Applications of fiber-optic biochemical sensor in microfluidic chips: A review

Advancements in optical fiber-based wearable sensors for smart health monitoring

Healthcare system is undergoing a significant transformation from a traditional hospital-centered to an individual-centered one, as a result of escalating chronic diseases, ageing populations, and ever-increasing healthcare costs,. Wearable sensors have become widely used in health monitoring systems since the COVID-19 pandemic. They enable continuous measurement of important health indicators like body temperature, wrist pulse, respiration rate, and non-invasive bio fluids like saliva and perspiration. Over the last few decades, the development has mostly concentrated on electrochemical and electrical wearable sensors. However, due to the drawbacks of such sensors, such as electronic waste, electromagnetic interference, non-electrical security, and poor performance, researchers are exhibiting a strong interest in optical principle-based systems. Fiber-based optical wearables are among the most promising healthcare systems because of advancements in high-sensitivity, durable, multiplexed sensing, and simple integration with flexible materials to improve wearability and simplicity. We present an overview of recent developments in optical fiber-based wearable sensors, focusing on two mechanisms: wavelength interrogation and intensity modulation for the detection of body temperature, pulse rate, respiration rate, body movements, and biomedical noninvasive fluids, with a thorough examination of their benefits and drawbacks. This review also focuses on improving working performance and application techniques for healthcare systems, including the integration of nanomaterials and the usage of the Internet of Things (IoT) with signal processing. Finally, the review concludes with a discussion of the future possibilities and problems for optical fiber-based wearables.

Exosome Isolation and Detection: From Microfluidic Chips to Nanoplasmonic Biosensor

Exosomes are becoming more widely acknowledged as significant circulating indicators for the prognosis and diagnosis of cancer. Circulating exosomes are essential to the development and spread of cancer, according to a growing body of research. Using existing technology, characterizing exosomes is quite difficult. Therefore, a direct, sensitive, and targeted approach to exosome detection will aid in illness diagnosis and prognosis. The review discusses the new strategies for exosome isolation and detection technologies from microfluidic chips to nanoplasmonic biosensors, analyzing the advantages and limitations of these new technologies. This review serves researchers to better understand exosome isolation and detection methods and to help develop better exosome isolating and detecting devices for clinical applications.

Rapid and sensitive parallel on-site detection of antibiotics and resistance genes in aquatic environments using evanescent wave dual-color fluorescence fiber-embedded optofluidic nanochip

Environmental antibiotics and antibiotic resistance genes (ARGs) pose considerable threat to humans and animals; thus, the rapid and sensitive parallel detection of these pollutants from a single sample is urgently required. However, traditional multiplexed analytic technologies detect only one type of target (e.g., small molecules or nucleic acids) per assay. To address this issue, Evanescent wave Dual-color fluorescence Fiber-embedded Optofluidic Nanochip (EDFON) was fabricated by integrating a fiber-embedded optofluidic nanochip with evanescent wave dual-color fluorescence technology. The EDFON was used for the parallel quantitative detection of sulfamerazine (SMR) and MCR-1 with high sensitivity and specificity by combining a heterogeneous immunoassay with a homogenous hybridization chain reaction based on time-resolved effects. LODs of 0.032 μg/L and 35 pM was obtained for SMR and MCR-1, respectively, within 20 min. To our best knowledge, the EDFON is the first device for the simultaneous detection of two type of targets in each test, which is highly valuable to prevent the global threats of antibiotics and ARGs. Comparison with liquid chromatography-mass spectrometry showed a strong linear relationship (R2 = 0.998) for SMR pollution in the Qinghe River, with spiked SMR and MCR-1 negative surface and wastewater samples showing recovery rates of 91.8-113.4%. These results demonstrate the excellent accuracy and reliability of the EDFON, with features such as multi-analyte detection, field-deployment, and minimal-equipment, rendering it revolutionary for environmental monitoring, food safety, and medical diagnostics.

Recent Progress on Microfluidics Integrated with Fiber-Optic Sensors for On-Site Detection

This review introduces a micro-integrated device of microfluidics and fiber-optic sensors for on-site detection, which can detect certain or several specific components or their amounts in different samples within a relatively short time. Fiber-optics with micron core diameters can be easily coated and functionalized, thus allowing sensors to be integrated with microfluidics to separate, enrich, and measure samples in a micro-device. Compared to traditional laboratory equipment, this integrated device exhibits natural advantages in size, speed, cost, portability, and operability, making it more suitable for on-site detection. In this review, the various optical detection methods used in this integrated device are introduced, including Raman, ultraviolet-visible, fluorescence, and surface plasmon resonance detections. It also provides a detailed overview of the on-site detection applications of this integrated device for biological analysis, food safety, and environmental monitoring. Lastly, this review addresses the prospects for the future development of microfluidics integrated with fiber-optic sensors.

In-situ label-free temperature-compensated DNA hybridization detection with a fiber-optic interferometer and a fiber Bragg grating for microfluidic chip

We demonstrated a temperature-compensated optofluidic DNA biosensor available for microfluidic chip. The optofluidic sensor was composed of an interferometer and a fiber Bragg grating (FBG) by femtosecond laser direct writing micro/nano processing technology. The sensing arm of the interferometer was suspended on the inner wall of the microchannel and could directly interact with the microfluid. With the immobilization of the single stranded probe DNA (pDNA), this optofluidic biosensor could achieve specific detection of single stranded complementary DNA (scDNA). The experimental results indicated that a linear response within 50 nM and the detection limit of 1.87 nM were achieved. In addition, the optofluidic biosensor could simultaneously monitor temperature to avoid temperature fluctuations interfering with the DNA hybridization detection process. And, the optofluidic detection channel could achieve fast sample replacement within 10 s at a flow rate of 2 μL/min and sample consumption only required nanoliters. This optofluidic DNA biosensor had the advantages of label-free, good specificity, dual parameter detection, low sample consumption, fast response, and easy repeatable preparation, which was of great significance for the field of DNA hybridization research and solving the temperature sensitivity problem of biosensors and had good prospects in biological analysis.

Rapid and noninvasive cell assay by microfluidic-integrated intracavity evanescent field absorption in a fiber ring laser

BACKGROUND

Highly sensitive and rapid detection of cell concentration and interfacial molecular events is of great value for biological, biomedical, and chemical research. Most traditional biosensors require large sample volumes and complicated functional modifications of the surface. It is of great significance to develop label-free biosensor platforms with minimal sample consumption for studying cell concentration changes and interfacial molecular events without labor-intensive procedures.

RESULTS

Here, a fiber-optic biosensor based on intracavity evanescent field absorption sensing is designed for sensitive and label-free cell assays for the first time. The interaction between the cells and the evanescent field is enhanced by introducing microfluidic-integrated intracavity absorption in a fiber ring laser. This strategy extends the range of targeted analytes to include quantification of a large number of targets on a surface and improves the detection sensitivity of the fiber-optic biosensor. The level of sensing resolution could be improved from 10-4 RIU to 10-7 RIU using this strategy. The stem cells were studied over a wide concentration range (from 500 to 1.2 × 105 cells/ml) and were measured sequentially. By measuring the output power of the intracavity absorption sensing system, the cell concentration can be directly determined in a label-free manner. The results show that dozens of stem cells can be sensitively detected with a sample consumption of 72 μL. The response was fast (15 s) with a low temperature cross-sensitivity of 0.031 cells·ml-1/°C.

SIGNIFICANCE

The proposed method suggests its capacity for true label-free and noninvasive cell assays with a low limit of detection and small sample consumption. This has the potential to be used as a universal tool for quantitative and qualitative characterization of various cells and other biochemical analytes.

Applications of flexible electronics related to cardiocerebral vascular system

Ensuring accessible and high-quality healthcare worldwide requires field-deployable and affordable clinical diagnostic tools with high performance. In recent years, flexible electronics with wearable and implantable capabilities have garnered significant attention from researchers, which functioned as vital clinical diagnostic-assisted tools by real-time signal transmission from interested targets in vivo. As the most crucial and complex system of human body, cardiocerebral vascular system together with heart-brain network attracts researchers inputting profuse and indefatigable efforts on proper flexible electronics design and materials selection, trying to overcome the impassable gulf between vivid organisms and rigid inorganic units. This article reviews recent breakthroughs in flexible electronics specifically applied to cardiocerebral vascular system and heart-brain network. Relevant sensor types and working principles, electronics materials selection and treatment methods are expounded. Applications of flexible electronics related to these interested organs and systems are specially highlighted. Through precedent great working studies, we conclude their merits and point out some limitations in this emerging field, thus will help to pave the way for revolutionary flexible electronics and diagnosis assisted tools development.

A 3D-Printed Micro-Optofluidic Chamber for Fluid Characterization and Microparticle Velocity Detection

This work proposes a multi-objective polydimethylsiloxane (PDMS) micro-optofluidic (MoF) device suitably designed and manufactured through a 3D-printed-based master-slave approach. It exploits optical detection techniques to characterize immiscible fluids or microparticles in suspension inside a compartment specifically designed at the core of the device referred to as the MoF chamber. In addition, we show our novel, fast, and cost-effective methodology, dual-slit particle signal velocimetry (DPSV), for fluids and microparticle velocity detection. Different from the standard state-of-the-art approaches, the methodology focuses on signal processing rather than image processing. This alternative has several advantages, including the ability to circumvent the requirement of complex and extensive setups and cost reduction. Additionally, its rapid processing speed allows for real-time sample manipulations in ongoing image-based analyses. For our specific design, optical signals have been detected from the micro-optics components placed in two slots designed ad hoc in the device. To show the devices' multipurpose capabilities, the device has been tested with fluids of various colors and densities and the inclusion of synthetic microparticles. Additionally, several experiments have been conducted to prove the effectiveness of the DPSV approach in estimating microparticle velocities. A digital particle image velocimetry (DPIV)-based approach has been used as a baseline against which the outcomes of our methods have been evaluated. The combination of the suitability of the micro-optical components for integration, along with the MoF chamber device and the DPSV approach, demonstrates a proof of concept towards the challenge of real-time total-on-chip analysis.

Opto-microfluidic coupling between optical waveguides and tilted microchannels in lithium niobate

This work presents a reconfigurable opto-microfluidic coupling between optical waveguides and tilted microfluidic channels in monolithic lithium niobate crystal. The light path connecting two waveguide arrays located on opposite sides of a microfluidic channel depends on the refractive index between the liquid phase and the hosting crystal. As a result, the optical properties of the flowing fluid, which is pumped into the microfluidic channel on demand, can be exploited to control the light pathways inside the optofluidic device. Proof-of-concept applications are herein presented, including microfluidic optical waveguide switching, optical refractive index sensing, and wavelength demultiplexing.

Multi working mode SPR chip laboratory for high refractive index detection

The Fiber SPR chip laboratory has become a popular choice in biochemical detection. To meet the needs of different kinds of analytes for the detection range and number of channels of the chip, we proposed a multi-mode SPR chip laboratory based on microstructure fiber in this paper. The chip laboratory was integrated with microfluidic devices made from PDMS and detection units made of bias three-core fiber and dumbbell fiber. By injecting light into different cores of a bias three-core fiber, different detection areas of dumbbell fiber can be selected, enabling the chip laboratory to enter high refractive index detection, multi-channel detection and other working modes. In the high refractive index detection mode, the chip can detect liquid samples with a refractive index range of 1.571-1.595. In multi-channel detection mode, the chip can achieve dual parameter detection of glucose and GHK-Cu, with sensitivities of 4.16 nm/(mg/mL) and 9.729 nm/(mg/mL), respectively. Additionally, the chip can switch to temperature compensation mode. The proposed multi working mode SPR chip laboratory, based on micro structured fiber, offers a new approach for the development of portable testing equipment that can detect multiple analytes and meet multiple requirements.

Emerging strategies of engineering retinal organoids and organoid-on-a-chip in modeling intraocular drug delivery: current progress and future perspectives

Retinal diseases are a rising concern as major causes of blindness in an aging society; therapeutic options are limited, and the precise pathogenesis of these diseases remains largely unknown. Intraocular drug delivery and nanomedicines offering targeted, sustained, and controllable delivery are the most challenging and popular topics in ocular drug development and toxicological evaluation. Retinal organoids (ROs) and organoid-on-a-chip (ROoC) are both emerging as promising in-vitro models to faithfully recapitulate human eyes for retinal research in the replacement of experimental animals and primary cells. In this study, we review the generation and application of ROs resembling the human retina in cell subtypes and laminated structures and introduce the emerging engineered ROoC as a technological opportunity to address critical issues. On-chip vascularization, perfusion, and close inter-tissue interactions recreate physiological environments in vitro, whilst integrating with biosensors facilitates real-time analysis and monitoring during organogenesis of the retina representing engineering efforts in ROoC models. We also emphasize that ROs and ROoCs hold the potential for applications in modeling intraocular drug delivery in vitro and developing next-generation retinal drug delivery strategies.

Impact of nanotechnology on conventional and artificial intelligence-based biosensing strategies for the detection of viruses

Recent years have witnessed the emergence of several viruses and other pathogens. Some of these infectious diseases have spread globally, resulting in pandemics. Although biosensors of various types have been utilized for virus detection, their limited sensitivity remains an issue. Therefore, the development of better diagnostic tools that facilitate the more efficient detection of viruses and other pathogens has become important. Nanotechnology has been recognized as a powerful tool for the detection of viruses, and it is expected to change the landscape of virus detection and analysis. Recently, nanomaterials have gained enormous attention for their value in improving biosensor performance owing to their high surface-to-volume ratio and quantum size effects. This article reviews the impact of nanotechnology on the design, development, and performance of sensors for the detection of viruses. Special attention has been paid to nanoscale materials, various types of nanobiosensors, the internet of medical things, and artificial intelligence-based viral diagnostic techniques.

A fully integrated nucleic acid analysis system for multiplex detection of genetic polymorphisms related to folic acid metabolism

A sufficient intake of folic acid is essential during pregnancy, but several genetic polymorphisms reduce its absorption, threaten the lives of pregnant women and cause congenital disabilities in newborns. Traditional laboratory detection of genetic variants related to folic acid metabolism is time-consuming and labor-intensive. Microfluidics-based molecular diagnosis integrates sample pre-processing and nucleic acid amplification on-chip to achieve rapid, sensitive, high-throughput, and automated detection. Here, we developed a fully integrated microfluidic system for the detection of genetic polymorphisms related to folic acid metabolism in a "sample in-answer out" style. The system consists of nucleic acid extraction and amplification modules. During nucleic acid extraction, blood cells are lysed, and DNA is captured and eluted through a silica-gel membrane. After that, multiple gene loci are detected using loop-mediated isothermal amplification (LAMP) and the color of the reaction chamber indicates whether genetic mutations are present. The experimental results demonstrate that the system can accurately detect gene polymorphisms associated with folic acid metabolism in blood samples with high sensitivity and no cross-contamination between chambers. The blood samples of five patients were tested for mutant alleles on this system, and the test results were consistent with qPCR and DNA sequencing observations. The operation is fully automated, and the detection is completed in approximately 70 minutes. The proposed system has great potential in prenatal diagnosis and other types of nucleic acid detection.

Optical Fiber Fabry-Pérot Microfluidic Sensor Based on Capillary Fiber and Side Illumination Method

In this paper, an optical fiber Fabry-Pérot (FP) microfluidic sensor based on the capillary fiber (CF) and side illumination method is designed. The hybrid FP cavity (HFP) is naturally formed by the inner air hole and silica wall of CF which is side illuminated by another single mode fiber (SMF). The CF acts as a naturally microfluidic channel, which can be served as a potential microfluidic solution concentration sensor. Moreover, the FP cavity formed by silica wall is insensitive to ambient solution refractive index but sensitive to the temperature. Thus, the HFP sensor can simultaneously measure microfluidic refractive index (RI) and temperature by cross-sensitivity matrix method. Three sensors with different inner air hole diameters were selected to fabricate and characterize the sensing performance. The interference spectra corresponding to each cavity length can be separated from each amplitude peak in the FFT spectra with a proper bandpass filter. Experimental results indicate that the proposed sensor with excellent sensing performance of temperature compensation is low-cost and easy to build, which is suitable for in situ monitoring and high-precision sensing of drug concentration and the optical constants of micro-specimens in the biomedical and biochemical fields.

Novel method in emerging environmental contaminants detection: Fiber optic sensors based on microfluidic chips

Recently, human industrial practices and certain activities have caused the widespread spread of emerging contaminants throughout the environmental matrix, even in trace amounts, which constitute a serious threat to human health and environmental ecology, and have therefore attracted the attention of research scholars. Different traditional techniques are used to monitor water pollutants, However, they still have some disadvantages such as high costs, ecological problems and treatment times, and require technicians and researchers to operate them effectively. There is therefore an urgent need to develop simple, inexpensive and highly sensitive methods to sense and detect these toxic environmental contaminants. Optical fiber microfluidic coupled sensors offer different advantages over other detection technologies, allowing manipulation of light through controlled microfluidics, precise detection results and good stability, and have therefore become a logical device for screening and identifying environmental contaminants. This paper reviews the application of fiber optic microfluidic sensors in emerging environmental contaminant detection, focusing on the characteristics of different emerging contaminant types, different types of fiber optic microfluidic sensors, methodological principles of detection, and specific emerging contaminant detection applications. The optical detection methods in fiber optic microfluidic chips and their respective advantages and disadvantages are analyzed in the discussion. The applications of fiber optic biochemical sensors in microfluidic chips, especially for the detection of emerging contaminants in the aqueous environment, such as personal care products, endocrine disruptors, and perfluorinated compounds, are reviewed. Finally, the prospects of fiber optic microfluidic coupled sensors in environmental detection and related fields are foreseen.

All-fiber SPR microfluidic chip for GDF11 detection

In order to perform microfluidic detection of cytokines with low concentration, such as growth differentiation factor 11 (GDF11), the most common method is to construct microfluidic channels and integrate them with SPR sensing units. In this paper, we proposed a novel all-fiber SPR microfluidic chip for GDF11 detection. The method was to construct the SPR sensing area on a designed D-shaped multimode fiber, which was nested inside a quartz tube to form a semi-cylindrical microfluidic channel. The surface of the SPR sensing area experienced sensitization and specifically modification to achieve the specific detection of GDF11. When the sensitivity of detection was 1.38 nm/lg(g/mL) and the limit of detection was 0.52 pg/mL, the sample consumption was only 0.4 µL for a single detection. The novel all-fiber SPR microfluidic detection chip has the advantages of flexible design, compact structure and low sample consumption, which is expected to be used in wearable biosensing devices for real-time online monitoring of trace cytokines in vivo.

Environmental photochemistry with thiol- and silica-modified plasmonic nanocomposites: SERS sensing of municipal solid waste and tannery waste leachate from groundwater

Mismanagement of obsolete solid waste generates a massive deteriorating effect on the environment. There is a high level of open trash disposal contaminating its neighboring water bodies. This despoliation trash causes an endangerment to the living environment. The waste management act is to hinder harmful effects on human beings, animals, plants, and their natural environment through the principles of waste prevention, waste processing, and waste disposal. Surface-enhanced Raman scattering (SERS) enhances the hazardous chemical sensing of environmental pollutants. To vigorously focus on the leaching of a couple of landfills in groundwater and surface water, an unusual combination of SERS-based poly vinyl thiol and silica-modified silver nanocomposites (PVT/SiO2@Ag NCs) was synthesized. The optical, crystalline, and structural properties of PVT/SiO₂@Ag NCs were described with UV-visible spectroscopy (UV-Vis), X-ray diffractometer (XRD), transmission electron microscope (TEM), and energy-dispersive X-ray analysis (EDX). The surface plasmon resonance (SPR) is detected at 403 nm from the PVT/SiO₂@Ag NPs. The average crystallite size of PVT/SiO₂ @ Ag NCs is estimated using the Scherrer formula as 11 nm. The calculated specific surface area (SSA), strains, and dislocation densities demonstrate the improved mechanical properties of the substrate. The well-separated spherical shape of NPs is also observed, and the composition of silica and sulfur element in addition of Ag was confirmed by EDAX. Negatively charged SiO₂ were bound strongly with the SH group and Ag NPs through electrostatic interaction mechanism as S-Ag-O-Si-O-Ag-S. SERS sensitivity is demonstrated by the prepared nanoparticles using an environmentally ignored leachate of municipal solid waste (MSW) and tannery waste (TW) landfill. PVT/SiO₂@Ag NCs has detected the presence of innards of MSW leachate viz., aromatic hydrocarbon, phenols, phthalates, and pesticide from the groundwater. Furthermore, the TW leachate compositions of benzenes, hydrocarbons, amines, and chromium VI were analytically identified. Also, the leaching of TW leachate was confirmed in the water samples referred. Hence, this study provides a novel SERS sensor of PVT/SiO₂@Ag NCs in the tile to detect and analyze environmentally ignored organic and inorganic compounds.

All-fiber biological detection microfluidic chip based on space division and wavelength division multiplexing technologies

To further reduce the size of a microfluidic detection chip and the sample consumption and to shorten the chip manufacturing cycle, an all-fiber SPR detection multichannel microfluidic chip was proposed and demonstrated in this paper. The microfluidic channel of the proposed chip was provided by the air channel of a double side-hole fiber, the detection unit was fabricated using a dumbbell fiber with a fiber core exposed to air, and the sensing probe was composed and packaged by fiber micro-processing technology. The internal double channels of the fiber constructed from double side-hole and dumbbell fibers can realize dual channel detection based on space division multiplexing. 30 nm silver and 50 nm gold films were respectively coated on the left and right sides of the dumbbell fiber, which can realize the dual channel simultaneous detection based on wavelength division multiplexing. We employed the proposed microfluidic chip to detect immunoglobulin G and dopamine molecules, where the average sensitivity is 0.252 nm (mg mL^-1)^-1 and 0.061 nm (μg mL^-1)^-1, and the LOD is 0.397 mg mL^-1 and 1.639 μg mL^-1, respectively. The microfluidic channel and detection unit of all-fiber multi-channel SPR detection microfluidic chip are provided by a soft and flexible fiber, which is compact in structure, flexible in fabrication and short in manufacturing cycle, making it possible for the microfluidic chip to enter the human body for detection and enabling a new approach for the fabrication of wearable detection microfluidic devices. This provides a new idea for the development of microfluidic chips.

Optical Fiber Sensors and Sensing Networks: Overview of the Main Principles and Applications

Optical fiber sensors present several advantages in relation to other types of sensors. These advantages are essentially related to the optical fiber properties, i.e., small, lightweight, resistant to high temperatures and pressure, electromagnetically passive, among others. Sensing is achieved by exploring the properties of light to obtain measurements of parameters, such as temperature, strain, or angular velocity. In addition, optical fiber sensors can be used to form an Optical Fiber Sensing Network (OFSN) allowing manufacturers to create versatile monitoring solutions with several applications, e.g., periodic monitoring along extensive distances (kilometers), in extreme or hazardous environments, inside structures and engines, in clothes, and for health monitoring and assistance. Most of the literature available on this subject focuses on a specific field of optical sensing applications and details their principles of operation. This paper presents a more broad overview, providing the reader with a literature review that describes the main principles of optical sensing and highlights the versatility, advantages, and different real-world applications of optical sensing. Moreover, it includes an overview and discussion of a less common architecture, where optical sensing and Wireless Sensor Networks (WSNs) are integrated to harness the benefits of both worlds.

Femtosecond laser direct writing of a 3D microcantilever on the tip of an optical fiber sensor for on-chip optofluidic sensing

Real-time detection of the concentration of input fluid is essential for optofluidic sensing, especially in the case of biochips and organ-on-a-chip systems. In this paper, a microcantilever structure that enables temperature and liquid concentration sensing was fabricated on the tip of the optical fiber by femtosecond laser direct writing (two-photon polymerization, TPP) technology. An open Fabry-Pérot interferometer (F-P) structure was formed between the end of the optical fiber and the cantilever, so the sensor becomes quite sensitive to the localized temperature, concentration and refractive index of the target liquids. The reasonable size parameters of the cantilever were determined by structural stress analysis and interference spectrum analysis. By integrating the fiber sensor with a microfluidic chip, an on-chip optofluidic sensing platform is developed, which shows high sensitivities of the temperature (92.7 pm °C^-1), concentration (0.3287 nm (g L^-1)^-1), and refractive index (1385.819 nm RIU^-1). The reported optofluidic sensing platform demonstrates reasonably high stability and satisfactory sensing effect, holding great promise for applications in lab-on-a-chip systems.

High-bioactivity microfluidic immunosensing platform for electrochemiluminescence determination of CYFRA 21-1 with the introduction of Fe3O4@Cu@Cu2O

Relying on the electrochemiluminescence (ECL) and microfluidic technology, an immunosensor chip with high bioactivity was designed for sensitive determination of cytokeratin 19 fragment 21-1 (CYFRA 21-1). The mesoporous nanomaterial Fe₃O₄@Cu@Cu₂O as the co-reaction accelerator was used to catalyze the S₂O₈^2- to produce more SO₄^•- to achieve the amplification of the ECL signal. In fact, the generating of SO₄^•- could not only be done with the aid of the reversible cycles of Fe²⁺ and Fe³⁺ and Cu⁺ and Cu²⁺, but could be achieved also through the catalase-like function of Fe₃O₄. What is more, it has also been proved that Fe₃O₄@Cu@Cu₂O exhibited better catalytic performance than single Fe₃O₄, Cu₂O, and Cu@Cu₂O, which supported its application in this system. In addition, a portable microfluidic immunosensor chip for CYFRA 21-1-sensitive determination was assembled, which showed high selectivity, sensitivity, and strong universality in clinical cancer screening and diagnosis. It should be noted that HWRGWVC (HWR) was introduced as the antibody fixator to improve the incubation and binding efficiency of the antibody, which increased the ECL intensity and improved the sensitivity of the immunosensor. This strategy provided a new idea for cancer identification and diagnosis in clinical medicine.

A Portable ‘Plug-and-Play’ Fibre Optic Sensor for In-Situ Measurements of pH Values for Microfluidic Applications

Microfluidics is used in many applications ranging from chemistry, medicine, biology and biomedical research, and the ability to measure pH values in-situ is an important parameter for creating and monitoring environments within a microfluidic chip for many such applications. We present a portable, optical fibre-based sensor for monitoring the pH based on the fluorescent intensity change of an acrylamidofluorescein dye, immobilized on the tip of a multimode optical fibre, and its performance is evaluated in-situ in a microfluidic channel. The sensor showed a sigmoid response over the pH range of 6.0–8.5, with a maximum sensitivity of 0.2/pH in the mid-range at pH 7.5. Following its evaluation, the sensor developed was used in a single microfluidic PDMS channel and its response was monitored for various flow rates within the channel. The results thus obtained showed that the sensor is sufficiently robust and well-suited to be used for measuring the pH value of the flowing liquid in the microchannel, allowing it to be used for a number of practical applications in ‘lab-on-a-chip’ applications where microfluidics are used. A key feature of the sensor is its simplicity and the ease of integrating the sensor with the microfluidic channel being probed.

A Direct Z-Scheme AgBr/CuBi2O4 Photocathode for Ultrasensitive Detection of Ciprofloxacin and Ofloxacin by Controlling the Release of Luminol in Self-Powered Microfluidic Photoelectrochemical Aptasensors

An innovative self-powered microfluidic photoelectrochemical (PEC) aptasensor was developed that uses photoactive AgBr/CuBi₂O₄ (ACO) composites as the photocathode matrix for ultrasensitive detection of ciprofloxacin (CIP) and ofloxacin (OFL). The formation of direct Z-scheme heterojunctions in ACO composites greatly aided electron/hole pair separation. Meanwhile, ZnIn₂S₄-decorated CdS nanorod arrays (CZIS) as the photoanode were used instead of a platinum counter electrode to provide electrons. The "signal-off" CIP detection was accomplished through the steric hindrance effect in the photoanode due to the combination of aptamer_(CIP) and CIP. To increase the cathodic photocurrent intensity for OFL determination, controlled release of luminol was first used. Luminol molecules were successfully embedded in the porous structure of silicon dioxide nanospheres (PSiO₂) by the electrostatic adsorption between PSiO₂ and aptamer_(OFL). The luminol released by specific recognition between OFL and aptamer_(OFL) could not only react with •O₂^- but also produce chemiluminescence emission, resulting in the "signal-on" state. Because of the signal "on-off-on", the proposed aptasensor exhibited wide linear ranges for CIP (0.001-100 ng/mL) and OFL (0.0005-100 ng/mL) detection. Furthermore, the low detection limits of CIP (0.06 pg/mL) and OFL (0.022 pg/mL) could achieve the ultrasensitive analysis.

Prefab Hollow Glass Microsphere-Based Immunosensor with Liquid Crystal Sensitization for Acute Myocardial Infarction Biomarker Detection

Quantitative detection of cardiac troponin biomarkers in blood is an important method for clinical diagnosis of acute myocardial infarction (AMI). In this work, a whispering gallery mode (WGM) microcavity immunosensor based on a prefab hollow glass microsphere (HGMS) with liquid crystal (LC) sensitization was proposed and experimentally demonstrated for label-free cardiac troponin I-C (cTnI-C) complex detection. The proposed fiber-optic immunosensor has a simple structure; the tiny modified HGMS serves as the key sensing element and the microsample reservoir simultaneously. A sensitive LC layer with cTnI-C recognition ability was deposited on the inner wall of the HGMS microcavity. The arrangement of LC molecules is affected by the cTnI-C antigen—antibody binding in the HGMS, and the small change of the surface refractive index caused by the binding can be amplified owing to the birefringence property of LC. Using the annular waveguide of the HGMS, the WGMs were easily excited by the coupling scanning laser with a microfiber, and an all-fiber cTnI-C immunosensor can be achieved by measuring the resonant wavelength shift of the WGM spectrum. Moreover, the dynamic processes of the cTnI-C antigen—antibody binding and unbinding was revealed by monitoring the wavelength shift continuously. The proposed immunosensor with a spherical microcavity can be a cost-effective tool for AMI diagnosis.

Temperature Sensors Based on Polymer Fiber Optic Interferometer

Temperature measurements are of great importance in many fields of human activities, including industry, technology, and science. For example, obtaining a certain temperature value or a sudden change in it can be the primary control marker of a chemical process. Fiber optic sensors have remarkable properties giving a broad range of applications. They enable continuous real-time temperature control in difficult-to-reach areas, in hazardous working environments (air pollution, chemical or ionizing contamination), and in the presence of electromagnetic disturbances. The use of fiber optic temperature sensors in polymer technology can significantly reduce the cost of their production. Moreover, the installation process and usage would be simplified. As a result, these types of sensors would become increasingly popular in industrial solutions. This review provides a critical overview of the latest development of fiber optic temperature sensors based on Fabry–Pérot interferometer made with polymer technology.

Ultrasensitive refractometer based on helical long-period fiber grating near the dispersion turning point

Precise and accurate measurements of the optical refractive index (RI) for liquids are increasingly finding applications in biochemistry and biomedicine. Here, we demonstrate a dual-resonance helical long-period fiber grating (HLPFG) near the dispersion turning point (DTP), which exhibits an ultrahigh RI sensitivity (∼25546 nm/RIU at ∼1.440). The achieved RI sensitivity is, to the best of our knowledge, more than one order of magnitude higher than a conventional HLPFG. The ultrahigh RI sensitivity can improve the RI measurement precision and accuracy significantly. Furthermore, ultralow wavelength shifts (nearly zero) with temperature and strain ranging from 20 to 100°C and 0 to 2226 µε, respectively, are also demonstrated for the proposed HLPFG, which may be a good candidate for developing new low-cross-talk sensors.

Fiber-Optic Theranostics (FOT): Interstitial Fiber-Optic Needles for Cancer Sensing and Therapy

Photonics has spurred a myriad of diagnostic and therapeutic applications for defeating cancer owing to its superiority in spatiotemporal maneuverability and minimal harm. The limits of light penetration depth and elusiveness of photosensitizer utilization, however, impede the implementation of the photodiagnostic and -therapy for determining and annihilating the deep-situated tumor. Herein, a promising strategy that harnesses functional optical fibers is developed and demonstrated to realize an in vivo endoscopic cancer sensing and therapy ensemble. Tumor detection is investigated using hypoxia-sensitive fluorescent fibers to realize fast and accurate tumor recognition and diagnosis. The tumor treatment is further performed by exploiting the endogenous photothermal effect of rare-earth-doped optical fibers. The eradication of orthotopic and subcutaneous xenografts significantly validates the availability of tumoricidal fibers. The strategy opens horizons to inspire the design of optical fiber-mediated "plug and play" precise tumor theranostics with high safety, which may intrigue broader fields, such as fiber optics, materials, chemistry, medicine, and clinics.

Advantages of optical fibers for facile and enhanced detection in droplet microfluidics

Droplet microfluidics offers a unique opportunity for ultrahigh-throughput experimentation with minimal sample consumption and thus has obtained increasing attention, particularly for biological applications. Detection and measurements of analytes or biomarkers in tiny droplets are essential for proper analysis of biological and chemical assays like single-cell studies, cytometry, nucleic acid detection, protein quantification, environmental monitoring, drug discovery, and point-of-care diagnostics. Current detection setups widely use microscopes as a central device and other free-space optical components. However, microscopic setups are bulky, complicated, not flexible, and expensive. Furthermore, they require precise optical alignments, specialized optical and technical knowledge, and cumbersome maintenance. The establishment of efficient, simple, and cheap detection methods is one of the bottlenecks for adopting microfluidic strategies for diverse bioanalytical applications and widespread laboratory use. Together with great advances in optofluidic components, the integration of optical fibers as a light guiding medium into microfluidic chips has recently revolutionized analytical possibilities. Optical fibers embedded in a microfluidic platform provide a simpler, more flexible, lower-cost, and sensitive setup for the detection of several parameters from biological and chemical samples and enable widespread, hands-on application much beyond thriving point-of-care developments. In this review, we examine recent developments in droplet microfluidic systems using optical fiber as a light guiding medium, primarily focusing on different optical detection methods such as fluorescence, absorbance, light scattering, and Raman scattering and the potential applications in biochemistry and biotechnology that are and will be arising from this.

Advances in droplet microfluidics for SERS and Raman analysis

Raman spectroscopy can realize qualitative and quantitative characterization, and surface-enhanced Raman spectroscopy (SERS) can further enhance its detection sensitivity. In combination with droplet microfluidics, some significant but insurmountable limitations of SERS and Raman spectroscopy can be overcome to some extent, thus improving their detection capability and extending their application. During the past decade, these systems have constantly developed and demonstrated a great potential in more applications, but there is no new review systematically summarizing the droplet microfluidics-based Raman and SERS analysis system since the first related review was published in 2011. Thus, there is a great need for a new review to summarize the advances. In this review, we focus on droplet microfluidics-based Raman and SERS analysis, and summarize two mainstream research directions on this topic up to now. The one is SERS or Raman detection in the moving droplet microreactors, including analysis of molecules, single cells and chemical reaction processes. The other one is SERS active microparticle fabrication via microfluidic droplet templates covering polymer matrix and photonic crystal microparticles. We also comment on the advantages, disadvantage and correlation resolution of droplet microfluidics for SERS or Raman. Finally, we summarize these systems and illustrate our perspectives for future research directions in this field.

Synergies between Hyperpolarized NMR and Microfluidics: A Review

Hyperpolarized nuclear magnetic resonance and lab-on-a-chip microfluidics are two dynamic, but until recently quite distinct, fields of research. Recent developments in both areas increased their synergistic overlap. By microfluidic integration, many complex experimental steps can be brought together onto a single platform. Microfluidic devices are therefore increasingly finding applications in medical diagnostics, forensic analysis, and biomedical research. In particular, they provide novel and powerful ways to culture cells, cell aggregates, and even functional models of entire organs. Nuclear magnetic resonance is a non-invasive, high-resolution spectroscopic technique which allows real-time process monitoring with chemical specificity. It is ideally suited for observing metabolic and other biological and chemical processes in microfluidic systems. However, its intrinsically low sensitivity has limited its application. Recent advances in nuclear hyperpolarization techniques may change this: under special circumstances, it is possible to enhance NMR signals by up to 5 orders of magnitude, which dramatically extends the utility of NMR in the context of microfluidic systems. Hyperpolarization requires complex chemical and/or physical manipulations, which in turn may benefit from microfluidic implementation. In fact, many hyperpolarization methodologies rely on processes that are more efficient at the micro-scale, such as molecular diffusion, penetration of electromagnetic radiation into a sample, or restricted molecular mobility on a surface. In this review we examine the confluence between the fields of hyperpolarization-enhanced NMR and microfluidics, and assess how these areas of research have mutually benefited one another, and will continue to do so.

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.

Rapid detection of Pseudomonas aeruginosa based on lab-on-a-chip platform using immunomagnetic separation, light scattering, and machine learning

The rapid detection of the pathogenic bacteria in patient samples is crucial to expedient patient care. The proposed approach reports the development of a novel lab-on-a-chip device for the rapid detection of P. aeruginosa based on immunomagnetic separation, optical scattering, and machine learning. The immunomagnetic particles with a diameter of 5 μm were synthesized for isolating P. aeruginosa from the test sample. A microfluidic chip was fabricated, and three optical fibers were embedded for connecting a laser light and two photodetectors. The laser light was pointed towards the channel to pass light through the sample. A pair of photodetectors via optical fibers were arranged symmetrically at 45° to the channel. The photodetectors acquired scattered light from the flowing sample and converted the light to an electrical signal. The sample containing immunomagnetic beads linked with bacteria was injected into the microfluidic chip. The optimized conditions for performing the experiments were characterized for real-time detection of P. aeruginosa. The data acquisition system recorded the real-time light scattering from the test sample. After removing noise from the output waveform, five different time-domain statistical features were extracted from each waveform: standard mean, standard variance, skewness, kurtosis, and coefficient of variation. The pathogens classification was performed by training the discrimination model using extracted features based on machine learning algorithms. The support vector machines (SVM) with a sigmoid function kernel showed superior classification performance with 97.9% accuracy among other classifiers, including k-nearest neighbors (KNN), logistic regression (LR), and naïve Bayes (NB). The method can detect P. aeruginosa specifically and quantitatively with a limit of detection of 10² CFU/mL. The device can classify P. aeruginosa within 10 min with a total assay time of 25 min. The device was used to test its ability to detect pathogen from the serum and sputum specimens spiked with 10⁵ CFU/mL concentration of P. aeruginosa. The results indicate that light scattering combined with machine learning can be used to detect P. aeruginosa. The proposed technique is anticipated to be helpful as a rapid device for diagnosing P. aeruginosa related infections.

Recent Development of Optofluidics for Imaging and Sensing Applications

Optofluidics represents the interaction of light and fluids on a chip that integrates microfluidics and optics, which provides a promising optical platform for manipulating and analyzing fluid samples. Recent years have witnessed a substantial growth in optofluidic devices, including the integration of optical and fluidic control units, the incorporation of diverse photonic nanostructures, and new applications. All these advancements have enabled the implementation of optofluidics with improved performance. In this review, the recent advances of fabrication techniques and cutting-edge applications of optofluidic devices are presented, with a special focus on the developments of imaging and sensing. Specifically, the optofluidic based imaging techniques and applications are summarized, including the high-throughput cytometry, biochemical analysis, and optofluidic nanoparticle manipulation. The optofluidic sensing section is categorized according to the modulation approaches and the transduction mechanisms, represented by absorption, reflection/refraction, scattering, and plasmonics. Perspectives on future developments and promising avenues in the fields of optofluidics are also provided.

Toward the Development of Rapid, Specific, and Sensitive Microfluidic Sensors: A Comprehensive Device Blueprint

Recent advances in nano/microfluidics have led to the miniaturization of surface-based chemical and biochemical sensors, with applications ranging from environmental monitoring to disease diagnostics. These systems rely on the detection of analytes flowing in a liquid sample, by exploiting their innate nature to react with specific receptors immobilized on the microchannel walls. The efficiency of these systems is defined by the cumulative effect of analyte detection speed, sensitivity, and specificity. In this perspective, we provide a fresh outlook on the use of important parameters obtained from well-characterized analytical models, by connecting the mass transport and reaction limits with the experimentally attainable limits of analyte detection efficiency. Specifically, we breakdown when and how the operational (e.g., flow rates, channel geometries, mode of detection, etc.) and molecular (e.g., receptor affinity and functionality) variables can be tailored to enhance the analyte detection time, analytical specificity, and sensitivity of the system (i.e., limit of detection). Finally, we present a simple yet cohesive blueprint for the development of high-efficiency surface-based microfluidic sensors for rapid, sensitive, and specific detection of chemical and biochemical analytes, pertinent to a variety of applications.

Evanescent Field Controllable MZ Sensor via Femtosecond Laser Processing and Mechanic Polishing

Recently, optical sensors interacting with evanescent fields and the external environment around waveguides have attracted extensive attention. In the process of light propagation in the waveguide, the depth of the evanescent field is closely related to the accuracy of the optical sensor, and adjusting the depth of the evanescent field to obtain higher accuracy has become the primary challenge in fabricating on-chip optical sensors. In this study, the waveguide structure of a Mach–Zehnder interferometer was written directly in Corning Eagle 2000 borosilicate glass by a femtosecond laser, and the sensing window was exposed out of the bulk material by mechanical polishing. The refractive index detection device based on the proposed on-chip Mach–Zehnder interferometer has the advantages of small volume, light weight, and good stability. Its sensitivity can reach 206 nm/RIU or 337 dB/RIU, and the theoretical maximum measurement range is 1–1.508. Therefore, it can measure the refractive index quickly and accurately in extreme or complex environments, and has excellent application prospects.

Development of a pulse-induced electrochemical biosensor based on gluconamide for Gram-negative bacteria detection

Pathogenic bacteria can cause the outbreaks of disease and threaten human health, which stimulates the development of advanced detection techniques. Herein, a specific and sensitive electrochemical biosensor for Gram-negative bacteria was established based on the conductive polymer with artificial muscle properties.  The effective recognition was achieved through the specific carbohydrate-carbohydrate interaction between gluconamide and lipopolysaccharide.  The application of impulse voltage enhances the efficiency of recognition and shortens the detection time through the temporary deformation of the electrode surface, with a limit of detection (LOD)  of 1 × 10⁰ CFU/mL and a linear range of 1 × 10⁰ - 1 × 10⁶ CFU/mL for Escherichia coli (E. coli). In addition  to the merits of low cost, high efficiency, and rapidity,  the developed label-free electrochemical biosensor can also be applicable for other Gram-negative bacteria, owning promising potential in the application of portable devices and paving a potential way for the construction of electrochemical biosensors.

Microbubble resonators for scattering-free absorption spectroscopy of nanoparticles

We present a proof-of-concept experiment where the absorbance spectra of suspensions of plasmonic nanoparticles are accurately reconstructed through the photothermal conversion that they mediate in a microbubble resonator. This thermal detection produces spectra that are insensitive towards light scattering in the sample, as proved experimentally by comparing the spectra of acqueos gold nanorods suspensions in the presence or absence of milk powder. In addition, the microbubble system allows for the interrogation of small samples (below 40 nl) while using a low-intensity beam (around 20 µW) for their excitation. In perspective, this system could be implemented for the characterization of turbid biological fluids through their optical absorption, especially when considering that the microbubble resonator naturally interfaces to a microfluidic circuit and may easily fit within portable or on-chip devices.

Simultaneous Absorbance and Fluorescence Measurements Using an Inlaid Microfluidic Approach

A novel microfluidic optical cell is presented that enables simultaneous measurement of both light absorbance and fluorescence on microlitre volumes of fluid. The chip design is based on an inlaid fabrication technique using clear and opaque poly(methyl methacrylate) or PMMA to create a 20.2 mm long optical cell. The inlaid approach allows fluid interrogation with minimal interference from external light over centimeter long path lengths. The performance of the optical cell is evaluated using a stable fluorescent dye: rhodamine B. Excellent linear relationships (R² > 0.99) are found for both absorbance and fluorescence over a 0.1-10 µM concentration range. Furthermore, the molar attenuation spectrum is accurately measured over the range 460-550 nm. The approach presented here is applicable to numerous colorimetric- or fluorescence-based assays and presents an important step in the development of multipurpose lab-on-chip sensors.

Analysis of single-mode fiber-optic extrinsic Fabry-Perot interferometric sensors with planar metal mirrors

We theoretically study the spectral characteristics and noise performance of wavelength-interrogated fiber-optic sensors based on an extrinsic Fabry-Perot (FP) interferometer (EFPI) formed by thin metal mirrors. We develop a model and use it to analyze the effect of key sensor parameters on the visibility and spectral width of the sensors, including the beam width of the incident light, metal coating film thickness, FP cavity length, and wedge angle of the two mirrors. Through Monte Carlo simulations, we obtain an empirical equation that can be used to estimate the wavelength resolution from the visibility and spectral width, which can be used as a figure-of-merit that is inherent to the sensor and independent on the system noises. The work provides a useful tool for designing, constructing, and interrogating high-resolution fiber-optic EFPI sensors.

Fiber Optic Based Distributed Mechanical Vibration Sensing

The distributed long-range sensing system, using the standard telecommunication single-mode optical fiber for the distributed sensing of mechanical vibrations, is described. Various events generating vibrations, such as a walking or running person, moving car, train, and many other vibration sources, can be detected, localized, and classified. The sensor is based on phase-sensitive optical time-domain reflectometry (ϕ-OTDR). Related sensing system components were designed and constructed, and the system was tested both in the laboratory and in the real deployment, with an 88 km telecom optical link, and the results are presented in this paper. A two-fiber sensor unit, with a double-sensing range was also designed, and its scheme is described. The unit was constructed and the initial measurement results are presented.

All Silica Micro-Fluidic Flow Injection Sensor System for Colorimetric Chemical Sensing

This paper presents a miniature, all-silica, flow-injection sensor. The sensor consists of an optical fiber-coupled microcell for spectral absorption measurements and a microfluidic reagent injection system. The proposed sensor operates in back reflection mode and, with its compact dimensions, (no more than 200 µm in diameter) enables operation in small spaces and at very low flow rates of analyte and reagent, thus allowing for on-line or in-line colorimetric chemical sensing.

Enhanced photothermal signal detection by graphene oxide integrated long period fiber grating for on-site quantification of sodium copper chlorophyllin

An enhanced photothermal signal detection method based on graphene oxide (GO) integrated long period fiber grating (LPFG) for on-site sodium copper chlorophyllin (SCC) quantification is proposed. SCC, as a porphyrin compound, can be photonically excited to induce a stronger photothermal effect. GO offers superior molecular adsorption and thermal conductivity properties; depositing it on the LPFG surface significantly improves the sensitivity and detection efficiency of the SCC photothermal signal, when irradiated with a 405 nm laser. The experimental results showed improved performance compared with those from uncoated LPFG, with a sensitivity of 0.0587 dB (mg L^-1)^-1 and a limit of detection (LOD) of 0.17 mg kg^-1, which is also an order of magnitude lower than that of traditional high-performance liquid chromatography. The proposed method has potential applications in the fields of real-time food safety monitoring, environmental pollutant detection, and disease diagnosis.

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.

BIO bragg gratings on microfibers for label-free biosensing

Discovering nanoscale phenomena to sense biorecognition events introduces new perspectives to exploit nanoscience and nanotechnology for bioanalytical purposes. Here we present Bio Bragg Gratings (BBGs), a novel biosensing approach that consists of diffractive structures of protein bioreceptors patterned on the surface of optical waveguides, and tailored to transduce the magnitude of biorecognition assays into the intensity of single peaks in the reflection spectrum. This work addresses the design, fabrication, and optimization of this system by both theoretical and experimental studies to explore the fundamental physicochemical parameters involved. Functional biomolecular gratings are fabricated by microcontact printing on the surface of tapered optical microfibers, and their structural features were characterized. The transduction principle is experimentally demonstrated, and its quantitative bioanalytical prospects are assessed in a representative immunoassay, based on patterned protein probes and selective IgG targets, in label-free conditions. This biosensing system involves appealing perspectives to avoid unwanted signal contributions from non-specific binding, herein investigated in human serum samples. The work also proves how the optical response of the system can be easily tuned, and it provides insights into the relevance of this feature to conceive multiplexed BBG systems capable to perform multiple label-free biorecognition assays in a single device.

Spatial intensity distribution model of fluorescence emission considering the spatial attenuation effect of excitation light

The fluorescence quantitative analysis method of a solution is widely applied in chemical analysis, clinical medicine testing, environmental monitoring, food safety detection, and so on. It is based on the linear relationship between the intensity of fluorescence emission and the concentration of the substance in solution. Without consideration of the spatial attenuation effect of excitation light, it is applied only to a dilute solution. In this research, a fluorescence emission model is established based on the interaction and propagation law between the excitation light and the fluorescent substances. The spatial attenuation effect of excitation light is analyzed by an element analysis method, and the spatial intensity distribution of fluorescence is revealed. Further, a high accuracy model between the received fluorescence intensity and concentration is obtained. Applications of this model and further design will allow for high throughput fluorescence analysis and the analysis of fluorescent substances with ultra-wide range concentration, such as on-line testing fluorescent dyes in the textile industry, monitoring protein plasma in biomedical field, and high-throughput DNA fluorescence analysis etc. As an example, based on this model, an ultra-wide concentration range (0.02 - 250 mg/L) detection of tryptophan with high accuracy (R² = 0.9994, RRMSE = 0.0356) is realized.

Fabrication and Bonding of Refractive Index Matched Microfluidics for Precise Measurements of Cell Mass

The optical properties of polymer materials used for microfluidic device fabrication can impact device performance when used for optical measurements. In particular, conventional polymer materials used for microfluidic devices have a large difference in refractive index relative to aqueous media generally used for biomedical applications. This can create artifacts when used for microscopy-based assays. Fluorination can reduce polymer refractive index, but at the cost of reduced adhesion, creating issues with device bonding. Here, we present a novel fabrication technique for bonding microfluidic devices made of NOA1348, which is a fluorinated, UV-curable polymer with a refractive index similar to that of water, to a glass substrate. This technique is compatible with soft lithography techniques, making this approach readily integrated into existing microfabrication workflows. We also demonstrate that this material is compatible with quantitative phase imaging, which we used to validate the refractive index of the material post-fabrication. Finally, we demonstrate the use of this material with a novel image processing approach to precisely quantify the mass of cells in the microchannel without the use of cell segmentation or tracking. The novel image processing approach combined with this low refractive index material eliminates an important source of error, allowing for high-precision measurements of cell mass with a coefficient of variance of 1%.