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In this work, we present the detection of proteins expressed by poxvirus with fiber-optic probes based on a semi-distributed interferometer (SDI) assisted by a fiber Bragg grating (FBG), performing the measurement directly into a wastewater sample. Modern biosafety applications benefit from real-time, dynamic-sensing technologies that can perform diagnostic tasks into a wide set of analytes, with a particular emphasis on wastewater, which appears to collect a significant number of viral titers in urban and indoor environments. The SDI/FBG probe can perform substantial progress in this field, as it embeds a dual sensitivity mechanism to refractive index changes (sensitivity up to 266.1 dB/RIU (refractive index units)) that can be exploited in biosensing, while simultaneously having the capability to measure the temperature (sensitivity 9.888 pm/°C), thus providing an intrinsic cross-sensitivity compensation. In addition, a standard FBG analyzer can be used as an interrogator, improving affordability and real-time detection over previous works. The probes have been functionalized with antibodies specific for L1, A27 and A33 vaccinia virus proteins, performing detection of a protein concentration in a scenario compatible with online viral threat detection. Direct detection of wastewater samples shows that the L1-functionalized sensor has a higher response, 9.1–11.3 times higher than A33 and A27, respectively, with a maximum response of up to 1.99 dB and excellent specificity. Dynamic detection in wastewater shows that the sensors have a response over multiple detection cycles, with a sensitivity of 0.024–0.153 dB for each 10-fold increase of concentration.

The research proposes and investigates an extraordinarily sensitive, label-free WaveFlex biosensor utilizing optical fiber technology for the detection of Staphylococcus aureus (S. aureus), a common foodborne bacterium. The WaveFlex biosensor (plasmon Wave based Flexible optical fiber Biosensor) is based on a novel flexible tapered single-mode fiber structure, utilizing gold nanoparticles (AuNPs) to trigger the phenomenon of localized surface plasmon resonance (LSPR). Additionally, the sensitivity is further enhanced using chitosan-coated iron(III) oxide nanoparticles (Fe3O4–CS NPs) and tungsten disulfide quantum dots (WS2-QDs). The optical fiber surface is functionalized with antibodies to achieve specific detection of S. aureus. For S. aureus concentrations at 1 × 108 CFU/mL (colony-forming units per milliliter), the sensor's maximum sensitivity of 2.74 nm/lg (CFU/mL), and a detection limit (LOD) of 6.67 CFU/mL. This ultra-sensitive biosensor holds great potential for widespread applications in various fields, including disease detection, medical diagnostics, and food safety inspection.

Presently, plasmonic sensors are widely employed for the detection of numerous biomolecules found in the human body, owing to their high sensitivity and selectivity even in complex media (e.g., serum, urine, saliva). The most advanced plasmonic sensing technique for real-time screening and monitoring of analyte interactions is surface plasmon resonance (SPR)/localized surface plasmon resonance (LSPR). In recent years, the advancement of signal amplification tags such as gold/silver thin films (nanoparticles) and diverse sensing substrates such as 2D materials (e.g., graphene/MXene) has accelerated the development of SPR/LSPR sensors. This review of the literature focuses on 2D materials-based plasmonic sensors for the detection of various biomolecules, including creatinine, cardiac troponin I, alanine aminotransferase, acetylcholine, cholesterol, glucose, uric acid, and p-cresol. The review concludes with an overview of the advantages and disadvantages of 2D diagnostic materials.

The development of a p-cresol biosensor for aquaculture, marine life, and healthcare applications is described in this study. The biosensor is based on localized surface plasmon resonance (LSPR) and employs a novel tapered-in-tapered fiber (TiTF) probe. Gold nanoparticles (AuNPs) and copper oxide nanoflowers (CuO-NFs) on TiTF structures are immobilized on this probe. The developed probe’s performance was evaluated by measuring the response to a variety of p-cresol solution concentrations. Combining AuNPs and CuO-NFs improves the sensitivity and anti-interference capability of the sensing probe. When the p-cresol solution reacts with the tyrosinase enzyme, the refractive index on the sensing region of the probe changes, and the resulting spectrum varies. The linear range, the limit of detection (LoD), and sensitivity of the proposed sensor are 0–1 mM, 0.14 mM, and 3.8 pm/mM, respectively. The probe is subjected to extensive testing, including LoD, repeatability, reusability, stability, selectivity, and pH testing, that all obtain satisfactory results. [ABSTRACT FROM AUTHOR]

This article presents the photonic crystal fiber (PCF) based surface plasmon resonance (SPR) biosensor for early detection of malaria disease in humans by measurement of the variation of red blood cells (RBCs). In the proposed PCF, two layers of air holes are arranged in a hexagonal lattice structure and a thin film of gold-coating is used over PCF for the occurrence of SPR phenomena. It occurs when surface plasmon polariton (SPP)-mode coupled with the core-mode during phase-matching conditions. Malaria infected RBCs samples are filled into the PCF, which have own refractive index (RI) that shift the SPR resonance wavelength during confinement loss measurement. The resonance wavelength of malaria-infected RBCs samples is different from their normal RBCs samples due to the difference in RI of infected and normal RBCs samples. The proposed work is helpful in the detection of different stages of malaria-infected RBCs such as ring phase, trophozoite phase and Schizont phase by measuring the shift in resonance wavelength. The calculated wavelength sensitivities of the proposed sensor for the ring phase, trophozoite phase and Schizont phase RBCs are 13714.29 nm/RIU, 9789.47 nm/RIU, and 8068.97 nm/RIU, respectively in x-polarized direction and 14285.71 nm/RIU, 10000 nm/RIU, and 8206.9 nm/RIU, respectively in y-polarized direction with the maximum detection limit of 0.029. The proposed PCF-based SPR biosensor is suitable for the early diagnosis of malaria disease due to its enhanced sensing performance (low detection limit and high sensitivity). [ABSTRACT FROM AUTHOR]

Optical Backscatter Reflectometry (OBR) is an advanced distributed sensing technique that makes use of optical fibers to detect and localize physical parameters, with spatial resolution below the millimeter. By tailoring the Rayleigh scattering properties of optical fibers, enhancing the backscattering contents, we can create 2 and 3-dimensional sensing networks that can extend OBR to multi-dimensional sensing, and even to biosensing. In this work, we provide a tutorial on distributed optical fiber sensors with enhanced backscattering, and on how to design sensing networks with these fibers; we also review the main applications and emerging topics. [ABSTRACT FROM AUTHOR]

• We propose a fiber optic sensor based on a semi-distributed interferometer (SDI). • The SDI device is a distributed cavity formed by a high-scattering fiber. • The SDI achieves average sensitivity of 92.5 dB/RIU. • Functionalized SDI probes have been reported for detection of CCL5 biomarker. • The detection limit is 17.6 aM in serum. We present an optical fiber label-free biosensor based on a partially stochastic Fabry-Perot interferometer for the detection of CCL5 (CC Chemokine Ligand 5) cancer biomarker. The sensor has a very simple fabrication process, with a splice-and-cleave approach that requires only one splice and a subsequent cleave at the fiber tip. The enhanced backscattering within the Mg-NP fiber paired with the Fresnel reflection at the fiber tip forms a low-finesse interferometric structure; the inner reflections due to Rayleigh scattering provide an additional layers of phase shifts, forming a semi-distributed interferometer (SDI). The average sensitivity of the SDI sensors has been reported to be 92.5 dB/RIU. Sensors were biofunctionalized for the purpose of detecting CCL5 by means of a silanization process. We report the detection of CCL5 in diluted serum with a sensitivity of 2.947 mRIU for each 10-fold concentration increase and a limit of detection of 17.6 aM. [ABSTRACT FROM AUTHOR]

The increasing demand for vitamin D status assessment has highlighted the need for rapid, sensitive, and user-friendly methods for its detection in biological samples potentially integrated in Point-of-Care (PoC) diagnostic devices. Detection of the major circulating form of vitamin D, 25-hydroxyvitamin D3-25(OH)D3, is particularly challenging due to the laborious procedures for sample preparation and its low molecular weight (∼400 Da), which requires highly sensitive detection methods. In this study, we developed a novel label-free Lab-on-Fiber biosensing platform for highly sensitive detection of 25(OH)D3 based on the integration of plasmonic metasurfaces (MSs) on the tip of a single-mode optical fiber (OF). A dedicated pipeline was carefully designed and developed to optimize the bio-functionalization of the plasmonic sensor tip to specifically detect the target biomolecule. The resulting MS-assisted Lab-on-fiber platform enables direct and highly sensitive detection of 25(OH)D3 in clinically relevant ranges (4–160 ng/mL), both in buffer solution and complex matrix, with limits of detection (LOD) of 1.40 ng/mL in saline buffer and 0.85 ng/mL in complex matrix. Overall, these results demonstrate that our platform can successfully and specifically detect small molecules in label-free configuration, with performances comparable to those of conventional methods used in clinical practice. The high degree of miniaturization combined with its high sensitivity makes our platform an exceptional building block for realizing valid diagnostic alternatives for label-free detection of clinically relevant analytes, which can be transformed into new low-cost, fast, simple, and ready-to-use PoC diagnostic devices with improved processability and performance compared to current methods. • A new metasurfaces-based Lab-on-Tip biosensing platform for the highly sensitive detection of 25(OH)D3 is developed • Metasurface-enhanced biosensor enables direct detection of 25(OH)D3 in clinically relevant ranges (4 – 160 ng/mL). • Optical Fiber Meta-Tip biosensor enables direct detection of 25(OH)D3 with LOD of 0.85 ng/mL in complex matrix. [ABSTRACT FROM AUTHOR]

A biosensor based on an etched Fiber Bragg Grating (EFBG) for thrombin detection is reported. The sensing system is based on a Fiber Bragg Grating (FBG) with a Bragg wavelength of 1550 nm, wet-etched in hydrofluoric acid (HF) for ~27 min, to achieve sensitivity to a refractive index (RI) of 17.4 nm/RIU (refractive index unit). Subsequently, in order to perform a selective detection of thrombin, the EFBG has been functionalized with silane-coupling agent 3-(aminopropyl)triethoxysilane (APTES) and a cross-linker, glutaraldehyde, for the immobilization of thrombin-binding aptamer. The biosensor has been validated for thrombin detection in concentrations ranging from 10 nM to 80 nM. The proposed sensor presents advantages with respect to other sensor configurations, based on plasmonic resonant tilted FBG or Long Period Grating (LPG), for thrombin detection. Firstly, fabricating an EFBG only requires chemical etching. Moreover, the functionalization method used in this study (silanization) allows the avoidance of complicated and expensive fabrications, such as thin film sputtering or chemical vapor deposition. Due to their characteristics, EFBG sensors are easier to multiplex and can be used in vivo. This opens new possibilities for the detection of thrombin in clinical settings.

A versatile lossy mode resonance (LMR) sensor is developed for Epinephrine monitoring based on the state-of-the-art molecular imprinting technique over an optical fiber. The optical absorption concept of the LMR-based sensor is proven by incorporating an amino silane-functionalized graphene oxide (SiO 2 -NH 2 @GO) as an adhesive layer for grafting Epinephrine imprinting polydopamine (Ep-IPDA) as a sensing layer onto the optical fiber curved surface. The accurate structural and morphological characterization confirmed the rough crystalline and spherical particles for Ep-IPDA and SiO 2 -NH 2 -GO onto optical fiber curved surface, while spectroscopic analysis confirms the formation of imprinting polymer and desirable absorbance characteristics. The optimized probe exhibits an excellent performance with the maximum sensitivity within two intervals of 0.3–1 µM and 1–90 µM along with the linearity coefficient of R2 = 0.99 possessing a low limit of detection of 0.07 µM. Additionally, this sensor selectively detects Ep in the presence of other species and showed good recovery in human urine and injection samples. This work opens a new avenue for developing bio-inspired LMR-based optical fiber biosensors and could be further extended to detect other catecholamine neurotransmitters. • A layer of SiO 2 -NH 2 @GO was used for grafting Ep-IPDA onto the optical fiber. • Characterization confirmed coating of Ep-IPDA and SiO 2 -NH 2 -GO onto optical fiber. • Operating fabrication parameters were fully optimized at different parameters. • Sensitivity for 0.3–1 µM and 1–90 µM Ep obtained with R2 = 0.99 and LOD of 2.8 nM. [ABSTRACT FROM AUTHOR]

• A novel SPR sensor based on modified plastic Light-Diffusing Fibers is presented. • The plasmonic LDFs platform structure presents a built-in measuring cell. • The micromachining process improves the sensor performances. • The SPR sensing region in the measuring cell can be combined with receptor layers. In this work, a novel Surface Plasmon Resonance (SPR) sensor based on plastic light-diffusing fibers (LDFs) has been developed and investigated. The plasmonic platform structure includes an integrated measuring cell to avoid complex microfluidic systems and all the downsides that characterize them. In a first step, the developed sensor configuration has been optically tested in a refractive index range between 1.332 and 1.371 and then compared with other configurations. The obtained results have highlighted an improvement of about 40% in terms of bulk sensitivity with respect to a similar experimental configuration based on the same LDF but without modification, despite a slight worsening in terms of Full Width at Half Maximum (FWHM), whose value increases of about 20%. So, the obtained experimental results have denoted the possibility and feasibility of using this plasmonic configuration in biochemical sensing application fields. In particular, the proposed SPR sensor platform offers two key characteristics: a convenient measuring cell into the optical fiber and better sensitivity in the considered refractive index range. Furthermore, the plasmonic sensing region in the measuring cell can be combined with simple microfluidic systems or a dropping approach. [ABSTRACT FROM AUTHOR]

• Minimalistic single-mode fiber biosensors are reviewed; • The fabrication methods for express, minimalistic biosensors are outlined; • A comparison between traditional and minimalistic biosensors paves the road for novel applications; • Minimalistic biosensors require the handling of quasi-random optical spectra. Optical fiber biosensors are receiving significant interest, as they allow real-time, low-limit, and high precision detection of biological analytes such as biomarkers, proteins, and small cells. Classical biosensor designs include gratings, interferometers, and plasmonic structures; however, these systems require a complex design, hard to manufacture on high volumes. Recently, several biosensors having a minimalistic design, rapid and suitable to be automated, have been proposed; the key asset is the scalability potential, in view of fabricating numerous devices for disposable use or for large parallel immunoassays. This new sensor class features reflector-less sensors, shallow tapers, and ball resonators; a pseudo-random spectrum characterizes all these biosensors. In this paper, we provide a bird-eye view of these minimalistic designs and a perspective of their use in advanced biosensing applications. [ABSTRACT FROM AUTHOR]

• Unconventional light-diffusing fiber (LDF) plasmonic platform for biosensing. • Novel data analysis methodology for the calculation of the resonance wavelength value. • IgG/anti-IgG in buffer and CRP/anti-CRP in serum bioassays implemented and tested on the proposed sensing system. • Thermo-stabilized microfluidic system for the stabilization of the signal and reduction of the noise. In this work, an unconventional light-diffusing fiber (LDF) plasmonic platform is exploited to efficiently monitor a bio-interaction. The surface plasmon resonance (SPR)-LDF sensor is used to detect the immunoglobulin G (IgG)/anti-IgG interaction as exemplifying bioassay. The IgG bioreceptor was deposited on the gold surface of the SPR-LDF platform, and the biological target was transported through a customized thermo-stabilized flow cell by means of a buffer fluid. Moreover, to test the usability of the proposed SPR-LDF biosensor also for immunosensing in complex matrices, a second assay was conducted by immobilizing anti-C-reactive protein (CRP) and detecting different concentrations of CRP in human serum. An innovative data analysis approach for the extraction of the best value of the resonance wavelength was developed and applied. The obtained results reveal that the unconventional platform represented by the LDF can be successfully exploited for the implementation of SPR-based biosensors with very good performances, also when compared to more common SPR systems. [ABSTRACT FROM AUTHOR]

Optical sensors for biomedical applications have gained prominence in recent decades due to their compact size, high sensitivity, reliability, portability, and low cost. In this review, we summarized and discussed a few selected techniques and corresponding technological platforms enabling the manufacturing of optical biomedical sensors of different types. We discussed integrated optical biosensors, vertical grating couplers, plasmonic sensors, surface plasmon resonance optical fiber biosensors, and metasurface biosensors, Photonic crystal-based biosensors, thin metal films biosensors, and fiber Bragg grating biosensors as the most representative cases. All of these might enable the identification of symptoms of deadly illnesses in their early stages; thus, potentially saving a patient's life. The aim of this paper was not to render a definitive judgment in favor of one sensor technology over another. We presented the pros and cons of all the major sensor systems enabling the readers to choose the solution tailored to their needs and demands. [ABSTRACT FROM AUTHOR]

A biosensor based on an etched Fiber Bragg Grating (EFBG) for thrombin detection is reported. The sensing system is based on a Fiber Bragg Grating (FBG) with a Bragg wavelength of 1550 nm, wet-etched in hydrofluoric acid (HF) for ~27 min, to achieve sensitivity to a refractive index (RI) of 17.4 nm/RIU (refractive index unit). Subsequently, in order to perform a selective detection of thrombin, the EFBG has been functionalized with silane-coupling agent 3-(aminopropyl)triethoxysilane (APTES) and a cross-linker, glutaraldehyde, for the immobilization of thrombin-binding aptamer. The biosensor has been validated for thrombin detection in concentrations ranging from 10 nM to 80 nM. The proposed sensor presents advantages with respect to other sensor configurations, based on plasmonic resonant tilted FBG or Long Period Grating (LPG), for thrombin detection. Firstly, fabricating an EFBG only requires chemical etching. Moreover, the functionalization method used in this study (silanization) allows the avoidance of complicated and expensive fabrications, such as thin film sputtering or chemical vapor deposition. Due to their characteristics, EFBG sensors are easier to multiplex and can be used in vivo. This opens new possibilities for the detection of thrombin in clinical settings. [ABSTRACT FROM AUTHOR]