Optical fiber SPR biosensor based on gold nanoparticle amplification for DNA hybridization detection

Surface electric field enhanced biosensor based on symmetrical U-tapered HCF structure for gastric carcinoma biomarker trace detection

In this article, a novel U-tapered hollow-core fiber (HCF) surface plasmon resonance (SPR) biosensor coated with PtS2 for early-stage gastric carcinoma (GC) diagnosis was demonstrated. The article proposed the first investigation to detect Interleukin-10 (IL10) and Interleukin-1β (IL1β) which were associated with the risk of developing gastric carcinoma, using optical fiber SPR technology. Herein, the sensitivity of sensor was effectively improved through a combination of tapered and U-shaped structures. Additionally, to further enhance the detection capability, two-dimensional material PtS2 was utilized to increase the surface electric field intensity of the sensor. Simultaneously, optimization of structural parameters such as taper ratio, bending diameters, and Au film thickness was conducted. Ultimately, the designed sensor achieved a remarkable sensitivity of 13210 nm/RIU within the refractive index (RI) range of 1.33-1.37. The sensor demonstrated exceptional performance, achieving sensitivities of 3.64 nm/(ng/ml) and 7.46 nm/(ng/ml) for the detection of IL10 and IL1β biomarkers, respectively, along with limit of detection (LOD) of 2.74 pg/ml and 1.33 pg/ml, and successfully detecting the presence of these biomarkers in the serum of gastric cancer patients. Overall, the proposed sensor exhibits significant potential in early gastric cancer detection and advances the application of optical fiber SPR sensors in trace biodetection.

Fluorometric determination of mecA gene in MRSA with a graphene-oxide based bioassay using flap endonuclease 1-assisted target recycling and Klenow fragment-triggered signal amplification

Methicillin-resistant Staphylococcus aureus (MRSA) is a multidrug-resistant bacterium that causes a wide range of illnesses, necessitating the development of new technologies for its detection. Herein, we propose a graphene oxide (GO)-based sensing platform for the detection of mecA gene in MRSA using flap endonuclease 1 (FEN1)-assisted target recycling and Klenow fragment (KF)-triggered signal amplification. Without the target, all the DNA probes were adsorbed onto GO, resulting in fluorescence quenching of the dye. Upon the addition of the target, a triple complex was formed that triggered FEN1-assisted target recycling and initiated two polymerization reactions with the assistance of KF polymerase, generating numerous dsDNA that were repelled by GO. These dsDNAs triggered fluorescence enhancement when SYBR Green I was added. Therefore, the target DNA was quantified by measuring the fluorescence at excitation and emission wavelengths of 480/526 nm. This mecA gene assay showed a good linear range from 1 to 50 nM with a lower limit of detection of 0.26 nM, and displayed good applicability to the analysis of real samples. Thus, a new method for monitoring MRSA has been developed that has great potential for early clinical diagnosis and treatment.

An enhanced SPR optical fiber biosensor using Ti3C2Tx MXene/AuNPs for label-free and sensitive detection of human IgG

Abnormal human immunoglobulin G (IgG) may induce the risk of immune system disorder, infectious diseases, tumors and so on. However, the current detection methods exhibit low sensitivity, which limits their practical application. In this work, an SPR optical fiber sensor (SPR-OFS) with high sensitivity is designed for label-free detection of human IgG. It is fabricated using a heterostructure optical fiber coated with Au film/AuNPs and the Ti3C2Tx MXene biofunctionalized with goat anti-human IgG by polydopamine (PDA). In the experiment, the optimal thickness of the Ti3C2Tx MXene was explored and determined to be about 93 nm by comprehensively considering the refractive index (RI) sensitivity and spectral bandwidth of the SPR sensor. When the largest figure of merit (FOM) is calculated to be 17.8279 RIU-1, its RI sensitivity was ultimately found to be 2804.5 nm per RIU. The SPR-OFS was employed to detect human IgG within the concentration range of 0-30 μg mL-1 and its sensitivity is demonstrated to be 1.7046 nm (μg mL-1)-1. The SPR-OFS was also proved to have excellent linearity, specificity and stability. The proposed sensor offers outstanding performance with simple fabrication, providing a cutting-edge bioanalytical platform with potential applications in clinical diagnosis.

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.

In Situ Measurement of Urea Concentration With an In-Fiber SPR-MZI Sensor

A fiber-optic urea sensor based on surface plasmon resonance (SPR) and Mach-Zehnder interference (MZI) combined principle was designed and implemented. By plating gold film on the single-mode-no-core-thin-core-single-mode fiber structure, we successfully excited both SPR and MZI, and constructed two parallel detection channels for simultaneously measurement of urea concentration and temperature. Urease was immobilized on the gold film by metal-organic zeolite skeleton (ZIF-8), which can not only fix a large number of urease to improve measurement sensitivity of urea, but also protect urease activity to ensure the sensor stability. Experimental results indicate that the designed urea sensor with temperature compensation function can detect urea solution with concentration of 1-9 mM, and the sensitivity is 1.4 nm/mM. The proposed measurement method provides a new choice for monitoring urea concentration in the field of medical diagnosis and human health monitoring.

Advances in Nanoplasmonic Biosensors: Optimizing Performance for Exosome Detection Applications

The development of sensitive and specific exosome detection tools is essential because they are believed to provide specific information that is important for early detection, screening, diagnosis, and monitoring of cancer. Among the many detection tools, surface-plasmon resonance (SPR) biosensors are analytical devices that offer advantages in sensitivity and detection speed, thereby making the sample-analysis process faster and more accurate. In addition, the penetration depth of the SPR biosensor, which is <300 nm, is comparable to the size of the exosome, making the SPR biosensor ideal for use in exosome research. On the other hand, another type of nanoplasmonic sensor, namely a localized surface-plasmon resonance (LSPR) biosensor, has a shorter penetration depth of around 6 nm. Structural optimization through the addition of supporting layers and gap control between particles is needed to strengthen the surface-plasmon field. This paper summarizes the progress of the development of SPR and LSPR biosensors for detecting exosomes. Techniques in signal amplification from two sensors will be discussed. There are three main parts to this paper. The first two parts will focus on reviewing the working principles of each sensor and introducing several methods that can be used to isolate exosomes. This article will close by explaining the various sensor systems that have been developed and the optimizations carried out to obtain sensors with better performance. To illustrate the performance improvements in each sensor system discussed, the parameters highlighted include the detection limit, dynamic range, and sensitivity.

Advancements and Perspectives in Optical Biosensors

Optical biosensors exhibit immense potential, offering extraordinary possibilities for biosensing due to their high sensitivity, reusability, and ultrafast sensing capabilities. This review provides a concise overview of optical biosensors, encompassing various platforms, operational mechanisms, and underlying physics, and it summarizes recent advancements in the field. Special attention is given to plasmonic biosensors and metasurface-based biosensors, emphasizing their significant performance in bioassays and, thus, their increasing attraction in biosensing research, positioning them as excellent candidates for lab-on-chip and point-of-care devices. For plasmonic biosensors, we emphasize surface plasmon resonance (SPR) and its subcategories, along with localized surface plasmon resonance (LSPR) devices and surface enhance Raman spectroscopy (SERS), highlighting their ability to perform diverse bioassays. Additionally, we discuss recently emerged metasurface-based biosensors. Toward the conclusion of this review, we address current challenges, opportunities, and prospects in optical biosensing. Considering the advancements and advantages presented by optical biosensors, it is foreseeable that they will become a robust and widespread platform for early disease diagnostics.

2D material-based surface plasmon resonance biosensors for applications in different domains: an insight

The design of surface plasmon resonance (SPR) sensors has been greatly enhanced in recent years by the advancements in the production and integration of nanostructures, leading to more compact and efficient devices. There have been reports of novel SPR sensors having distinct nanostructures, either as signal amplification tags like gold nanoparticles (AuNPs) or as sensing substrate-like two-dimensional (2D) materials including graphene, transition metal dichalcogenides (TMDCs), MXene, black phosphorus (BP), metal-organic frameworks (MOFs), and antimonene. Such 2D-based SPR biosensors offer advantages over conventional sensors due to significant increases in their sensitivity with a good figure of merit and limit of detection (LOD). Due to their atomically thin structure, improved sensitivity, and sophisticated functionalization capabilities, 2D materials can open up new possibilities in the field of healthcare, particularly in point-of-care diagnostics, environmental and food monitoring, homeland security protection, clinical diagnosis and treatment, and flexible or transient bioelectronics. The present study articulates an in-depth analysis of the most recent developments in 2D material-based SPR sensor technology. Moreover, in-depth research of 2D materials, their integration with optoelectronic technology for a new sensing platform, and the predicted and experimental outcomes of various excitation approaches are highlighted, along with the principles of SPR biosensors. Furthermore, the review projects the potential prospects and future trends of these emerging materials-based SPR biosensors to advance in clinical diagnosis, healthcare biochemical, and biological applications.

Advancing MicroRNA Detection: Enhanced Biotin-Streptavidin Dual-Mode Phase Imaging Surface Plasmon Resonance Aptasensor

MicroRNAs (miRNAs) are novel tumor biomarkers owing to their important physiological functions in cell communication and the progression of multiple diseases. Due to the small molecular weight, short sequence length, and low concentration levels of miRNA, miRNA detection presents substantial challenges, requiring the advancement of more refined and sensitive techniques. There is an urgent demand for the development of a rapid, user-friendly, and sensitive miRNA analysis method. Here, we developed an enhanced biotin-streptavidin dual-mode phase imaging surface plasmon resonance (PI-SPR) aptasensor for sensitive and rapid detection of miRNA. Initially, we evaluated the linear sensing range for miRNA detection across two distinct sensing modalities and investigated the physical factors that influence the sensing signal in the aptamer-miRNA interaction within the PI-SPR aptasensor. Then, an enhanced biotin-streptavidin amplification strategy was introduced in the PI-SPR aptasensor, which effectively reduced the nonspecific adsorption by 20% and improved the limit of detection by 548 times. Furthermore, we have produced three types of tumor marker chips, which utilize the rapid sensing mode (less than 2 min) of PI-SPR aptasensor to achieve simultaneous detection of multiple miRNA markers in the serum from clinical cancer patients. This work not only developed a new approach to detect miRNA in different application scenarios but also provided a new reference for the application of the biotin-streptavidin amplification system in the detection of other small biomolecules.

Optical Fiber Surface Plasmon Resonance Sensor for Glyceryl Tributyrate Detection Based on the PAA/CS Composite Hydrogel Embedding Protease Method

Glycerol tributyrate as a low-density lipoprotein plays a crucial role in drug development and food safety. In this work, a novel high-stability fiber optic sensor for glyceryl tributyrate based on the poly(acrylic acid) (PAA) and chitosan (CS) composite hydrogel embedding method is first proposed. Compared with traditional functionalization, the lipase in a polymer network structure used in this article can not only avoid chemical reactions that cause damage to the enzyme structure but also avoid the instability of ionic bonds and physical adsorption. Therefore, the PAA/CS hydrogel method proposed in this article can effectively retain enzyme structure. First, the impact of different layers (one to five layers) of PAA/CS on pH sensing performance was explored, and it was determined that layers 1-3 could be used for subsequent sensing experiments. Within the linear detection range of 0.5-10 mM, the detection sensitivities of the one to three layers of the biosensor are divided into 0.65, 0.95, and 1.51 nm/mM, respectively, with the three layers having the best effect. When the number of coating layers is three, the detection limit of the sensor is 0.47 mM, meeting the millimole level detection standard for anticancer requirement. Furthermore, the stability and selectivity of the sensor (in the presence of hemoglobin, urea, cholesterol, acetylcholine, and glucose) were analyzed. The three-layer sensor is used for sample detection. At concentrations of 1-10 mM, the absolute value of the recovery percentage (%) is 82-99%, which can accurately detect samples. The sensor proposed in this paper has the advantages of low sample consumption, high sensitivity, simple structure, and label-free measurement. The enzyme-embedding method provides a new route for rapid and reliable glyceryl tributyrate detection, which has potential applications in food safety as well as the development of anticancer drugs.

Magnetic microspheres enhanced peanut structure cascaded lasso shaped fiber laser biosensor for cancer marker-CEACAM5 detection in serum

The detection of trace cancer markers in body fluids such as blood/serum is crucial for cancer diseases screening and treatment, which requires high sensitivity and specificity of biosensors. In this study, a peanut structure cascaded lasso (PSCL) shaped fiber sensing probe based on fiber laser demodulation method was proposed to specifically detect the carcinoembryonic antigen related cell adhesion molecules 5 (CEACAM5) protein in serum. Thanks for the narrow linewidth and high signal-to-noise ratio (SNR) of the laser spectrum, it is easier to distinguish small spectral changes than interference spectrum. Adding the antibody modified magnetic microspheres (MMS) to form the sandwich structure of "antibody-antigen-antibody-MMS", and amplified the response caused by biomolecular binding. The limit of detection (LOD) for CEACAM5 in buffer could reach 0.11 ng/mL. Considering the common threshold of 5 ng/mL for CEA during medical screening and the cut off limit of 2.5 ng/mL for some kits, the LOD of proposed biosensor meets the actual needs. Human serum samples from a hospital were used to validate the real sensing capability of proposed biosensor. The deviation between the measured value in various serum samples and the clinical value ranged from 1.9 to 9.8 %. This sensing scheme holds great potential to serve as a point of care testing (POCT) device and extend to more biosensing applications.

Portable optical fiber biosensors integrated with smartphone: technologies, applications, and challenges [Invited]

The increasing demand for individualized health monitoring and diagnostics has prompted considerable research into the integration of portable optical fiber biosensors integrated with smartphones. By capitalizing on the benefits offered by optical fibers, these biosensors enable qualitative and quantitative biosensing across a wide range of applications. The integration of these sensors with smartphones, which possess advanced computational power and versatile sensing capabilities, addresses the increasing need for portable and rapid sensing solutions. This extensive evaluation thoroughly examines the domain of optical fiber biosensors in conjunction with smartphones, including hardware complexities, sensing approaches, and integration methods. Additionally, it explores a wide range of applications, including physiological and chemical biosensing. Furthermore, the review provides an analysis of the challenges that have been identified in this rapidly evolving area of research and concludes with relevant suggestions for the progression of the field.

Highly sensitive ammonia sensor based on a PMMA/PANI microwire structure

In this paper, a highly sensitive ammonia (N H 3) sensor based on a polymethyl methacrylate/polyaniline (PMMA/PANI) microwire structure is designed and implemented. First, a micron-sized PMMA microwire was fabricated and connected with two tapered single-mode fibers to form a coupling structure; thus, the Mach-Zehnder (MZ) interference was successfully excited due to the good light conductivity of the PMMA. It was demonstrated that the coupling structure behaved with a high refractive index detection sensitivity of 3044 nm/RIU. To make it sensitive to N H 3, the PANI was selected to mix with PMMA and then formed a micron-level PMMA/PANI fiber. The experimental results showed that the PMMA/PANI fiber can selectively sense N H 3 with a high sensitivity of 65.3 pm/ppm. This proposed N H 3 sensor not only solves the problem of sensitive film shedding, but also possesses the advantages of good integration, high sensitivity, good selectivity, and short response time.

An in-fiber sensor for simultaneous measurement of cholesterol concentration and temperature based on SPR and MMI

In this paper, we design an in-fiber two-parameter sensor with multimode fiber (MMF)-Au film coated hollow fiber (HCF)-MMF structure, which can simultaneously excite Surface Plasmon Resonance (SPR) effect and Multimode Interference (MMI) effect. A composite material of Au nanoparticles/β-cyclodextrin (AuNPs/β-CD) is deposited on the surface of the Au film coated HCF to realize highly-sensitive measurement of cholesterol concentration. Here, the AuNPs can not only enhance the measurement sensitivity of the SPR sensor, but also increase the numbers of combination sites of β-CD and cholesterol. Then, to solve the cross-sensitivity problem between temperature and cholesterol, the glycerin is selected as a temperature-sensitive material to fill into the inner channel of the HCF, making the MMI sensor sensitive to temperature, and finally realizing the simultaneous measurement of cholesterol concentration and temperature. The experimental results demonstrate that the wavelength shift of the SPR and the MMI are 12.7 nm and 7.9 nm, respectively, when the cholesterol concentration changes from 0 to 500 nM. The temperature sensitivity of the SPR and the MMI are -0.9 nm/°C and 2.64 nm/°C, respectively, in the temperature range of 30°C-46 °C. In addition, the sensor shows good recognition ability of cholesterol molecules in serum environment, with good stability, selectivity and repeatability, and has broad application prospects in the biomedical field.

Label-Free DNA Hybridization Detection Using a Highly Sensitive Fiber Microcavity Biosensor

A novel label-free optical fiber biosensor, based on a microcavity fiber Mach-Zehnder interferometer, was developed and practically demonstrated for DNA detection. The biosensor was fabricated using offset splicing standard communication single-mode fibers (SMFs). The light path of the sensor was influenced by the liquid sample in the offset open cavity. In the experiment, a high sensitivity of -17,905 nm/RIU was achieved in the refractive index (RI) measurement. On this basis, the probe DNA (pDNA) was immobilized onto the sensor's surface using APTES, enabling real-time monitoring of captured complementary DNA (cDNA) samples. The experimental results demonstrate that the biosensor exhibited a high sensitivity of 0.32 nm/fM and a limit of detection of 48.9 aM. Meanwhile, the sensor has highly repeatable and specific performance. This work reports an easy-to-manufacture, ultrasensitive, and label-free DNA biosensor, which has significant potential applications in medical diagnostics, bioengineering, gene identification, environmental science, and other biological fields.

A New Approach to the Quantification of Fibroblast Growth Factor 23-An Array Surface Plasmon Resonance Imaging Biosensor

A new biosensor based on the "surface plasmon resonance imaging (SPRi)" detection technique for the quantification of "fibroblast growth factor 23 (FGF23)" has been developed. FGF23 is mainly produced in bone tissues as a phosphaturic hormone that forms a trimeric complex with "fibroblast growth factor receptor 1 (FGFR1)" and αKlotho upon secretion. FGF23 stimulates phosphate excretion and inhibits the formation of active vitamin D in the kidneys. FGF23 has been shown to play a role in bone carcinogenesis and metastasis. The newly developed method, based on the array SPRi biosensor, was validated-the precision, accuracy, and selectivity were acceptable, and yielded less than ±10% recovery. The rectilinear response of the biosensor ranges from 1 to 75 pg/mL. The limit of detection was 0.033 pg/mL, and the limit of quantification was 0.107 pg/mL. The biosensor was used to determine FGF23 concentrations in the blood plasma of healthy subjects and patients with "clear cell" renal cell carcinoma (ccRCC). The obtained results were compared with those measured through an "enzyme-linked immunosorbent assay (ELISA)". The determined Pearson correlation coefficients were 0.994 and 0.989, demonstrating that the newly developed biosensor can be used as a competitive method for the ELISA.

A L-glutamine binding protein modified MNM structured optical fiber biosensor based on surface plasmon resonance sensing for detection of L-glutamine metabolism in vitro embryo culture

A surface plasmon resonance (SPR) optical fiber sensor with multimode-coreless-multimode (MNM) structure was developed, which modified by L-glutamine-binding protein (QBP) for detection of L-glutamine (Gln). The QBP was immobilized on the surface of gold films by chemical cross-linking and exhibited a binding affinity for L-glutamine. The conformation of QBP can be changed from the "open" to the "closed", which led to a red-shift of the SPR peak when QBP bounded to L-glutamine. There was a good linear correlation between is a dependence of the SPR peak on and the concentration of L-glutamine concentration in the range 10-100 μM, with a sensitivity of 10.797nm/log10[Gln] for L-glutamine in the in vitro embryo culture (IVC) medium environment, and the limit of detection (LOD) is 1.187 μM. This QBP-modified MNM structure optical fiber SPR sensor provides a new idea for the developmental potential assessment of embryos in the process of in vitro embryo culture.

Optical Fibre-Based Sensors-An Assessment of Current Innovations

Optical fibre sensors are an essential subset of optical fibre technology, designed specifically for sensing and measuring several physical parameters. These sensors offer unique advantages over traditional sensors, making them gradually more valuable in a wide range of applications. They can detect extremely small variations in the physical parameters they are designed to measure, such as analytes in the case of biosensing. This high sensitivity allows them to detect subtle variations in temperature, pressure, strain, the refractive index of analytes, vibration, and other environmental factors with exceptional accuracy. Moreover, these sensors enable remote sensing capabilities. Since light signals are used to carry information, the sensing elements can be placed at distant or inaccessible sites and still communicate the data back to the central monitoring system without signal degradation. In recent times, different attractive configurations and approaches have been proposed to enhance the sensitivity of the optical fibre-based sensor and are briefly explained in this review. However, we believe that the choice of optical fibre sensor configuration should be designated based on the specific application. As these sensors continue to evolve and improve, they will play an increasingly vital role in critical monitoring and control applications across various industries.

Molecular Biomarkers and Recent Liquid Biopsy Testing Progress: A Review of the Application of Biosensors for the Diagnosis of Gliomas

Gliomas are the most common primary central nervous system tumors, with a high mortality rate. Early and accurate diagnosis of gliomas is critical for successful treatment. Biosensors are significant in the detection of molecular biomarkers because they are simple to use, portable, and capable of real-time analysis. This review discusses several important molecular biomarkers as well as various biosensors designed for glioma diagnosis, such as electrochemical biosensors and optical biosensors. We present our perspectives on the existing challenges and hope that this review can promote the improvement of biosensors.

Fiber Laser-Based Lasso-Shaped Biosensor for High Precision Detection of Cancer Biomarker-CEACAM5 in Serum

Detection of trace tumor markers in blood/serum is essential for the early screening and prognosis of cancer diseases, which requires high sensitivity and specificity of the assays and biosensors. A variety of label-free optical fiber-based biosensors has been developed and yielded great opportunities for Point-of-Care Testing (POCT) of cancer biomarkers. The fiber biosensor, however, suffers from a compromise between the responsivity and stability of the sensing signal, which would deteriorate the sensing performance. In addition, the sophistication of sensor preparation hinders the reproduction and scale-up fabrication. To address these issues, in this study, a straightforward lasso-shaped fiber laser biosensor was proposed for the specific determination of carcinoembryonic antigen (CEA)-related cell adhesion molecules 5 (CEACAM5) protein in serum. Due to the ultra-narrow linewidth of the laser, a very small variation of lasing signal caused by biomolecular bonding can be clearly distinguished via high-resolution spectral analysis. The limit of detection (LOD) of the proposed biosensor could reach 9.6 ng/mL according to the buffer test. The sensing capability was further validated by a human serum-based cancer diagnosis trial, enabling great potential for clinical use. The high reproduction of fabrication allowed the mass production of the sensor and extended its utility to a broader biosensing field.

Fiber SPR biosensor sensitized by MOFs for MUC1 protein detection

The concentration of tumor markers is low, which needs a highly sensitive, stable and fast detection method. In this paper, we proposed and demonstrated a U-shape fiber SPR biosensor sensitized by MOFs materials. The surface of the U-shape SPR sensor was modified with MOFs materials to enhance the sensitivity, and the nucleic acid aptamer was immobilized on the sensor surface because of the biocompatibility of MOFs materials. By the high specificity of the nucleic acid aptamer, the MUC1 protein was recognized and detected. The testing results indicate that the sensor has a logarithmic linear response in the MUC1 protein concentration detection range of 1 pg/ml-100 μg/ml, its sensitivity and detection limit are 5.33 nm/log(μg/ml) and 0.16 pg/ml respectively. After being sensitized by MOFs, the detection sensitivity of the sensor can be increased by 1.62 times，the LOD can be decreased by 0.75 times. The sensor has high sensitivity and specificity, which has broad application prospects in clinical detection of tumor markers.

Applications of Optical Fiber in Label-Free Biosensors and Bioimaging: A Review

Biosensing and bioimaging are essential in understanding biological and pathological processes in a living system, for example, in detecting and understanding certain diseases. Optical fiber has made remarkable contributions to the biosensing and bioimaging areas due to its unique advantages of compact size, immunity to electromagnetic interference, biocompatibility, fast response, etc. This review paper will present an overview of seven common types of optical fiber biosensors and optical fiber-based ultrasound detection in photoacoustic imaging (PAI) and the applications of these technologies in biosensing and bioimaging areas. Of course, there are many types of optical fiber biosensors. Still, this paper will review the most common ones: optical fiber grating, surface plasmon resonance, Sagnac interferometer, Mach-Zehnder interferometer, Michelson interferometer, Fabry-Perot Interferometer, lossy mode resonance, and surface-enhanced Raman scattering. Furthermore, different optical fiber techniques for detecting ultrasound in PAI are summarized. Finally, the main challenges and future development direction are briefly discussed.

Advances in Novel Nanomaterial-Based Optical Fiber Biosensors-A Review

This article presents a concise summary of current advancements in novel nanomaterial-based optical fiber biosensors. The beneficial optical and biological properties of nanomaterials, such as nanoparticle size-dependent signal amplification, plasmon resonance, and charge-transfer capabilities, are widely used in biosensing applications. Due to the biocompatibility and bioreceptor combination, the nanomaterials enhance the sensitivity, limit of detection, specificity, and response time of sensing probes, as well as the signal-to-noise ratio of fiber optic biosensing platforms. This has established a practical method for improving the performance of fiber optic biosensors. With the aforementioned outstanding nanomaterial properties, the development of fiber optic biosensors has been efficiently promoted. This paper reviews the application of numerous novel nanomaterials in the field of optical fiber biosensing and provides a brief explanation of the fiber sensing mechanism.

Fabrication of Silicon Nanowire Sensors for Highly Sensitive pH and DNA Hybridization Detection

A highly sensitive silicon nanowire (SiNW)-based sensor device was developed using electron beam lithography integrated with complementary metal oxide semiconductor (CMOS) technology. The top-down fabrication approach enables the rapid fabrication of device miniaturization with uniform and strictly controlled geometric and surface properties. This study demonstrates that SiNW devices are well-aligned with different widths and numbers for pH sensing. The device consists of a single nanowire with 60 nm width, exhibiting an ideal pH responsivity (18.26 × 10⁶ Ω/pH), with a good linear relation between the electrical response and a pH level range of 4–10. The optimized SiNW device is employed to detect specific single-stranded deoxyribonucleic acid (ssDNA) molecules. To use the sensing area, the sensor surface was chemically modified using (3-aminopropyl) triethoxysilane and glutaraldehyde, yielding covalently linked nanowire ssDNA adducts. Detection of hybridized DNA works by detecting the changes in the electrical current of the ssDNA-functionalized SiNW sensor, interacting with the targeted ssDNA in a label-free way. The developed biosensor shows selectivity for the complementary target ssDNA with linear detection ranging from 1.0 × 10⁻¹² M to 1.0 × 10⁻⁷ M and an attained detection limit of 4.131 × 10⁻¹³ M. This indicates that the use of SiNW devices is a promising approach for the applications of ion detection and biomolecules sensing and could serve as a novel biosensor for future biomedical diagnosis.