Esophageal pressure, bile content and pH in the gastroesophageal apparatus are important parameters to be monitored in gastroesophageal diseases. An all-optical device was developed for their simultaneous measurement and utilizes a catheter where plastic optical fibres for the measurement of bile and pH and a glass fibre with FBGs for pressure monitoring are integrated. The interrogation device contains two different modules: one for the pressure monitoring based on the measurement of the wavelength shift of the grating peaks, and the other one for bile and pH measurement, based on absorption changes caused by the esophageal content.

Optical sensors are demonstrating the largest potential for Lab-on-a-chip (LOC) systems to perform sensitive, quantitative, and fast sensing for healthcare and environmental monitoring. Among all options, biosensors based on refractometric sensing schemes combine high sensitivity with label-free detection, however, most of them still have not yet been miniaturized in LOC devices for the analysis of biological targets. Here, we demonstrate for the first time a fully miniaturized optical biosensor based on plasmonic-sensing that enables quantitative detection of biological analytes that are potentially found in milk (lactoferrin, streptomycin). The sensor relies on the unprecedented combination of i) miniaturized, monolithically integrated, and cost-effective optical transduction elements such as organic light-emitting diodes and organic photodiodes, and ii) immunoassay-based bio-recognition elements, for highly sensitive and specific localized surface plasmon resonance (LSPR) based detection via a nanostructured plasmonic grating. The sensor is also equipped with portable read-out electronics and microfluidic circuitry, allowing fast, reproducible and reliable functioning. The quantitative response is calibrated through reference samples and it allows reaching a limit of detection of 10-4 refractive index units (RIU) as LSPR sensor. The quantitative and analyte-specific detection is demonstrated for lactoferrin in the laboratory, giving a sensitivity as low as 9 ug/mL. The presented work opens the way for the universal application of optical biosensors in LOC devices, for on-site food analysis, and health monitoring, among others. This work received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 780839 (MOLOKO) and no. 101016706 (h-ALO).

The need to develop clinical tests and rapid sensors for SARS-CoV-2 became evident early in the pandemic to monitor active infections and evaluate seroprevalence. While nucleic acid and antigen tests serve to detect active infections, antibody tests are an essential tool later in the pandemic to monitor past infections and to provide an indication of the immune response of an individual to COVID-19 and to vaccination. To address the need for antibody tests, we have developed surface plasmon resonance (SPR) sensors to detect antibodies expressed towards the nucleocapsid (N) protein and to the spike (S) protein and its receptor binding domain (RBD). We then applied the SPR sensors to determine the maturation of the affinity of the antibodies in the 24-week period post infection, and following vaccination. We developed an in vitro surrogate neutralization assay where the spike protein (the native and a few variants) was immobilized to the SPR sensors to evaluate if convalescent sera inhibited the interaction of spike with ACE-2. SERS assays were also developed to screen individuals that were infected from SARS-CoV-2 naïve individuals and for the multiplexed detection of antibody isotype prevalence at different times post infection.

Surface-enhanced Raman scattering (SERS) sensors, although label-free and extremely sensitive, are still not reproducible and not uniform enough for practical adoption. We propose an unique approach to quantitative SERS sensors satisfies all the sought-after characteristics: a SERS substrate that is uniform, reproducible, sensitive, large, and cost-effective. Specifically, we achieve a sensing uniformity of 4.2% averaged over 4 points and 2.3% over 16 points throughout the entire 6” substrate, and a SERS enhancement of 4.6x108. SERS spectra from four DNA bases are measured and their corresponding peaks are well defined down to 10 pM concentration.

Optical biosensors are a technology that holds promise to address numerous applications in medical research and diagnostics. Affinity biosensors based on surface plasmons (sometimes called plasmonic biosensors) represent the most advanced optical label-free biosensor technology. They have been widely used to investigate biomolecular interactions related to the onset or progression of diseases and to detect and quantify disease biomarkers. In this lecture, we discuss the main challenges in developing plasmonic biosensors for medical diagnostics and present a few selected advances in plasmonic biosensor research that aim to address some of these challenges. These include advances in plasmonic nanostructures and instrumentation, microfluidic systems, functional materials, and detection assays. We also discuss two applications of plasmonic biosensors related to the diagnosis of Myelodysplastic syndromes (MDS - a group of hematological malignancies with a risk of progression into acute myeloid leukemia). First, we present a new extremely sensitive assay for detecting MDS-related microribonucleic acids (miRNAs) and demonstrate that it enables the detection of miRNAs in blood plasma with a limit of detection < 350 aM. Second, we present a biosensor-based approach to the monitoring of progression of MDS based on the analysis of the interaction between an array of proteins and blood plasma samples and show that this interaction approach allows for discrimination among different stages of MDS and healthy controls.

Rolling circle amplification (RCA) for enhancement of the sensor response utilizing surface plasmon resonance and surface plasmon-enhanced fluorescence spectroscopy is reported. In order to maximize the efficiency of RCA, dedicated biointerface is developed for specific capture of target analyte and to guide the generated long oligonucleotide chains at the sensor surface within the confined probing surface plasmon field. The enhancement of the limit of detection by two orders of magnitude to 260 fM concentration is achieved for molecular ensembles and possible counting of individual captured molecules enables reaching limit of detection at low fM concentrations.

An open microfluidic point-of-care diagnostic (POC) platform will be presented that not only combines the ability to carry out various kinds of immunological, molecular or clinical chemistry tests at the point-of-care, allows for different sample types and can be used with a variety of detection technologies but in particular serves as open platform for users to integrate their own assays. The key advantages are as follows: 1) A standardized microfluidic cartridge architecture, with a common footprint, defined areas for functions allows for a toolbox-like development of a whole family of cartridges all using the same manufacturing tool and validated modules. 2) This finds its correspondence in the instrument which runs the cartridges. Standard footprint and common locations for functional elements makes the instrument versatile and able to run a variety of different assays in one instrument or allows for a rapid adaptation to new assays. 3) From an assay developer standpoint, such platforms with a proven system architecture provide a convenient pathway towards a simplified regulatory approval. On the presented platform, we have implemented a variety of assays, molecular diagnostics assays for infectious diseases. In case of these assays, the preferred detection method uses fluorescence. For immunoassays, colorimetric measurements with a simpler camera system are possible. In addition, the system also allows for the integration of sensors for detection. All cartridges include the complete assay flow from sample introduction to read-out. This includes all sample-preparation steps such as sample homogenization, sample lysis and nucleic acid extraction and concentration. In addition, all reagents required are embedded in the cartridge, either in liquid form or as dried reagents in dedicated locations. Overall, this platform allows especially small and medium-sized diagnostic companies and initiatives a rapid transition from bench to the market at a reasonable cost, significantly less compared to an ab-initio development.

Optics have always played a fundamental role in the development of biosensors for medical applications. In recent years, the demand from physicians has grown enormously for devices capable of measuring chemical and biochemical parameters of clinical interest in a reasonably short time and sufficiently compact, or better transportable, to be placed near the patient's bed, so as to allow the formulation of a rapid and reliable diagnosis and/or the choice of the most appropriate therapy, avoiding both the need for analysis of centralized laboratories and the waiting of a few hours and sometimes of a whole day to get the results. Even if the physicians’ general attitude is to use non-invasive sensors both to minimise the risk and to avoid as much as possible any inconvenience for the patient, in some cases the need for continuous monitoring makes the use of invasive sensors unavoidable. In this context, optical fibres play a fundamental role thanks to their geometrical versatility, easy handling, high degree of miniaturisation as well as to their intrinsic safety for the patient, guaranteed by optical fibre dielectricity and by the low light power used for detection. Sometimes the determination of a single parameter is sufficient, but it is important to emphasize that it is often necessary to monitor a panel of biomarkers associated with the onset and/or the development of a definite pathology. In this context, the optical biochip can play an essential role in the development of POCT equipment where the optical biochip can be defined as an array of optical probes on a substrate which uses specific chemical/biochemical reactions to provide an optical signal through which the detection of chemical/biochemical compounds can be achieved. A view from the past to the future will be given with particular attention to the new trends.

This conference presentation, “Semiconductor photonic biosensor for quasi-continuous monitoring of environmental water for the presence of pathogenic bacteria” was recorded for the Biophotonics in Point-of-Care II conference at SPIE Photonics Europe 2022.

The development of an in-situ sensor for the monitoring of concentration of metallic ions in oceans and freshwaters is needed for environmental and industrial studies. To detect multiple ions, in real time, without any tag, we have developed a multi spectral Surface plasmon resonance-based sensor. Capture of ions is achieved using an ion-imprinted polymer functionalized gold surface. The gold film is sequentially illuminated by a finite number of wavelengths and the spectral position of the plasmonic resonance is extracted from this set of images, over the whole sensor surface.

The recording of the action potentials in electrogenic cells plays a central role in many fields of research spanning from neuroscience to cardiology, cell biology and pharmacology. To this aim, many techniques have been developed both in research and in clinical applications. Broadly speaking they can be divided into two categories: direct electrical measurements performed with micro-electrodes (such as patch-clamp and multi-electrode arrays (MEAs) and optical measurements collected from fluorescent reporters administrated to the cell cultures. However, regardless of the field of application some fundamental needs are still not met. Among them the ability of accurate monitoring combined with zero-invasiveness and large spatial scalability (investigation of networks). In this talk, we will show a radically new concept for monitoring action potentials in human cells that overcomes the mentioned limitations [1]. It bases on the concept of “mirror charge” in classical electrodynamics: electric charges placed in proximity of a conductor affect its spatial charge distribution thus generating mirror charges into the conductor itself. Hence, by monitoring the dynamics of the mirror charges one can monitor the dynamics of the “source charges” and the related electric potential, i.e. the action potential. The latter can be done by using charged dyes whose dynamics can be monitored by conventional optical methods. However, being the dyes placed in microfluidic chip, separated from the cell culture, the cells are subjected neither to dye contact, nor to direct light illumination, but are in a perfectly unperturbed physiological state. Remarkably, the optical signal perfectly resembles an action potential (AP) even without the need of cell membrane poration as for conventional electrical recording. We reported a set of experiments on human-derived cardiomyocytes that uniquely support our statements. Such an innovative configuration could inspire a new disruptive class of electro-optical sensors or hybrid devices for optical computing. [1] A. Barbaglia et al., Mirroring Action Potentials. Advanced Materials 2021, 33, 2004234.

We demonstrated an inexpensive, simple and ultra-sensitive refractive index (RI) sensor based on a long tapered tip optical fiber combined with a straightforward image analysis method. The tapering length was optimized through beam propagation simulations and trapezoidal tip fibers were fabricated using a single-step chemical etch process. A simple measurement setup was built that consists of a single wavelength light source (λc= 660 nm), a cuvette, an objective lens, and a camera. The sensitivity of the fibers was measured using saline solutions with different concentrations. The light rays exiting the fiber tip along the tapered section form a circular interference pattern on the camera, whose size in the central part very strongly depends on the surrounding refractive index. By analyzing the areal changes in the center of the fringe patterns for different saline solutions, we obtained an unprecedented sensitivity value of 24160 dB/RIU (refractive index unit), which is the highest value reported so far among intensity-modulated fiber refractometers. We also performed beam propagation simulations to predict the behavior of the tapered tip fiber sensor. The experimental results are consistent with the simulations. This sensor is ultra-sensitive, simple, easy-to-fabricate, and low-cost, which makes it a promising tool for on-site measurements and point-of-care applications such as DNA tests based on loop-mediated isothermal amplification.