Optical Biosensor System Research Articles

Metal-organic framework/enzyme coated optical fibers as waveguide-based biosensors

Metal organic frameworks (MOFs) have applied as promising vectors for encapsulating enzymes due to their porous structures. Glucose oxidase (GOx) encapsulated zeolitic imidazole-based metal organic frameworks (ZIF-8) were integrated, with long period grating (LPG) to develop highly stable, label-free optical fiber biosensors. Various morphologies of ZIF-8/GOx composites were synthetized with different concentrations of GOx, Zn2+ and 2-methylimidazole (2-MIM) in precursor solutions. The composites can achieve high protein encapsulation efficiency and show high activity and stability under harsh conditions. In the optical biosensing system, the ZIF-8(Zn-based MOF) acts not only as a protective shell for GOx but also as an analyte collector on fibers. The wavelength shifts are linearly corelated with glucose concentrations in range of 1–8 mM with a response coefficient of ˜0.5 nm/mM. The ZIF-8/GOx shows high stability under harsh conditions that would decompose free GOx.

A Wearable Pulse Oximeter With Wireless Communication and Motion Artifact Tailoring for Continuous Use.

Advances in several engineering fields have led to a trend toward miniaturization and portability of wearable biosensing devices, which used to be confined to large tools and clinical settings. Various systems to continuously measure electrophysiological activity through electrical and optical methods are one category of such devices. Being wearable and intended for prolonged use, the amount of noise introduced on sensors by movement remains a challenge and requires further optimization. User movement causes motion artifacts that alter the overall quality of the signals obtained, hence corrupting the resulting measurements. This paper introduces a fully wearable optical biosensing system to continuously measure pulse oximetry and heart rate, utilizing a reflectance-based probe. Furthermore, a novel data-dependent motion artifact tailoring algorithm is implemented to eliminate noisy data due to the motion artifact and measure oxygenation level with high accuracy in real time. By taking advantages of current wireless transmission and signal processing technologies, the developed wearable photoplethysmography device successfully captures the measured signals and sends them wirelessly to a mobile device for signal processing in real time. After applying motion artifact tailoring, evaluating accuracy with a continuous clinical device, the blood oxygenation measurements obtained from our system yielded an accuracy of at least 98%, when compared to a range of 93.6%-96.7% observed before from the same initial data. Additionally, heart rate accuracy above 97% was achieved. Motion artifact tailoring and removal in real time, continuous systems will allow wearable devices to be truly wearable and a reliable electrophysiological monitoring and diagnostics tool for everyday use.

Fabrication and application of substoichiometric tungsten oxide with tunable localized surface plasmon resonances

Substoichiometric tungsten oxide (WO3-x) has become one of the interesting candidates for localized surface plasmon resonance (LSPR) hosts because of its fascinating properties. Herein, we report that substoichiometric WO3-x can be fabricated via a facile solid phase reduction method, and at the same time it exhibits a strong LSPR in the near infrared region. Tunable plasmon resonances can be observed in a wide range by changing their stoichiometry. In the bovine serum albumin (BSA) based optical bio-sensing system, the plasmonic WO3-x displays superior sensitivity. Moreover, the hybrid nanocomposites combining the plasmonic WO3-x and plasmonic Ag can be also obtained, which show great potentials in heterogeneous catalysis. Specially, the WO3-x prepared at the reduction temperature of 350 °C (WO3-350) exerts improved photocatalytic performance toward methylene blue degradation, which is due to the synergistic effect of the strong plasmonic effect of WO3-350 and Ag nanoparticles.

Real-time fish stress visualization came true：A novel multi-stage color-switching wireless biosensor system

An optical communication type biosensor system has been developed which can measure blood glucose concentration, which is a stress indicator of fish, in real-time while fish swimming freely. However, this system is hard to make instant acknowledgment of fish stress level which has to contain an unavoidable delay in the judgment. In this research, we aimed to develop a novel stress visualization system which can quickly judge the levels for fish stress response instantly based on a color changeable LED while another LED was designed to send data. The present system is based on the principle of converting the output current value measured by the glucose biosensor corresponding to the stress response into a voltage value. Then, the color and stress switching points of the LED (Red, Yellow, Green) were decided based on the voltage value gained from the biosensor which mentioned above. Furthermore, we attempted to use our biosensor system to make real-time monitoring of fish stress in vivo. As results, the proposed sensor can make real-time measurement of glucose and shows a great response to those of actual fish sample in the range from 35.36 to 300 mg dl−1 (R = 0.9899). When the glucose concentration in the collected sample was switched to the concentration pre-sett, it was successful to switch the LED color according to the gained voltage value both in vitro and in vivo. Furthermore, when monitoring the stress responses of the fish in vivo, color switching corresponding to the sensor output current value was observed successfully.

Development of novel portable and reusable fiber optical chemiluminescent biosensor and its application for sensitive detection of microcystin-LR

A novel portable fiber optical chemiluminescent biosensor (FOCB) system was successfully constructed using fiber optic bio-probe as biorecognition element as well as transducer and a Si-based photodiode detector (PD-3000). The compact design of FOCB with free magnetic beads and photomultiplier allows it to be portable and suitable for on-site and automatic detection of targets, as well as to be cost-effective and small sample volume (only 40.0 µL). The sensitivity of 5 fW could be obtained for the FOCB due to the high performance of PD-3000 and no background light signal. Next, the FOCB was applied for the CL-based detection of microcystin-LR (MC-LR) in water using hapten-carrier protein conjugates modified fiber optic bio-probe as biorecognition element. Based on indirect competitive sandwich-like CL immunoassay principle, the highly sensitive detection of MC-LR was achieved using FOCB system. Under optimal conditions, the limit of detection for MC-LR is 0.03 µg/L, which is comparable with that of most reported MC-LR immunoassay methods. The robustness of the hapten–carrier protein-modified biosensor surface allowed multiple MC-LR immunoassays without any significant loss of performance, which ensured accurate and cost-effective detection results. The proposed strategy demonstrated good recovery, precision, and accuracy through the evaluation of the spiked water samples. The FOCB system can be readily extended toward the on-site real-time sensitive detection of other targets in the field of environment, food, and medical diagnosis.

Resonant Wavelength Shift Detection System Based on a Gradient Grating Period Guided-Mode Resonance

A resonant wavelength detection system based on a gradient grating period guided-mode resonance (GGP-GMR) filter and a linear charge-coupled device is demonstrated. The GGP-GMR used in this work consists of a subwavelength grating structure with a grating period that varies from 250 to 550 nm in increments of 2 nm. We successfully demonstrate that by using this system, we can monitor the shift in a sensor's dip wavelength caused by different sucrose concentrations. This technology has the potential to replace the spectrometer used in most optical biosensor systems. Given its compactness, the system can be integrated with lab-on-a-chip systems for numerous biosensing applications.

Optical Biosensing System for the Detection of Survivin mRNA in Colorectal Cancer Cells Using a Graphene Oxide Carrier-Bound Oligonucleotide Molecular Beacon.

The anti-apoptotic protein survivin is one of the most promising cancer biomarkers owing to its high expression in human cancers and rare occurrence in normal adult tissues. In this work, we have investigated the role of supramolecular interactions between a graphene oxide (GO) nanosheet nanocarrier and a survivin molecular beacon (SurMB), functionalized by attaching fluorophore Joe and quencher Dabcyl (SurMB-Joe). Molecular dynamics simulations revealed hydrogen bonding of Joe moiety and Dabcyl to GO carriers that considerably increase the SurMB-GO bonding strength. This was confirmed in experimental work by the reduced fluorescence background in the OFF state, thereby increasing the useful analytical signal range for mRNA detection. A new mechanism of hairpin–hairpin interaction of GO@SurMB with target oligonucleotides has been proposed. A low limit of detection, LOD = 16 nM (S/N = 3), has been achieved for complementary tDNA using GO@SurMB-Joe nanocarriers. We have demonstrated an efficient internalization of SurMB-Joe-loaded GO nanocarriers in malignant SW480 cells. The proposed tunability of the bonding strength in the attached motifs for MBs immobilized on nanocarriers, via structural modifications, should be useful in gene delivery systems to enhance the efficacy of gene retention, cell transfection and genomic material survivability in the cellular environment.

Plasmonic Nanomaterial-Based Optical Biosensing Platforms for Virus Detection.

Plasmonic nanomaterials (P-NM) are receiving attention due to their excellent properties, which include surface-enhanced Raman scattering (SERS), localized surface plasmon resonance (LSPR) effects, plasmonic resonance energy transfer (PRET), and magneto optical (MO) effects. To obtain such plasmonic properties, many nanomaterials have been developed, including metal nanoparticles (MNP), bimetallic nanoparticles (bMNP), MNP-decorated carbon nanotubes, (MNP-CNT), and MNP-modified graphene (MNP-GRP). These P-NMs may eventually be applied to optical biosensing systems due to their unique properties. Here, probe biomolecules, such as antibodies (Ab), probe DNA, and probe aptamers, were modified on the surface of plasmonic materials by chemical conjugation and thiol chemistry. The optical property change in the plasmonic nanomaterials was monitored based on the interaction between the probe biomolecules and target virus. After bioconjugation, several optical properties, including fluorescence, plasmonic absorbance, and diffraction angle, were changed to detect the target biomolecules. This review describes several P-NMs as potential candidates of optical sensing platforms and introduces various applications in the optical biosensing field.

CO2‐Assisted Fabrication of Two‐Dimensional Amorphous Molybdenum Oxide Nanosheets for Enhanced Plasmon Resonances

AbstractAs a remarkable class of plasmonic materials, two dimensional (2D) semiconductor compounds have attracted attention owing to their controlled manipulation of plasmon resonances in the visible light spectrum, which outperforms conventional noble metals. However, tuning of plasmonic resonances for 2D semiconductors remains challenging. Herein, we design a novel method to obtain amorphous molybdenum oxide (MoO3) nanosheets, in which it combines the oxidation of MoS2 and subsequent supercritical CO2‐treatment, which is a crucial step for the achievement of amorphous structure of MoO3. Upon illumination, hydrogen‐doped MoO3 exhibits tuned surface plasmon resonances in the visible and near‐IR regions. Moreover, a unique behavior of the amorphous MoO3 nanosheets has been found in an optical biosensing system; there is an optimum plasmon resonance after incubation with different BSA concentrations, suggesting a tunable plasmonic device in the near future.

CO2 -Assisted Fabrication of Two-Dimensional Amorphous Molybdenum Oxide Nanosheets for Enhanced Plasmon Resonances.

As a remarkable class of plasmonic materials, two dimensional (2D) semiconductor compounds have attracted attention owing to their controlled manipulation of plasmon resonances in the visible light spectrum, which outperforms conventional noble metals. However, tuning of plasmonic resonances for 2D semiconductors remains challenging. Herein, we design a novel method to obtain amorphous molybdenum oxide (MoO3 ) nanosheets, in which it combines the oxidation of MoS2 and subsequent supercritical CO2 -treatment, which is a crucial step for the achievement of amorphous structure of MoO3 . Upon illumination, hydrogen-doped MoO3 exhibits tuned surface plasmon resonances in the visible and near-IR regions. Moreover, a unique behavior of the amorphous MoO3 nanosheets has been found in an optical biosensing system; there is an optimum plasmon resonance after incubation with different BSA concentrations, suggesting a tunable plasmonic device in the near future.

Ambient light-based optical biosensing platform with smartphone-embedded illumination sensor

We present a hand-held optical biosensing system utilizing a smartphone-embedded illumination sensor that is integrated with immunoblotting assay method. The smartphone-embedded illumination sensor is regarded as an alternative optical receiver that can replaces the conventional optical analysis apparatus because the illumination sensor can respond to the ambient light in a wide range of wavelengths, including visible and infrared. To demonstrate the biosensing applicability of our system employing the enzyme-mediated immunoblotting and accompanying light interference, various types of ambient light conditions including outdoor sunlight and indoor fluorescent were tested. For the immunoblotting assay, the biosensing channel generating insoluble precipitates as an end product of the enzymatic reaction is fabricated and mounted on the illumination sensor of the smartphone. The intensity of penetrating light arrives on the illumination sensor is inversely proportional to the amount of precipitates produced in the channel, and these changes are immediately analyzed and quantified via smartphone software. In this study, urinary C-terminal telopeptide fragment of type II collagen (uCTX-II), a biomarker of osteoarthritis diagnosis, was tested as a model analyte. The developed smartphone-based sensing system efficiently measured uCTX-II in the 0–5ng/mL concentration range with a high sensitivity and accuracy under various light conditions. These assay results show that the illumination sensor-based optical biosensor is suitable for point-of-care testing (POCT).

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.

Introduction of an angle interrogated, MEMS-based, optical waveguide grating system for label-free biosensing

The presented label-free optical biosensor system relies on a MEMS micro-mirror to interrogate waveguide grating regions at a high repetition rate in the kHz range by scanning the angle of the incident coherent light. The angle-tunable MEMS mirror permits an extended scanning range and offers the flexibility to measure at various wavelengths and optical powers – an interesting feature for an enhanced surface-to-bulk sensitivity ratio and extended, multiplexed sensor arrays.An excellent refractometric sensitivity with a limit of detection towards effective refractive index changes of Δneff<2×10−7 and long-term stability (<10−6min−1) is reported, as well as the capability to perform affinity measurements for large (>150kDa) and small (<250Da) molecules. With fully-integrated optics, electronics and fluidics, the compact, low-power and affordable sensor unit is well-suited for in situ environmental monitoring or point-of-care diagnostics.

Real-time monitoring of DNA hybridization for rapid detection of Vibrio cholerae O1

Effective control and treatment of the severe diarrheal disease caused by Vibrio cholerae requires rapid detection of the bacteria. For this purpose, an optical DNA sensor has been developed to detect real-time DNA hybridization after amplifying the bacterium's ctx gene. This sensor was prepared by immobilizing the 5′-biotinylated oligonucleotide probe containing the ctx sequence on the surface of a poly[methyl methacrylate] (PMMA) prism, using neutravidin. A Cy5-labelled primer for the ctx gene was used for PCR amplification. The PCR amplicon was applied to the active surface of the ctx gene chip to detect hybridization, and evanescent field light of 635 nm revealed 680 nm emission light from the Cy5-labelled DNA target hybridized to the DNA probe. It was estimated that the lower limit of detection of the Cy5-labelled DNA target was 0.2 nM, and the fluorescence signal detected by this sensor chip showed that all 12 V. cholerae O1 were positive for the ctx gene. Of the 12 bacterial strains not belonging to the cholera strains, none produced amplicons with a ctx-specific primer. Within minutes after PCR, this optical biosensor system can detect the ctx gene of V. cholerae O1 with high specificity and sensitivity.

Uricase-immobilization on radiation grafted polymer support for detection of uric acid using Ag-nanoparticle based optical biosensor

A functional polymer support was designed for covalent immobilization of enzyme uricase, which was further utilized in a single enzyme based silver nanoparticles (Ag-NPs)-optical biosensor system for estimation of uric acid. A carboxylic acid functionalized polymer support was fabricated via gamma radiation induced mutual-irradiation grafting of polyacrylic acid (PAA) on to non-woven polypropylene (PP) matrix. Grafting parameters, such as dose, monomer concentration, homopolymer inhibitor and inorganic acid concentration were studied to optimize the grafting process. PAA-g-PP samples were characterized by grafting yield measurement, water uptake, FTIR, TGA and SEM techniques. Uricase enzyme was immobilized on to the PAA-g-PP support via covalent amide linkage using coupling agents, namely N-hydroxysuccinimide (NHS) and N-ethyl-N′-(3-(dimethylamino)propyl)carbodiimide (EDC). The catalytic activity of uricase was investigated spectrophotometrically using uric acid as a substrate. Study of kinetic parameters (Km, Vmax) revealed the value of Km for covalently immobilized uricase to be ∼1.2-fold higher than that of free enzyme. The uricase-immobilized-PAA-g-PP samples could be repeatedly used for ∼20 cycles over a period of 30 days when stored in phosphate buffer (pH∼7.4) at 4°C without significant decrease in the enzyme activity. The uricase immobilized samples were successfully used in conjunction with the radiolytically synthesized Ag-NPs as a LSPR-optical biosensor for estimation of uric acid.

The transformation of common office supplies into a low-cost optical biosensing platform

By reassembling common office supplies, an optical biosensing system was developed. A laser pointer and the solar cell from a calculator were utilized in the developed optical biosensing system as the light source and signal transducer, respectively. For intuitive signal evaluation, a multimeter was used. The following two types of conventional enzymatic colorimetric assays were employed with the optical biosensing system: (i) the Trinder׳s reaction-based enzymatic assay; and (ii) the competitive enzyme-linked immunosorbent assay. These colorimetric assays were performed in reaction channels made from transparent polymer and glass. By matching the maximum absorption spectra of the colored end products from the assays with the emission spectra of the laser diodes, the biochemical reaction rate was manifested as a change in the intensity of the laser beam. This change was then converted by the solar cell into voltage and displayed on the connected multimeter. To verify the detection performance of the system, glucose and an osteoarthritis biomarker (urinary collagen type II C-telopeptide fragments [uCTX-II]) were quantified. With glucose, the voltages registered were linearly correlated with the glucose concentration, from 0 to 10mM. Using a competitive immunoassay for uCTX-II, the system exhibited a calibration curve with a dynamic detection range between 1.3 and 10ng/mL uCTX-II. Given the advantages of the proposed biosensing system, including its high sensitivity, facile fabrication, and the high obtainability and cost-effectiveness of the components used to make it, we expect that this study will provide a basis for the production of a low-cost optical biosensor.

Label-free CRP detection using optical biosensor with one-step immobilization of antibody on nitrocellulose membrane

To assess the potential of using the MCLW sensor as a label-free optical biosensor system for clinical diagnosis, we evaluated the potential of detecting C-reactive protein (CRP) in a diluted real serum sample by using nitrocellulose as an adlayer. Nitrocellulose was coated on the MCLW sensor chip via spin coating and the CRP antibody was directly immobilized on the sensor surface by hydrophobic physical adsorption. Biosensing using the nitrocellulose surface is highly convenient and does not require any additional treatment for the immobilization of ligand. We optimized the condition for the deposition of nitrocellulose on the MCLW sensor chip with the goal of generating the largest signal difference of the sample against the control signal. In addition, label-free immunosensing of CRP was achieved using the nitrocellulose-coated MCLW sensor in real time. As a result, we were able to quantitatively detect CRP in a human serum within a concentration range of 0.1–10μg/mL.

Automated Online Optical Biosensing System for Continuous Real-Time Determination of Microcystin-LR with High Sensitivity and Specificity: Early Warning for Cyanotoxin Risk in Drinking Water Sources

The accelerated eutrophication of surface water sources and climate change have led to an annual occurrence of cyanobacterial blooms in many drinking water resources. To minimize the health risks to the public, cyanotoxin detection methods that are rapid, sensitive, real time, and high frequency must be established. In this study, an innovative automated online optical biosensing system (AOBS) was developed for the rapid detection and early warning of microcystin-LR (MC-LR), one of the most toxic cyanotoxins and most frequently detected in environmental water. In this system, the capturing molecular MC-LR-ovalbumin (MC-LR-OVA) was covalently immobilized onto a biochip surface. By an indirect competitive detection mode, samples containing different concentrations of MC-LR were premixed with a certain concentration of fluorescence-labeled anti-MC-LR-mAb, which binds to MC-LR with high specificity. Then, the sample mixture was pumped onto the biochip surface, and a higher concentration of MC-LR led to less fluorescence-labeled antibody bound onto the biochip surface and thus to lower fluorescence signal. The quantification of MC-LR ranges from 0.2 to 4 μg/L, with a detection limit determined as 0.09 μg/L. The high specificity and selectivity of the sensor were evaluated in terms of its response to a number of potentially interfering cyanotoxins. Potential interference of the environmental sample matrix was assessed by spiked samples, and the recovery of MC-LR ranged from 90 to 120% with relative standard deviation values <8%. The immunoassay performance of the AOBS was validated with respect to that of conventional high-performance liquid chromatography, and the correlation between methods agreed well (R(2) = 0.9762). This system has successfully been applied to long-term, continuous determination and early warning for MC-LR in Lake Tai from June 2011 to May 2012. Thus, the AOBS paves the way for a vital routine online analysis that satisfies the high demand for ensuring the safety of drinking water sources. The AOBS can also serve as early warning system for accidental or intentional water pollution.

Development of a Plate-Based Optical Biosensor Fragment Screening Methodology to Identify Phosphodiesterase 10A Inhibitors

We describe the development of a novel fragment screening methodology employing a plate-based optical biosensor system that can operate in a 384-well format. The method is based on the "inhibition in solution assay" (ISA) approach using an immobilized target definition compound (TDC) that has been specifically designed for this purpose by making use of available structural information. We demonstrate that this method is robust and is sufficiently sensitive to detect fragment hits as weak as KD 500 μM when confirmed in a conventional surface plasmon resonance approach. The application of the plate-based screen, the identification of fragment inhibitors of PDE10A, and their structural characterization are all discussed in a forthcoming paper.

A simple and rapid detection of viral protein using RNA oligonucleotide in a biosensor

The monitoring of non-structural viral protein 3 (NS3) has been of considerable interest in developing simple and reliable methods for detection of hepatitis C virus (HCV) for applications in diagnostic medicine. Although enzyme-linked immunosorbent assay (ELISA) is the most general method in HCV detection, using antibody brings problems. This method is temperature-sensitive and requires specific reactions condition. In addition, secondary antibody conjugated with enzyme and fluorescent dye is required. To overcome these bottlenecks, we designed a streptavidin-biotin conjugation method, namely, the RNA oligonucleotide sensor system that could monitor viral protein with detection limit of 500 pg/mL by using biotin-tagged RNA oligonucleotide in forteBio’s Octet optical biosensor system. In this study, we proposed an efficient method for simple and convenient detection of HCV viral protein, with the advantage of target specific monitoring.