A reusable evanescent wave immunosensor for highly sensitive detection of bisphenol A in water samples

Splitter-Based Sensors Realized via POFs Coupled by a Micro-Trench Filled with a Molecularly Imprinted Polymer

An optical-chemical sensor based on two modified plastic optical fibers (POFs) and a molecularly imprinted polymer (MIP) is realized and tested for the detection of 2-furaldehyde (2-FAL). The 2-FAL measurement is a scientific topic of great interest in different application fields, such as human health and life status monitoring in power transformers. The proposed sensor is realized by using two POFs as segmented waveguides (SW) coupled through a micro-trench milled between the fibers and then filled with a specific MIP for the 2-FAL detection. The experimental results show that the developed intensity-based sensor system is highly selective and sensitive to 2-FAL detection in aqueous solutions, with a limit of detection of about 0.04 mg L-1. The proposed sensing approach is simple and low-cost, and it shows performance comparable to that of plasmonic MIP-based sensors present in the literature for 2-FAL detection.

Optomechanical effects caused by non-zero field quantities in multiple evanescent waves

Evanescent waves, with their high energy density, intricate local momentum, and spatial distribution of spins, have been the subject of extensive recent study. These waves offer promising applications in near-field particle manipulation. Consequently, it becomes imperative to gain a deeper understanding of the impacts of scattering and gradient forces on particles in evanescent waves to enhance and refine the manipulation capabilities. In this study, we employ the multipole expansion theory to present analytical expressions for the scattering and gradient forces exerted on an isotropic sphere of any size and composition in multiple evanescent waves. The investigation of these forces reveals several unusual optomechanical phenomena. It is well known that the scattering force does not exist in counter-propagating homogeneous plane waves. Surprisingly, in multiple pairs of counter-propagating evanescent waves, the scattering force can arise due to the nonzero orbital momentum (OM) density and/or the curl part of the imaginary Poynting momentum (IPM) density. More importantly, it is found that the optical scattering force can be switched on and off by simply tuning the polarization. Furthermore, optical forces typically vary with spatial position in an interference field. However, in the interference field generated by evanescent waves, the gradient force becomes a spatial constant in the propagating plane as the particle's radius increases. This is attributed to the decisive role of the non-interference term of the electromagnetic energy density gradient. Our study establishes a comprehensive and rigorous theoretical foundation, propelling the advancement and optimization of optical manipulation techniques harnessed through multiple evanescent waves. Specifically, these insights hold promise in elevating trapping efficiency through precise control and manipulation of optical scattering and gradient forces, stimulating further explorations.

Overview of Optical Biosensors for Early Cancer Detection: Fundamentals, Applications and Future Perspectives

Conventional cancer detection and treatment methodologies are based on surgical, chemical and radiational processes, which are expensive, time consuming and painful. Therefore, great interest has been directed toward developing sensitive, inexpensive and rapid techniques for early cancer detection. Optical biosensors have advantages in terms of high sensitivity and being label free with a compact size. In this review paper, the state of the art of optical biosensors for early cancer detection is presented in detail. The basic idea, sensitivity analysis, advantages and limitations of the optical biosensors are discussed. This includes optical biosensors based on plasmonic waveguides, photonic crystal fibers, slot waveguides and metamaterials. Further, the traditional optical methods, such as the colorimetric technique, optical coherence tomography, surface-enhanced Raman spectroscopy and reflectometric interference spectroscopy, are addressed.

Ultrasensitive detection of endocrine disruptors via superfine plasmonic spectral combs

The apparent increase in hormone-induced cancers and disorders of the reproductive tract has led to a growing demand for new technologies capable of detecting endocrine disruptors. However, a long-lasting challenge unaddressed is how to achieve ultrahigh sensitive, continuous, and in situ measurement with a portable device for in-field and remote environmental monitoring. Here we demonstrate a simple-to-implement plasmonic optical fiber biosensing platform to achieve an improved light-matter interaction and advanced surface chemistry for ultrasensitive detection of endocrine disruptors. Our platform is based on a gold-coated highly tilted fiber Bragg grating that excites high-density narrow cladding mode spectral combs that overlap with the broad absorption of the surface plasmon for high accuracy interrogation, hence enabling the ultrasensitive monitoring of refractive index changes at the fiber surface. Through the use of estrogen receptors as the model, we design an estradiol-streptavidin conjugate with the assistance of molecular dynamics, converting the specific recognition of environmental estrogens (EEs) by estrogen receptor into surface-based affinity bioassay for protein. The ultrasensitive platform with conjugate-induced amplification biosensing approach enables the subsequent detection for EEs down to 1.5 × 10^-3 ng ml^-1 estradiol equivalent concentration level, which is one order lower than the defined maximal E₂ level in drinking water set by the Japanese government. The capability to detect EEs down to nanogram per liter level is the lowest limit of detection for any estrogen receptor-based detection reported thus far. Its compact size, flexible shape, and remote operation capability open the way for detecting other endocrine disruptors with ultrahigh sensitivity and in various hard-to-reach spaces, thereby having the potential to revolutionize environment and health monitoring.

Surface-Plasmonic-Field-Induced Photoredox Catalysis and Mediated Electron Transfer for Washing-Free DNA Detection

Distance-dependent electromagnetic radiation and electron transfer have been commonly employed in washing-free fluorescence and electrochemical bioassays, respectively. In this study, we combined the two distance-dependent phenomena for sensitive washing-free DNA detection. A distance-dependent surface plasmonic field induces rapid photoredox catalysis of surface-bound catalytic labels, and distance-dependent mediated electron transfer allows for rapid electron transfer from the surface-bound labels to the electrode. An optimal system consists of a chemically reversible acceptor (Ru(NH₃ )₆ ³⁺ ), a chemically reversible photoredox catalyst (eosin Y), and a chemically irreversible donor (triethanolamine). Side reactions with O₂ do not significantly decrease the efficiency of photoredox catalysis. Energy transfer quenching between the electrode and the label can be lowered by increasing the distance between them. Washing-free DNA detection had a detection limit of approximately 0.3 nm in buffer and 0.4 nm in serum without a washing step.

A Review on the Role of Nanosensors in Detecting Cellular miRNA Expression in Colorectal Cancer

BACKGROUND

Colorectal cancer (CRC) is one of the leading causes of death across the globe. Early diagnosis with high sensitivity can prevent CRC progression, thereby reducing the condition of metastasis.

OBJECTIVE

The purpose of this review is (i) to discuss miRNA based biomarkers responsible for CRC, (ii) to brief on the different methods used for the detection of miRNA in CRC, (iii) to discuss different nanobiosensors so far found for the accurate detection of miRNAs in CRC using spectrophotometric detection, piezoelectric detection.

METHODS

The keywords for the review like micro RNA detection in inflammation, colorectal cancer, nanotechnology, were searched in PubMed and the relevant papers on the topics of miRNA related to CRC, nanotechnology-based biosensors for miRNA detection were then sorted and used appropriately for writing the review.

RESULTS

The review comprises a general introduction explaining the current scenario of CRC, the biomarkers used for the detection of different cancers, especially CRC and the importance of nanotechnology and a general scheme of a biosensor. The further subsections discuss the mechanism of CRC progression, the role of miRNA in CRC progression and different nanotechnology-based biosensors so far investigated for miRNA detection in other diseases, cancer and CRC. A scheme depicting miRNA detection using gold nanoparticles (AuNPs) is also illustrated.

CONCLUSION

This review may give insight into the different nanostructures, like AuNPs, quantum dots, silver nanoparticles, MoS2derived nanoparticles, etc., based approaches for miRNA detection using biosensors.

In-Parallel Polar Monitoring of Chemiluminescence Emission Anisotropy at the Solid–Liquid Interface by an Optical Fiber Radial Array

Chemiluminescence (CL) detection is widely employed in biosensors and miniaturized analytical devices since it offers high detectability and flexible device design (there are no geometry requirements for the measurement cell, except the ability to collect the largest fraction of emitted photons). Although the emission anisotropy phenomenon for an emitting dipole bound to the interface between two media with different refractive index is well known for fluorescence, it is still poorly investigated for CL reactions, in which the excited-state reaction products can diffuse in solution before the photon emission event. In this paper, we propose a simple method for the real-time evaluation of the CL emission anisotropy based on a radial array of optical fibers, embedded in a poly(methyl methacrylate) semicylinder and coupled with a Charge-Coupled Device (CCD) camera through a suitable interface. The polar-time evolutions of the CL emission have been studied for catalyzing enzymes immobilized onto a solid surface (heterogeneous configuration) or free in solution (homogeneous configuration). Evidence of the anisotropy phenomenon is observed, indicating that the lifetime of the excited-state products of the enzyme-catalyzed reactions is shorter than the time required for their diffusion in solution at a distance at which the CL can be considered isotropic. These results open new perspectives in the development of CL-based miniaturized analytical devices.

Automatic Range Adjustment of the Fluorescence Immunochromatographic Assay Based on Image Processing

As an emerging technology, fluorescence immunochromatographic assay (FICA) has the advantages of high sensitivity, strong stability and specificity, which is widely used in the fields of medical testing, food safety and environmental monitoring. The FICA reader based on image processing meets the needs of point-of-care testing because of its simple operation, portability and fast detection speed. However, the image gray level of common image sensors limits the detection range of the FICA reader, and high-precision image sensors are expensive, which is not conducive to the popularization of the instrument. In this paper, FICA strips' image was collected using a common complementary metal oxide semiconductor (CMOS) image sensor and a range adjustment mechanism was established to automatically adjust the exposure time of the CMOS image sensor to achieve the effect of range expansion. The detection sensitivity showed a onefold increase, and the upper detection limit showed a twofold increase after the proposed method was implemented. In addition, in the experiments of linearity and accuracy, the fitting degree (R²) of the fitted curves both reached 0.999. Therefore, the automatic range adjustment method can obviously improve the detection range of the FICA reader based on image processing.

Optical Biosensors for Label-Free Detection of Small Molecules

Label-free optical biosensors are an intriguing option for the analyses of many analytes, as they offer several advantages such as high sensitivity, direct and real-time measurement in addition to multiplexing capabilities. However, development of label-free optical biosensors for small molecules can be challenging as most of them are not naturally chromogenic or fluorescent, and in some cases, the sensor response is related to the size of the analyte. To overcome some of the limitations associated with the analysis of biologically, pharmacologically, or environmentally relevant compounds of low molecular weight, recent advances in the field have improved the detection of these analytes using outstanding methodology, instrumentation, recognition elements, or immobilization strategies. In this review, we aim to introduce some of the latest developments in the field of label-free optical biosensors with the focus on applications with novel innovations to overcome the challenges related to small molecule detection. Optical label-free methods with different transduction schemes, including evanescent wave and optical fiber sensors, surface plasmon resonance, surface-enhanced Raman spectroscopy, and interferometry, using various biorecognition elements, such as antibodies, aptamers, enzymes, and bioinspired molecularly imprinted polymers, are reviewed.

Recent Developments in Enzyme, DNA and Immuno-Based Biosensors

Novel sensitive, rapid and economical biosensors are being developed in a wide range of medical environmental and food applications. In this paper, we review some of the main advances in the field over the past few years by discussing recent studies from literature. A biosensor, which is defined as an analytical device consisting of a biomolecule, a transducer and an output system, can be categorized according to the type of the incorporated biomolecule. The biomolecules can be enzymes, antibodies, ssDNA, organelles, cells etc. The main biosensor categories classified according to the biomolecules are enzymatic biosensors, immunosensors and DNA-based biosensors. These sensors can measure analytes produced or reduced during reactions at lower costs compared to the conventional detection techniques. Numerous types of biosensor studies conducted over the last decade have been explored here to reveal their key applications in medical, environmental and food industries which provide comprehensive perspective to the readers. Overviews of the working principles and applications of the reviewed sensors are also summarized.

Optofluidic Technology for Water Quality Monitoring

Water quality-related incidents are attracting attention globally as they cause serious diseases and even threaten human lives. The current detection and monitoring methods are inadequate because of their long operation time, high cost, and complex process. In this context, there is an increasing demand for low-cost, multiparameter, real-time, and continuous-monitoring methods at a higher temporal and spatial resolution. Optofluidic water quality sensors have great potential to satisfy this requirement due to their distinctive features including high throughput, small footprint, and low power consumption. This paper reviews the current development of these sensors for heavy metal, organic, and microbial pollution monitoring, which will breed new research ideas and broaden their applications.

Chimeric DNA/LNA-based biosensor for the rapid detection of African swine fever virus

African swine fever (ASF) virus is a DNA virus responsible for a severe haemorrhagic fever in pigs, which (still in the absence of vaccination strategies) results in high mortality rates. Herein, we present a biosensor-based method for the detection of ASF viral DNA in the blood of pigs. The biosensor exploits a single-strand DNA probe with locked nucleic acid nucleotides (LNA) substitutions as the complementary recognition element for the conserved region of vp72 gene of ASF virus. The biosensor was calibrated using qPCR-quantified ASF viral DNA extracted from the blood of pigs experimentally infected with the virulent Italian isolate 49/08, genotype I. Globally, the proposed biosensor showed good sensitivity and specificity, with the limits of detection (LOD) and quantification (LOQ) being 178 and 245 copies/μL of genomic ASF viral DNA, respectively. The reversible nature of the interaction between the DNA/LNA probe and the target DNA sequence granted multiple rapid analyses, with up to 40 analyses per single surface possible, and a single test requiring approximately 5 min. When applied to non-amplified DNA extracts from the blood of field-infected pigs, the assay discriminated between ASFV-infected and ASFV non-infected animals, and allowed the rapid quantification of ASF viral DNA, with values falling in the range 373-1058 copies/μL of genomic ASFV DNA. In this range, excellent correlation was observed between the results of this biosensor and OIE-approved qPCR. This method represents a promising screening assay for preliminary ASF diagnosis, having the major advantages in the relative rapidity, ease-of-use, the reusability of the sensing surface, and low cost per single test.

Practical Application of Aptamer-Based Biosensors in Detection of Low Molecular Weight Pollutants in Water Sources

Water pollution has become one of the leading causes of human health problems. Low molecular weight pollutants, even at trace concentrations in water sources, have aroused global attention due to their toxicity after long-time exposure. There is an increased demand for appropriate methods to detect these pollutants in aquatic systems. Aptamers, single-stranded DNA or RNA, have high affinity and specificity to each of their target molecule, similar to antigen-antibody interaction. Aptamers can be selected using a method called Systematic Evolution of Ligands by EXponential enrichment (SELEX). Recent years we have witnessed great progress in developing aptamer selection and aptamer-based sensors for low molecular weight pollutants in water sources, such as tap water, seawater, lake water, river water, as well as wastewater and its effluents. This review provides an overview of aptamer-based methods as a novel approach for detecting low molecular weight pollutants in water sources.

Compact 3D printed module for fluorescence and label-free imaging using evanescent excitation

Total internal reflection fluorescence (TIRF) microscopy is widely used for selective excitation and high-resolution imaging of fluorophores, and more recently label-free nanosized objects, with high vertical confinement near a liquid-solid interface. Traditionally, high numerical aperture objectives (>1.4) are used to simultaneously generate evanescent waves and collect fluorescence emission signals which limits their use to small area imaging (<0.1 mm²). Objective-based TIRFs are also expensive as they require dichroic mirrors and efficient notch filters to prevent specular reflection within the objective lenses. We have developed a compact 3D module called cTIRF that can generate evanescent waves in microscope glass slides via a planar waveguide illumination. The module can be attached as a fixture to any existing optical microscope, converting it into a TIRF and enabling high signal-to-noise ratio (SNR) fluorescence imaging using any magnification objective. As the incidence optics is perpendicular to the detector, label-free evanescent scattering-based imaging of submicron objects can also be performed without using emission filters. SNR is significantly enhanced in this case as compared to cTIRF alone, as seen through our model experiments performed on latex beads and mammalian cells. Extreme flexibility and the low cost of our approach makes it scalable for limited resource settings.

Advances in sensing and biosensing of bisphenols: A review

Bisphenols (BPs) are well known endocrine disrupting chemicals (EDCs) that cause adverse effects on the environment, biotic life and human health. BPs have been studied extensively because of an increasing concern for the safety of the environment and for human health. They are major raw materials for manufacturing polycarbonates, thermal papers and epoxy resins and are considered hazardous environmental contaminants. A vast array of sensors and biosensors have been developed for the sensitive screening of BPs based on carbon nanomaterials (carbon nanotubes, fullerenes, graphene and graphene oxide), quantum dots, metal and metal oxide nanocomposites, polymer nanocomposites, metal organic frameworks, ionic liquids and molecularly imprinted polymers. This review is devoted mainly to a variety of sensitive, selective and reliable sensing and biosensing methods for the detection of BPs using electrochemistry, fluorescence, colorimetry, surface plasmon resonance, luminescence, ELISAs, circular dichroism, resonance Rayleigh scattering and adsorption techniques in plastic products, food samples, food packaging, industrial wastes, pharmaceutical products, human body fluids and many other matrices. It summarizes the advances in sensing and biosensing methods for the detection of BPs since 2010. Furthermore, the article discusses challenges and future perspectives in the development of novel sensing methods for the detection of BP analogs.

Optical biosensors

Optical biosensors represent the most common type of biosensor. Here we provide a brief classification, a description of underlying principles of operation and their bioanalytical applications. The main focus is placed on the most widely used optical biosensors which are surface plasmon resonance (SPR)-based biosensors including SPR imaging and localized SPR. In addition, other optical biosensor systems are described, such as evanescent wave fluorescence and bioluminescent optical fibre biosensors, as well as interferometric, ellipsometric and reflectometric interference spectroscopy and surface-enhanced Raman scattering biosensors. The optical biosensors discussed here allow the sensitive and selective detection of a wide range of analytes including viruses, toxins, drugs, antibodies, tumour biomarkers and tumour cells.

Isoelectric Bovine Serum Albumin: Robust Blocking Agent for Enhanced Performance in Optical-Fiber Based DNA Sensing

Surface blocking is a well-known process for reducing unwanted nonspecific adsorption in sensor fabrication, especially important in the emerging field where DNA/RNA applied. Bovine serum albumin (BSA) is one of the most popular blocking agents with an isoelectric point at pH 4.6. Although it is widely recognized that the adsorption of a blocking agent is strongly affected by its net charge and the maximum adsorption is often observed under its isoelectric form, BSA has long been perfunctorily used for blocking merely in neutral solution, showing poor blocking performances in the optical-fiber evanescent wave (OFEW) based sensing toward DNA target. To meet this challenge, we first put forward the view that isoelectric BSA (iep-BSA) has the best blocking performance and use an OFEW sensor platform to demonstrate this concept. An optical-fiber was covalently modified with amino-DNA, and further coupled with the optical system to detect fluorophore labeled complementary DNA within the evanescent field. A dramatic improvement in the reusability of this DNA modified sensing surface was achieved with 120 stable detection cycles, which ensured accurate quantitative bioassay. As expected, the iep-BSA blocked OFEW system showed enhanced sensing performance toward target DNA with a detection limit of 125 pM. To the best of our knowledge, this is the highest number of regeneration cycles ever reported for a DNA immobilized optical-fiber surface. This study can also serve as a good reference and provide important implications for developing similar DNA-directed surface biosensors.

Evanescent wave fluorescence biosensors: Advances of the last decade

Biosensor development has been a highly dynamic field of research and has progressed rapidly over the past two decades. The advances have accompanied the breakthroughs in molecular biology, nanomaterial sciences, and most importantly computers and electronics. The subfield of evanescent wave fluorescence biosensors has also matured dramatically during this time. Fundamentally, this review builds on our earlier 2005 review. While a brief mention of seminal early work will be included, this current review will focus on new technological developments as well as technology commercialized in just the last decade. Evanescent wave biosensors have found a wide array applications ranging from clinical diagnostics to biodefense to food testing; advances in those applications and more are described herein.

Structural and light coupling characteristics of patterned silica–titania sol–gel thin films with/without nano gold coatings

Soft lithography-based 1-dimensional/2-dimensional patterned silica–titania sol–gel thin films with/without nano-Au coatings and their light coupling characteristics.

Portable and reusable optofluidics-based biosensing platform for ultrasensitive detection of sulfadimidine in dairy products

Sulfadimidine (SM₂) is a highly toxic and ubiquitous pollutant which requires rapid, sensitive and portable detection method for environmental and food monitoring. Herein, the use for the detection of SM₂ of a portable optofluidics-based biosensing platform, which was used for the accurate detection of bisphenol A, atrazine and melamine, is reported for the first time. The proposed compact biosensing system combines the advantages of an evanescent wave immunosensor and microfluidic technology. Through the indirect competitive immunoassay, the detection limit of the proposed optofluidics-based biosensing platform for SM₂ reaches 0.05 μg·L⁻¹ at the concentration of Cy5.5-labeled antibody of 0.1 μg·mL⁻¹. Linearity is obtained over a dynamic range from 0.17 μg·L⁻¹ to 10.73 μg·L⁻¹. The surface of the fiber probe can be regenerated more than 300 times by means of 0.5% sodium dodecyl sulfate solution (pH = 1.9) washes without losing sensitivity. This method, featuring high sensitivity, portability and acceptable reproducibility shows potential in the detection of SM₂ in real milk and other dairy products.