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

Identification and ultrasensitive quantification of H. pylori infections on gastric and stool human samples with a photonic label-free nanobiosensor

Helicobacter pylori is a widespread bacterium that infects the stomach, causing gastric disorders associated with high morbidity and mortality worldwide. Current methods for identifying and quantifying this pathogen rely on invasive and non-invasive tests. Although combining these methods allows accurate diagnosis, they have multiple drawbacks, and there is no single reliable gold standard test. New, more sensitive strategies involving molecular techniques, such as digital PCR, have been developed but require complex and expensive instruments. Herein, we implement and validat a nanophotonic bimodal waveguide (BiMW) biosensor for the sensitive and accurate detection of H. pylori in gastric biopsies and stool. This biosensor offers real-time, label-free detection, high sensitivity, and the capability to be integrated into compact devices. By employing monoclonal antibodies targeting specific membrane proteins found in H. pylori, the biosensor enables unique recognition of the bacterium, demonstrating its potential as an alternative diagnostic tool. The BiMW biosensor provides highly accurate H. pylori quantification in under 20 min, with limits of detection (LOD) of 89 ± 35 CFU/mL for antrum gastric biopsies and 82 ± 9 CFU/mL for stool samples. Clinical validation with 40 samples (20 gastric biopsies and 20 stool samples) showed sensitivity and specificity of 90 % for gastric biopsies and 95 % for stool samples, offering diagnostic reliability equivalent to semiquantitative ELISA tests and enabling more efficient and timely detection of H. pylori infections. This test can significantly improve the speed of diagnosis and contribute to the development of more effective strategies for H. pylori eradication.

Advances in portable fiber optic-based aptasensors for on-site detection: design, evolution, and application

The emergence of on-site detection using portable devices has transformed traditional analytical methods, which rely on precise but bulky laboratory instruments, into a promising technique for point-of-care testing. In this case, fiber optic (FO)-based aptasensors, featuring miniaturized devices, high sensitivity, and strong specificity, are candidates to meet the requirement of on-site detection. To enhance the interaction between light and the surrounding environment, numerous FO probes with novel micro/nano-structures have been designed, including tilted fiber Bragg grating (TFBG), long-period grating (LPG), bent, microfiber, D-shaped, and photonic bandgap fibers. Aptamers fold into unique tertiary structure to specifically and sensitively bind with their targets through a direct reaction or a binding-induced structural switch. Benefitting from advancements in FO probes and aptamers, multiple FO-based aptasensors have been constructed for sensitive detection, including evanescent wave-based, fluorescent-, localized surface plasmon resonance (LSPR)-based, and interferometer-based sensors. To date, FO-based aptasensors have been widely applied in clinical diagnosis, environmental monitoring, and food safety. This review focuses on design strategies, evolution, and applications of FO-based aptasensors. The opportunities and challenges of FO-based aptasensors for on-site detection are discussed in depth. This review aims to highlight the significance of FO-based aptasensors for on-site detection and promote their development from laboratory research to practical application.

Comprehensive Analysis of Advancement in Optical Biosensing Techniques for Early Detection of Cancerous Cells

This investigation presents an overview of various optical biosensors utilized for the detection of cancer cells. It covers a comprehensive range of technologies, including surface plasmon resonance (SPR) sensors, which exploit changes in refractive index (RI) at the sensor surface to detect biomolecular interactions. Localized surface plasmon resonance (LSPR) sensors offer high sensitivity and versatility in detecting cancer biomarkers. Colorimetric sensors, based on color changes induced via specific biochemical reactions, provide a cost-effective and simple approach to cancer detection. Sensors based on fluorescence work using the light emitted from fluorescent molecules detect cancer-specific targets with specificity and high sensitivity. Photonics and waveguide sensors utilize optical waveguides to detect changes in light propagation, offering real-time and label-free detection of cancer biomarkers. Raman spectroscopy-based sensors utilize surface-enhanced Raman scattering (SERS) to provide molecular fingerprint information for cancer diagnosis. Lastly, fiber optic sensors offer flexibility and miniaturization, making them suitable for in vivo and point-of-care applications in cancer detection. This study provides insights into the principles, applications, and advancements of these optical biosensors in cancer diagnostics, highlighting their potential in improving early detection and patient outcomes.

Microextraction-Driven Optical Fiber Sensor Coupled with Signal Enhancement by Gold Nanostars for Detection of Antibiotics in Food and Water

In this work, a portable optical fiber-based "microextraction sensing" platform coupled with gold nanostars (Au NSRs) was designed for the detection of kanamycin (Kana). Replaceable optical fibers were used as solid-phase microextraction (SPME) devices and sensing probes. Au NSRs and Kana aptamers were sequentially modified onto a fiber core as sensing elements. The evanescent wave generated from the fiber interacted with the surface of the Au NSR, and the localized surface plasmon resonance (LSPR) effect was triggered. In the presence of Kana, the refractive index of the Au NSR surface changed, causing the LSPR characteristic peak to shift, thereby enabling the quantitative detection of Kana. Benefiting from the strong "hot spot" effect produced by the sharp branches of the Au NSR, the intensity of the signals was greatly increased. Under optimal conditions, the sensing platform exhibited high selectivity toward Kana. The calibration linear range was 0.5-500 nM (r2 = 0.997), and a limit of detection of 0.138 nM was achieved. The optical fiber could be easily disassembled and reused. Signal stability remained intact even after a replaceable optical fiber probe was cleaned and used 10 times. The sensor was successfully applied to the analysis of Kana residues in genuine cow's milk samples. The procedure was also applied to river water samples. This assay has unique advantages of low cost, simplicity, and recyclability, making it a promising approach for food analysis and environmental monitoring.

Localized surface plasmon resonance sensing based on monometallic gold nanoparticles: from material preparation to detection of bioanalytes

The tunable geometrical properties of gold nanoparticles (AuNPs) endow them with the capacity to exhibit distinct behaviors with respect to both macroscopic (color) and microscopic (resonance wavelength) aspects, which has been extensively utilized in localized surface plasmon resonance (LSPR) sensing platforms. Additionally, functionalizing AuNP surfaces enhances the platforms' capabilities, allowing for the detection of a wide range of molecules related to various aspects of human health. In this review, we comprehensively elucidate the fundamental principles of LSPR biosensing and provide an in-depth survey of the preparation processes for metal nanoparticles, encompassing deposition technology for large-scale particle production as well as ion reduction methods that afford superior control over the particles' physical and chemical attributes. The sensing strategies based on adjustment of the dielectric environment and particle dispersion-aggregation levels are thoroughly reviewed and discussed. The discussion focused on a specific class of nanoparticles, characterized by their uniform shape and size, with each section bifurcated into two parts: a summary of the salient features and recent discoveries pertaining to the sensing strategy, as well as illustrations of representative, cutting-edge applications employing the strategy. We specifically aim to scrutinize analytes commonly encountered in the biomedical realm, encompassing biomarkers that serve as indicators of a wide range of diseases and microbial pathogens, while also prognosticating the future development trends of LSPR optical biosensor platforms within the biomedical field.

High sensitivity tapered fiber refractive index biosensor using hollow gold nanoparticles

A localized surface plasmon resonance (LSPR) sensor based on tapered optical fiber (TOF) using hollow gold nanoparticles (HAuNPs) for measuring the refractive index (RI) is presented. This optical fiber sensor is a good candidate for a label-free RI biosensor. In practical biosensors, bioreceptors are immobilized on nanoparticles (NPs) that only absorb specific biomolecules. The binding of these biomolecules to the receptors changes the local RI around the sensor and this change is detected by the transmittance spectrum of the fiber. Fast, accurate, easy and low-cost disease diagnosis are the advantages of optical fiber biosensors. In this paper, the structure theory is reviewed and the sensor is simulated by the finite difference time domain (FDTD) method and the finite element method (FEM) and the effect of the thickness and diameter of the HAuNPs and the waist diameter of the TOF is investigated. For the structure with HAuNPs thickness (2.5 nm), diameter (50 nm), and the fiber waist diameter of 10 μm, the wavelength sensitivity of 489.8 nm/RIU and full width at half maximum (FWHM) of 50 nm are obtained, which are better than those specifications in some other LSPR fiber sensors. In addition, the sensitivity of the sensor increases about 2-3 times compared to those of sensors with the same structure. Although there are many parameters in human blood that can change its RI, in practical work, the special bioreceptors on the sensor can deactivate other markers except the specific cancer markers, which changes the effective RI. Therefore, this optical fiber sensor is used for label-free detecting the RI of cancer cells and can be used as a biosensor for the detection of early stages of cancers in a non-invasive way, just using human blood samples.

A disposable fiber-optic plasmonic sensor for chemical sensing

The integration of fiber optics and plasmonic sensors is promising to improve the practical usability over conventional bulky sensors and systems. To achieve high sensitivity, it typically requires fabrication of well-defined plasmonic nanostructures on optical fibers, which greatly increases the cost and complexity of the sensors. Here, we present a fiber-optic sensor system by using chemical absorption of gold nanoparticles and a replaceable configuration. By functioning gold nanoparticles with aptamers or antibodies, we demonstrate the applications in chemical sensing using two different modes. Measuring shift in resonance wavelength enables the Pb2+ detection with a high linearity and a limit of detection of 0.097 nM, and measuring absorption peak amplitude enables the detection of E. coli in urinary tract infection with a dynamic range between 103 to 108 CFU/mL. The high sensitivity, simple fabrication and disposability of this sensing approach could pave the way for point-of-care testing with fiber-optic plasmonic sensors.

Ω-Shaped fiber optic LSPR coated with hybridized nanolayers for tumor cell sensing and photothermal treatment

Circulating tumor cell (CTC) in the blood is the main cause of cancer metastasis for death in cancer patients. It is extremely important for cancer diagnosis at an early stage and treatment to simultaneously detect and kill the CTCs. In this work, a new hybridized nanolayer, namely gold nanoparticle/gold nanorods@ Polydopamine (AuNPs/AuNRs@PDA), was coated on the Ω-shaped fiber optics (Ω-FO) for localized surface plasmonic resonance (LSPR) to perform tumor cell sensing and photothermal treatment (PTT). The PDA nanolayer was formed on a bare fiber optic through the self-polymerization of dopamine under mild conditions. The AuNRs and AuNPs were absorbed on the surface of the PDA nanolayer to form a hybridized nanolayer. The hybridized nanolayer-modified Ω-FO LSPR exhibited a high refractive index sensitivity (RIS) of 37.59 (a.u/RIU) and photothermal conversion efficiency. After being modified with the recognition element of aptamer, the Ω-FO LSPR was used to develop a sensitive and specifical tumor cell sensing. Under the irradiation of near-infrared light (NIR) laser, the Ω-FO LSPR can kill the captured tumor cells with the apoptotic/necrotic rate of 62.6 % and low side-effect for the nontarget cells. The FO LSPR sensor realized the dual functions of CTC sensing and PTT, which provided a new idea for the early diagnosis and treatment of cancer.

Sandwich Layer-Modified Ω-Shaped Fiber-Optic LSPR Enables the Development of an Aptasensor for a Cytosensing-Photothermal Therapy Circuit

The metastasis of cancer cells is a principal cause of morbidity and mortality in cancer. The combination of a cytosensor and photothermal therapy (PTT) cannot completely eliminate cancer cells at one time. Hence, this study aimed to design a localized surface plasmonic resonance (LSPR)-based aptasensor for a circuit of cytosensing-PTT (COCP). This was achieved by coating a novel sandwich layer of polydopamine/gold nanoparticles/polydopamine (PDA/AuNPs/PDA) around the Ω-shaped fiber-optic (Ω-FO). The short-wavelength peak of the sandwich layer with strong resonance exhibited a high refractive index sensitivity (RIS). The modification with the T-shaped aptamer endowed FO-LSPR with unique characteristics of time-dependent sensitivity enhancement behavior for a sensitive cytosensor with the lowest limit of detection (LOD) of 13 cells/mL. The long-wavelength resonance peak in the sandwich layer appears in the near-infrared region. Hence, the rate of increased localized temperature of FO-LSPR was 160 and 30-fold higher than that of the bare and PDA-coated FO, indicating strong photothermal conversion efficiency. After considering the localized temperature distribution around the FO under the flow environment, the FO-LSPR-enabled aptasensor killed 77.6% of cancer cells in simulated blood circulation after five cycles of COCP. The FO-LSPR-enabled aptasensor improved the efficiency of the cytosensor and PTT to effectively kill cancer cells, showing significant potential for application in inhibiting cancer metastasis.

Recent advances in portable devices for environmental monitoring applications

Environmental pollution remains a major societal problem, leading to serious impacts on living organisms including humans. Human activities such as civilization, urbanization, and industrialization are major causes of pollution. Imposing stricter rules helps control environmental pollutant levels, creating a need for reliable pollutant monitoring in air, water, and soil. The application of traditional analytical techniques is limited in low-resource areas because they are sophisticated, expensive, and bulky. With the development of biosensors and microfluidics technology, environmental monitoring has significantly improved the analysis time, low cost, portability, and ease of use. This review discusses the fundamentals of portable devices, including microfluidics and biosensors, for environmental control. Recently, publications reviewing microfluidics and biosensor device applications have increased more than tenfold, showing the potential of emerging novel approaches for environmental monitoring. Strategies for enzyme-, immunoassay-, and molecular-based analyte sensing are discussed based on their mechanisms and applications. Microfluidic and biosensor platforms for detecting major pollutants, including metal ions, pathogens, pesticides, and antibiotic residues, are reviewed based on their working principles, advantages, and disadvantages. Challenges and future trends for the device design and fabrication process to improve performance are discussed. Miniaturization, low cost, selectivity, sensitivity, high automation, and savings in samples and reagents make the devices ideal alternatives for in-field detection, especially in low-resource areas. However, their operation with complicated environmental samples requires further research to improve the specificity and sensitivity. Although there is a wide range of devices available for environmental applications, their implementation in real-world situations is limited. This study provides insights into existing issues that can be used as references and a comparative analysis for future studies and applications.

Nanomaterials revolutionize biosensing: 0D-3D designs for ultrasensitive detection of microorganisms and viruses

Various diseases caused by harmful microorganisms and viruses have caused serious harm and huge economic losses to society. Thus, rapid detection of harmful microorganisms and viruses is necessary for disease prevention and treatment. Nanomaterials have unique properties that other materials do not possess, such as a small size effect and quantum size effect. Introducing nanomaterials into biosensors improves the performance of biosensors for faster and more accurate detection of microorganisms and viruses. This review aims to introduce the different kinds of biosensors and the latest advances in the application of nanomaterials in biosensors. In particular, this review focuses on describing the physicochemical properties of zero-, one-, two-, and three-dimensional nanostructures as well as nanoenzymes. Finally, this review discusses the applications of nanobiosensors in the detection of microorganisms and viruses and the future directions of nanobiosensors.

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.

Four-core fiber-based multi-tapered WaveFlex biosensor for rapid detection of Vibrio parahaemolyticus using nanoparticles-enhanced probes

Infections caused by Vibrio parahaemolyticus (V. parahaemolyticus) can be highly fatal, making rapid and sensitive detection of them is essential. A new optical fiber biosensor based on localized surface plasmon resonance (LSPR) phenomenon is developed in this paper. A tapered-in-tapered fiber structure based on MFM is constructed by using four-core fiber (FCF) and multi-mode fiber (MMF) to qualitatively detect different concentrations of V. parahaemolyticus. The sensor successfully excites the LSPR phenomenon and increases the attachment point of biomolecules on the probe surface by fixing gold nanoparticles (AuNPs), molybdenum disulfide nanoparticles (MoS2-NPs) and cerium dioxide nanorods (CeO2-NRs). The functionalization of polyclonal antibodies on the probe surface can improve the specificity of the sensor. The linear detection range of the developed sensor was 1 × 100-1 × 107 CFU/mL, the sensitivity was 1.61 nm/[CFU/mL], and the detection limit was 0.14 CFU/mL. In addition, the reusability, reproducibility, stability, and selectivity of the sensor probe are also tested, which shows that the sensor has great application prospects.

Critical Issues on the Surface Functionalization of Plasmonic Au-Ag/TiO2 Thin Films with Thiolated Oligonucleotide-Based Biorecognition Elements

This work reports on the surface functionalization of a nanomaterial supporting localized surface plasmon resonances (LSPRs) with (synthetic) thiolated oligonucleotide-based biorecognition elements, envisaging the development of selective LSPR-based DNA biosensors. The LSPR thin-film transducers are composed of noble metal nanoparticles (NPs) embedded in a TiO2 dielectric matrix, produced cost-effectively and sustainably by magnetron sputtering. The study focused on the immobilization kinetics of thiolated oligonucleotide probes as biorecognition elements, followed by the evaluation of hybridization events with the target probe. The interaction between the thiolated oligonucleotide probe and the transducer's surface was assessed by monitoring the LSPR signal with successive additions of probe solution through a microfluidic device. The device was specifically designed and fabricated for this work and adapted to a high-resolution LSPR spectroscopy system with portable characteristics. Benefiting from the synergetic characteristics of Ag and Au in the form of bimetallic nanoparticles, the Au-Ag/TiO2 thin film proved to be more sensitive to thiolated oligonucleotide binding events. Despite the successful surface functionalization with the biorecognition element, the detection of complementary oligonucleotides revealed electrostatic repulsion and steric hindrance, which hindered hybridization with the target oligonucleotide. This study points to an effect that is still poorly described in the literature and affects the design of LSPR biosensors based on nanoplasmonic thin films.