The development of rapid and reliable point-of-care testing (POCT) devices requires optical platforms capable of combining fast readout, sensitivity, and robustness. In this work, a fully integrated optoelectronic platform for fluorescence detection in multichannel microfluidic chips is presented, based on a parallel optical interrogation strategy. The platform employs a diffractive optical element (DOE) to achieve simultaneous excitation of multiple microchannels and an array of waveguide absorption filters (WAFs) for parallel fluorescence collection and efficient rejection of excitation light. This configuration eliminates mechanical scanning and enables optical interrogation within a few seconds. The platform is integrated with a microfluidic handling system and dedicated control software, allowing automated execution of immunoassays. Stability and reproducibility were demonstrated through repeated chip loading experiments, showing low variability across microchannels. As a proof of concept, a fluorescence sandwich immunoassay for C-reactive protein (CRP) was implemented in plasma, achieving a limit of detection of 0.32 µg mL⁻1 with good intra- and inter-chip reproducibility. The proposed approach demonstrates the potential of parallel optical architectures for the development of rapid, scalable, and reliable fluorescence-based POCT platforms.

We present the design, fabrication, and optical characterization of fully polymer-based high performance Fabry-Pérot microcavities for sensing and lasing applications. Two microcavity types (Cavity A and B) were realized using polymeric Distributed Bragg Reflector (DBR) films offering distinct spectral properties. Cavity A achieved a high quality factor (Q ≈ 2.15 × 105), demonstrating excellent sensitivity for bulk refractive index sensing with an ultrahigh figure of merit of 5.89 × 104 and a theoretical detection limit down 3.4 × 10−7 RIU. Cavity B was optimized for lasing applications. When filled with a Rhodamine B dye solution, it exhibited clear lasing action with a low threshold (1.83 μJ/mm2) and resonant peaks consistent with its free spectral range. These results highlight the potential of cost-effective polymeric cavities for disposable photonic sensor platforms and integrated biolaser devices.

In this work we propose a high quality optofluidic Fabry- Perot (FP) microcavity, entirely fabricated by using low-cost polymeric materials. The cavity, the mirrors and the substrates, including the microfluidic layer, are assembled by a simple and low-cost lamination process. The cavity length is L=50 µm. By exploring the different polymeric mirrors, resonators with quality factor up Q=1.8 ×105 and finesse of F=486 have been obtained. Refractometric sensing capability of about 300 nm/RIU has been measured. The straightforward fabrication, high quality factor (Q), and small modal volume, makes the proposed optofluidic FPs very promising in sensing applications of liquid sample, including biomedical and environmental monitoring.

Optofluidics is an interdisciplinary domain merging optics and microfluidics and has driven significant progress in the development of small-scale, high-performance optical biosensors, aiming at the final concept of lab-on-chip. The successful development of these outcomes requires overcoming challenges related to the effective integration of optics, microfluidics, and biorecognition elements at a micron-scale level. The opportunities offered by optofluidics, including efficient liquid handling and strong light-matter interaction, have inspired the creation of many optofluidic biosensors with high performance and versatile applications, ranging from single molecule detection up to cell analysis. The review presents and critically analyzes various biosensors schemes and their related fabrication techniques. Different integration strategies with microfluidics and bioassays are examined for their impact on device performance and feasibility. Finally, the manuscript discusses the open challenges and future trends in this field, pointing towards the ongoing evolution of optofluidic biosensors as a promising area of research and application.

A distributed optical fiber system for spectrophotometric analysis of liquid samples based on light diffusing fiber (LDF) is presented. The sensor is based on a high-density white light emitting diode (LED) strip, which is side coupled to a glass based light-diffusing fiber (LDF) that acts as distributed optical receiver. The light emitted from a single LED propagates through the sample medium, is collected by the LDF and is then detected at the end of the fiber by a mini spectrometer. By sequentially turning on one LED at a time, the system permits the spectrophotometric analysis of the sample medium along the entire fiber length. This approach is capable of a continuous monitoring of absorbance spatial profile of liquid sample in the whole visible spectrum with a single low-cost spectrometer. The experimental results confirm the possibility of distributed measurements with a spatial resolution of about 12mm over 1m of measurement range. The approach has been successfully employed to the distributed detection and localization of azo dyes in water with a limit of detection lower than 1ppm.

An optical fiber sensor system for distributed optical absorption spectroscopy based on light diffusing optical fiber is proposed and evaluated. The sensor is composed by two light-diffusing glass fibers radiatively coupled. The light from a pulsed laser diode (PLD) propagates along the first fiber and is locally diffused out into the medium between the fibers. The light transmitted by the medium is partially collected by the second fiber and detected at the end of the fiber by an optical time-domain reflectometry (OTDR) detection scheme. The system permits distributed measurements of the optical absorption properties of the sample medium between the fibers. The experimental results confirm the possibility of distributed measurements with a spatial resolution of about 17 cm over 4 m of measurement range. Distributed chemical sensing has also been evaluated by measuring the absorption of water solutions containing copper ions. A limit of detection (LOD) of 710 ppm has been achieved.

A fluorescence-based device was developed for immunosuppressants. A measuring chip with ten parallel microchannels allows the simultaneous detection of more than one analyte with replicate measurements. The device is equipped with a microfluidic circuitry, which handles the sample mixing with necessary chemicals using an additional chip and its pumping into the measuring chip, and with integrated thin-film amorphous silicon photodiodes for the fluorescence detection. Submicrometric fluorescent magnetic particles are used to improve the efficiency of the assay. Results on the measurements of mycophenolic acid and cyclosporine A in both spiked solutions and microdialysate samples from patient blood are reported.

The power coupling between two light diffusing multimodal optical fibers of equal and finite lengths that are parallel oriented, and which are coupled through scattering processes, is investigated both theoretically and experimentally.In particular, a simple analytical model of the inherent coupling coefficient, derived according to a perturbation approach in a weak-coupling regime, is developed.The modelling results have been compared with the measurements performed, as a function of fiber distance and coupling length at three different wavelengths, and a close agreement is proved.The obtained results provide a better understanding of the power coupling mechanism and of the inherent functional dependence on the main structural parameters of the two-fiber configuration.

High quality factor bulk resonators made in different materials have demonstrated outstanding performance in key functionalities that are very challenging to achieve in planar photonics. However, they have made no significant technological impact mainly because of their stability and scalability limitations related to the way they are connected to the outside world using prisms or tapered fibers. Here, we show several demonstrations of efficient coupling of bulk resonators to integrated waveguides using different materials like lithium niobate or polymers. Preliminary results of a universal integrated coupler that can be implemented using silicon photonics are also presented.

BACKGROUND:Peptidoglycan is an essential component of the cell wall in all bacteria. In particular, the cell walls of Gram-positive bacteria are composed mostly of a thick layer of peptidoglycan. Its accessibility has important implications for their sensing in whole bacterial detection methodologies. Indeed, there is an urgent demand for rapid tests which can identify whole bacteria, e.g., directly at the point of care.OBJECTIVE:The aim of this work is to explore the suitability of RipA, a key cell division protein of M. tuberculosis, for whole cell biosensing of Gram-positive bacteria.METHODS:We here conducted Molecular Dynamics (MD) studies aimed at the understanding of the structural and dynamic features of active RipA and at the design of a suitable bioreceptor. Based on these studies, we engineered a RipA variant for covalent oriented immobilisation on golden surfaces and are able to bind peptidoglycan, albeit without degrading it. Surface Plasmon Resonance (SPR) was employed to check the ability of functionalized golden chips to recognize whole bacteria.RESULTS:MD analyses elucidated the structural details of the active form of RipA and suggested that this enzyme, once inactivated, presents a rigid and well-exposed peptidoglycan recognition cleft. We engineered RipA for proper oriented immobilisation on golden chips for SPR studies. Results show that once chemically coupled to a golden chip, the developed RipA-based bioreceptor is able to detect B. subtilis, used as a model in a concentration-dependent mode.CONCLUSION:Results highlight the potential of the engineered molecule to be integrated in the development of early warning biosensors for Gram-positive contamination in clinical diagnosis or food-borne infections.

We report an optofluidic hybrid silicon-polymer planar ring resonator with integrated microfluidic channels for efficient liquid delivery. The device features a planar architecture of intersecting liquid-core waveguides and microfluidic channels. A low-loss integration of microfluidic channels is accomplished by exploiting the interference pattern created by the self-imaging effect in the multimode interference-based coupler waveguides. Numerical simulations have been performed in order to minimize the propagation losses along the ring loop caused by the integration of microfluidic channels. The device has been fabricated and optically characterized by measuring the quality factor, obtaining a value of 4 × 103. This result is comparable with the quality factor of an optofluidic ring with the same optical layout but without integrated microfluidic channels, thus, confirming the suitability of the proposed approach for microfluidics integration in planar optofluidic design.

In this work, we demonstrated the possibility realize a continuous measurement of liquid level based on light diffusing fibers (LDFs). The sensor consists of two parallel LDFs coupled together. The illuminating fiber is connected to a laser diode. The light scattered into the liquid is then coupled, always by the scattering, to the detection fiber and delivered to a detector. By setting a working wavelength that is strongly absorbed by the liquid, the power coupled between the fibers depends on liquid level. The sensor is made by a polymeric beam of Polyvinyl chloride (PVC), on which two LDF (3M Fibrance) with a diffusion length of 1m have been glued side by side at a distance of 1.5mm. The fiber has a core diameter of 170 μm, a low-index polymeric cladding with a diameter of 230 μm, and loose tube PVC jacket with an outer diameter of 900 μm. As light source a 1550nm fiber coupled laser diode is used. At this wavelength, water, employed as the test liquid, exhibits a strong absorption (=1210 m-1). A high sensitivity photodetector connected to a data acquisition module (DAQ) is used for measuring the detection fiber output power at different liquid levels The optical coupling phenomena between the fibers could be modelled by coupled power equations. Co-propagation and counter-propagation coupling configurations have been analyzed and experimentally validated. The measurements results are in good agreement with the theory, and demonstrate that both configurations could be used for liquid level sensing. The counter-propagation configuration exhibits a nonlinear response as function of the liquid level, while the co-propagation coupling configuration response is linear simplifying the calibration procedure. In the co-propagation configuration, the resolution ranges from ±8mm at low liquid level up to ±2mm at high liquid level over a 1m length measurement range.

A full polymeric optofluidic Fabry-Perot (FP) resonator with a high quality factor (Q) is proposed and tested. The device is based on multilayer optical polymeric films that act as high reflectivity interference mirrors. The all-polymeric laminated structure avoids any deposition or etching process, simplifying the fabrication procedure while retaining a high quality optical surface. The measured quality factor of the FP resonator is 3.03×104, and the finesse is 91 around 700 nm. The refractometric sensing properties have been measured, and a sensitivity of 314 nm/RIU with a limit of detection of 2.55×10-5RIU could be achieved. The device exhibits a very high figure of merit of 1.36×104RIU-1 that is comparable with the performance attainable with sensors based on photonic crystal and whispering gallery mode resonators.

The present paper describes a compact point of care (POC) optical device for therapeutic drug monitoring (TDM). The core of the device is a disposable plastic chip where an immunoassay for the determination of immunosuppressants takes place. The chip is designed in order to have ten parallel microchannels allowing the simultaneous detection of more than one analyte with replicate measurements. The device is equipped with a microfluidic system, which provides sample mixing with the necessary chemicals and pumping samples, reagents and buffers into the measurement chip, and with integrated thin film amorphous silicon photodiodes for the fluorescence detection. Submicrometric fluorescent magnetic particles are used as support in the immunoassay in order to improve the efficiency of the assay. In particular, the magnetic feature is used to concentrate the antibody onto the sensing layer leading to a much faster implementation of the assay, while the fluorescent feature is used to increase the optical signal leading to a larger optical dynamic change and consequently a better sensitivity and a lower limit of detection. The design and development of the whole integrated optical device are here illustrated. In addition, detection of mycophenolic acid and cyclosporine A in spiked solutions and in microdialysate samples from patient blood with the implemented device are reported.