There is a growing demand for inexpensive and user-friendly detection technologies that can identify various biomarkers in a sustainable manner. Microfluidic thread-based analytical devices (μTADs) are rapidly growing because of their biocompatibility, flexibility, and absence of complex treatments. Additionally, μTADs are highly compact, allowing for the use of small sample volumes, with the potential to compete with low-cost paper in point-of-care (POC) applications. Here, we present a chemiluminescent thread-based device for user-friendly detection of lactate in sweat, which is an indicator of performance in athletic training programs, and it can provide vital information connected to ischemia and insufficient oxidative metabolism. Lactate oxidase (LOx)-catalyzed reaction coupled with the luminol/H₂O₂/horseradish peroxidase (HRP) system was exploited by immobilizing substrate and enzymes on different sides of the same thread, avoiding undesired premature reactions. Small-volume samples (2 µL) were used on an optimized “X-shaped” device with an incubation time of 5 min. Different supports were tested from the perspective of wearability of the biosensing thread, including polypropylene, mother of pearl buttons and, to improve sustainability, grape and apple skin obtained from agro-food waste. Smartphone detection allowed a simple and quantitative readout for the end-user. Under optimized conditions, the biosensor achieved detection limits of 0.27, 0.24, and 0.15 mM for lactate spiked in artificial sweat samples at pH 5.5, 6.5, and 8.0, respectively, showing promising applications for POC applications.

Biomolecular detection has been revolutionized by the integration of advanced optical and photonic technologies with biosensors, offering unprecedented sensitivity and specificity. This review covers recent advances in biosensor technologies that exploit 2D materials, photonic crystals, and plasmonic enhancements for biomedical applications.

Graphene, MXenes, transition metal dichalcogenides, and 2D materials have been introduced into the field of optical biosensors, where they enhance detection by Surface Plasmon Resonance and Fluorescence Resonance Energy Transfer techniques. Similarly, with photonic crystal-based biosensors, such as one-dimensional photonic crystals (1D PCs), rapid and sensitive bacterial detection has been developed. Quantum dots and plasmonic nanomaterials connectedly form biosensors that have improved optical responses, thereby broadening their application in medical diagnostics.

Innovations in photonic biosensors have been applied in waterborne pathogen detection where multilayer photonic crystal structures break symmetry upon interaction with bacterial samples and produce unique resonance shifts. These systems, optimized based on transfer matrix methods, demonstrate enhanced sensitivity, along with superior performance compared to previously designed ones. Furthermore, SPR biosensors based on PCF that are co-modified with gold nanoparticles and polydopamine display excellent biosensing capabilities for immunoassays at low detection limits and high refractive index sensitivity.

Silicon-on-insulator (SOI)-based optofluidic biosensor arrays offer a promising multi-tumor marker detection tool for cancer diagnostics. Utilizing nanobeam resonator transducers and microfluidic integration, these biosensors offer label-free, high-sensitivity detection of carcinoembryonic antigens, thus leading to point-of-care diagnostics.

There remain several challenges with these advances: material stability, reproducibility, and translation to the clinical arena. Research should be concentrated on overcoming such barriers through sustainable material synthesis, better fabrication techniques, and more integrated biomedical systems that would finally translate to the commercialization of next-generation biosensors.

Oligonucleotide optical switches are short, precisely engineered nucleic acid molecules that alter or activate their light emission upon interaction with specific molecular targets. Their optical response is typically based on fluorescence mechanisms, particularly Förster Resonance Energy Transfer (FRET), or alternative approaches such as Surface-Enhanced Raman Scattering (SERS) [1].

DNA’s versatility extends beyond genetic information storage; in biosensing applications, DNA fragments provide exceptional molecular recognition, enabling highly specific analytical systems. More than just recognition elements, DNA-based structures can be designed as dynamic nanoscale tools to monitor intracellular processes in real time. These capabilities allow oligonucleotide optical switches to serve both as diagnostic sensors and potential therapeutic agents.

Among recent advancements in optical biosensing, oligonucleotide optical switches have emerged as particularly promising due to their ability to provide a rapid, sensitive, and highly specific detection of biomolecules [2]. However, challenges remain, including optimizing signal-to-noise ratios, ensuring stability in biological environments, and integrating these nanosensors with advanced detection platforms. Despite these hurdles, continuous research is expanding their applications, from fundamental cellular studies to medical diagnostics and targeted therapies. Their potential to bridge biosensing and therapeutic intervention positions them as key players in the future of molecular nanotechnology.

References

[1] M. Banchelli et al., “Molecular beacon decorated silver nanowires for quantitative miRNA detection by a SERS approach”, Anal. Methods. (2023) 15, 6165-6176

[2] A. Giannetti et al., “Oligonucleotide optical switches for intracellular sensing” Anal. Bioanal. Chem. (2013) 45(19) 6181-6196.

Funding/Acknowledgement

The authors were supported by the Next Generation EU project titled “Progetto di ricerca di Rilevante Interesse Nazionale PRIN 2022 - PNRR, P2022R85AA, BioEMC - Biochips for Emerging Micro-Contaminants”.

Growing attention in deep space exploration lies in protecting crew health and maintaining peak performance by devising preventive measures and on-site diagnostic techniques. The harsh conditions of space present serious health threats, such as muscle degradation, bone density loss, and cardiac dysfunction (https://doi.org/10.1016/j.lssr.2023.09.003). Consequently, cutting-edge solutions for real-time biomarker analyses are critical to tracking astronauts' health throughout their missions (https://doi.org/10.3390/bios14020072).

C-reactive protein (CRP), a protein associated with inflammatory conditions, has demonstrated a significant correlation with infarct severity, complications, and poor outcomes in ischemic patients. Elevated CRP levels in particular have been linked to sudden coronary death due to plaque rupture and a heightened risk of sudden death in otherwise healthy individuals (https://doi.org/10.1093/eurheartj/ehr487).

We developed a disposable microfluidic cartridge coupled with an array of hydrogenated amorphous silicon (a-Si:H) photosensors for the detection of CRP in biological fluids.

The device is made up of a cartridge containing microchannels within which specific anti-CRP antibodies have been chemically immobilized to the photosensors required for signal detection in the presence of the target.

Upon the application of a sample, the target was recognized by the immobilized specific antibodies and detected by the biotin-labeled secondary antibody and streptavidin conjugated with horseradish peroxidase. Upon the addition of the luminol/peroxide chemiluminescence cocktail, the emitted photons were acquired by the photosensor array.

The preliminary results show a strong linear correlation between the CRP concentration and the CL signal, with a detection limit of 2.8 ng/mL, suitable for clinical applications.

Future advancements will focus on improving the method's robustness and providing a multiplexing ability, ultimately making it suitable for use in space applications.

This research was supported by the Space It Up project funded by the Italian Space Agency, ASI, and the Ministry of University and Research, MUR, under contract n. 2024-5-E.0 - CUP n. I53D24000060005.

The opportunistic Gram-negative bacterium Pseudomonas aeruginosa poses significant challenges in both clinical and environmental settings due to its pathogenicity and resilience. Quorum-sensing (QS) molecules have emerged as promising biomarkers for the detection of P. aeruginosa. This study focused on the development of an alginate-based bioreporter encapsulation system designed for the identification of QS molecules, utilizing a custom-engineered coating formed through the assembly of poly-lysine (PLL). This PLL coating facilitates the passive diffusion of external QS molecules, resulting in a measurable, dose-dependent bioluminescent response. The microbeads reinforced with PLL exhibited substantial stability in the presence of cation scavengers, enabling prolonged shelf life and functionality. The encapsulated bacterial system demonstrated consistent, dose-dependent detection of QS molecules in media containing synthetic autoinducers and in cell-free supernatants derived from wild-type P. aeruginosa (PAO1) cultures. These bioreporter beads maintained their stability during extended storage at both 4 °C and -80 °C, allowing for immediate, on-site sensing without the need for recovery processes. The RhlR-based bioreporter displayed a dynamic detection range of 10 μM to 0.1 nM, with a sensitivity threshold of 50 pM for the designated QS molecules. The LasR-based bioreporter demonstrated a broader range of 5 μM to 0.2 nM and a lower detection threshold of 0.1 nM for 3-oxo-C12-HSL. Furthermore, the bioreporter beads effectively detected the presence of the synthetic QS inhibitor furanone C-30 in a dose-dependent manner. This proof-of-concept optical-fiber-based whole-cell biosensor illustrates the feasibility of employing an encapsulated bioreporter system for the detection of bacteria through specific QS molecules. The results of this study hold promise for potential applications in diagnostics, environmental monitoring, and screening for quorum-sensing inhibitors.

Long-period gratings (LPGs) have attracted increased attention for label-free biosensing; their structure allows for the transmission characteristics of light in these sensors to be modified by variations in the refractive index of the solution in contact with the fiber. This results from an evanescent wave arising from the fiber, which propagates into the external medium over distances of several hundred nanometers.

The implementation of a specialized biolayer on the fiber surface, composed of a biological recognition element (BRE) that is selective for the chosen target, enables the detection of surface refractive index changes resulting from the unique biochemical interaction between the target and the BRE. The same approach can be applied to investigate the deposition or growth of hydrogels and polymers, including novel soft molecularly imprinted polymers (MIPs) derived from neurotransmitters.

The application of these sensitive and adaptable fiber optic sensors has facilitated a comprehensive characterization of the photo-polymerization of acrylamide to produce polyacrylamide (PA) hydrogels; these polymers are used to create a functional and porous layer for the immobilization of antibodies and aptamers for bacterial capture. This aims to analyze the antibiotic resistance of the specific collected microorganisms. The utilization of optical fiber sensors and their integration into specifically constructed, thermally stabilized microfluidic systems harnesses the advantages of the investigated polymers and hydrogels combined with the essential characteristics of LPG sensors, particularly their versatility, cost-effectiveness, and portability.

Acknowledgments:

We acknowledge financial support under the National Recovery and Resilience Plan (PNRR), Mission 4, Component 2, Investment 1.1, Call for tender No. 104 published on 2.2.2022 by the Italian Ministry of University and Research (MUR), funded by the European Union – NextGenerationEU– Projects 202259W5FY_PE4_PRIN2022 Point-Of-Care electroanalytical platform for the detection of bacteria and antibiotic resistance – CUP B53D23013430006, and 2022JRKETK_PE7_PRIN2022 Versatile hybrid in-fiBer Optical-electrocHemical systEMs for wIdely Applicable biosensing – CUP B53D23002670006.

S.T., C.T., and S.S. also acknowledge financial support under the National Recovery and Resilience Plan (PNRR), Mission 4, Component 2, Investment 1.1, Call for tender No. 1409 published on 14.9.2022 by the Italian Ministry of University and Research (MUR), funded by the European Union – NextGenerationEU– Project Title P20227PWE5.PE4 PRIN2022PNRR Discovering the SEcret woRld of pOlyseroTONin for green molecular ImprINting and its application in bioanalytics – CUP B53D23025260001- Grant Assignment Decree No. 1386 adopted on 01/09/2023 by the Italian Ministry of Ministry of University and Research (MUR).

Mid-infrared (IR) sensing keeps evolving with developments in semiconductor materials, laser technologies, and quantum optics. Gases with different absorption bands in this range can be detected in the mid-IR area. Furthermore, molecules can be identified as chemical species with excellent selectivity thanks to their distinct vibrational absorption signatures in the mid-IR band. A metasurface is a type of material engineered to have properties that are not found in naturally occurring materials. The metasurface, composed of a thin layer of structured material, has the ability to control electromagnetic waves, particularly those in the mid-infrared spectrum. This work presents a dual-band, tunable, wide-angle, polarization-insensitive mid-IR sensor composed of L-shaped gold metasurfaces on a dielectric spacer and a gold ground surface. A commercial simulator (Comsol Multiphysics) based on the finite element method is used to engineer the metasurfaces in the shape of double and quadruple L-shaped structures. The absorption spectra of the L-shaped metasurfaces show two different peaks, as shown by the numerical findings. The peaks are confirmed to result from magnetic polariton modes produced at two distinct resonant wavelengths by analyzing the electric field distribution. Furthermore, the proposed structure exhibits strong sensing stability across a broad range of incident angles for both TE and TM polarization. Moreover, we show that by altering the separation between two successive L-shaped structures, such a structure may be tailored to desired wavelengths. When the device's top medium is switched from air to water, the suggested metasurfaces provide a sensitivity of 800 nm/RIU. In conclusion, the proposed metasurfaces in mid-IR sensing are a state-of-the-art technology that combines spectroscopy with sophisticated materials engineering to enable sensing devices that are very sensitive, small, and adaptable for various applications.

The detection of heavy metal contamination is critical for environmental and food safety, given the toxicity of metals like cadmium (Cd²⁺), lead (Pb²⁺), and copper (Cu²⁺). Optical biosensors have emerged as a powerful solution due to their sensitivity, rapid response time, and adaptability for in situ monitoring. Recent advances have integrated novel materials, whole-cell approaches, and functional nanomaterials to enhance optical transduction mechanisms. For example, Durrieu et al. developed an optical algal biosensor utilizing Chlorella vulgaris cells with alkaline phosphatase as the biological recognition element, demonstrating strong inhibition of enzyme activity in the presence of cadmium and lead ions, measurable through fluorescence detection​ [1]. Similarly, Tsai et al. designed a sol–gel-based urease biosensor for detecting Cu²⁺ and Cd²⁺, utilizing FITC-dextran as a pH-sensitive fluorescent probe immobilized within a sol–gel matrix, achieving detection limits as low as 10 µM​ [2].

The incorporation of synthetic biology in whole-cell biosensors has also been shown to improved optical signal generation. For instance, Singh and Kumar reviewed genetically engineered whole-cell biosensors with optical readouts, highlighting the use of bacterial transcriptional regulators such as ArsR and MerR families for arsenic (As³⁺) and mercury (Hg²⁺) detection [3]. Further advancements have utilized quantum dots and gold nanoparticles for signal amplification in fluorescence- and surface plasmon resonance (SPR)-based sensors. These nanomaterials enhance sensitivity by lowering detection limits into the nanomolar range. This review highlights the most recent innovations in optical biosensing for heavy metals, focusing on enzyme inhibition-based methods, whole-cell biosensors, and nanomaterial-enhanced platforms. Optical biosensors represent a promising and sustainable approach to address heavy metal contamination in environmental and food systems.

Fiber gratings have long been utilized as optical sensors, particularly for measuring chemical, biochemical, and physical parameters. These sensors typically operate by detecting changes in the external refractive index or by monitoring physical parameters such as strain, temperature, and pressure. Fiber gratings can be categorized into two main types based on the grating period and their distinct optical characteristics: (i) long-period gratings (LPGs), with grating periods of hundreds of micrometers, couple guided light from the fiber core to the cladding, facilitating interaction with the surrounding environment, and are primarily used for chemical and biochemical sensing; (ii) fiber Bragg gratings (FBGs), with grating periods of hundreds of nanometers, reflect light within the core's fundamental mode and are mainly employed for physical parameter sensing.

This work presents two practical applications of these methodologies. First, we characterize an LPG optical sensor inscribed in an optical fiber, enhanced with a 40 nm gold layer. The gold coating offers several benefits, such as ease of functionalization and the potential for multiphysics sensing, including its use as an electrode for electrical measurements. The fiber sensor is integrated into a thermostated microfluidic system. Our experimental results indicate that the sensor's sensitivity, with the gold coating, is comparable to a similar sensor without the coating. However, the gold layer introduces significant opportunities for integrating electrical and optical sensing capabilities.

The second application involves the design and implementation of a remote sensing apparatus for monitoring deformation and temperature in large structures, such as bridges. This system employs two FBGs: one for strain and one for tilt sensing. The FBG interrogation is managed by a single-board computer, and custom software is developed for data acquisition, analysis, and remote monitoring. The system is designed for low power consumption, with provisions for battery power and solar charging, ensuring energy efficiency and sustainability.

Acknowledgements:
We acknowledge the support of the European Union by the Next Generation EU project PRIN2022 – 2022JRKETK_PE7 - Versatile hybrid in-fiBer Optical-electrocHemical systEMs for wIdely Applicable bioseNsing – BOHEMIAN, and the support of CNR DIITET Project FOE 2022 STRIVE “INOSTRI”.

Abstract:

Solar energy harvesting systems are made up of stages like energy harvesting, DC-DC conversion, MPPT (maximum power point tracker) controllers, and storage. These stages can vary in number and configuration, but they all have the same basic structure: energy harvesting, DCDC conversion/elevation, and storage. Energy-harvesting systems are crucial for the continuous supply of energy in autonomous systems or devices, which is why they are important for Internet of Things applications. A conversion stage is essential for any solar energy-gathering device. Low-power systems use DC-DC converters to increase or decrease the input energy in a voltage that the system needs. For usage in electrical devices, a DC-AC converter transforms the panel's direct current into alternating current. As a renewable and eco-friendly resource that can be utilized for a variety of purposes, including powering sensor networks, the utilization of solar energy to create electricity has expanded the uses of energy harvesting. Voltage multiplier cells used in non-isolated boost DC-DC converters for solar energy harvesting applications are analyzed in this research. One inductor, two capacitors, and two diodes were used to build voltage multiplier cells. The design calculation was used to determine the performance characteristics. The MATLAB/Simulink software was used to test the performance parameter. The results showed that the power efficiency of the boost DC-DC converter based on voltage multiplier cells was 75%. This converter produced ripple voltage, which was 0.0341% of the output voltage with a ripple content of 0.55 volts. Such voltage multiplier cell-based boost converters can be utilized for low-power voltage lifting in solar energy-harvesting systems.