C-reactive protein (CRP) evaluation in human urine using optical sensor supported by machine learning.

The rapid and sensitive indicator of inflammation in the human body is C-Reactive Protein (CRP). Determination of CRP level is important in medical diagnostics because, depending on that factor, it may indicate, e.g., the occurrence of inflammation of various origins, oncological, cardiovascular, bacterial or viral events. In this study, we describe an interferometric sensor able to detect the CRP level for distinguishing between no-inflammation and inflammation states. The measurement head was made of a single mode optical fiber with a microsphere structure created at the tip. Its surface has been biofunctionalized for specific CRP bonding. Standardized CRP solutions were measured in the range of 1.9 µg/L to 333 mg/L and classified in the initial phase of the study. The real samples obtained from hospitalized patients with diagnosed Urinary Tract Infection or Urosepsis were then investigated. 27 machine learning classifiers were tested for labeling the phantom samples as normal or high CRP levels. With the use of the ExtraTreesClassifier we obtained an accuracy of 95% for the validation dataset. The results of real samples classification showed up to 100% accuracy for the validation dataset using XGB classifier.

A novel interface for cortical columnar neuromodulation with multipoint infrared neural stimulation.

Cutting edge advances in electrical visual cortical prosthetics have evoked perception of shapes, motion, and letters in the blind. Here, we present an alternative optical approach using pulsed infrared neural stimulation. To interface with dense arrays of cortical columns with submillimeter spatial precision, both linear array and 100-fiber bundle array optical fiber interfaces were devised. We deliver infrared stimulation through these arrays in anesthetized cat visual cortex and monitor effects by optical imaging in contralateral visual cortex. Infrared neural stimulation modulation of response to ongoing visual oriented gratings produce enhanced responses in orientation-matched domains and suppressed responses in non-matched domains, consistent with a known higher order integration mediated by callosal inputs. Controls include dynamically applied speeds, directions and patterns of multipoint stimulation. This provides groundwork for a distinct type of prosthetic targeted to maps of visual cortical columns.

Ultrasensitive optical fiber SPR sensor enhanced by Au-NPs-film modified with functionalized CQDs for label-free detecting cobalt (II) ion.

BACKGROUND: Cobalt, an essential trace element, is vital for maintaining human nervous system function, aiding in DNA synthesis, and contributing to red blood cell production. It is helpful for disease diagnosis and treatment plan evaluation by precisely monitoring its concentration changes in the human body. Despite extensive efforts made, due to its ultra-low concentration, the current limit of detection (LOD) as reported is still inadequate and cannot be satisfied with the precise clinical applications. Therefore, it is crucial to develop novel label-free sensors with high sensitivity and excellent selectivity for detecting trace amounts of Co2+. RESULTS: Here, an ultrasensitive optical fiber SPR sensor was designed and fabricated for label-free detection of Co2+ with ultra-low concentration. It is achieved by modifying the carboxyl-functionalized CQDs on the AuNPs/Au film-coated hetero-core fiber, which can specifically capture the Co2+, leading to changes in the fiber's surface refractive index (RI) and subsequent SPR wavelength shifts in the transmission spectrum. Both the Au film and AuNPs on the fiber are modified with CQDs, leveraging their large surface area to enhance the number of active sites and probes. The sensor exhibits an ultra-high sensitivity of approximately 6.67 × 1019 nm/M, and the LOD is obtained as low as 5.36 × 10-20 M which is several orders of magnitude lower compared to other conventional methods. It is also experimentally demonstrated that the sensor possesses excellent specificity, stability, and repeatability, which may be adapted for detecting real clinical samples. SIGNIFICANCE: The CQDs-functionalized optical fiber SPR sensor exhibits substantial potential for precisely detecting Co2+ of trace amounts, which is especially vital for scarce clinical samples. Additionally, the sensing platform with sample sensor fabrication and measurement configuration introduces a novel, highly sensitive approach to biochemical analysis, particularly adapting for applications involving the detection of trace targets, which could also be employed to detect various biochemical targets by facile modification of CQDs with specific groups or biomolecules.

Fluid-Solid Interaction Analysis for Developing In-Situ Strain and Flow Sensors for Prosthetic Valve Monitoring.

Transcatheter aortic valve implantation (TAVI) was initially developed for adult patients, but there is a growing interest to expand this procedure to younger individuals with longer life expectancies. However, the gradual degradation of biological valve leaflets in transcatheter heart valves (THV) presents significant challenges for this extension. This study aimed to establish a multiphysics computational framework to analyze structural and flow measurements of TAVI and evaluate the integration of optical fiber and photoplethysmography (PPG) sensors for monitoring valve function. A two-way fluid-solid interaction (FSI) analysis was performed on an idealized aortic vessel before and after the virtual deployment of the SAPIEN 3 Ultra (S3) THV. Subsequently, an analytical analysis was conducted to estimate the PPG signal using computational flow predictions and to analyze the effect of different pressure gradients and distances between PPG sensors. Circumferential strain estimates from the embedded optical fiber in the FSI model were highest in the sinus of Valsalva; however, the optimal fiber positioning was found to be distal to the sino-tubular junction to minimize bending effects. The findings also demonstrated that positioning PPG sensors both upstream and downstream of the bioprosthesis can be used to effectively assess the pressure gradient across the valve. We concluded that computational modeling allows sensor design to quantify vessel wall strain and pressure gradients across valve leaflets, with the ultimate goal of developing low-cost monitoring systems for detecting valve deterioration.

Optically printed plasmonic fiber tip-assisted SERS-based chemical sensing and single biological cell studies.

BACKGROUND: Precise localized printing of plasmonic nanoparticles at desired locations can find a plethora of applications in diverse areas, including nanophotonics, nanomedicine, and microelectronics. The focused laser beam-assisted optical printing technique has illustrated its potential for the localized printing of differently shaped plasmonic particles. However, the technique is either time-consuming or often requires focused optical radiation, limiting its practical applications. While the optothermal printing technique has recently emerged as a promising technique for the direct and rapid printing of plasmonic nanoparticles onto transparent substrates at lower laser intensities, its potential to print the plasmonic nanoparticles to the core of the optical fiber platforms and utilize it for biological cell trapping as well as an analytical platform remains unexplored. RESULTS: Herein, we demonstrate the thermal-convection-assisted printing of the Ag plasmonic nanoparticles from the plasmonic colloidal solution onto the core of single-mode optical fiber and its multi-functional applications. The direct printing of plasmonic structure on the fiber core via the thermal-convection mechanism is devoid of the requirement of any additional chemical ligand to the fiber core. Further, we demonstrated the potential of the developed plasmonic fiber probe as a multifunctional surface-enhanced Raman spectroscopic (SERS) platform for sensing, chemical reaction monitoring, and single-cell studies. The developed SERS fiber probe is found to detect crystal violet in an aqueous solution as low as 100 pM, with a plasmonic enhancement of 107. Additionally, the capability of the fiber-tip platform to monitor the surface plasmon-driven chemical reaction of 4-nitrothiophenol (4NTP) dimerizing into p, p'-dimercaptoazobenzene (DMAB) is demonstrated. Further, the versatility of the fiber probe as an effective platform for opto-thermophoretic trapping of single biological cells such as yeast, along with its Raman spectroscopic studies, is also shown here. SIGNIFICANCE: In this study, we illustrate for the first time the optothermal direct printing of plasmonic nanoparticles onto the core of a single-mode fiber. Further, the study demonstrates that such plasmonic nanoparticle printed fiber tip can act as a multi-functional analytical platform for optothermally trap biological particles as well as monitoring plasmon-driven chemical reactions. In addition, the plasmonic fiber tip can be used as a cost-effective SERS analytical platform and is thus expected to find applications in diverse areas.

High-Precision Optical Fiber-Based Lickometer.

Quantifying and analyzing licking behavior can offer valuable insights into fundamental neurobiological mechanisms controlling animal consummatory behaviors. Lickometers are typically based on electrical properties, a strategy that comes with limitations, including susceptibility to electrical interference and generation of electrical disturbances in electrophysiological measurements. While optical lickometers offer an alternative method to measure licks and quantify fluid intake in animals, they are prone to false readings and susceptibility to outside light sources. To overcome this problem, we propose a low-cost open-source lickometer that combines a restricted infrared beam defined by optical fibers, with a poke design that allows easy access to the tongue while limiting access of other body parts and external light sources. This device also includes features for detecting nose pokes and presenting visual cues during behavioral tasks. We provide validation experiments that demonstrate the optical lickometer's reliability, high-sensitivity and precision, and its application in a behavioral task, showcasing the potential of this tool to study lick microstructure in combination with other techniques, such as imaging of neural activity, in freely moving mice.

Demixing fluorescence time traces transmitted by multimode fibers.

Optical methods based on thin multimode fibers (MMFs) are promising tools for measuring neuronal activity in deep brain regions of freely moving mice thanks to their small diameter. However, current methods are limited: while fiber photometry provides only ensemble activity, imaging techniques using of long multimode fibers are very sensitive to bending and have not been applied to unrestrained rodents yet. Here, we demonstrate the fundamentals of a new approach using a short MMF coupled to a miniscope. In proof-of-principle in vitro experiments, we disentangled spatio-temporal fluorescence signals from multiple fluorescent sources transmitted by a thin (200 µm) and short (8 mm) MMF, using a general unconstrained non-negative matrix factorization algorithm directly on the raw video data. Furthermore, we show that low-cost open-source miniscopes have sufficient sensitivity to image the same fluorescence patterns seen in our proof-of-principle experiment, suggesting a new avenue for novel minimally invasive deep brain studies using multimode fibers in freely behaving mice.

Cellulose nanocrystals-based optical organohydrogel fiber with customizable iridescent colors for strain and humidity response.

Stimuli-responsive optical hydrogels are widely used in various fields including environmental sensing, optical encryption, and intelligent display manufacturing. However, these hydrogels are susceptible to water losses when exposed to air, leading to structural damage, significantly shortened service lives, and compromised durability. This study presents mechanically robust, environmentally stable, and multi-stimuli responsive optical organohydrogel fibers with customizable iridescent colors. These fibers are fabricated by incorporating tunicate cellulose nanocrystals, alginate, and acrylamide in a glycerol-water binary system. The synthesized fibers exhibit high strength (1.38 MPa), moisture retention capabilities, and elastic properties. Furthermore, a sensor based on these fibers demonstrates high- and low-temperature resistance along with stimuli-responsive characteristics, effectively detecting changes in environmental humidity and strains. Moreover, the fiber sensor demonstrates continuous, repeatable, and quantitatively predictable moisture discoloration responses across a humidity range of 11 % and 98 %. During strain sensing, the optical-organohydrogel-based sensor demonstrates a large working strain (50 %) and excellent cycling stability, underscoring its potential for effectively monitoring a wide range of intricate human motions. Overall, the synthesized fibers and their simple fabrication method can elicit new avenues for numerous related applications including the large-scale implementation of advanced wearable technology.

A pathway for detection of gastric cancer biomarkers via using a layer-by-layer coated D-shaped grinding long-period fiber grating sensor.

Gastric cancer significantly contributes to global cancer mortality, often leading to inoperable stages and high recurrence rates post-surgery. Elevated levels of G-17 and G-gly have been identified as potential risk factors, particularly in patients with duodenal ulcers. This study introduces an innovative D-shaped grinding long-period fiber grating sensor (D-LLPFGs) designed for non-invasive detection of the gastrin G-17 antigen, employing a layer-by-layer chemical self-assembly to bond G-17 antibodies onto the fiber surface through hydrogen bonding. The D-LLPFGs sensor demonstrated significant spectral shifts within 1 min of antigen-antibody interaction, highlighting its rapid detection capability. At an optimized antibody concentration of 4 µg/ml, antigen testing across different concentrations (10, 12.5, 20, 50 µg/ml) showed peak changes at 12.5 µg/ml antigen, with a 1.186 nm shift and 0.503 dB loss. The sensor exhibited a wavelength sensitivity of 0.095 nm/µg/ml, indicating its high sensitivity and potential in gastric cancer classification, diagnosis, and treatment. This research concludes that the D-shaped fiber sensor is an effective and sensitive tool for detecting G-17 antigen levels, presenting a significant advancement in non-invasive gastric cancer diagnosis. Its quick response time and high sensitivity highlight its potential for broad biomedical applications, offering a new avenue for early cancer detection and improving patient prognosis. The success of this study opens the door to further exploration and implementation of fiber optic sensors in clinical settings, marking a significant step forward in the fight against gastric cancer.

A temperature compensated fiber probe for highly sensitive detection in virus gene biosensing.

This research presents an innovative reflective fiber optic probe structure, mutinously designed to detect H7N9 avian influenza virus gene precisely. This innovative structure skillfully combines multimode fiber (MMF) with a thin-diameter seven-core photonic crystal fiber (SCF-PCF), forming a semi-open Fabry-Pérot (FPI) cavity. This structure has demonstrated exceptional sensitivity in light intensity-refractive index (RI) response through rigorous theoretical and experimental validation. The development of a quasi-distributed parallel sensor array, which provides temperature compensation during measurements, has achieved a remarkable RI response sensitivity of up to 532.7 dB/RIU. The probe-type fiber optic sensitive unit, expertly functionalized with streptavidin, offers high specificity in detecting H7N9 avian influenza virus gene, with an impressively low detection limit of 10-2 pM. The development of this biosensor marks a significant development in biological detection, offering a practical engineering solution for achieving high sensitivity and specificity in light-intensity-modulated biosensing. Its potential for wide-ranging applications in various fields is now well-established.

Efficient CO2 Conversion through a Novel Dual-Fiber Reactor System.

Carbon dioxide (CO2) can be converted to valuable organic chemicals using light irradiation and photocatalysis. Today, light-energy loss, poor conversion efficiency, and low quantum efficiency (QE) hamper the application of photocatalytic CO2 reduction. To overcome these drawbacks, we developed an efficient photocatalytic reactor platform for producing formic acid (HCOOH) by coating an iron-based metal-organic framework (Fe-MOF) onto side-emitting polymeric optical fibers (POFs) and using hollow-fiber membranes (HFMs) to deliver bubble-free CO2. The photocatalyst, Fe-MOF with amine-group (-NH2) decoration, provided exceptional dissolved inorganic carbon (DIC) absorption. The dual-fiber system gave a CO2-to-HCOOH conversion rate of 116 ± 1.2 mM h-1 g-1, which is ≥18-fold higher than the rates in photocatalytic slurry systems. The 12% QE obtained using the POF was 18-fold greater than the QE obtained by a photocatalytic slurry. The conversion efficiency and product selectivity of CO2-to-HCOOH were up to 22 and 99%, respectively. Due to the dual efficiencies of bubble-free CO2 delivery and the high QE achieved using the POF platform, the dual-fiber system had energy consumption of only 0.60 ± 0.05 kWh mol-1, 3000-fold better than photocatalysis using slurry-based systems. This innovative dual-fiber design enables efficient CO2 valorization without the use of platinum group metals or rare earth elements.

Chassis-based fiber-coupled optical probe design for reproducible quantitative diffuse optical spectroscopy measurements.

Advanced optical neuromonitoring of cerebral hemodynamics with hybrid diffuse optical spectroscopy (DOS) and diffuse correlation spectroscopy (DCS) methods holds promise for non-invasive characterization of brain health in critically ill patients. However, the methods' fiber-coupled patient interfaces (probes) are challenging to apply in emergent clinical scenarios that require rapid and reproducible attachment to the head. To address this challenge, we developed a novel chassis-based optical probe design for DOS/DCS measurements and validated its measurement accuracy and reproducibility against conventional, manually held measurements of cerebral hemodynamics in pediatric swine (n = 20). The chassis-based probe design comprises a detachable fiber housing which snaps into a 3D-printed, circumferential chassis piece that is secured to the skin. To validate its reproducibility, eight measurement repetitions of cerebral tissue blood flow index (BFI), oxygen saturation (StO2), and oxy-, deoxy- and total hemoglobin concentration were acquired at the same demarcated measurement location for each pig. The probe was detached after each measurement. Of the eight measurements, four were acquired by placing the probe into a secured chassis, and four were visually aligned and manually held. We compared the absolute value and intra-subject coefficient of variation (CV) of chassis versus manual measurements. No significant differences were observed in either absolute value or CV between chassis and manual measurements (p > 0.05). However, the CV for BFI (mean ± SD: manual, 19.5% ± 9.6; chassis, 19.0% ± 10.8) was significantly higher than StO2 (manual, 5.8% ± 6.7; chassis, 6.6% ± 7.1) regardless of measurement methodology (p<0.001). The chassis-based DOS/DCS probe design facilitated rapid probe attachment/re-attachment and demonstrated comparable accuracy and reproducibility to conventional, manual alignment. In the future, this design may be adapted for clinical applications to allow for non-invasive monitoring of cerebral health during pediatric critical care.

An Efficient Bio-Receptor Layer Combined with a Plasmonic Plastic Optical Fiber Probe for Cortisol Detection in Saliva.

Cortisol is a clinically validated stress biomarker that takes part in many physiological and psychological functions related to the body's response to stress factors. In particular, it has emerged as a pivotal tool for understanding stress levels and overall well-being. Usually, in clinics, cortisol levels are monitored in blood or urine, but significant changes are also registered in sweat and saliva. In this work, a surface plasmon resonance probe based on a D-shaped plastic optical fiber was functionalized with a glucocorticoid receptor exploited as a highly efficient bioreceptor specific to cortisol. The developed plastic optical fiber biosensor was tested for cortisol detection in buffer and artificial saliva. The biosensor response showed very good selectivity towards other hormones and a detection limit of about 59 fM and 96 fM in phosphate saline buffer and artificial saliva, respectively. The obtained detection limit, with a rapid detection time (about 5 min) and a low-cost sensor system, paved the way for determining the cortisol concentration in saliva samples without any extraction process or sample pretreatment via a point-of-care test.

Recognition of apnea and hypopnea by non-contact optical fiber mattress and its application in the diagnosis of obstructive sleep apnea hypopnea syndrome: a retrospective study.

Objectives: This study sought to evaluate the diagnostic value of a non-contact optical fiber mattress for apnea and hypopnea and compare it with traditional polysomnography (PSG) in adult obstructive sleep apnea hypopnea syndrome (OSAHS). Methods: To determine the value of a non-contact optical fiber mattress for apnea and hypopnea, six healthy people and six OSAHS patients were selected from Tongji Hospital to design a program to identify apnea or hypopnea. A total of 108 patients who received polysomnography for drowsiness, snoring or other suspected OSAHS symptoms. All 108 patients were monitored with both the non-contact optical fiber mattress and PSG were collected. Results: Six healthy controls and six patients with OSAHS were included. The mean apnea of the six healthy controls was 1.22 times/h, and the mean hypopnea of the six healthy controls was 2 times/h. Of the six patients with OSAHS, the mean apnea was 12.63 times/h, and the mean hypopnea was 19.25 times/h. The non-contact optical fiber mattress results showed that the mean apnea of the control group was 3.17 times/h and the mean hypopnea of the control group was 3.83 times/h, while the mean apnea of the OSAHS group was 11.95 times/h and the mean hypopnea of the OSAHS group was 17.77 times/h. The apnea index of the non-contact optical fiber mattress was positively correlated with the apnea index of the PSG (P < 0.05, r = 0.835), and the hypopnea index of the non-contact optical fiber mattress was also positively correlated with the hypopnea index of the PSG (P < 0.05, r = 0.959). The non-contact optical fiber mattress had high accuracy (area under curve, AUC = 0.889), specificity (83.4%) and sensitivity (83.3%) for the diagnosis of apnea. The non-contact fiber-optic mattress also had high accuracy (AUC = 0.944), specificity (83.4%) and sensitivity (100%) for the diagnosis of hypopnea. Among the 108 patients enrolled, there was no significant difference between the non-contact optical fiber mattress and the polysomnography monitor in total recording time, apnea hypopnea index (AHI), average heart rate, tachycardia index, bradycardia index, longest time of apnea, average time of apnea, longest time of hypopnea, average time of hypopnea, percentage of total apnea time in total sleep time and percentage of total hypopnea time in total sleep time. The AHI value of the non-contact optical fiber mattress was positively correlated with the AHI value of the PSG (P < 0.05, r = 0.713). The specificity and sensitivity of the non-contact optical fiber mattress AHI in the diagnosis of OSAHS were 95% and 93%, with a high OSAHS diagnostic accuracy (AUC = 0.984). Conclusion: The efficacy of the non-contact optical fiber mattress for OSAHS monitoring was not significantly different than PSG monitoring. The specificity of the non-contact optical mattress for diagnosing OSAHS was 95% and its sensitivity was 93%, with a high OSAHS diagnostic accuracy.

An advanced optic-fiber differential sensing system enhanced by molecularly imprinted polymer for specific sodium benzoate detection.

A molecularly imprinted polymer (MIP) based microfiber differential demodulation sensing system for sodium benzoate (SB) concentration detection is proposed. The specific binding of MIP on the surface of microfibers with SB can lead to changes in local refractive index (RI). RI change induces a drift in the interference wavelength, which can be monitored by the power difference between two fiber Bragg gratings (FBGs). The sensing system can detect SB in the concentration range of 0.1-50 µg/ml, and interference wavelength and FBG power difference sensitivities are 0.55 nm/(µg/ml) and 2.64 dB/(µg/ml) in the low concentration range of 0.1-1 µg/ml, respectively, with a limit of detection (LOD) of 0.1 µg/ml. This microfiber differential demodulation sensing system is not only simple to fabricate, but also simplifies the demodulation equipment to reduce the cost, which providing a simple, reliable and low-cost technique for the quantitative detection of SB concentration in beverages and flavoured foods.

Dual-Function Wearable Hydrogel Optical Fiber for Monitoring Posture and Sweat pH.

In recent years, wearable devices have been widely used for human health monitoring. Such monitoring predominantly relies on the principles of optics and electronics. However, electronic detection is susceptible to electromagnetic interference, and traditional optical fiber detection is limited in functionality and unable to simultaneously detect both physical and chemical signals. Hence, a wearable, embedded asymmetric color-blocked optical fiber sensor based on a hydrogel has been developed. Its sensing principle is grounded in the total internal reflection within the optical fiber. The method for posture sensing involves changes in the light path due to fiber bending with color blocks providing wavelength-selective modulation by absorption changes. Sweat pH sensing is facilitated by variations in fluorescence intensity triggered by sweat-induced conformational changes in Rhodamine B. With just one fiber, it achieves both physical and chemical signal detection. Fabricated using a molding technique, this fiber boasts excellent biocompatibility and can accurately discern single and multiple bending points, with a recognition range of 0-90° for a single segment, a detection limit of 0.02 mm-1 and a sweat pH sensing linear regression R2 of 0.993, alongside great light propagation properties (-0.6 dB·cm-1). With its extensive capabilities, it holds promise for applications in medical monitoring.

AI-Assisted Insole Sensing System for Multifunctional Plantar-Healthcare Applications.

The pervasive global issue of population aging has led to a growing demand for health monitoring, while the advent of electronic wearable devices has greatly alleviated the strain on the industry. However, these devices come with inherent limitations, such as electromagnetic radiation, complex structures, and high prices. Herein, a Solaris silicone rubber-integrated PMMA polymer optical fiber (S-POF) intelligent insole sensing system has been developed for remote, portable, cost-effective, and real-time gait monitoring. The system is capable of sensitively converting the pressure of key points on the sole into changes in light intensity with correlation coefficients of 0.995, 0.952, and 0.910. The S-POF sensing structure demonstrates excellent durability with a 4.8% variation in output after 10,000 cycles and provides stable feedback for bending angles. It also exhibits water resistance and temperature resistance within a certain range. Its multichannel multiplexing framework allows a smartphone to monitor multiple S-POF channels simultaneously, meeting the requirements of convenience for daily care. Also, the system can efficiently and accurately provide parameters such as pressure, step cadence, and pressure distribution, enabling the analysis of gait phases and patterns with errors of only 4.16% and 6.25% for the stance phase (STP) and the swing phase (SWP), respectively. Likewise, after comparing various AI models, an S-POF channel-based gait pattern recognition technique has been proposed with a high accuracy of up to 96.87%. Such experimental results demonstrate that the system is promising to further promote the development of rehabilitation and healthcare.

Dual-Mode Comb Plasmonic Optical Fiber Sensing.

Surface plasmon (SP) excitation in metal-coated tilted fiber Bragg gratings (TFBGs) has been a focal point for highly sensitive surface biosensing. Previous efforts focused on uniform metal layer deposition around the TFBG cross section and temperature self-compensation with the Bragg mode, requiring both careful control of the core-guided light polarization and interrogation over most of the C + L bands. To circumvent these two important practical limitations, we studied and developed an original platform based on partially coated TFBGs. The partial metal layer enables the generation of dual-comb resonances, encompassing highly sensitive (TM/EH mode families) and highly insensitive (TE/HE mode families) components in unpolarized transmission spectra. The interleaved comb of insensitive modes acts as wavelength and power references within the same spectral region as the SP-active modes. Despite reduced fabrication and measurement complexity, refractometric accuracy is not compromised through statistical averaging over seven individual resonances within a narrowband window of 10 nm. Consequently, measuring spectra over 60 nm is no longer needed to compensate for small temperature or power fluctuations. This sensing platform brings the following important practical assets: (1) a simpler fabrication process, (2) no need for polarization control, (3) limited bandwidth interrogation, and (4) maintained refractometric accuracy, which makes it a true game changer in the ever-growing plasmonic sensing domain.

Simple Characterization of Cylindrical Diffuser Fibers With a Fluorescent Layer.

OBJECTIVES: A fast, simple, versatile, and reliable method to record light emission intensity profiles of cylindrical light diffusers (CDFs) in air and transparent liquids has been developed. METHODS: A fluorescent color glass filter (RG695) converts red light emitted by a cylindrical diffuser fiber into near-infrared light in an emission angle-independent manner. The red light was provided from a diode laser system at 635 nm. Near-infrared fluorescence from the RG695 was imaged with a camera. Images from this camera were processed to obtain emission intensity profiles. Cylindrical diffuser fiber profiles of four different manufacturers were compared. RESULTS: The proposed method provides angle-independent intensity profiles of cylindrical diffuser fibers with a single camera shot. It could be demonstrated that dependent on the underlying principle of how the diffuser fiber tips emit light, the emission profile can change significantly in media with different refractive indices. CONCLUSIONS: By converting the light emitted by a diffuser fiber tip into fluorescence light one can eliminate the dependence of the recorded profile on the emission angle from the diffusor. This approach allows for easily taking into account refraction-index (mis)matching by placing the equipment into a suitable liquid. The proposed measurement principle bears potential for quality assurance measurements of CDFs used for interstitial laser thermotherapy or photodynamic therapy.

Development of a biophotonic fiber sensor using direct-taper and anti-taper techniques with seven-core and four-core fiber for the detection of doxorubicin in cancer treatment.

Doxorubicin (DOX) is an important drug for cancer treatment, but its clinical application is limited due to its toxicity and side effects. Therefore, detecting the concentration of DOX during treatment is crucial for enhancing efficacy and reducing side effects. In this study, the authors developed a biophotonic fiber sensor based on localized surface plasmon resonance (LSPR) with the multimode fiber (MMF)-four core fiber (FCF)-seven core fiber (SCF)-MMF-based direct-taper and anti-taper structures for the specific detection of DOX. Compared to other detection methods, it has the advantages of high sensitivity, low cost, and strong anti-interference ability. In this experiment, multi-walled carbon nanotubes (MWCNTs), cerium-oxide nanorods (CeO2-NRs), and gold nanoparticles (AuNPs) were immobilized on the probe surface to enhance the sensor's biocompatibility. MWCNTs and CeO2-NRs provided more binding sites for the fixation of AuNPs. By immobilizing AuNPs on the surface, the LSPR was stimulated by the evanescent field to detect DOX. The sensor surface was functionalized with DOX aptamers for specific detection, enhancing its specificity. The experiments demonstrated that within a linear detection range of 0-10 µM, the sensitivity of the sensor is 0.77 nm/µM, and the limit of detection (LoD) is 0.42 µM. Additionally, the probe's repeatability, reproducibility, stability, and selectivity were evaluated, indicating that the probe has high potential for detecting DOX during cancer treatment.