Biosensing based on surface plasmon resonance and living cells

Surface plasmon resonance for cell-based clinical diagnosis

Non-invasive real-time observations and the evaluation of living cell conditions and functions are increasingly demanded in life sciences. Surface plasmon resonance (SPR) sensors detect the refractive index (RI) changes on the surface of sensor chips in label-free and on a real-time basis. Using SPR sensors, we and other groups have developed techniques to evaluate living cells' reactions in response to stimuli without any labeling in a real-time manner. The SPR imaging (SPRI) system for living cells may visualize single cell reactions and has the potential to expand application of SPR cell sensing for clinical diagnosis, such as multi-array cell diagnostic systems and detection of malignant cells among normal cells in combination with rapid cell isolation techniques.

Real-time sensing of enteropathogenic E. coli-induced effects on epithelial host cell height, cell-substrate interactions, and endocytic processes by infrared surface plasmon spectroscopy

Enteropathogenic Escherichia coli (EPEC) is an important, generally non-invasive, bacterial pathogen that causes diarrhea in humans. The microbe infects mainly the enterocytes of the small intestine. Here we have applied our newly developed infrared surface plasmon resonance (IR-SPR) spectroscopy approach to study how EPEC infection affects epithelial host cells. The IR-SPR experiments showed that EPEC infection results in a robust reduction in the refractive index of the infected cells. Assisted by confocal and total internal reflection microscopy, we discovered that the microbe dilates the intercellular gaps and induces the appearance of fluid-phase-filled pinocytic vesicles in the lower basolateral regions of the host epithelial cells. Partial cell detachment from the underlying substratum was also observed. Finally, the waveguide mode observed by our IR-SPR analyses showed that EPEC infection decreases the host cell's height to some extent. Together, these observations reveal novel impacts of the pathogen on the host cell architecture and endocytic functions. We suggest that these changes may induce the infiltration of a watery environment into the host cell, and potentially lead to failure of the epithelium barrier functions. Our findings also indicate the great potential of the label-free IR-SPR approach to study the dynamics of host-pathogen interactions with high spatiotemporal sensitivity.

Elucidating the signal responses of multi-parametric surface plasmon resonance living cell sensing: a comparison between optical modeling and drug-MDCKII cell interaction measurements

In vitro cell-based assays are widely used during the drug discovery and development process to test the biological activity of new drugs. Most of the commonly used cell-based assays, however, lack the ability to measure in real-time or under dynamic conditions (e.g. constant flow). In this study a multi-parameter surface plasmon resonance approach in combination with living cell sensing has been utilized for monitoring drug-cell interactions in real-time, under constant flow and without labels. The multi-parameter surface plasmon resonance approach, i.e. surface plasmon resonance angle versus intensity plots, provided fully specific signal patterns for various cell behaviors when stimulating cells with drugs that use para- and transcellular absorption routes. Simulated full surface plasmon resonance angular spectra of cell monolayers were compared with actual surface plasmon resonance measurements performed with MDCKII cell monolayers in order to better understand the origin of the surface plasmon resonance signal responses during drug stimulation of cells. The comparison of the simulated and measured surface plasmon resonance responses allowed to better understand and provide plausible explanations for the type of cellular changes, e.g. morphological or mass redistribution in cells, that were induced in the MDCKII cell monolayers during drug stimulation, and consequently to differentiate between the type and modes of drug actions. The multi-parameter surface plasmon resonance approach presented in this study lays the foundation for developing new types of cell-based tools for life science research, which should contribute to an improved mechanistic understanding of the type and contribution of different drug transport routes on drug absorption.

Application of SPR imaging sensor for detection of individual living cell reactions and clinical diagnosis of type I allergy

A technique to visualize living cell activation in a real time manner without any labeling is required in the fields of life sciences and medicine. We have reported that surface plasmon resonance (SPR) sensors detect large changes of refractive index (RI) with living cells, such as mast cells, human basophils and lymphocytes. However conventional SPR sensors detect only an average change of RI with thousands of cells at detectable area on a sensor chip. Therefore, we developed an SPR imaging (SPRI) sensor with a CMOS camera and an objective lens in order to visualize RI of individual living cells and their changes upon stimuli. The SPRI sensor we developed could detect reactions of individual rat basophilic leukemia (RBL-2H3) cells and mouse keratinocyte cells in response to specific or nonspecific stimuli. Moreover, the sensor could detect the reactions of individual human basophils isolated from patients in response to antigens (allergens). Thus the technique can visualize the effect of various stimuli, inhibitors and/or conditions on cell reactions as change of intracellular RI distribution at single cell levels. Establishment of the technique to rapidly isolate cells from patient blood should enable us to utilize SPRI system as a high throughput screening system in clinical diagnosis, such as type I hypersensitivity and drug hypersensitivity, and as a tool to reveal novel phenomena in evanescent fields around plasma membranes.

Development of a novel two dimensional surface plasmon resonance sensor using multiplied beam splitting optics

A novel two dimensional surface plasmon resonance (SPR) sensor system with a multi-point sensing region is described. The use of multiplied beam splitting optics, as a core technology, permitted multi-point sensing to be achieved. This system was capable of simultaneously measuring nine sensing points. Calibration curves for sucrose obtained on nine sensing points were linear in the range of 0–10% with a correlation factor of 0.996–0.998 with a relative standard deviation of 0.090–4.0%. The detection limits defined as S/N = 3 were 1.98 × 10⁻⁶–3.91 × 10⁻⁵ RIU. This sensitivity is comparable to that of conventional SPR sensors.

Angle-multiplexed waveguide resonance of high sensitivity and its application to nanosecond dynamics of molecular assemblies

We report here the experimental demonstration of a high-performance optical waveguide resonance (WR) platform based on a judicious design of a dielectric/metal stack and a fabrication process that delivers an extraordinarily low-loss optical waveguide over a noble-metal thin film. By using an atomic layer deposition process to grow a dielectric film (Al(2)O(3)) of exceptional optical quality and precise thickness over a metal layer (Ag), we have reached a deep and narrow WR that allowed us to experimentally measure a performance of the WR device that is 20 times superior to the conventional surface plasmon resonance sensor. To the best of our knowledge, these results represent the best performance of a WR device reported so far in the literature. In addition, we have created an experimental setup based on diffraction-limited optical components to launch and collect a broad angular spectrum that is able to resolve the sharp angular waveguide resonance at a fast pace. Such configuration has enabled us to reach nanosecond time scale resolution, and we provide here experimental evidence of the fast coupling of the optical signal from a submonolayer of a ruthenium complex adsorbed to the interrogation surface. The high sensitivity and nanosecond detection capability of the WR optical platform demonstrated here are expected to find useful applications for researchers interested in studies of surface-mediated molecular interactions and interfacial phenomena.

DNA-directed capture of primary cells from a complex mixture and controlled orthogonal release monitored by SPR imaging

Many biological samples are composed of several cell types. Qualitative and quantitative analysis of these complex mixtures is of major interest for both diagnostic and biomedical applications. Because large amounts of biological material are often challenging to collect, tremendous efforts have been made for a decade to design miniaturized platforms-such as lab-on-a-chip or microarrays-to run sensitive and reliable analysis from tiny quantities of starting material. Although barely explored so far, the release of resolved cellular samples constitutes an exciting strategy for further cell analysis. Herein, we propose a DNA-based biochip suitable for cell-type analysis in a label-free manner. The DNA-array is firstly converted into antibody-array using antibody-DNA conjugates. These protein-DNA hybrid molecules are chemically synthesized by covalent coupling of short oligonucleotides to antibodies directed against cell-type specific markers. We show not only specific capture of primary spleen cells on protein-DNA microarray spots but also their fast and specific orthogonal release according to the antibody-DNA combinations by incorporating restriction sites in DNA. Both molecular and cellular interactions occurring on the biochip are monitored by surface plasmon resonance (SPR) imaging. This optical technique turns out to be a powerful way to monitor, in real-time, biological interactions occurring on the microarrayed features.

Antigen-specific T cell phenotyping microarrays using grating coupled surface plasmon resonance imaging and surface plasmon coupled emission

The circulating population of peripheral T lymphocytes obtained from a blood sample can provide a large amount of information about an individual's medical status and history. Recent evidence indicates that the detection and functional characterization of antigen-specific T cell subsets within the circulating population may provide a diagnostic indicator of disease and has the potential to predict an individual's response to therapy. In this report, a microarray detection platform that combines grating-coupled surface plasmon resonance imaging (GCSPRI) and grating-coupled surface plasmon coupled emission (SPCE) fluorescence detection modalities were used to detect and characterize CD4(+) T cells. The microspot regions of interest (ROIs) printed on the array consisted of immobilized antibodies or peptide loaded MHC monomers (p/MHC) as T cell capture ligands mixed with additional antibodies as cytokine capture ligands covalently bound to the surface of a corrugated gold sensor chip. Using optimized parameters, an unlabeled influenza peptide reactive T cell clone could be detected at a frequency of 0.1% in a mixed T cell sample using GCSPRI. Additionally, after cell binding was quantified, differential TH1 cytokine secretion patterns from a T cell clone cultured under TH1 or TH2 inducing conditions was detected using an SPCE fluorescence based assay. Differences in the secretion patterns of 3 cytokines, characteristic of the inducing conditions, indicated that differences were a consequence of the functional status of the captured cells. A dual mode GCSPRI/SPCE assay can provide a rapid, high content T cell screening/characterization tool that is useful for diagnosing disease, evaluating vaccination efficacy, or assessing responses to immunotherapeutics.

Real-time monitoring of epithelial cell-cell and cell-substrate interactions by infrared surface plasmon spectroscopy

The development of novel technologies capable of monitoring the dynamics of cell-cell and cell-substrate interactions in real time and a label-free manner is vital for gaining deeper insights into these most fundamental cellular processes. However, the label-free technologies available today provide only limited information on these processes. Here, we report a new (to our knowledge) infrared surface plasmon resonance (SPR)-based methodology that can resolve distinct phases of cell-cell and cell-substrate adhesion of polarized Madin Darby canine kidney epithelial cells. Due to the extended penetration depth of the infrared SP wave, the dynamics of cell adhesion can be detected with high accuracy and high temporal resolution. Analysis of the temporal variation of the SPR reflectivity spectrum revealed the existence of multiple phases in epithelial cell adhesion: initial contact of the cells with the substrate (cell deposition), cell spreading, formation of intercellular contacts, and subsequent generation of cell clusters. The final formation of a continuous cell monolayer could also be sensed. The SPR measurements were validated by optical microscopy imaging. However, in contrast to the SPR method, the optical analyses were laborious and less quantitative, and hence provided only limited information on the dynamics and phases of cell adhesion.

Studying cell-surface interactions in vitro: a survey of experimental approaches and techniques

A better understanding of the interactions of animal (or human) cells with in vitro surfaces is the key to the successful development, improvement and optimization of biomaterials for biomedical or biotechnological purposes. State-of-the-art experimental approaches and techniques are a prerequisite for further and deeper insights into the mechanisms and processes involved in cell-surface adhesion. This chapter provides a brief but not complete survey of optical, mechanical, electrochemical and acoustic devices that are currently used to study the structural and functional properties of the cell-surface junction. Each technique is introduced with respect to the underlying principles before example data are discussed. At the end of the chapter all techniques are compared in terms of their strengths, limitations and technical requirements.

Integrated active mixing and biosensing using surface acoustic waves (SAW) and surface plasmon resonance (SPR) on a common substrate

This article presents a device incorporating surface plasmon resonance (SPR) sensing and surface acoustic wave (SAW) actuation integrated onto a common LiNbO(3) piezoelectric substrate. The device uses Rayleigh-type SAW to provide active microfluidic mixing in the fluid above the SPR sensor. Validation experiments show that SAW-induced microfluidic mixing results in accelerated binding kinetics of an avidin-biotin assay. Results also show that, though SAW action causes a parasitic SPR response due to heat injection into the fluid, a relatively brief relaxation time following the SAW pulses allows the effect to dissipate, without affecting the overall assay response. Since both SPR sensors and SAW transducers can be fabricated simultaneously using low-cost microfabrication methods on a single substrate, the proposed design is well-suited to lab-on-chip applications.

Real-time monitoring of transferrin-induced endocytic vesicle formation by mid-infrared surface plasmon resonance

We report on the application of surface plasmon resonance (SPR), based on Fourier transform infrared spectroscopy in the mid-infrared wavelength range, for real-time and label-free sensing of transferrin-induced endocytic processes in human melanoma cells. The evanescent field of the mid-infrared surface plasmon penetrates deep into the cell, allowing highly sensitive SPR measurements of dynamic processes occurring at significant cellular depths. We monitored in real-time, infrared reflectivity spectra in the SPR regime from living cells exposed to human transferrin (Tfn). We show that although fluorescence microscopy measures primarily Tfn accumulation in recycling endosomes located deep in the cell's cytoplasm, the SPR technique measures mainly Tfn-mediated formation of early endocytic organelles located in close proximity to the plasma membrane. Our SPR and fluorescence data are very well described by a kinetic model of Tfn endocytosis, suggested previously in similar cell systems. Hence, our SPR data provide further support to the rather controversial ability of Tfn to stimulate its own endocytosis. Our analysis also yields what we believe is novel information on the role of membrane cholesterol in modulating the kinetics of endocytic vesicle biogenesis and consumption.