Science behind the platform.

Liquid biopsy is expected to become widespread in the coming years thanks to point of care devices, which can include label-free biosensors. The surface functionalization of biosensors is a crucial aspect that influences their overall performance, resulting in the accurate, sensitive, and specific detection of target molecules. Here, the surface of a microring resonator (MRR)-based biosensor was functionalized for the detection of protein biomarkers. Among the several existing functionalization methods, a strategy based on aptamers and mercaptosilanes was selected as the most highly performing approach. All steps of the functionalization protocol were carefully characterized and optimized to obtain a suitable protocol to be transferred to the final biosensor. The functionalization protocol comprised a preliminary plasma treatment aimed at cleaning and activating the surface for the subsequent silanization step. Different plasma treatments as well as different silanes were tested in order to covalently bind aptamers specific to different biomarker targets, i.e., C-reactive protein, SARS-CoV-2 spike protein, and thrombin. Argon plasma and 1% v/v mercaptosilane were found as the most suitable for obtaining a homogeneous layer apt to aptamer conjugation. The aptamer concentration and time for immobilization were optimized, resulting in 1 µM and 3 h, respectively. A final passivation step based on mercaptohexanol was also implemented. The functionalization protocol was then evaluated for the detection of thrombin with a photonic biosensor based on microring resonators. The preliminary results identified the successful recognition of the correct target as well as some limitations of the developed protocol in real measurement conditions.

In the recent years, the number of Point-Of-Care-Tests (POCTs) available for clinical diagnostic has steadily increased. POCTs provide a near-patient testing with the potential to generate a result quickly so that appropriate treatment can be implemented, leading to improved clinical outcomes compared to traditional laboratory testing. Technological advances, such as miniaturization of sensors and improved instrumentation, have revolutionized POCTs, enabling the development of smaller and more accurate devices. In this context, it has also gained increasing importance the screening of various analytes simultaneously to increase specificity and improve the characterization of the disease. This study is aimed at developing and characterizing a photonic integrated circuit for multiple markers detection, which represents the functional core towards a full developed POCT device for clinical pathology applications. The photonic sensor, based on microring resonators (MRRs), is functionalized by immobilizing specific antibodies on a copolymer layer deposited on the MRR’s surfaces. Surface chemical techniques were employed to analyse the surface chemical characteristics while fluorescence microscopy was involved to analyse the resulting bioreceptor surface density. The photonic sensor is characterized for the parallel detection of two biomarkers, the C-Reactive Protein (CRP) and the Creatine-Kinase-MB (CK-MB). The analyte-antibody binding curves were obtained both in buffer and in filtered un-diluted artificial saliva showing promising results both in terms of sensitivity, with limit of detection (LOD) of 103 pM for CRP and 140 pM for CK-MB, and in terms of specificity. These encouraging results let the assembly of a highly sensitive POC device for molecular diagnostics.

Biosensors are powerful tools for detecting specific molecules by leveraging biological interactions to generate measurable signals. This research focuses on the development of advanced label-free biosensors using Silicon Nitride integrated optical circuits, employing Mach-Zehnder Interferometer (MZI) structures as the sensing elements. MZIs, which combine waveguiding and interferometry, offer high sensitivity by detecting phase shifts induced by analyte binding in real time. The development process encompasses component simulation, chip design, chip fabrication, packaging, optical and electrical characterization and biological testing. Although the Silicon Nitride sensor is still under development, preliminary results from silicon waveguide-based MZI devices have demonstrated their ability to accurately monitor binding kinetics. A key advantage of Silicon Nitride is its compatibility with visible wavelengths, where optical losses are lower when using aqueous cladding, as is common in biological testing. This research holds significant potential for advancing label-free optical biosensing technologies, with applications spanning healthcare, environmental monitoring, and beyond.

This work presents the development of label-free biosensors based on silicon nitride (SiN) photonic integrated circuits (PICs), using Mach–Zehnder interferometers (MZIs) as the core sensing elements. Two SiN platforms were optimized for operation at telecom (1550 nm) and visible (780 nm) wavelengths to evaluate the impact of waveguide geometry and wavelength on sensitivity and optical losses. Experimental measurements indicate propagation losses of approximately 1.0 dB/cm at 780 nm and 0.6 dB/cm at 1550 nm in TE polarization. An active control system based on integrated Ti/TiN/Ti heaters provides precise phase tuning, with a π-shift power of 57 mW at 780 nm and 120 mW at 1550 nm when deep trenches are used for thermal isolation. At 1550 nm, this value can be further reduced to 13.3 mW by adopting suspended heaters. Preliminary biological validation was carried out at 1550 nm using a conventional passive readout approach based on monitoring the MZI spectral response during a sandwich assay for C-reactive protein (CRP), achieving detection down to 5 pM.