Dual-optofluidic waveguide in-line fiber biosensor for real-time label-free detection of interferon-gamma with temperature compensation

All-fiber label-free optical fiber biosensors: from modern technologies to current applications [Invited]

Biosensors are established as promising analytical tools for detecting various analytes important in biomedicine and environmental monitoring. Using fiber optic technology as a sensing element in biosensors offers low cost, high sensitivity, chemical inertness, and immunity to electromagnetic interference. Optical fiber sensors can be used in in vivo applications and multiplexed to detect several targets simultaneously. Certain configurations of optical fiber technology allow the detection of analytes in a label-free manner. This review aims to discuss recent advances in label-free optical fiber biosensors from a technological and application standpoint. First, modern technologies used to build label-free optical fiber-based sensors will be discussed. Then, current applications where these technologies are applied are elucidated. Namely, examples of detecting soluble cancer biomarkers, hormones, viruses, bacteria, and cells are presented.

Femtosecond-laser-inscribed Bragg grating in hollow-core fiber for highly sensitive optofluidic sensing

An optofluidic sensor based on a Bragg grating in hollow-core fiber (HCF) is experimentally demonstrated. The grating is inscribed into the HCF by femtosecond laser illumination through a phase mask. Periodic index modulation is introduced into the silica material surrounding the hollow core, causing cladding mode resonance, and multiple reflection peaks are observed in the grating spectrum. These reflection peaks later shift to longer wavelengths when high-index liquid is infiltrated into the HCF. The new reflection peak results from the backward coupling of the liquid core mode of the waveguide, the mode field of which overlaps with the grating modulation surrounding the liquid core. The resonant wavelength of the liquid-core fiber grating increases with the index value of the infiltrating liquid, and optofluidic refractive index sensing is realized with the device. The highest refractive index sensitivity, 1117 nm/RIU, is obtained experimentally in the index range of 1.476-1.54. The infiltrated hollow-core fiber Bragg grating also exhibits high temperature sensitivity due to the high thermal-optic coefficient of the liquid, and a sensitivity of -301 pm/°C is achieved in the temperature range of 25°C to 60°C.

Interferon-γ detection in point of care diagnostics: Short review

Interferon (IFN)-γ is a cytokine secreted by immune cells. The elevated levels of IFN-γ are an early indicator of multiple diseases such as tuberculosis and autoimmune diseases. This short review focuses on different sensing methods based on optical, electrochemical, and mechanical principles. We explain how specific biorecognition molecules such as antibodies and aptamers are employed in the sensing methods. We also compare different surface functionalization methods and their details. Although the review gives an overview of only IFN-γ sensing, the same strategies can be applied to sensing other analytes with appropriate modifications.

Label-Free Physical Techniques and Methodologies for Proteins Detection in Microfluidic Biosensor Structures

Proteins in biological fluids (blood, urine, cerebrospinal fluid) are important biomarkers of various pathological conditions. Protein biomarkers detection and quantification have been proven to be an indispensable diagnostic tool in clinical practice. There is a growing tendency towards using portable diagnostic biosensor devices for point-of-care (POC) analysis based on microfluidic technology as an alternative to conventional laboratory protein assays. In contrast to universally accepted analytical methods involving protein labeling, label-free approaches often allow the development of biosensors with minimal requirements for sample preparation by omitting expensive labelling reagents. The aim of the present work is to review the variety of physical label-free techniques of protein detection and characterization which are suitable for application in micro-fluidic structures and analyze the technological and material aspects of label-free biosensors that implement these methods. The most widely used optical and impedance spectroscopy techniques: absorption, fluorescence, surface plasmon resonance, Raman scattering, and interferometry, as well as new trends in photonics are reviewed. The challenges of materials selection, surfaces tailoring in microfluidic structures, and enhancement of the sensitivity and miniaturization of biosensor systems are discussed. The review provides an overview for current advances and future trends in microfluidics integrated technologies for label-free protein biomarkers detection and discusses existing challenges and a way towards novel solutions.

Overview and emerging trends in optical fiber aptasensing

Optical fiber biosensors have attracted growing interest over the last decade and quickly became a key enabling technology, especially for the detection of biomarkers at extremely low concentrations and in small volumes. Among the many and recent fiber-optic sensing amenities, aptamers-based sensors have shown unequalled performances in terms of ease of production, specificity, and sensitivity. The immobilization of small and highly stable bioreceptors such as DNA has bolstered their use for the most varied applications e.g., medical diagnosis, food safety and environmental monitoring. This review highlights the recent advances in aptamer-based optical fiber biosensors. An in-depth analysis of the literature summarizes different fiber-optic structures and biochemical strategies for molecular detection and immobilization of receptors over diverse surfaces. In this review, we analyze the features offered by those sensors and discuss about the next challenges to be addressed. This overview investigates both biochemical and optical parameters, drawing the guiding lines for forthcoming innovations and prospects in this ever-growing field of research.

Self-Assembled DNA Nanoflowers Triggered by a DNA Walker for Highly Sensitive Electrochemical Detection of Staphylococcus aureus

With the development of DNA nanotechnology, DNA has been widely used to construct a variety of nanomachines. Among them, a DNA walker is a unique nanomachine that can move continuously along a specific orbit to fulfill diverse functions. In this paper, a dual signal amplification electrochemical biosensor based on a DNA walker and DNA nanoflowers is constructed for high sensitivity detection of Staphylococcus aureus (S. aureus). Two groups of double-stranded DNA are modified on the surface of a gold electrode. The binding of S. aureus with its aptamer induces the disintegration of the long double strands and releases the DNA walker. With the help of exonuclease III (Exo III), the DNA walker moves along the electrode surface and continuously hydrolyzes the anchored short double strands. The introduction of a specially customized circular DNA and phi29 DNA polymerase initiates the rolling circle amplification (RCA) reaction. DNA nanoflowers are formed at high local concentration of DNA in the solution, which provide binding sites for electroactive methylene blue (MB) and thus produce intense signal. Under the best conditions, the current response is linearly related to the logarithm of the concentration of S. aureus ranging from 60 to 6 × 10⁷ CFU/mL, and the detection limit is 9 CFU/mL. In addition, the proposed biosensor has achieved satisfactory results in the detection of actual water samples and diluted honey samples, which confirm the practicability of the biosensor and its application potential in environmental monitoring and food safety.