Ultrasensitive biosensor based on magnetic microspheres enhanced microfiber interferometer

Ultrasensitive detection of SCCA employing a graphene oxide integrated microfiber ring laser biosensor

Squamous cell carcinoma antigen (SCCA) is one of the most commonly detected cancer biomarkers for a variety of cancers. In this paper, a microfiber ring laser biosensor with a graphene oxide linking layer for SCCA detection was proposed and experimentally demonstrated. SCCA antibody immobilized on graphene oxide surface binds specifically to SCCA, and induces refractive index variation over the surface of the microfiber biosensor, which leads to a wavelength shift of the microfiber ring laser biosensor. The experimental results show that the proposed laser biosensor can detect SCCA with concentrations from 0.01 to 50 ng/mL, and the calculated detection limit can be as low as 1.3 pg/mL. Additionally, the label-free quantitative detection of SCCA using the proposed microfiber biosensor was verified experimentally according to the corresponding regression equation, and the results agree well with clinical examination detection. This constructed microfiber biosensor may have promising practical applications in analytical detection, medical diagnostics, etc.

Highly selective and sensitive colorimetric chemosensor using PVA/chitosan ion-imprinted nanofibers for copper ion detection and removal

Herein, a highly efficient colorimetric chemosensor incorporating ion-imprinted electrospun nanofiber was developed for the removal and detection of Cu2+ ions. In this regard, PVA/chitosan composites were used as the polymeric matrix, and 1-(2-pyridylazo)-2-naphthol was employed for complex formation. The prepared naked-eye sensor was characterized using Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, atomic force microscopy, differential scanning calorimetry, thermogravimetric analysis, and X-ray diffraction analysis, revealing the morphological, structural, and molecular properties of the sensor. The results showed that the colorimetric chemosensor based on copper-imprinted nanofiber (Cu-INF) possesses higher selectivity for Cu2+ compared to interference ions. The selectivity coefficient (k) and relative selectivity coefficient (K') indicated the selective behavior of Cu-INF in the adsorption of Cu2+ in binary systems including Cu2+/Co2+, Cu2+/Ni2+, and Cu2+/Zn2+. Furthermore, the ion-imprinted nanofiber was used for the preconcentration of copper ions, demonstrating a high adsorption capacity of 128.205 mg g-1 for Cu2+. The equilibrium adsorption isotherm and adsorption kinetics of Cu2+ on Cu-INF followed the Freundlich adsorption isotherm and a pseudo-second-order model, respectively. The developed sensor exhibited a linear detection range of 5 × 10-8 - 2 × 10-7 M with a limit of detection (LOD) of 1.07 × 10-8 M for copper ions. The results indicated satisfactory adsorption and successful detection of Cu2+ at trace concentrations.

Designing an Electrochemical Biosensor Based on Voltammetry for Measurement of Human Chorionic Gonadotropin

Background

Human chorionic gonadotropin (hCG) is a polypeptide hormone synthesized during pregnancy and is also upregulated in some pathologic conditions such as certain tumors. Its measurement is essential for diagnosing pregnancy and malignancies. Despite numerous attempts to introduce an accurate method capable of detecting hCG levels, several limitations are found in previous techniques. This study aimed to address the limitations of current hCG assay methods by designing an electrochemical biosensor based on voltammetry for the rapid, selective, inexpensive, and sensitive measurement of hCG levels.

Methods

A carbon paste electrode was prepared and functionalized by para-aminobenzoic acid. The primary anti-β-hCG monoclonal antibody was immobilized on the electrode surface by activating the carboxyl groups with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide solutions. The study also involved optimizing parameters such as the time for primary antibody fixation, the time for hCG attachment, and the pH of the hydrogen peroxide solution to maximize the biosensor response. Different concentrations of hCG hormone were prepared and loaded on the electrode surface, the secondary antibody labeled with HRP enzyme was applied, thionine in phosphate-buffered saline solution was placed on the electrode surface, and the differential pulse electrical signal was recorded.

Results

The linear range ranged from 5 to 100 mIU/ml, and the limit of detection was calculated as 0.11 mIU. The relative standard deviation was 3% and 2% for five repeated measurements of commercial standard samples with concentrations of 2 and 20 mIU/mL, respectively. The percent recovery was obtained from 98.3% to 101.5%.

Conclusion

The sensor represents a promising advancement in hCG level measurement, offering a potential solution to overcome the existing limitations in current diagnostic strategies. Simple and inexpensive design, detecting hCG in its important clinical range during early pregnancy, and successful measurement of hCG in real serum samples are the advantages of this sensor.

Simultaneous measurement of bidirectional magnetic field and temperature with a dual-channel sensor based on the whispering gallery mode

What we believe is a novel dual-channel whispering gallery mode (WGM) sensor for concurrently measuring bidirectional magnetic field and temperature is proposed and demonstrated. Two sensing microcavities [magnetic fluid (MF)-infiltrated capillary and polydimethylsiloxane (PDMS)-coated microbottle, respectively, referred as Channel 1 (CH1) and Channel 2 (CH2)] are integrated into a silica capillary to facilitate the dual-channel design. Resonant wavelengths corresponding to CH1 and CH2 mainly depend on the change in the magneto-induced refractive index and the change in the thermo-induced parameter (volume and refractive index) of the employed functional materials, respectively. The MF-infiltrated capillary enables bidirectional magnetic field sensing with maximum sensitivities of 46 pm/mT and -3 pm/mT, respectively. The PDMS-coated structure can realize the temperature measurement with a maximum sensitivity of 79.7 pm/°C. The current work possesses the advantage of bidirectionally magnetic tunability besides the temperature response, which is expected to be used in field such as vector magnetic fields and temperature dual-parameter sensing.

Quantification of hCG Hormone Using Tapered Optical Fiber Decorated with Gold Nanoparticles

In this study, a novel technique for the quantification of the human chorionic gonadotropin (hCG) hormone using localized surface plasmons and a tapered optical fiber decorated with gold nanoparticles (Au-NPs) is reported. The tapered optical fiber fabrication process involves stretching a single-mode optical fiber using the flame-brushing system. The waist of the tapered optical fiber reaches a diameter of 3 μm. Decoration of the taper is achieved through the photodeposition of 100 nm Au-NPs using the drop-casting technique and a radiation source emitting at 1550 nm. The presence of the hCG hormone in the sample solutions is verified by Fourier-transform infrared spectroscopy (FTIR), revealing the presence of bands related to functional groups, such as C=O (1630 cm-1), which are associated with proteins and lipids, components of the hCG hormone. Quantification tests for hormone concentrations were carried out by measuring the optical power response of the tapered optical fiber with Au-NPs under the influence of hCG hormone concentrations, ranging from 1 mIU/mL to 100,000 mIU/mL. In the waist of the tapered optical fiber, the evanescent field is amplified because of localized surface plasmons generated by the nanoparticles and the laser radiation through the optical fiber. Experimental results demonstrated a proportional relationship between measured radiation power and hCG concentration, with the optical power response decreasing from 4.45 mW down to 2.5 mW, as the hCG hormone concentration increased from 1 mIU/mL up to 100,000 mIU/mL. Furthermore, the spectral analysis demonstrated a spectral shift of 14.2 nm with the increment of the hCG hormone concentration. The measurement system exhibits promising potential as a sensor for applications in the biomedical and industrial fields.

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.

Integrated label-free erbium-doped fiber laser biosensing system for detection of single cell Staphylococcus aureus

A critical challenge to realize ultra-high sensitivity with optical fiber interferometers for label free biosensing is to achieve high quality factors (Q-factor) in liquid. In this work a high Q-factor of 10⁵, which significantly improves the detection resolution is described based on a structure of single mode -core-only -single mode fiber (SCS) with its multimode (or Mach-Zehnder) interference effect as a filter that is integrated into an erbium-doped fiber laser (EDFL) system for excitation. In the case study, the section of core-only fiber is functionalized with porcine immunoglobulin G (IgG) antibodies, which could selectively bind to bacterial pathogen of Staphylococcus aureus (S. aureus). The developed microfiber-based biosensing platform called SCS-based EDFL biosensors can effectively detect concentrations of S. aureus from 10 to 10⁵ CFU/mL, with a responsivity of 0.426 nm wavelength shift in the measured spectrum for S. aureus concentration of 10 CFU/mL. The limit of detection (LoD) is estimated as 7.3 CFU/mL based on the measurement of S. aureus with minimum concentration of 10 CFU/mL. In addition, when a lower concentration of 1 CFU/mL is applied to the biosensor, a wavelength shift of 0.12 nm is observed in 10% of samples (1/10), indicating actual LoD of 1 CFU/mL for the proposed biosensor. Attributed to its good sensitivity, stability, reproducibility and specificity, the proposed EDFL based biosensing platform has great potentials for diagnostics.

Long-Period Fiber Grating Sensors for Chemical and Biomedical Applications

Optical fiber biosensors (OFBS) are being increasingly proposed due to their intrinsic advantages over conventional sensors, including their compactness, potential remote control and immunity to electromagnetic interference. This review systematically introduces the advances of OFBS based on long-period fiber gratings (LPFGs) for chemical and biomedical applications from the perspective of design and functionalization. The sensitivity of such a sensor can be enhanced by designing the device working at or near the dispersion turning point, or working around the mode transition, or their combination. In addition, several common functionalization methods are summarized in detail, such as the covalent immobilization of 3-aminopropyltriethoxysilane (APTES) silanization and graphene oxide (GO) functionalization, and the noncovalent immobilization of the layer-by-layer assembly method. Moreover, reflective LPFG-based sensors with different configurations have also been introduced. This work aims to provide a comprehensive understanding of LPFG-based biosensors and to suggest some future directions for exploration.

Post chemical etching of tapered seven-core fiber sensor for enhanced figure of merit

A post chemical etching process to a tapered seven-core fiber (TSCF) is proposed and experimentally demonstrated to effectively adjust the mode profiles of high-order supermodes, aimed to improve the figure of merit (FOM). The experimental results show that the FOM of an etched TSCF is as high as 1431.36 1/RIU, a 7.32-times enhancement compared with that of TSCF without etching, provided the TSCF has the same taper waist diameter of 19.20 µm. The proposed method opens a new, to the best of our knowledge, method for optimizing optical fiber sensor performance.

Optical microfiber sensor for detection of Ni2+ ions based on ion imprinting technology

The detection of ultralow heavy metal ion concentration is highly significant for protecting human health and maintaining the stability of the ecological environment. Herein, a microfiber interferometer chemical sensor for the detection of Ni²⁺ ions was proposed and experimentally demonstrated. The microfiber sensor was coated with an ion-imprinted chitosan polymer using Ni²⁺ as the template ion. Experimental results demonstrated a high sensitivity of 0.0454 nm nM^-M for detect-ing Ni²⁺ in the range of 10 nM to 100 nM, and a limit of detection as low as 6.5 nM was achieved. The microfiber sensor was verified using two different non-template heavy ions, Cu²⁺ and Cr³⁺, and was determined to be highly selective to Ni²⁺. Furthermore, the regeneration characteristics of the sensor were experimentally assessed by three repeated adsorption-desorption cycles, and the results showed that the microfiber sensor achieved good stability without a significant loss in sensitivity. Besides, the detecting tests of Ni²⁺ in lake water and industrial sewage samples demonstrated the sensor's practical application. This proposed sensor has the advantages of simple configuration, high selectivity and sensitivity, fast response, and the ability to serve as a platform for water safety monitoring and remote sensing.

A review of specialty fiber biosensors based on interferometer configuration

Optical fiber biosensors have attracted extensive research attention in fields such as public health research, environmental science, bioengineering, disease diagnosis and drug research. Accurate detection of biomolecules is essential to limit the extent of disease outbreaks and provide valuable guidance for regulatory agencies to take timely measures. Among many optical fiber sensors, optical fiber biosensors based on specialty fibers have the advantages of biocompatibility, small size, high measurement resolution, high stability and immunity to electromagnetic interference. In this paper, four types interferometer biosensors based on specialty fiber, namely Mach-Zehnder interferometer, Michelson interferometer, Fabry - Perot interferometer and Sagnac interferometer, are reviewed in terms of operating principles, sensing structure and application fields. The fiber types are further divided into micro-nano optical fiber, thin core fiber, polarization maintaining fiber, polymer fiber, microstructure optical fiber. Furthermore, this paper evaluates the advantages and disadvantages of these interferometer biosensors. Finally, main challenging problems and expectational development direction of specialty fiber interferometer biosensors are summarized. This text clearly shows the huge development potential of optical fiber biosensors in biomedical.

Photonic-Plasmonic Nanostructures for Solar Energy Utilization and Emerging Biosensors

Issues related to global energy and environment as well as health crisis are currently some of the greatest challenges faced by humanity, which compel us to develop new pollution-free and sustainable energy sources, as well as next-generation biodiagnostic solutions. Optical functional nanostructures that manipulate and confine light on a nanometer scale have recently emerged as leading candidates for a wide range of applications in solar energy conversion and biosensing. In this review, recent research progress in the development of photonic and plasmonic nanostructures for various applications in solar energy conversion, such as photovoltaics, photothermal conversion, and photocatalysis, is highlighted. Furthermore, the combination of photonic and plasmonic nanostructures for developing high-efficiency solar energy conversion systems is explored and discussed. We also discuss recent applications of photonic-plasmonic-based biosensors in the rapid management of infectious diseases at point-of-care as well as terahertz biosensing and imaging for improving global health. Finally, we discuss the current challenges and future prospects associated with the existing solar energy conversion and biosensing systems.