In this work, we present an ethanol sensor based on a D-shaped optical fiber functionalized with a nanostructured layer of gold nanostars (AuNSs). The functionalization was achieved via a seed-mediated growth method, enabling uniform and controlled nanoparticle deposition on the fiber surface. The sensor was integrated into a custom-designed microfluidic chip, allowing precise control of analyte delivery and ensuring highly reproducible measurements. The sensing mechanism relies on the interaction between the evanescent field of the D-shaped fiber and the AuNSs, which enhances light–matter interaction and increases sensitivity to refractive index variations induced by ethanol concentration changes. The device exhibited a highly linear response (R² = 99.960) over a concentration range of 0–40%, with a detection limit of 0.07% and a response time of approximately 10 s. The combination of nanostructured plasmonic materials and microfluidic integration results in improved sensitivity, repeatability, and response speed. These results demonstrate the potential of D-shaped fiber platforms functionalized with gold nanostructures for the development of compact and efficient chemical sensing systems.

We demonstrate a compact, low-cost fibre Bragg grating interrogation system combining an externally injected gain-switched dual optical frequency comb with embedded real time processing that achieves 0.6 pm resolution at 1011 Hz interrogation rates and <75 fm resolution at measurement rates below 3Hz. The system employs optical heterodyning and receiver integrated curve fitting algorithms to enable real-time operation. Comprehensive characterization of dual-comb stability, receiver processing performance, and algorithm accuracy validates the system's capabilities and identifies wavelength-dependent resolution behaviour linked to variations in comb-line signal-to-noise ratio. The demonstrated resolution speed trade-off and femtometre-scale measurement capability establish this architecture to be well-suited for high-sensitivity, fast-response sensing applications.

Significance:Optical-quality bioresorbable implants, which gradually dissolve within the body, are gaining increasing interest due to their potential to eliminate the need for revision surgeries. These implants show significant promise in treating deep-seated tumors in high-risk areas, such as the brain, and offer extended capabilities for monitoring interstitial physiological parameters or pharmacokinetics through photonic technologies. Aim:A proof-of-principle validation has been conducted on calcium phosphate glass (CPG)-based bioresorbable optical fibers to assess their capability to monitor the spatial distribution of photosensitizing (PS) drugs in tumors-an essential parameter to optimize for enhanced treatment outcomes in photodynamic therapy (PDT). Approach:Ex vivo validation was performed on liquid phantoms with solid tumor-mimicking inclusions containing the fluorescent PS drug. In-house developed bioresorbable fibers, with optical characteristics similar to silica fibers used in current PDT systems, were utilized. For the first time, these fibers were used for the interstitial acquisition of fluorescent signals, followed by the tomographic reconstruction of the drug distribution in the phantom. The results were compared with those obtained from a standard clinical system equipped with silica fibers. Results:The reconstructed drug distribution with bioresorbable fibers agreed with that obtained using the same system with standard silica fibers. Conclusions:We reveal the potential of further exploring CPG bioresorbable optical fibers for interstitial PDT.

Continuous and real-time physiological pressure monitoring is essential for diagnosing and managing conditions such as intracranial hypertension, cardiovascular diseases, and gastrointestinal motility disorders. While fiber Bragg gratings (FBGs) offer several advantages over conventional electrical sensors, including immunity to electromagnetic interference and multiplexing capability for simultaneous multi-point sensing, their inherent low-pressure sensitivity limits their applicability in biomedical environments. This study investigates the enhancement of FBG pressure sensitivity through a polymer coating, such as polydimethylsiloxane (PDMS), is used to improve strain transfer and amplify the Bragg wavelength shift, with coating dimensions (∼500 µ m) compatible with pressure guidewires or catheters. A combined approach of finite element modeling and experimental validation demonstrated that, compared to uncoated sensors, PDMS-coated FBGs achieved up to 43-fold and 154-fold sensitivity enhancements for 500 µ m and 800 µ m coatings on 125 µ m cladding fibers, and up to 212-fold and 339-fold improvements for corresponding coatings on 80 µ m cladding FBGs. Under dynamic pressure, the sensors exhibited minimum detectable pressure amplitudes of 0.5 mmHg. These enhancements bring standard FBG sensors closer to real-time, minimally invasive continuous monitoring in pressure-guided catheters. Additionally, the mechanical robustness and multiplexing potential of coated FBGs enable non-invasive applications, such as smart walkers or wearable devices, broadening their utility across clinical and rehabilitative settings.

In this study, the authors demonstrate a low cost, flexible, and versatile photonic sensing system utilising a dual optical frequency comb (D-OFC) and a real-time receiver. The D-OFC is generated using two mutually injected gain switched lasers (MI-GSLs) and its performance for sensing application demonstrated by tracking the wavelength shift of a fibre Bragg grating. The receiver comprises a low-speed photodetector, a 10 MS/s ADC and a 600 MHz ARM Cortex-M7 microcontroller. The system achieves a high accuracy, with a sensing resolution of 0.855 pm at 43 Hz capture rate

We report on preliminary results of a low cost SERS optical fiber probe fabricated by ion-exchange processes.

In this work, we present a high-resolution strain sensing system based on Dual Optical Frequency Comb (DOFC) interrogation of Fiber Bragg Gratings (FBGs), employing optimized signal processing methods for both reflection and transmission spectra. Femtosecond (fs) written FBGs with non-uniform profiles with bandwidths of similar to 0.5 nm were interrogated using a mutually coherent DOFC generated by externally injected gain-switched lasers (EI-GSLs). Different algorithms were used to process the DOFC signal to extract the FBG frequency shifts caused by the various strain increments. Using these approaches, we could detect strains with a sub-mu & varepsilon; resolution (0.32 mu & varepsilon;), sensitivities ranging from 0.7-1 pm/mu & varepsilon;, and a dynamic range of 422 mu & varepsilon;. These methods increased low-strain sensitivity typical of DOFC interrogation systems, enabling precise monitoring of standard off-the-shelf fs-written FBGs. The DOFC system showed enhanced linearity (R-2 similar to 0.98) and Figure of Merit (FoM - 2.58/mu & varepsilon;) at lower strains than a standard commercial interrogator (R-2 similar to 0.82 and FoM - 0.88/mu & varepsilon;). Our findings highlight the potential of the DOFC-FBG interrogation as a powerful tool for real-time high-resolution sensing applications, ranging from structural health monitoring to biomedical diagnostics.

Bioresorbable fibers are an exciting prospect as probes and implants to provide optical access to the human body. In this work, we demonstrate interstitial spectroscopy with bioresorbable fibers at null distance, using time-domain diffuse optics that disentangles absorption from scattering properties and probes the tissues up to a depth of a few cm around the fiber tips. We exploit a fast-gated single-photon avalanche diode with >55 dB of dynamic range to overcome the burst of 'early' photons hiding the information of absorption from deep tissues. We tested the absorption linearity-retrieving the water spectrum in the 700-950 nm range with >85% accuracy over two decades of absorption change-and verified the hypothesis of a scattering-independent absorption retrieval. Further, we were able to detect spectral changes at a distance of 1 cm from an inclusion embedded in a biological tissue. Time-domain diffuse optical spectroscopy with bioresorbable fibers could detect spectral changes without being affected by blood extravasation at the fiber tips and could help for long-term monitoring in tissue healing, thermal treatment, photodynamic therapy and ultimately, towards minimally invasive medical procedures.

We demonstrate the usability of bioresorbable phosphate glass fibers for time-domain diffuse optical spectroscopy (TD-DOS) in the short-wave infrared (SWIR) region of 950-1600 nm, with the use of an InGaAs detector. Bioresorbable fibers for diffuse optics present an exciting prospect due to their ability to be left implanted while retrieving optical properties from deeper regions (few cm) for monitoring treatments. Extending TD-DOS to the SWIR region could be useful to better identify biomarkers such as water, lipids and collagen, given their increase in absorption in this range. We attempt to use the bioresorbable fibers to spectrally identify these biomarkers by measuring a series of biological samples known to contain them, such as porcine muscle, porcine fat and bone. We further validate our measurements by comparing the optical properties of high-scattering solid silicone phantoms retrieved with these bioresorbable fibers with those by a standard Si fiber.

This study deploys the application of Fiber Bragg Gratings (FBGs) in physiological pressure monitoring by integrating an elastomeric, biocompatible coating ranging from 300-500μm, designed to improve sensor functionality for in-vivo pressure monitoring applications. FBGs are favored for their sensitivity, immunity to electromagnetic interference, and compact size, making them ideal for embedding within medical devices such as catheters and guidewires. However, their use has been limited by low inherent pressure sensitivity (3.14 pm/MPa) and the impracticality of thicker coatings described in previous studies. Our approach demonstrates that this unique coating not only boosts the pressure sensitivity significantly—surpassing 1.63 orders of magnitude (43.10 times)—but also enhances the signal-to-noise ratio of the optical signal. These advancements enable potential applications in high-resolution manometry, gastrointestinal pressure monitoring, intracranial and intracoronary blood pressure measurements, marking a significant step forward in medical diagnostics and monitoring.

Optical quality bioresorbable materials have been gaining interest in recent years for various interstitial biomedical/medical application. An example of this is when the implant gradually dissolves in the body, providing physiological information over extended periods of time, hence reducing the need for revision surgeries. This study reports for the first time the in-house fabrication of single mode (at 785 nm) calcium phosphate glass (CPG) based bioresorbable optical fibers and investigates their suitability for microvascular blood flow monitoring using diffuse correlation spectroscopy (DCS). Ex vivo experiments in liquid phantom and non-invasive in vivo experiments on the human forearm muscle were conducted using multimode and single mode CPG bioresorbable optical fibers. The retrieved flow index from the correlation curves acquired using CPG fibers was in good agreement with that obtained using standard silica (Si) fibers, both ex vivo and in vivo. The results demonstrate the potential of CPG optical fibers for further exploration.

Surface-enhanced Raman spectroscopy (SERS) sensors are commonly based on metal nanoparticles in colloidal suspension followed by deposition on a substrate. Despite its simplicity, this approach leads to non-uniform SERS substrates that are hampered by features such as coffee rings. Seed-mediated growth starting from nanoparticles already deposited on a flat substrate potentially allows for creating more uniform and reliable sensors. However, the deposition process, the control of the distribution of the seed nanoparticles, and their optimal growth have not been thoroughly explored. In this work, we present a systematic approach to designing and fabricating gold nanostructured surfaces, tailoring their SERS responses on demand. By controlling and tuning the deposition of nanoparticles, assisted by an experimental and theoretical investigation, we achieved good control over the spatial distribution of the deposited seeds. After enlarging such seeds through chemical reduction, the optimized SERS substrates show great uniformity in their hotspots, a critical feature for sensors. The so-fabricated substrates were used for detecting Skatole in water, achieving a detection limit of 42.2 ppt. The developed methodology has significant implications for the advancement of several fields, particularly SERS-based sensing, enabling the design and targeting of specific excitation wavelengths and Raman bands while obtaining uniform and reliable substrates.

Bioresorbable photonic implants are emerging as potential material choice for interstitial theranostic and monitoring applications. They gradually dissolve within the physiological environment in a clinically relevant period, eliminating the need for extraction surgeries. In the present study, we tested the suitability of in-house fabricated bioresorbable optical fibres based on calcium phosphate (CaP) glass for diffuse correlation spectroscopic (DCS) and diffuse fluorescence tomographic (DFT) applications. The results represent the potential of bioresorbable fibers for the monitoring of interstitial microvascular blood flow and the spatial distribution of fluorescent photosensitizer drugs that are administered prior to therapies. Together or separate, the continuous monitoring of these parameters can have significant implications in planning, optimizing and in predicting or monitoring the outcomes in interstitial photodynamic therapy (PDT).

Calcium phosphate glass based single-mode and multi-mode bioresorbable optical fibers were in-house manufactured. Ex-vivo studies were then conducted to test the suitability of these fibers for time gated diffuse optics spectroscopy, photodynamic therapy and diffuse correlation spectroscopy applications which can be respectively employed for the diagnosis, treatment, and monitoring of malignant tissues. The results demonstrated the potential of calcium phosphate glass-based fiber optic devices towards the realization of an implantable multi-functional class of devices with functionalities ranging from cancer detection to monitoring of the healing process all integrated into a single bioresorbable platform. Acknowledgement: This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 860185

We report on the design, fabrication, and characterization of a novel germanate glass host for efficient 2 µm eye-safe laser operation. Spectroscopic characterization and CW laser generation with Tm3+ and Ho3+ doping is investigated.

Development of optical quality bioresorbable fibers is an emerging area of study where researchers are trying to advance the field by assessing the suitability of these fibers for various biomedical applications. These types of fiber implants dissolve in the human body over a clinically relevant time scale eliminating the need for extraction surgeries. We conducted both ex-vivo and in vivo diffuse correlation spectroscopic studies using our fibers to measure blood flow and a preliminary trial to integrate a biocompatible electrode material on the fiber for electrical signal measurements. The results demonstrated the potential of Calcium Phosphate glass-based fiber-optic devices in future physiological monitoring applications which can be implanted inside the body without the need of an explant procedure. Acknowledgement: This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 860185.

Calcium phosphate (CaP) glass has recently gained popularity as a promising material for a wide range of biomedical applications. Recent developments have seen CaP glasses moving from a passive implant material to an active degradable material, particularly as a major constituent of bioresorbable photonic devices. This holds great promise in advanced biomedical applications, since the main constituents of CaP glasses are present in the human body. In this review, the progressive advancements in the biomedical applications of calcium phosphate glass-based devices over the past 50 years are discussed. An overview of their role as reinforcing agents and the studies on doping their matrices for ion releasing and drug and gene delivery are reviewed. Recent applications of CaP glass and fibers in soft-tissue engineering and their potential for optical quality bioresorbable devices are then discussed along with the current challenges and potential future directions, emphasizing the promising role of CaP glass in the next generation of biomaterials. Considering their progress and potential in performing several biomedical functionalities over time, CaP glass-based devices hold promise for becoming enabling tools as an implantable, bioresorbable, multifunctional class of devices in future biomedicine.