumination has been computed, fabricated and tested. In order to shape the incident beam into a helicoidal phase profile and generate light carrying phase singularities, a method based on transmission through high-order spiral phase plates (SPPs) has been used. The phase pattern of the designed holographic DOEs has been fabricated using high-resolution Electron-Beam Lithography (EBL) over glass substrates coated with a positive photoresist layer (polymethylmethacrylate). To the best of our knowledge, the present study is the first attempt, in a comprehensive work, to design, fabricate and characterize computer-generated holograms encoding information for structured light carrying OAM and phase singularities. These optical devices appear promising as high-security optical elements for anti-counterfeiting applications.Comment: 24 pages, 9 figures. Supplementary info: 8 pages, 3 figure

Mismatch detection in DNA monolayers by atomic force microscopy and electrochemical impedance spectroscopy

6noThe availability of devices for cancer biomarker detection at early stages of the disease is one of the most critical issues in biomedicine. Towards this goal, to increase the assay sensitivity, device miniaturization strategies empowered by the employment of high affinity protein binders constitute a valuable approach. In this work we propose two different surface-based miniaturized platforms for biomarker detection in body fluids: the first platform is an atomic force microscopy (AFM)-based nanoarray, where AFM is used to generate functional nanoscale areas and to detect biorecognition through careful topographic measurements; the second platform consists of a miniaturized electrochemical cell to detect biomarkers through electrochemical impedance spectroscopy (EIS) analysis. Both devices rely on robust and highly-specific protein binders as aptamers, and were tested for thrombin detection. An active layer of DNA-aptamer conjugates was immobilized via DNA directed immobilization on complementary single-stranded DNA self-assembled monolayers confined on a nano/micro area of a gold surface. Results obtained with these devices were compared with the output of surface plasmon resonance (SPR) assays used as reference. We succeeded in capturing antigens in concentrations as low as a few nM. We put forward ideas to push the sensitivity further to the pM range, assuring low biosample volume (μL range) assay conditions.openopenNkoua Ngavouka, Maryse D.; Capaldo, Pietro; Ambrosetti, Elena; Scoles, Giacinto; Casalis, Loredana; Parisse, PietroNKOUA NGAVOUKA, MARYSE DADINA; Capaldo, Pietro; Ambrosetti, Elena; Scoles, Giacinto; Casalis, Loredana; Parisse, Pietr

Holographic Silicon Metasurfaces for Total Angular Momentum Demultiplexing Applications in Telecom

The simultaneous processing of orbital angular momentum (OAM) and polarization has recently acquired particular importance and interest in a wide range of fields ranging from telecommunications to high-dimensional quantum cryptography. Due to their inherently polarization-sensitive optical behavior, Pancharatnam–Berry optical elements (PBOEs), acting on the geometric phase, have proven to be useful for the manipulation of complex light beams with orthogonal polarization states using a single optical element. In this work, different PBOEs have been computed, realized, and optically analyzed for the sorting of beams with orthogonal OAM and polarization states at the telecom wavelength of 1310 nm. The geometric-phase control is obtained by inducing a spatially-dependent form birefringence on a silicon substrate, patterned with properly-oriented subwavelength gratings. The digital grating structure is generated with high-resolution electron beam lithography on a resist mask and transferred to the silicon substrate using inductively coupled plasma-reactive ion etching. The optical characterization of the fabricated samples confirms the expected capability to detect circularly-polarized optical vortices with different handedness and orbital angular momentum

Pancharatnam–Berry Optical Elements for Spin and Orbital Angular Momentum Division Demultiplexing

A Pancharatnam⁻Berry optical element is designed, fabricated, and optically characterized for the demultiplexing of beams with different polarization and orbital angular momentum states at the telecom wavelength of 1310 nm. The geometric phase control is achieved by fabricating properly-oriented subwavelength gratings on a silicon substrate, inducing a spatially-variant form birefringence. The digital grating pattern is transferred to the silicon substrate with a two-step nanofabrication protocol, using inductively coupled plasma reactive ion etching to transfer the resist pattern generated with high-resolution electron beam lithography. The optical characterization of the sample confirms the expected capability to sort circularly polarized optical beams with different handedness and orbital angular momentum. Encompassing optical element design and silicon photonics, the designed silicon metasurface paves the way to innovative devices for total angular momentum mode division multiplexing with unprecedented levels of integration