E. Pasqualotto

Palladium on plastic substrates for plasmonic devices.

Innovative chips based on palladium thin films deposited on plastic substrates have been tested in the Kretschmann surface plasmon resonance (SPR) configuration. The new chips combine the advantages of a plastic support that is interesting and commercially appealing and the physical properties of palladium, showing inverted surface plasmon resonance (ISPR). The detection of DNA chains has been selected as the target of the experiment, since it can be applied to several medical early diagnostic tools, such as different biomarkers of cancers or cystic fibrosis. The results are encouraging for the use of palladium in SPR-based sensors of interest for both the advancement of biodevices and the development of hydrogen sensors.

Enhancement and control of surface plasmon resonance sensitivity using grating in conical mounting configuration

In this work we propose a method to enhance and control the angular sensitivity of a grating coupled surface plasmon resonance (GCSPR) sensor. We lighted a silver grating, mounted in conical configuration, with a laser source and we measured the transmittance of the grating as a function of the azimuthal angle. To evaluate the sensitivity, grating surface was functionalized with four different alkanethiol self assembled monolayers (SAM) and the correspondent azimuthal transmittance peak shifts were measured. The sensitivity control was performed by simply change the light incident angle. This method offers the possibility to design dynamic GCSPR sensor benches that can be used to amplify the SPR angle shift at any step of a biological detection process.

An automated method to determine angular preferentiality using LFPs recorded from rat barrel cortex by brain-chip interface under mechanical whisker stimulation

The sensory information processing in the rodents is mainly done by whisking, through which they explore the environment, perform object localization, texture and shape discrimination very precisely. During whisking, microcircuits in the corresponding barrel columns get activated to segregate and integrate the tactile information through the information processing pathway. To primarily understand the whisking mechanism angular preferentiality determination is very important. In this work we propose an automated method to determine different events present in the local field potentials (LFPs), calculate latencies and amplitudes related to those events and use them along with the stimulation angle information to determine the angular preferentiality. The method is extensively tested on LFPs recorded from S1 barrel cortex of anesthetized rats using EOSFET (Electrolyte-Oxide-Semiconductor Field Effect Transistor) based neuronal probes.

Development of a complete plasmonic grating-based sensor and its application for self-assembled monolayer detection

This work presents an integrated plasmonic biosensing device consisting of a one-dimensional metallic lamellar grating designed to exploit extraordinary transmission of light toward an underlying silicon photodetector. By means of finite element simulations, the grating parameters have been optimized to maximize the light transmission variation induced by the functionalization of the gold nanostructures. An optimized grating was fabricated using an electron beam process and an optoelectronic test bench suitable for sample tests was developed. A clear difference in the grating transmitted light due to surface functionalization was observed in presence of TM polarized illumination.

Comparative study of two measurement/modeling techniques for biodevices functionalization assessment in agri-food applications

In this work we have analyzed and compared two techniques for label-free biosensors characterization: Surface Plasmon Resonance (SPR) and Electrochemical Impedance Spectroscopy (EIS). We have been able to quantitatively characterize both thickness and surface coverage of deposited Self Assembled Monolayers (SAM) produced with molecules of different lengths and concentrations. To this purpose, we have performed both SPR and EIS measurements on nominally identical nanostructured devices functionalized with the same protocols. The experimental results are in general agreement between the two methods, with some differences related to the different sensitivity to details of the surface coverage. Exploiting also the complementary capabilities of SPR and EIS can help developing reliable in-field characterization methods of label free biosensors, such as in agri-food applications.

Modeling of SAM Impedance Onto Gold and Silver Thin-Film Mass-Produced Electrodes and Their Use for Optimization of Lactic Acid Detection

In this work, we demonstrate how an innovative, out-of-cleanroom customized CD/DVD fabrication process can be successfully used for mass production of biosensors with thin-film electrodes. We show that silver and gold electrodes can be used for impedimetric and voltammetric biosensing applications, both in presence and absence of a redox mediator. We modeled the redox/non-redox electrodes impedance through equivalent electrical circuits, and we evaluated their transfer function sensitivity with a one-factor-at-a-time approach. Using this approach, we introduced a new prediction method to find which equivalent electrical circuit elements contribute more to the transfer function variations, then we experimentally validated the predictions measuring the electrodes electrochemical impedance spectroscopy responses with relevant self-assembled monolayer molecules immobilized on them, i.e., MCH and DTSP. We also assess the silver electrodes long-term stability with impedance spectroscopy measurements over a period of 1200 hours, proving their possible use in point-of-care applications. Finally, we also prove that the sensors correctly perform in a practical case, i.e., as a lactic acid biosensor, by studying the optimization of the biosensor efficiency through different enzyme immobilization methods. By comparing lactate oxidase enzyme direct adsorption and covalent binding to DTSP self-assembling monolayers, we found that covalent binding to DTSP can boost the catalytic current of about 40% with respect to that obtained from the direct adsorption of the same enzyme concentration.

Optimization of Cyclic Voltammetric Curve Parameters to Measure Lactate Concentration in Urine Samples

In this work, veal urine dilutions in Hepes-buffered Ringer’s solution (HBRS) are tested by both UV-visible absorption spectroscopy and Cyclic Voltammetry (CV) to assess their viability as mediums for the detection of lactate, through the Lactate Dehydrogenase enzyme (LDH) reaction which involves the formation of NADH. Several data analysis algorithms for the recorded CV data are proposed and compared, in order to optimize the NADH detection in the urine samples dilutions. UV-visible spectroscopy was adopted as reference for NADH quantification.

Novel compact architecture for high-resolution sensing with plasmonic gratings in conical mounting

A novel compact architecture implementing grating-coupled surface plasmon resonance (GCSPR) based on polarization modulation in conical mounting is presented. In this system a plasmonic grating is azimuthally rotated in order to support the excitation of high-sensitivity surface plasmon polaritons (SPPs). At SPP resonance, a scan of the incident polarization is performed before and after the binding event and the phase term of the output trend is exploited as sensing parameter. The mechanical complexity of the SPR system is significantly reduced and a resolution down to 10-7 refractive index units is assured. In this work a numerical study of the polarization-based grating-coupled SPR technique is performed and analyzed with Chandezon’s method. Therefore an experimental test on an assembled prototype is presented and applied to the detection of binding events on the grating surface (avidin/biotin reaction, DNA/PNA probes).