A Highly Sensitive Dual-Core Photonic Crystal Fiber Based on a Surface Plasmon Resonance Biosensor with Silver-Graphene Layer

A highly sensitive dual-core photonic crystal fiber based on a surface plasmon resonance (PCF-SPR) biosensor with a silver-graphene layer is described. The silver layer with a graphene coating not only prevents oxidation of the silver layer but also can improve the silver sensing performance due to the large surface-to-volume ratio of graphene. The dual-core PCF-SPR biosensor is numerically analyzed by the finite-element method (FEM). An average spectral sensitivity of 4350 nm/refractive index unit (RIU) in the sensing range between 1.39 and 1.42 and maximum spectral sensitivity of 10,000 nm/RIU in the sensing range between 1.43 and 1.46 are obtained, corresponding to a high resolution of 1 × 10⁻⁶ RIU as a biosensor. Our analysis shows that the optical spectra of the PCF-SPR biosensor can be optimized by varying the structural parameters of the structure, suggesting promising applications in biological and biochemical detection.

     

Amperometric glucose biosensor based on single-walled carbon nanohorns

The biosensing application of single-walled carbon nanohorns (SWCNHs) was demonstrated through fabrication of an amperometric glucose biosensor. The biosensor was constructed by encapsulating glucose oxidase in the Nafion-SWCNHs composite film. The cyclic voltammograms for glucose oxidase immobilized on the composite film displayed a pair of well-defined and nearly symmetric redox peaks with a formal potential of -0.453 V. The biosensor had good electrocatalytic activity toward oxidation of glucose. To decrease detection potential, ferrocene monocarboxylic acid was used as a redox mediator. The mediated glucose biosensor shows a linear range from 0 to 6.0 mM. The biosensor shows high sensitivity (1.06 microA/mM) and stability, and can avoid the commonly coexisted interference. Because of impressive properties of SWCNHs, such as high purity and high surface area, SWCNHs and their composites are expected to be promising material for biomolecular immobilization and biosensing applications.     

Generic method for quantification of FLAG-tagged fusion proteins by a real time biosensor

Availability of rapid quantitative protein-expression analysis is often the bottleneck in high throughput screening applications. A real time biosensor was employed to establish a quantitative assay for FLAG fusion proteins using FLAG-tagged bacterial alkaline phosphatase as standard. A range of FLAG-tagged bacterial alkaline phosphatase concentrations were injected over the anti-FLAG M2 antibody surface of the biosensor and used as standards to determine the concentration of different FLAG-tagged proteins with a molecular mass of 18.1 kDa respectively 49.3 kDa from yeast culture supernatants. The M2 immobilized chip was found to retain binding capacity following regeneration for at least 120 cycles. This real time biosensor method allows the quantitation of proteins from culture supernatants using a calibration curve obtained with a different protein. Further benefits include the short assay time of approximately 5 min, the small amount of sample required (35 microl per injection) and the ability to monitor the binding event in real time.     

Ultrasensitive detection of cortisol with enzyme fragment complementation technology using functionalized nanowire

Cortisol is a member of the glucocorticoid hormone family and a key metabolic regulator. Increased intracellular cortisol levels have been implicated in type 2 diabetes, obesity, and metabolic syndrome. Cortisol is an important bio-marker of stress and its detection is also important in sports medicine. However, rapid methods for sensitive detection of cortisol are limited. Functionalized gold nanowires were used to enhance the sensitivity and selectivity of cortisol detection. Gold nanowires are used to improve the electron transfer between the electrodes. Moreover, the large surface to volume ratio, small diffusion time and high electrical conductivity and their aligned nature will enhance the sensitivity and detection limit of the biosensor several fold. The biosensor was fabricated using, aligned gold (Au) nanowires to behave as the working electrode, platinum deposited on a silicon chip to function as the counter electrode, and silver/silver chloride as reference electrode. The gold nanowires were coupled with cortisol antibodies using covalent linkage chemistry and a fixed amount of 3alpha-hydroxysteroid dehydrogenase was introduced into the reaction cell during each measurement to convert (reduce) ketosteroid into hydroxyl steroid. Furthermore, the micro-fluidic, micro-fluid part of the sensor was fabricated using micro-electro-mechanical system (MEMS) technology to have better control on liquid flow over Au nanowires to minimize the signal to noise ratio. The biosensor was characterized using SEM, AFM and FTIR technique. The response curve of the biosensor was found to be linear in the range of 10-80 microM of cortisol. Moreover, the presence of hydrocortisone is sensitively detected in the range of 5-30 microM. It is concluded that the functionalized gold nanowires with micro-fluidic device using enzyme fragment complementation technology can provide an easy and sensitive assay for cortisol detection in serum and other biological fluids.     

Clinical application of a novel sliver nanoparticles biosensor based on localized surface plasmon resonance for detecting the microalbuminuria

In order to explore the clinical application of the nanobiosensor based on localized surface plasmon resonance (LSPR), we used our LSPR biosensor to detect the microalbuminuria in this work. The sliver nanoparticles were fabricated by using nanosphere lithography. The anti-human albumin antibody was immobilized on the sensor surface by amine coupling method. The different concentrations of commercial albumin and albumin in urine samples from three mild preeclampsia patients were determined according to the peak of LSPR extinction spectra. Under optimum conditions, our results showed that the biosensor displayed a detection limit of 1 ng/ml and wide dynamic range of 1 ng/ml to 1 μg/ml. Furthermore, the microalbuminuria of three patients was determined by our biosensor within a short assay time, without sample purification. This biosensor proposed herein is easy to prepare and could be used for low-cost, rapid, label-free, and sensitive screening of the microalbuminuria. This approach provides a promising platform for developing clinical diagnostic applications.     

Monitoring bioactive and total antibody concentrations for continuous process control by surface plasmon resonance spectroscopy

Monoclonal antibodies have become an increasingly important part of fundamental research and medical applications. To meet the high market demand for monoclonal antibodies in the biopharmaceutical sector, industrial manufacturing needs to be achieved by large scale, highly productive and consistent production processes. These are subject to international guidelines and have to be monitored intensely due to high safety standards for medical applications. Surface plasmon resonance spectroscopy — a fast, real‐time, and label‐free bio‐sensing method — represents an interesting alternative to the quantification of monoclonal antibody concentrations by enzyme‐linked immunosorbent assay during monoclonal antibody production. For the application of monitoring bioactive and total monoclonal antibody concentrations in cell culture samples, a surface plasmon resonance assay using a target‐monoclonal antibody model system was developed. In order to ensure the subsequent detection of bioactive monoclonal antibody concentrations, suitable immobilization strategies of the target were identified. A significant decrease of the limit of detection was achieved by using an adapted affinity method compared to the commonly used amine coupling. Furthermore, the system showed limit of detection in the low ng/mL range similar to control quantifications by enzyme‐linked immunosorbent assay. Moreover, the comparison of total to bioactive monoclonal antibody concentrations allows analysis of antibody production efficiency. The development of an alternative quantification system to monitor monoclonal antibody production was accomplished using surface plasmon resonance with the advantage of low analyte volume, shorter assay time, and biosensor reusability by target‐layer regeneration. The established method provides the basis for the technical development of a surface plasmon resonance‐based system for continuous process monitoring.     

Use of a thin film biosensor for rapid visual detection of PCR products in a multiplex format

Rapid, sensitive assays for nucleic acid amplification products have utility for the identification of bacterial or viral infections. We have developed a nucleic acid hybridization assay utilizing thin film technology that permits visual detection of hybrids. The silicon-based biosensor detects the presence of target sequences by enzymatically transducing the formation of nucleic acid hybrids into molecular thin films. These films alter the interference pattern of light on the biosensor surface, producing a perceived color change. We have applied this technology to the development of a chip containing capture probes specific for human respiratory virus sequences including respiratory syncytial virus, influenza virus A and B, parainfluenza virus types 1 and 3, and rhinovirus. In a ten-minute assay, the biosensor permits unambiguous identification of viral-specific RT/PCR products from infected cell lysates.     

Generic method for quantification of FLAG-tagged fusion proteins by a real time biosensor

Availability of rapid quantitative protein-expression analysis is often the bottleneck in high throughput screening applications. A real time biosensor was employed to establish a quantitative assay for FLAG fusion proteins using FLAG-tagged bacterial alkaline phosphatase as standard. A range of FLAG-tagged bacterial alkaline phosphatase concentrations were injected over the anti-FLAG M2 antibody surface of the biosensor and used as standards to determine the concentration of different FLAG-tagged proteins with a molecular mass of 18.1 kDa respectively 49.3 kDa from yeast culture supernatants. The M2 immobilized chip was found to retain binding capacity following regeneration for at least 120 cycles. This real time biosensor method allows the quantitation of proteins from culture supernatants using a calibration curve obtained with a different protein. Further benefits include the short assay time of approximately 5 min, the small amount of sample required (35 μl per injection) and the ability to monitor the binding event in real time.     

An ultrasensitive and stable potentiometric immunosensor

We describe a novel quantitative polypyrrole based potentiometric biosensor that provides broad-spectrum assay capability. The biosensor allows for capture of analytes of interest from complex real samples such as serum and whole blood, and subsequent measurement in a controlled matrix environment. The technology is rapid (<15 min), ultrasensitive (<50 fM) and reproducible (CV<5% at 0.1 ng/ml). In addition the system has shown a wide dynamic range (four to five orders of magnitude), and good stability, 37 degrees C for at least 4 months. This potentiometric biosensor detects enzyme labelled immuno-complexes formed at the surface of a polypyrrole coated, screenprinted gold electrode. Detection is mediated by a secondary reaction that produces charged products (a 'charge-step' procedure). A shift in potential is measured at the sensor surface, caused by local changes in redox state, pH and/or ionic strength. The magnitude of the difference in potential is related to the concentration of the formed receptor-target complex. The potentiometric sensing technology has been demonstrated in assays for hepatitis B surface antigen (HBsAg) (Mw>300 kDa), Troponin I (Mw approximately 23 kDa), Digoxin (Mw 780 Da) and tumour necrosis factor (hTNF-alpha) (Mw approximately 23 kDa). These model targets were chosen to represent analytes of a range of molecular weights, and because of their requirement for assays of high analytical sensitivity and precision. All these assays were performed using complex fluid samples and the presence of any non-specific binding has no significant effect on the final measurement. New assays can be transferred and optimised readily.     

Biosensor for the enantioselective analysis of S-perindopril

Because S-perindopril enantiomer is the eutomer which is responsible for the angiotensin-converting enzyme inhibition activity, it is necessary to develop a reliable method for its assay from its distomer, the R-enantiomer. For this purpose, an amperometric biosensor was developed based on L-amino acid oxidase. The working range of the described biosensor was 20pmol/L-10 micromol/L on the 7.0-7.4 pH range, with a detection limit of 2pmol/L. The low enantioselectivity for R-perindopril, as compared with S-enantiomer, was demonstrated by both mixed solutions and separate solutions methods (amperometric selectivity coefficient is 1.0 x 10(-4)). The biosensor was also selective towards D-proline and polyvinylpyrrolidone. The amperometric biosensor can be used for enantioselective analysis of S-perindopril in raw material, with an RSD < 1%. The life time (t95%) of the biosensor is three weeks.     

Porous silicon-based biosensor for pathogen detection

A porous silicon-based biosensor for rapid detection of bacteria was fabricated. Silicon (0.01 ohmcm, p-type) was anodized electrochemically in an electrochemical Teflon cell containing ethanoic hydrofluoric acid solution to produce sponge-like porous layer of silicon. Anodizing conditions of 5 mA/cm2 for 85 min proved best for biosensor fabrication. A single-tube chemiluminescence-based assay, previously developed, was adapted to the biosensor for detection of Escherichia coli. Porous silicon chips were functionalized with a dioxetane-Polymyxin B (cell wall permeabilizer) mixture by diffusion and adsorption on to the porous surface. The reaction of beta-galactosidase enzyme from E. coli with the dioxetane substrate generated light at 530 nm. Light emission for the porous silicon biosensor chip with E. coli was significantly greater than that of the control and planar silicon chip with E. coli (P<0.01). Sensitivity of the porous silicon biosensor was determined to be 101-102 colony forming units (CFU) of E. coli. The porous silicon-based biosensor was fabricated and functionalized to successfully detect E. coli and has potential applications in food and environmental testing.     

Comparison of label-free biosensing in microplate, microfluidic, and spot-based affinity capture assays

Using both experimental assays and fluid-dynamic finite element simulation models, we directly compared the achievable performance limits of four distinct assay configurations for label-free detection of an analyte from a test sample on a biosensor surface. The assay configurations studied in this work included a biosensor incorporated into the bottom surface of a microplate well and a microfluidic channel. For each configuration, we compared assay performance for the scenario in which the entire bottom surface of the fluid-handling vessel is coated with capture ligands with assay performance for the scenario in which the capture ligands are applied in the form of localized spots. As a model system, we used detection of the protein biomarker tumor necrosis factor-alpha (TNF-α) using immobilized TNF-α capture antibody. Results show that the microfluidic assay format dramatically reduces the time required to establish a stable equilibrium. Spot-based assays are advantageous for microplate-based detection for reducing the time required for equilibrium sensor response. The results derived are generally applicable to any label-free biosensor technology and any ligand-analyte system with adjustable variables that include sensor mass density sensitivity, analyte-ligand adsorption/desorption rate constants, immobilized ligand density, flow channel geometry, flow rate, and spot size.     

Localized surface plasmon coupled fluorescence fiber-optic biosensor for alpha-fetoprotein detection in human serum

In this study, we demonstrated that the fiber-optic biosensor based on localized surface plasmon coupled fluorescence (LSPCF) is capable of detecting alpha-fetoprotein (AFP) in human serum. The sensitivity of LSPCF fiber-optic biosensor is not only enhanced but also the specific selectivity is improved since the fluorophores are excited by the localized surface plasmon with high efficiency. Experimentally, this fiber-optic biosensor is able to detect AFP concentration in phosphate buffered saline (PBS) solution from 0.1ng/mL to 100ng/mL whereas the linear relationship between the AFP concentrations and the fluorescence signals is shown. Furthermore, a linear response between the fluorescence signals and the concentrations of AFP in human serum from 2.33ng/mL to 143.74ng/mL is also obtained. As a result, the detection limit of the LSPCF fiber-optic biosensor on AFP detection is comparable with the conventional enzyme-linked immunosorbent assay (ELISA). Additionally, the LSPCF fiber-optic biosensor benefits on inexpensive, disposable and simpler optical geometry that can become a high efficient immunoassay comparable with the conventional ELISA and radioimmunoassay (RIA) clinically.     

A simple and reliable assay for detecting specific nucleotide sequences in plants using optical thin-film biosensor chips

Here we report the adaptation and optimization of an efficient, accurate and inexpensive assay that employs custom-designed silicon-based optical thin-film biosensor chips to detect unique transgenes in genetically modified (GM) crops and SNP markers in model plant genomes. Briefly, aldehyde-attached sequence-specific single-stranded oligonucleotide probes are arrayed and covalently attached to a hydrazine-derivatized biosensor chip surface. Unique DNA sequences (or genes) are detected by hybridizing biotinylated PCR amplicons of the DNA sequences to probes on the chip surface. In the SNP assay, target sequences (PCR amplicons) are hybridized in the presence of a mixture of biotinylated detector probes and a thermostable DNA ligase. Only perfect matches between the probe and target sequences, but not those with even a single nucleotide mismatch, can be covalently fixed on the chip surface. In both cases, the presence of specific target sequences is signified by a color change on the chip surface (gold to blue/purple) after brief incubation with an anti-biotin IgG horseradish peroxidase (HRP) to generate a precipitable product from an HRP substrate. Highly sensitive and accurate identification of PCR targets can be completed within 30 min. This assay is extremely robust, exhibits high sensitivity and specificity, and is flexible from low to high throughput and very economical. This technology can be customized for any nucleotide sequence-based identification assay and widely applied in crop breeding, trait mapping, and other work requiring positive detection of specific nucleotide sequences.     

A high density microelectrode array biosensor for detection of E. coli O157:H7

A high density microelectrode array biosensor was developed for the detection of Escherichia coli O157:H7. The biosensor was fabricated from (100) silicon with a 2 microm layer of thermal oxide as an insulating layer, an active area of 9.6 mm2 and consists of an interdigitated gold electrode array. The sensor surface was functionalised for bacterial detection using heterobifunctional crosslinkers and immobilised polyclonal antibodies to create a biological sensing surface. Bacteria suspended in solution became attached to the immobilised antibodies when the biosensor was tested in liquid samples. The change in impedance caused by the bacteria was measured over a frequency range of 100 Hz-10 M Hz. The biosensor was evaluated for E. coli O157:H7 detection in pure culture and inoculated food samples. The biosensor was able to discriminate between cellular concentrations of 10(4)-10(7)CFU/mL and has applications in detecting pathogens in food samples.     

Functionalized nanopipettes: toward label-free, single cell biosensors

Nanopipette technology has been proven to be a label-free biosensor capable of identifying DNA and proteins. The nanopipette can include specific recognition elements for analyte discrimination based on size, shape, and charge density. The fully electrical read-out and the ease and low-cost fabrication are unique features that give this technology an enormous potential. Unlike other biosensing platforms, nanopipettes can be precisely manipulated with submicron accuracy and used to study single cell dynamics. This review is focused on creative applications of nanopipette technology for biosensing. We highlight the potential of this technology with a particular attention to integration of this biosensor with single cell manipulation platforms.     

A self referencing platinum nanoparticle decorated enzyme-based microbiosensor for real time measurement of physiological glucose transport

Glucose is the central molecule in many biochemical pathways, and numerous approaches have been developed for fabricating micro biosensors designed to measure glucose concentration in/near cells and/or tissues. An inherent problem for microsensors used in physiological studies is a low signal-to-noise ratio, which is further complicated by concentration drift due to the metabolic activity of cells. A microsensor technique designed to filter extraneous electrical noise and provide direct quantification of active membrane transport is known as self-referencing. Self-referencing involves oscillation of a single microsensor via computer-controlled stepper motors within a stable gradient formed near cells/tissues (i.e., within the concentration boundary layer). The non-invasive technique provides direct measurement of trans-membrane (or trans-tissue) analyte flux. A glucose micro biosensor was fabricated using deposition of nanomaterials (platinum black, multiwalled carbon nanotubes, Nafion) and glucose oxidase on a platinum/iridium microelectrode. The highly sensitive/selective biosensor was used in the self-referencing modality for cell/tissue physiological transport studies. Detailed analysis of signal drift/noise filtering via phase sensitive detection (including a post-measurement analytical technique) are provided. Using this highly sensitive technique, physiological glucose uptake is demonstrated in a wide range of metabolic and pharmacological studies. Use of this technique is demonstrated for cancer cell physiology, bioenergetics, diabetes, and microbial biofilm physiology. This robust and versatile biosensor technique will provide much insight into biological transport in biomedical, environmental, and agricultural research applications.     

A portable surface plasmon resonance sensor system for real-time monitoring of small to large analytes

Many environmental applications exist for biosensors capable of providing real-time analyses. One pressing current need is monitoring for agents of chemical- and bio-terrorism. These applications require systems that can rapidly detect small organics including nerve agents, toxic proteins, viruses, spores and whole microbes. A second area of application is monitoring for environmental pollutants. Processing of grab samples through chemical laboratories requires significant time delays in the analyses, preventing the rapid mapping and cleanup of chemical spills. The current state of development of miniaturized, integrated surface plasmon resonance (SPR) sensor elements has allowed for the development of inexpensive, portable biosensor systems capable of the simultaneous analysis of multiple analytes. Most of the detection protocols make use of antibodies immobilized on the sensor surface. The Spreeta 2000 SPR biosensor elements manufactured by Texas Instruments provide three channels for each sensor element in the system. A temperature-controlled two-element system that monitors for six analytes is currently in use, and development of an eight element sensor system capable of monitoring up to 24 different analytes will be completed in the near future. Protein toxins can be directly detected and quantified in the low picomolar range. Elimination of false positives and increased sensitivity is provided by secondary antibodies with specificity for different target epitopes, and by sensor element redundancy. Inclusion of more than a single amplification step can push the sensitivity of toxic protein detection to femtomolar levels. The same types of direct detection and amplification protocols are used to monitor for viruses and whole bacteria or spores. Special protocols are required for the detection of small molecules. Either a competition type assay where the presence of analyte inhibits the binding of antibodies to surface-immobilized analyte, or a displacement assay, where antibodies bound to analyte on the sensor surface are displaced by free analyte, can be used. The small molecule detection assays vary in sensitivity from the low micromolar range to the high picomolar.

     

A portable surface plasmon resonance sensor system for real-time monitoring of small to large analytes

Many environmental applications exist for biosensors capable of providing real-time analyses. One pressing current need is monitoring for agents of chemical- and bio-terrorism. These applications require systems that can rapidly detect small organics including nerve agents, toxic proteins, viruses, spores and whole microbes. A second area of application is monitoring for environmental pollutants. Processing of grab samples through chemical laboratories requires significant time delays in the analyses, preventing the rapid mapping and cleanup of chemical spills. The current state of development of miniaturized, integrated surface plasmon resonance (SPR) sensor elements has allowed for the development of inexpensive, portable biosensor systems capable of the simultaneous analysis of multiple analytes. Most of the detection protocols make use of antibodies immobilized on the sensor surface. The Spreeta 2000 SPR biosensor elements manufactured by Texas Instruments provide three channels for each sensor element in the system. A temperature-controlled two-element system that monitors for six analytes is currently in use, and development of an eight element sensor system capable of monitoring up to 24 different analytes will be completed in the near future. Protein toxins can be directly detected and quantified in the low picomolar range. Elimination of false positives and increased sensitivity is provided by secondary antibodies with specificity for different target epitopes, and by sensor element redundancy. Inclusion of more than a single amplification step can push the sensitivity of toxic protein detection to femtomolar levels. The same types of direct detection and amplification protocols are used to monitor for viruses and whole bacteria or spores. Special protocols are required for the detection of small molecules. Either a competition type assay where the presence of analyte inhibits the binding of antibodies to surface-immobilized analyte, or a displacement assay, where antibodies bound to analyte on the sensor surface are displaced by free analyte, can be used. The small molecule detection assays vary in sensitivity from the low micromolar range to the high picomolar.     

Detection of embryonic stem cell lysate biomarkers by surface plasmon resonance with reduced nonspecific adsorption

Surface plasmon resonance imaging (SPRi) has emerged as a versatile biosensor to detect a wide range of biomolecular interactions with divergent potential applications. However, the use of this advanced-level technology for stem cell lysate study is still not much explored. Cell lysates are significant biological analytes used for disease diagnostics and proteomic studies, but their complex nature limits their use as an analyte for SPRi biosensors. Here, we review the problems associated with the use of SPRi for stem cell lysate study and examine the role of surface chemistry, running buffer, and blocking solution in order to minimize nonspecific adsorption (NSA). We detect the expression of Oct4, Sox2, Nanog, Rex1, and Lin28 biomarkers present in mouse embryonic stem cell (mESC) lysate against their corresponding antibodies immobilized on the sensor surface with reduced NSA. The current study shows that the conjunction of SPRi and microarray can be used as a label-free, high-throughput, and rapid technique for detection of biomarkers and their relative abundance in stem cell lysate study.