Towards on-site pathogen detection using antibody-based sensors

In this paper, the recent progress within biosensors for plant pathogen detection will be reviewed. Bio-recognition layers on sensors can be designed in various ways, however the most popular approach is to immobilise antibodies for specific capture of analytes. Focus will be put on antibody surface-immobilisation strategies as well as the use of antibodies in the widely used sensors, quartz crystal microbalance, surface plasmon resonance and cantilevers. We will describe the available data on antibody-based plant pathogen detection and furthermore use examples from detection of the pathogens Salmonella, Listeria monocytogenes, Streptococcus mutans, Bacillus cereus, Bacillus anthracis, Campylobacter and Escherichia coli. We will touch upon optimal assay design and further discuss the strengths and limitations of current sensor technologies for detection of viruses, bacteria and fungi.     

Determining kinetics and affinities of protein interactions using a parallel real-time label-free biosensor, the Octet

ForteBio’s Octet optical biosensor harnesses biolayer interferometry to detect and quantify molecular interactions using disposable fiber-optic biosensors that address samples from an open shaking microplate without any microfluidics. We recruited a monoclonal antibody against a panel of peptides to compare the Octet directly with Biacore’s well-established 3000 platform and Bio-Rad’s recently launched ProteOn XPR36 array system, which use surface plasmon resonance (SPR) to detect the binding of one analyte over four surfaces and six analytes over six surfaces, respectively. A sink method was used to prevent analyte from rebinding the ligand-coated Octet tips and enabled us to extract accurate kinetic rate constants, as judged by their close agreement with those determined by SPR. Although the Octet is not sensitive enough to detect the binding of small molecules directly, it can access their affinities indirectly via solution competition experiments. We conducted similar experiments on the SPR instruments to validate these measurements. The Octet is emerging as a versatile complement to other more sophisticated biosensors, and the ProteOn provides high-quality data near the sensitivity of Biacore but in a more multiplexed format. Our results provide a benchmark for assessing the performance of the above-mentioned sensors.     

Surface plasmon resonance sensors in cell biology: basics and application

Optical sensors based on the excitation of surface plasmons, referred to as surface plasmon resonance (SPR) sensors, have become a central analytical tool for characterizing and quantifying a wide variety of macromolecular interactions, like receptor–ligand contacts. Besides this classical field of application, in the last 15 years, the development of SPR sensors aiming for the detection and analysis of ligand/cell or host/pathogen interactions, cell/cell contacts, and cellular reactions gained considerable momentum. The number of publications reporting about applications of SPR sensors implementing vital prokaryotic or eukaryotic cells as biorecognition elements for medical diagnostics, environmental monitoring, or biological safety is steadily growing. This review gives a short introduction to the technique of surface plasmon resonance and the parameters that are important for its application in the field of vital cell sensors. Furthermore, the publications concerning the application of such sensors in the analysis of cellular interactions and cellular reactions to extra- and intracellular stimuli are summarized.     

High-Sensitivity Refractive Index Sensor Based on D-Shaped Photonic Crystal Fiber with Rectangular Lattice and Nanoscale Gold Film

We propose and investigate a D-shaped photonic fiber refractive index sensor with rectangular lattice based on surface plasmon resonance. In such sensor, the nanoscale gold metal film is deposited on the flat surface where it is side polished. Numerical results show that the average sensitivity of Au-metalized surface plasmon resonance (SPR) sensor could reach as high as 8,129 nm/refractive index unit (RIU) in the dynamic index range from 1.35 to 1.41 as well as 2,000 nm/RIU from 1.33 to 1.35. Compared to conventional Au-metalized SPR sensors, the performance of our device is obviously better, and the production process is greatly simplified.     

Longitudinal Localized Surface Plasmons in Trimer Nanocylinder System

We report the near field localized surface plasmon characteristics of triangular system of silver nanocylinders and shell nanocylinders interacting with incident plane wave, studied using finite element method. The trimer nanocylinder system possesses far greater structural tunability than either a single nanorod or a nanoshell, along with much larger local field intensity enhancements and far greater sensitivity. The effect of geometrical as well as material parameters on the longitudinal localized plasmon resonance of the trimer nanosystem was investigated. The results provide insight in to the possible tunability of the localized plasmon modes which could find application in designing of chemical and biological sensors, electron emitters, etc.     

Surface Plasmon Resonance-Based Sensors Using Nano-Ribbons of Graphene and WSe2

Plasmonics - We show performance enhancement of surface plasmon resonance (SPR)-based sensors using the nano-ribbons of 2D materials such as graphene and WSe2. 2D material-based structures are...     

Analysis of carbohydrates using liquid chromatography--surface plasmon resonance immunosensing systems

An immunosensing system based on surface plasmon resonance (SPR) was used for on-line detection and characterization of carbohydrate molecules separated by high-performance liquid chromatography. These analytes, with or without serum, were continuously separated and analyzed in the combined liquid chromatography-surface plasmon resonance (LC-SPR) system. By using weak and readily reversible monoclonal antibodies, the SPR system allowed specific on-line monitoring of the substances. To increase the specificity of the immunosensor, nonrelevant antibodies were used as reference in a serial flow cell. The sensitivity of the LC-SPR system was dependent on molecular weight of the carbohydrate, affinity of binding, and design of the sensor.     

Substrate-Independent Lattice Plasmon Modes for High-Performance On-Chip Plasmonic Sensors

We systematically study the lattice plasmon resonance structures, which are known as core/shell SiO₂/Au nanocylinder arrays (NCAs), for high-performance, on-chip plasmonic sensors using the substrate-independent lattice plasmon modes (LPMs). Our finite-difference time-domain simulations reveal that new modes of localized surface plasmon resonances (LSPRs) show up when the height-diameter aspect ratio of the NCAs is increased. The height-induced LSPRs couple with the superstrate diffraction orders to generate the substrate-independent LPMs. Moreover, we show that the high wavelength sensitivity and the narrow linewidth of the substrate-independent LPMs lead to the plasmonic sensors with high figure of merit (FOM) and high signal-to-noise ratio (SNR). In addition, the plasmonic sensors are robust in asymmetric environments for a wide range of working wavelengths. Our further study of both far- and near-field electromagnetic distribution in the NCAs confirms the height-enabled tunability of the plasmonic “hot spots” at the sub-nanoparticle resolution and the large field enhancement in the substrate-independent LPMs, which are responsible for the high FOM and SNR of the plasmonic sensors.     

Review of Some Interesting Surface Plasmon Resonance-enhanced Properties of Noble Metal Nanoparticles and Their Applications to Biosystems

Noble metal, especially gold (Au) and silver (Ag) nanoparticles exhibit unique and tunable optical properties on account of their surface plasmon resonance (SPR). In this review, we discuss the SPR-enhanced optical properties of noble metal nanoparticles, with an emphasis on the recent advances in the utility of these plasmonic properties in molecular-specific imaging and sensing, photo-diagnostics, and selective photothermal therapy. The strongly enhanced SPR scattering from Au nanoparticles makes them useful as bright optical tags for molecular-specific biological imaging and detection using simple dark-field optical microscopy. On the other hand, the SPR absorption of the nanoparticles has allowed their use in the selective laser photothermal therapy of cancer. We also discuss the sensitivity of the nanoparticle SPR frequency to the local medium dielectric constant, which has been successfully exploited for the optical sensing of chemical and biological analytes. Plasmon coupling between metal nanoparticle pairs is also discussed, which forms the basis for nanoparticle assembly-based biodiagnostics and the plasmon ruler for dynamic measurement of nanoscale distances in biological systems.     

Plasmonic Perfect Absorbers for Biosensing Applications

We present a theoretical modal investigation of plasmonic perfect absorbers (PPAs) based on the localized surface plasmon resonance (LSPR) for biosensing applications. We design the PPA geometry with a layer of periodic metallic nanoparticles on one side of a dielectric substrate and a single metallic layer on the opposite side. The electromagnetic (EM) fields confine partly in the surrounding medium above the substrate and within the substrate itself. We examine the modes of the PPA geometry for a wavelength range of 600–1500 nm. The fundamental mode of the system provides perfect absorption for a wide angle of incidence 0–70°. The second-order mode shows a strong angular dependence with a sharp resonance and exhibits perfect optical absorption when the critical coupling condition for LSPR is achieved. The coupling condition depends on the size, periodicity, dielectric spacer, and the surrounding material of the system. The strong dependence on the surrounding material makes it a promising candidate for biosensing applications. We introduce a novel approach to investigate the angular dependence of the refractive index change for the PPA system. This novel technique contributes the significant attributes of the LSPR sensors, can be used for any required resonance wavelength depending on geometric design, and it also provides sensitivity analogous to the standard surface plasmon resonance (SPR) biosensors.     

Refractive Index Sensor Using Long-Range Surface Plasmon Resonance with Prism Coupler

Plasmonics - Long-range surface plasmon resonance (LRSPR)-based sensors exhibit high sensitivity as compared to the conventional SPR sensors due to low losses. A high refractive index prism and low...     

A Polarization-Independent SPR Fiber Sensor

The resonance of surface plasma waves in metallic layers is a strongly polarization-dependent phenomenon by the very nature of the physical effect responsible of that resonance. This implies the necessity of polarization-controlling elements to be added to any operative surface-plasmon-resonance-based sensor. A fully symmetrical, circular-section double deposition of a metallic and a dielectric layer on a uniform-waist tapered optical fiber (SymDL-UWT) permits us to completely eliminate the dependence on polarization of the plasmon excitation, with the corresponding operative advantages and basic theoretical consequences. We depict the fabrication process of these transducers, which is based on the use of a simple and efficient rotating element developed by us, and show the characteristics of the produced devices. No such device has been depicted up to date. As our experimental results show, this kind of devices can be considered a very good option for the development of simple, compact, and efficient chemical and biological sensors.     

Temperature Effects on the Resolution of Surface-Plasmon-Resonance-Based Sensor

Plasmonics - The fluctuation of the ambient temperature during the sensing action may seriously affect the performance characteristics of optical sensors based on surface plasmon resonance (SPR)....     

Performance Enhancement of Surface Plasmon Resonance Biosensors Based on Noble Metals-Graphene-WS2 at Visible and Near-Infrared Wavelengths

Plasmonics - In this paper, some biological sensors based on surface plasmon resonance are proposed at visible and near-infrared wavelengths and their performance is improved. The structure of...     

Non-thermal effects in the microwave induced unfolding of proteins observed by chaperone binding

We study the effect of microwaves at 2,450 MHz on protein unfolding using surface plasmon resonance sensing. Our experimental method makes use of the fact that unfolding proteins tend to bind to chaperones on their unfolding pathway and this attachment is readily monitored by surface plasmon resonance. We use the protein citrate synthase (CS) for this study as it shows strong binding to the chaperone alpha crystallin when stressed by exposure to excess temperature. The results of microwave heating are compared with the effect of ambient heating and a combination of ambient and microwave heating to the same final temperature. We study the temperature distributions during the heating process. We show that microwaves cause a significantly higher degree of unfolding than conventional thermal stress for protein solutions heated to the same maximum temperature.     

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.     

A genetically encoded, high-signal-to-noise maltose sensor

We describe the generation of a family of high-signal-to-noise single-wavelength genetically encoded indicators for maltose. This was achieved by insertion of circularly permuted fluorescent proteins into a bacterial periplasmic binding protein (PBP), Escherichia coli maltodextrin-binding protein, resulting in a four-color family of maltose indicators. The sensors were iteratively optimized to have sufficient brightness and maltose-dependent fluorescence increases for imaging, under both one- and two-photon illumination. We demonstrate that maltose affinity of the sensors can be tuned in a fashion largely independent of the fluorescent readout mechanism. Using literature mutations, the binding specificity could be altered to moderate sucrose preference, but with a significant loss of affinity. We use the soluble sensors in individual E. coli bacteria to observe rapid maltose transport across the plasma membrane, and membrane fusion versions of the sensors on mammalian cells to visualize the addition of maltose to extracellular media. The PBP superfamily includes scaffolds specific for a number of analytes whose visualization would be critical to the reverse engineering of complex systems such as neural networks, biosynthetic pathways, and signal transduction cascades. We expect the methodology outlined here to be useful in the development of indicators for many such analytes.     

Mechanistic Modeling for Performance Engineering of SPR-Based Fiber-Optic Sensor Employing Ta2O5 and Graphene Multilayers in Phase Interrogation Scheme

Plasmonics - This work elucidates the numerical simulations carried out for the performance analysis of surface plasmon resonance (SPR)–based fiber-optic sensors using thin layers of tantalum...     

Assays Based on Differential Adsorption of Single-stranded and Double-stranded DNA on Unfunctionalized Gold Nanoparticles in a Colloidal Suspension

Under certain conditions, single-stranded DNA adsorbs to negatively charged gold nanoparticles in a colloid whereas double-stranded DNA does not. We present evidence that this phenomenon can be explained by the difference in their electrostatic properties that in turn reflects conformational differences. The ability to discriminate the hybridization state of DNA on the basis of adsorption behavior can be utilized to design simple colorimetric and fluorimetric assays that take advantage of plasmon resonance in the gold nanoparticles. We present examples where we detect specific target sequences in oligonucleotides and in genomic DNA. Because conformational changes in special DNA sequences can also be induced by analytes such as potassium, we report a potassium ion detection scheme based on the same principle.     

Development and application of surface plasmon resonance-based biosensors for the detection of cell-ligand interactions

Surface plasmon resonance (SPR)-based biosensors were investigated with a view to providing a portable, inexpensive alternative to existing technologies for "real-time" biomolecular interaction analysis of whole cell-ligand interactions. A fiber optic SPR-based (FOSPR) biosensor, employing wavelength-dependent SPR, was constructed to enable continuous real-time data acquisition. In addition, a commercially available integrated angle-dependent SPR-based refractometer (ISPR) was modified to facilitate biosensing applications. Solid-phase detection of whole red blood cells (RBCs) using affinity-captured blood group specific antibodies was demonstrated using the BIACORE 1000, BIACORE Probe, FOSPR, and ISPR sensors. Nonspecific binding of RBCs to the hydrogel-based biointerface was negligible. However, the background noise level of the FOSPR-based biosensor was approximately 25-fold higher than that of the widely used BIACORE 1000 system while that of the ISPR-based biosensor was over 100-fold higher. Nevertheless, the FOSPR biosensor was suitable for the analysis of macromolecular analytes contained in crude matrices.