Fiber Optic Probe Research Articles

Experimental investigation of radio frequency heating uniformity of wheat flour surrounded by deionized water and NaCl solution

The present study proposes an approach to overcome the problem of corner/edge overheating of foods undergoing radio frequency heating. For testing, a container with a central rectangular compartment surrounded by a frame of four compartments was used. Wheat flour, a representative of low-moisture foods, was packed inside the rectangular compartment to provide a density of 800 kg/m3. Afterwards, in the surrounding compartments, air, deionized water and NaCl solution were used for independent radio frequency heating tests. Two different electrode gaps (135 and 145 mm) were employed. The temperature of the sample was measured continuously using fibre optic probes at four different internal locations. The difference between the maximum and the minimum temperatures for three different cases (a: air, b: deionized water and c: NaCl solution) were as follows for electrode gaps of 135 and 145 mm, respectively: (a) 27.3 and 26.1 °C, (b) 2.5 and 4.8 °C and (c) 3.7 and 1.8 °C. Uniformity index values were also calculated. The results showed that temperature variation within the sample was greatly reduced when the sample was surrounded by deionized water or NaCl solution. PRACTICAL APPLICATION The project findings will provide processors with a practical means to achieve more uniform radio frequency heating of low-moisture foods.

Potential of Raman spectroscopy for in-line measurement of raw milk composition

A method for the in-line measurement of raw milk composition is beneficial for the dairy industry as it allows processors to make timely decisions, i.e., standardization, prior to the milk entering a process. It facilitates more enhanced operational control and offers the potential for improved process efficiencies. One such technology of potential commercial value is Raman spectroscopy due to its ability to measure macromolecules in an aqueous environment and compatibility with in-line measurements. This study investigated the suitability of Raman spectroscopy to measure macro components (fat, protein, and lactose) in raw milk. 80 raw milk samples were analysed using a Raman spectroscopy instrument coupled with an optical fibre probe. Variations in process variables such as temperature and the effect of agitation on Raman spectral features (intensity, shape, and wavelength shift) were considered prior to model development. Due to the overlapping response of fat, protein, and lactose in the Raman spectrum of raw milk, multivariate regression models were developed for their quantification. The developed partial least squares (PLS) regression models predicted the percentage of fat, protein, and lactose in raw milk with a root mean square error of prediction (RMSEP) of 0.15, 0.11 and 0.04, coefficient of determination for prediction (R2p) 0.96, 0.89 and 0.89, and the ratio of prediction error to deviation (RPD) of 8.16, 3.16, and 2.89.

Non-destructive and in-situ detection of shrimp freshness using mid-infrared fiber-optic evanescent wave spectroscopy.

There is strong interest in non-destructive and rapid determination of food freshness in food research. In this study, mid-infrared (MIR) fiber-optic evanescent wave (FOEW) spectroscopy was applied to monitor shrimp freshness through the evaluation of protein, chitin, and calcite contents in conjunction with a Partial Least Squares Discriminant Analysis (PLS-DA) model. Shrimp shells were wiped with a micro fiber-optic probe to obtain a FOEW spectrum which quickly and nondestructively allowed evaluation of the shrimp freshness. Peaks for proteins, chitin, and calcite, which are closely related to shrimp freshness, were detected and quantified. Compared with the standard indicator for evaluating shrimp freshness (total volatile basic nitrogen), the PLS-DA model gave recognition rates for shrimp freshness using calibration and validation sets of the FOEW data of 87.27%, 90.28%, respectively. Our results show that FOEW spectroscopy is a feasible method for non-destructive and in-site detection of shrimp freshness.

REcaNet: Residual neural networks with initialized weights and attention mechanism for image propagating in multimode optical fiber restoration

Training a neural network to reconstruct images from time-series waveforms obtained from fiber optic probes not only yields high-quality, content-aware images but can also acquire different types of images from lower quality training images. Image reconstruction, as an inverse problem, involves using collected signals and system models to retrieve desired images, encountering mathematical challenges like distortion and degradation. In this paper, we introduce REcaNet, a multi-mode fiber image restoration model based on an enhanced residual convolutional neural network (CNN). The network employs a symmetrical architecture that downscales the image before upscaling it for restoration, and it reconstructs the high-level semantic feature map generated by the encoder to the original image resolution. Additionally, we incorporate weight initialization, attention mechanisms, and residual connections to enhance the final restored feature map with more low-dimensional features and promote fusion of features from distinct layers. The algorithm performs well on three datasets collected by multi-mode fibers, namely Minist, Clothes, and Omiglot. Among them, various indicators such as SSIM have been significantly improved.

Fluctuation analysis and spatial distribution model of particle concentration in a lab-scale scrubbing-cooling chamber

The motion and distribution of ash from coal gasification during the scrubbing and cooling process are crucial for revealing the fluid flow pattern and improving the efficiency of multiphase separation. Experimental measurements of the local solid holdup (εs) in the liquid pool of a laboratory-scale gas-liquid-solid three-phase scrubbing-cooling chamber were carried out using an optical fiber probe. The fluctuations of εs in time and frequency domains under different operating conditions were discussed. The axial and radial distribution of εs was quantitatively analyzed. The results showed that inter-particle collision and particle-fluid interaction are the key factors leading to a fluctuation in particle concentration. Axial uniformity of particle concentration can be quantified by solid-phase volume fraction, particle Reynolds number, Archimedes number, and Morton number; εs in different regions is expressed according to the degree of influence of bubble wake as a correlation equation consisting only of cross-sectional average solid holdup and dimensionless radial position; a dimensionless expression for εs concerning operating conditions was established.

Non-contact optical spectroscopy for tumor-sensitive diffuse reflectance and fluorescence measurements on murine subcutaneous tissue models: Monte Carlo modeling and experimental validations.

Fiber-optic probes are commonly used in biomedical optical spectroscopy platforms for light delivery and collection. At the same time, it was reported that the inconsistent probe-sample contact could induce significant distortions in measured optical signals, which consequently cause large analysis errors. To address this challenge, non-contact optical spectroscopy has been explored for tissue characterizations. However, existing non-contact optical spectroscopy platforms primarily focused on diffuse reflectance measurements and may still use a fiber probe in which the probe was imaged onto the tissue surface using a lens, which serves as a non-contact probe for the measurements. Here, we report a fiber-probe-free, dark-field-based, non-contact optical spectroscopy for both diffuse reflectance and fluorescence measurements on turbid medium and tissues. To optimize the system design, we developed a novel Monte Carlo method to simulate such a non-contact setup for both diffuse reflectance and fluorescence measurements on murine subcutaneous tissue models with a spherical tumor-like target. We performed Monte Carlo simulations to identify the most tumor-sensitive configurations, from which we found that both the depth of the light focal point in tissue and the lens numerical aperture would dramatically affect the system's tumor detection sensitivity. We then conducted tissue-mimicking phantom studies to solidify these findings. Our reported Monte Carlo technique can be a useful computational tool for designing non-contact optical spectroscopy systems. Our non-contact optical setup and experimental findings will potentially offer a new approach for sensitive optical monitoring of tumor physiology in biological models using a non-contact optical spectroscopy platform to advance cancer research.

Label-free Raman microspectroscopic imaging with chemometrics for cellular investigation of apple ring rot and nondestructive early recognition using near-infrared reflection spectroscopy with machine learning

Apple ring rot caused by Botryosphaeria dothidea can cause fruit decay during the growth and storage stages of apple fruit. Understanding the infection process and cellular defense response at the cellular micro-level holds immense importance in the field of prevention and control. Consequently, there is a pressing need to develop suitable chemical imaging analysis methods. Here we proposed a label-free, high-throughput imaging method for cellular investigation of apple fruit ring rot infected by Botryosphaeria dothidea, based on confocal Raman microspectroscopic imaging technology combined with multivariate curve resolution-alternating least squares algorithm (MCR-ALS). We conducted Raman measurements on every apple fruit and obtain an image cube. This cube was then unfolded into an augmented matrix in a column-wise manner. We proceeded with simultaneous MCR-ALS analysis, resolving the single-substance spectrum and concentration profile from the mixed signals. Lastly, the accurate and pure molecular imaging of low methoxyl pectin, high methoxyl pectin, cellulose, lignin, and phenols were realized by refolding the resolved concentration data to construct the composition image. Thereafter, we realized the study of the spatial-temporal changes distribution of the above substances in the cuticle and cell wall of green and red apples at different stages of infection. The imaging method proposed in this paper is expected to provide a chemical imaging strategy for studying pathogen infection process and fruit defense response at the cellular level. In addition, by utilizing a fiber-optic probe near-infrared reflection spectrometer in conjunction with machine learning, we developed a rapid and non-destructive classification method. This method allows for the timely identification of apples exhibiting early infection by Botryosphaeria dothidea. Notably, both principal component analysis-quadratic discriminant analysis and support vector machine achieved a classification accuracy of 100%.

Development of a two-beveled-fiber polarized fiber-optic Raman probe coupled with a ball lens for in vivo superficial epithelial Raman measurements in endoscopy.

We report on the development of a two-beveled-fiber polarized (TBFP) fiber-optic Raman probe coupled with a ball lens for in vivo superficial epithelial Raman measurements in endoscopy. The two-beveled fibers positioned symmetrically along a ball lens, in synergy with paired parallel-polarized polarizers integrated between the fibers and the ball lens, maximize the Raman signal excitation and collection from the superficial epithelium where gastrointestinal (GI) precancer arises. Monte Carlo (MC) simulations and two-layer tissue phantom experiments show that the probe developed detects ∼90% of the Raman signal from the superficial epithelium. The suitability of the probe developed for rapid (<3 s) superficial epithelial Raman measurements is demonstrated on fresh swine esophagus, stomach, and colon tissues, followed by their differentiation with high accuracies (92.1% for esophagus [sensitivity: 89.3%, specificity: 93.2%], 94.1% for stomach [sensitivity: 86.2%, specificity: 97.2%], and 94.1% for colon [sensitivity: 93.2%, specificity: 94.7%]). The presented results suggest the great potential of the developed probe for enhancing in vivo superficial epithelial Raman measurements in endoscopy.

Improved Thermal Sensitivity Using Virtual Monochromatic Imaging Derived from Photon Counting Detector CT Data Sets: Ex Vivo Results of CT-Guided Cryoablation in Porcine Liver

PurposeTo investigate differences in thermal sensitivity of virtual monoenergetic imaging (VMI) series generated from photon-counting detector (PCD) CT data sets, regarding their use to improve discrimination of the ablation zone during percutaneous cryoablation.Materials and MethodsCT-guided cryoablation was performed using an ex vivo model of porcine liver on a PCD-CT system. The ablation zone was imaged continuously for 8 min by acquiring a CT scan every 5 s. Tissue temperature was measured using fiberoptic temperature probes placed parallel to the cryoprobe. CT-values and noise were measured at the tip of the temperature probes on each scan and on VMI series from 40 to 130 keV. Correlation of CT-values and temperature was assessed using linear regression analyses.ResultsFor the whole temperature range of [− 40, + 20] °C, we observed a linear correlation between CT-values and temperature in reference 70 keV images (R2 = 0.60, p < 0.001) with a thermal sensitivity of 1.4HU/°C. For the most dynamic range of [− 15, + 20] °C, the sensitivity increased to 2.4HU/°C (R2 = 0.50, p < 0.001). Using VMI reconstructions, the thermal sensitivity increased from 1.4 HU/°C at 70 keV to 1.5, 1.7 and 2.0HU/°C at 60, 50 and 40 keV, respectively (range [− 40, + 20] °C). For [− 15, + 20]°C, the thermal sensitivity increased from 2.4HU/°C at 70 keV to 2.5, 2.6 and 2.7HU/°C at 60, 50 and 40 keV, respectively. Both CT-values and noise also increased with decreasing VMI keV-levels.ConclusionDuring CT-guided cryoablation of porcine liver, low-keV VMI reconstructions derived from PCD-CT data sets exhibit improved thermal sensitivity being highest between + 20 and − 15 °C.Graphical

Excessive whole-body exposure to 28 GHz quasi-millimeter wave induces thermoregulation accompanied by a change in skin blood flow proportion in rats.

Limited information is available on the biological effects of whole-body exposure to quasi-millimeter waves (qMMW). The aim of the present study was to determine the intensity of exposure to increase body temperature and investigate whether thermoregulation, including changes in skin blood flow, is induced in rats under whole-body exposure to qMMW. The backs of conscious rats were extensively exposed to 28 GHz qMMW at absorbed power densities of 0, 122, and 237 W/m2 for 40 minutes. Temperature changes in three regions (dorsal and tail skin, and rectum) and blood flow in the dorsal and tail skin were measured simultaneously using fiber-optic probes. Intensity-dependent temperature increases were observed in the dorsal skin and the rectum. In addition, skin blood flow was altered in the tail but not in the dorsum, accompanied by an increase in rectal temperature and resulting in an increase in tail skin temperature. These findings suggest that whole-body exposure to qMMW drives thermoregulation to transport and dissipate heat generated on the exposed body surface. Despite the large differences in size and physiology between humans and rats, our findings may be helpful for discussing the operational health-effect thresholds in the standardization of international exposure guidelines.

Fiber Optical Temperature Sensor Based on 980nm Excitation of CaWO4: Yb3+, Er3+ with Up-conversion Fluorescence Intensity Ratio

The Yb3+, Er3+ co-doped calcium tungstate materials were prepared. The temperature-sensitive fiber optic probes made from CaWO4:Yb3+, Er3+ were prepared by the high-temperature solid-phase sintering method. The XRD lattice structure of CaWO4: Yb3+, Er3+ was tested. The fluorescence spectra of the probe under 980nm excitation were tested, and the variable temperature profile of the probe was analyzed to derive its two-photon absorption process. The temperature characteristics of the up-conversion fluorescence intensity ratio (FIR) of the probe in the temperature range of 303-673K were investigated, and the results showed that this optical fiber probe can be used as a fiber optic temperature sensor with a linearity of 5.8% and a temperature measurement return difference of only 1.5%; it was found that the temperature characteristic curve of FIR of this fiber optic probe was reproducible. These properties show that CaWO4: Yb3+, Er3+ is feasible to be made into a fiber optic sensor.

Self-pressurized rapid freezing at arbitrary cryoprotectant concentrations.

Self-pressurized rapid freezing (SPRF) has been proposed as a simple alternative to traditional high pressure freezing (HPF) protocols for vitrification of biological samples in electron microscopy and cryopreservation applications. Both methods exploit the circumstance that the melting point of ice reaches a minimum when subjected to pressure of around 210 [MPa], however, in SPRF its precise quantity depends on sample properties and hence, is generally unknown. In particular, cryoprotective agents (CPAs) are expected to be a factor; though eschewed by many SPRF experiments, vitrification of larger samples notably cannot be envisaged without them. Thus, in this study, we address the question of how CPA concentration affects pressure inside sealed capillaries, and how to design SPRF experiments accordingly. By embedding a fiber-optic probe in samples and performing Raman spectroscopy after freezing, we first present a direct assessment of pressure buildup during SPRF, enabled by the large pressure sensitivity of the Raman shift of hexagonal ice. Choosing dimethyl sulfoxide (DMSO) as a model CPA, this approach allows us to demonstrate that average pressure drops to zero when DMSO concentrations of 15 wt % are exceeded. Since a trade-off between pressure and DMSO concentration represents an impasse with regards to vitrification of larger samples, we introduce a sample architecture with two chambers, separated by a partition that allows for equilibration of pressure but not DMSO concentrations. We show that pressure and concentration in the fiber-facing chamber can be tuned independently, and present differential scanning calorimetry (DSC) data supporting the improved vitrification performance of two-chamber designs. Lay version of abstract for "Self-pressurized rapid freezing at arbitrary cryoprotectant concentrations" Anyone is familiar with pipes bursting in winter because the volume of ice is greater than that of liquid water. Less well known is the fact that inside a thick-walled container, sealed and devoid of air bubbles, this pressure buildup will allow a fraction of water to remain unfrozen if the sample is also cooled sufficiently rapidly far below the freezing point. This phenomenon has already been harnessed for specimen preparation in microscopy, where low temperatures are useful to immobilize the sample, but harmful if ice-formation occurs. However, specimen preparation cannot always rely on this pressure-based effect alone, but sometimes requires addition of chemicals to inhibit ice-formation. Not enough is known directly about how these chemicals affect pressure buildup: Indeed, rapid cooling below the freezing point is only possible for small sample volumes, typically placed inside sealed capillaries, so that space is generally insufficient to accommodate a pressure sensor. By means of a compact sensor, based on an optical fiber, laser and spectrometer, we present the first direct assessment of pressure inside sealed capillaries. We show that addition of chemicals reduces pressure build-up and present a two-chambered capillary to circumvent the resulting trade-off. Also, we present evidence showing that the two-chambered capillary design can avoid ice-formation more readily than a single-chambered one. This article is protected by copyright. All rights reserved.

Fiber-optic temperature probe based on low-coherence Brillouin optical correlation-domain reflectometry

We present a new fiber-optic temperature sensing approach that enables temperature measurements near the tip of an optical fiber without requiring any special processing. By leveraging low-coherence Brillouin optical correlation-domain reflectometry, our proposed configuration eliminates the need for an independent reference light path and instead utilizes the Fresnel reflected light from the fiber tip as the reference. Through experimental validation, we successfully demonstrate the capability to measure temperature within a 40-cm-long region near the fiber tip. This achievement comes with a spatial resolution estimated at 26 cm, which is obtained from the measured laser linewidth. This method offers significant cost and labor savings due to its simplified implementation. © 2023 Elsevier Science. All rights reserved.

Electric field sensing and polarisation measurement using advanced multi-pass interrogation type fiber-optic beam deflection probe

We present an experimental demonstration of precise determination of electric field and polarisation properties of the sample using fiber-optic beam deflection transducer. We use a cantilever-deflection fiber probe formed by coating an optimized composition of cobalt-modified bismuth ferrite nanocomposite over a selected length at the tip of deflecting fiber to sense the surrounding electric field. In a chronological development through designing and investigating a series of experiments, we establish a configuration exhibiting a high-performance electric field sensing scheme. First, we devise a Sagnac loop assisted beam deflection assembly that doubly modulates light with the varying electric field. The observed results of the sensor are theoretically modeled using the associated parameters, and the polarisation properties of the probe sample are fairly determined. To deploy a multi-pass signal circulation through the probe for enhanced sensitivity, we then conceive of a promising ring resonator design and tested. Next, incorporating the beam-deflection probe in the resonator circuit, we test and optimize the performance of the transducer. The signal modulation in the resonator cavity caused by electric field-induced deflection of fiber is then accurately analysed to understand its response and interpret the variety of experimental results. We demonstrate a high-performance electric field sensor that operates precisely in the 0–0.75 kV/cm range. The polarisation properties of the probe sample for the low field range of 0–0.8 kV/cm are also determined. The method is all-optical and safe for deployment in any hazardous environment. Also, it enjoys all the advantages of optical fiber-based instrumentation and can be suitably adapted to explore higher-order design for applications based on electric field sensing.

Assessing Fermentation Broth Quality of Pineapple Vinegar Production with a Near-Infrared Fiber-Optic Probe Coupled with Stability Competitive Adaptive Reweighted Sampling.

In this study, the performance of a near-infrared (NIR) fiber-optic probe coupled with stability competitive adaptive reweighted sampling (SCARS) was investigated for the analysis of acetic acid, ethanol, total soluble solids, caffeic acid, gallic acid, and tannic acid in the broth of pineapple vinegar during fermentation. The NIR spectra of the broth samples in the region of 11,536-3956 cm-1 were collected during vinegar fermentation promoted by Acetobacter aceti. This continuous biological process led to changes in the concentrations of all analytes studied. SCARS provided optimized and stabilized NIR spectral variables for the construction of a partial least squares (PLS) model for each analyte using a small number of optimal variables (under 88 variables). The SCARS-PLS model outperformed the conventional PLS model, and achieved excellent accuracy in accordance with ISO 12099:2017 for the four prediction models of acetic acid, ethanol, caffeic acid, and gallic acid, with root-mean-square error of prediction values of 0.137%, 0.178%, 0.637 μg/mL and 0.640 μg/mL, respectively. In contrast, only an acetic acid content prediction model constructed via the conventional PLS method and using the whole spectral region (949 variables) could pass with acceptable accuracy. These results indicate that the NIR optical probe coupled with SCARS is an appropriate method for the continuous monitoring of multianalytes during vinegar fermentation, particularly acetic acid and ethanol contents, which are indicators of the finished fermentation of pineapple vinegar.

Feasibility studies of multimodal nonlinear endoscopy using multicore fiber bundles for remote scanning from tissue sections to bulk organs

Here, we report on the development and application of a compact multi-core fiber optical probe for multimodal non-linear imaging, combining the label-free modalities of Coherent Anti-Stokes Raman Scattering, Second Harmonic Generation, and Two-Photon Excited Fluorescence. Probes of this multi-core fiber design avoid moving and voltage-carrying parts at the distal end, thus providing promising improved compatibility with clinical requirements over competing implementations. The performance characteristics of the probe are established using thin cryo-sections and artificial targets before the applicability to clinically relevant samples is evaluated using ex vivo bulk human and porcine intestine tissues. After image reconstruction to counteract the data’s inherently pixelated nature, the recorded images show high image quality and morpho-chemical conformity on the tissue level compared to multimodal non-linear images obtained with a laser-scanning microscope using a standard microscope objective. Furthermore, a simple yet effective reconstruction procedure is presented and demonstrated to yield satisfactory results. Finally, a clear pathway for further developments to facilitate a translation of the multimodal fiber probe into real-world clinical evaluation and application is outlined.

Clinical wIRA-hyperthermia: heating properties and effectiveness in lower trunk regions and its accordance with ESHO quality criteria for superficial hyperthermia

Purpose The heating characteristics of water-filtered infrared-A (wIRA) radiation were investigated in vivo in two body regions of healthy humans according to the quality standards of the European Society for Hyperthermic Oncology (ESHO) using an irradiance (infrared-A) of 146 W m−2 as recommended for clinical superficial hyperthermia (HT). Methods wIRA was applied to the abdominal wall and lumbar region for 60 min. Skin surface temperature was limited to ≤43 °C. Tissue temperatures were measured invasively at 1-min intervals before, during and after wIRA exposure using five fiber-optical probes at depths of 1–20 mm. Results Significant differences between body regions occurred during the heating-up phase at depths of 5–15 mm. Thermal steady states were reached at depths ≤5 mm after exposures of 5–6 min, and ≤20 mm after 20 min. On average, the minimum requirements of ESHO were exceeded in both regions by the following factors: ≈3 for the heating rate, ≈2 for the specific absorption rate and ≈1.4 for the temperature rise. Tissue depths with T 90 ≥ 40 °C and T 50 > 41 °C were ≤10 mm, and ≤20 mm for T max ≤ 43 °C. The temperature decay time after termination of irradiation was 1–5 min. Corresponding temperatures were ≤42.2 °C for CEM43 and ≤41.8 °C for CEM43 T 90, i.e., they are inadequate for direct thermal cell killing. Conclusions Thermography-controlled wIRA-HT complies with the ESHO criteria for superficial HT as a radiosensitizer and avoids the risk of thermal skin toxicity.

An ultrasensitive J-shaped optical fiber LSPR aptasensor for the detection of Helicobacter pylori

The development of label-free and sensitive detection of pathogenic bacteria is of great significance for disease prevention and public health protection. In this study, an originally bent structure, named as J-shaped optical fiber probe, was first designed to engineer a localized surface plasmon resonance (LSPR) aptamer biosensor for the rapid and ultrasensitive detection of Helicobacter pylori (H. pylori). The J-shaped optical fiber probe exhibited a significant improvement in refractive index sensitivity (RIS) and LSPR signal response. Meantime, the original sequence of aptamer was truncated in order to effectively capture H. pylori on the optical fiber surface. Besides, a spacer nucleic acid with short stem-loop structure was adopted to control the aptamer density on gold nanoparticles (AuNPs) on the surface of the J-shaped optical fiber probe, which displayed a further enhancement in LSPR signal response. Benefitting from these creative designs, the proposed LSPR biosensor can realize label-free and sensitive detection of H. pylori with a detection limit as low as 45 CFU/mL and a wide linear range from 1.0 × 102 CFU/mL to 1.0 × 108 CFU/mL. At the same time, the sensing strategy can detect the pathogenic bacteria from actual water samples in one step just in 30 min without any sample pretreatment. Due to the advantages of ease-to-preparation, high sensitivity, and rapid analysis, this proposed J-shaped optical fiber LSPR aptasensor can provide a potential strategy for point-of-caring detection of pathogenic bacteria in environmental monitoring and disease diagnosis.

Development of a multi-needle fiberoptic Raman spectroscopy technique for simultaneous multi-site deep tissue Raman measurements in the brain.

We report on the development of a multi-needle fiberoptic Raman spectroscopy (MNF-RS) technique for simultaneous multi-site deep Raman measurements in brain tissue. The multi-needle fiberoptic Raman probe is designed and fabricated using a number of 100 µm core diameter, aluminum-coated fibers under a coaxial laser excitation and Raman collection scheme, enabling simultaneous collection of deep tissue Raman spectra from a number of tissue sites. We have also developed a Raman retrieval algorithm based on the transformation matrix of each individual needle fiber probe projected to different pixels of a charge-coupled device (CCD) for recovering the tissue Raman spectra collected by each needle fiber probe, allowing simultaneous multi-channel detection by a single Raman spectrometer. High-quality tissue Raman spectra of different tissue types (e.g., muscle, fat, gray matter, and white matter in porcine brain) can be acquired in both the fingerprint (900-1800 cm-1) and high-wavenumber (2800-3300 cm-1) regions within sub-second times using the MNF-RS technique. We also demonstrate that by advancing the multi-needle fiberoptic Raman probe into deep porcine brain, tissue Raman spectra can be acquired simultaneously from different brain regions (e.g., cortex, thalamus, midbrain, and cerebellum). The significant biochemical differences across different brain tissues can also be distinguished, suggesting the promising potential of the MNF-RS technique for label-free neuroscience study at the molecular level.

Enhancing fibre optic sensor signals via gold nanoparticle-decorated agarose hydrogels

The main objective of this work was to create a novel sensing material using different sizes of gold nanoparticles (AuNPs) embedded in agarose hydrogel (AG) encapsulated fibre optic sensors. AuNPs (4 nm–40 nm) were synthesized using the chemical reduction method with a reducing agent of sodium borohydride (1% w/v) and trisodium citrate (40 mM). The core of the fibre optic was coated either using a single-layer (4 nm AuNPs, 15 nm AuNPs and AG) or two-layer coating (Au-AG) with the first layer being AG then followed by AuNPs (4 nm or 15 nm). The signal resulting from the AuNPs-AG coated fibre optic probe was tested using spectroscopy with a scanning range from 200 to 1000 nm to establish which sample generated the highest sensing signal. The result demonstrated that the smaller size of AuNPs provides a higher signal compared to a larger size, while the two-layered coating of 4 nm Au-AG significantly boosts the signal of the fibre optic sensor up to 47%. The overall performance of the 4 nm Au-AG coated fibre optic probe was highly promising, demonstrating a refractive index (RI) sensitivity of 3669.8 ± 5.232 RIU−1, with an R2 value of 0.9802. This optimized configuration of coating materials presents the sensor platform as an excellent candidate for further exploration in designing specific sensing applications, such as gas sensors or biosensors. Its remarkable ability to enhance sensor sensitivity holds great promise for advancing sensing technologies.