Development of antibody-based fiber-optic sensors for detection of a benzo[a]pyrene metabolite

Si Nanostrip Optical Waveguide for On-Chip Broadband Molecular Overtone Spectroscopy in Near-Infrared

The ability to probe the molecular fundamental or overtone (high harmonics) vibrations is fundamental to modern healthcare monitoring techniques and sensing technologies since it provides information about the molecular structure. However, since the absorption cross section of molecular vibration overtones is much smaller compared to the absorption cross section of fundamental vibrations, their detection is challenging. Here, a silicon nanostrip rib waveguide structure is proposed for label-free on-chip overtone spectroscopy in near-infrared (NIR). Utilizing the large refractive index contrast (Δ n > 2) between the silicon core of the waveguide and the silica substrate, a broadband NIR lightwave can be efficiently guided. We show that the sensitivity for chemical detection is increased by more than 3 orders of magnitude when compared to the evanescent-wave sensing predicted by the numerical model. This spectrometer distinguished several common organic liquids such as N-methylaniline and aniline precisely without any surface modification to the waveguide through the waveguide scanning over the absorption dips in the NIR transmission spectra. Planar NIR Si nanostrip waveguide is a compact sensor that can provide a platform for accurate chemical detection. Our NIR Si nanostrip rib waveguide device can enable the development of sensors for remote, on-site monitoring of chemicals.

Applications of fiber-optics-based nanosensors to drug discovery

BACKGROUND

Fiber-optic nanosensors are fabricated by heating and pulling optical fibers to yield sub-micron diameter tips and have been used for in vitro analysis of individual living mammalian cells. Immobilization of bioreceptors (e.g., antibodies, peptides, DNA) selective to targeting analyte molecules of interest provides molecular specificity. Excitation light can be launched into the fiber, and the resulting evanescent field at the tip of the nanofiber can be used to excite target molecules bound to the bioreceptor molecules. The fluorescence or surface-enhanced Raman scattering produced by the analyte molecules is detected using an ultra-sensitive photodetector.

OBJECTIVE

This article provides an overview of the development and application of fiber-optic nanosensors for drug discovery.

CONCLUSIONS

The nanosensors provide minimally invasive tools to probe subcellular compartments inside single living cells for health effect studies (e.g., detection of benzopyrene adducts) and medical applications (e.g., monitoring of apoptosis in cells treated with anticancer drugs).

Nanosensing at the single cell level

This article presents an overview of the development, operation, and applications of optical nanobiosensors for use in in vivo detection of biotargets in individual living cells. The nanobiosensors are equipped with immobilized bioreceptor probes (e.g., antibodies, enzyme substrate) selective to specific molecular targets. Laser excitation is transmitted into the fiber producing an evanescent field at the tip of the fiber in order to excite target molecules bound to the bioreceptors immobilized at the fiber tips. A photometric system detects the optical signal (e.g., fluorescence) originated from the analyte molecules or from the analyte-bioreceptor reaction. Examples of detection of biospecies and molecular signaling pathways of apoptosis in a living cell are discussed to illustrate the potential of the nanobiosensor technology for single cell analysis.

Intracellular measurements in mammary carcinoma cells using fiber-optic nanosensors

Submicrometer fiber-optic biosensors have been developed and used to measure toxic chemicals within single cells. Optical fibers that have been pulled to a distal-end diameter of less than 1 micrometer are coated with antibodies to selectively bind the species of interest. This paper describes the use of these fibers to selectively measure the concentration of benzo[a]pyrene tetrol (BPT), a metabolite of benzo[a]pyrene, within individual cells of two different cell lines, human mammary carcinoma cells and rat liver epithelial cells. The results from these measurements have been used to determine the sensitivity, reproducibility, and usefulness of these nanosensors. The detection limit of these biosensors has been determined to be 0.64 +/- 0.17 x 10(-11) M for BPT.

Development of a new capillary electrophoresis-based fibre optic sensor

A new fluorescence-based fibre optic sensor is described which combines the sensitivity offered by laser-induced fluorescence with the selectivity offered by capillary electrophoresis (CE). A single optical fibre directly probes the terminus of a 5-8 cm separation capillary. The linear geometry associated with this sensor necessitates a 'single reservoir' design, thus presenting major challenges to overcome in comparison to the conventional two-reservoir configuration common to a typical laboratory setup. Some of the challenges confronted by the design features presented in this work include the reduction of gravity-driven hydrostatic flow, the ejection of electrolytic gases evolved at the detection-side electrode and the establishment a suitable compromise between detectability and separation performance. The success of such design features demonstrates the feasibility of a CE-based sensor which offers several amenities particularly useful for in situ sensing. Such attributes include selectivity, diminutive size, flexibility, reusability, high sensitivity, speed, and remote control. Detailed descriptions of sensor fabrication are included, including two variations on a general design concept. In addition, the single-fibre optical detection system is described. Separation characteristics of the new CE-based sensor are presented, highlighted by an observed separation efficiency of up to 8000 theoretical plates (for a 5 cm capillary). The separation of a three-component mixture of the laser dyes, Rhodamine 6G, fluorescein isothyocyanate and sodium fluorescein, is demonstrated.

Antibody-antigen binding kinetics. A model for multivalency antibodies for large antigen systems

This work presents a theoretical analysis of the influence of multivalency of antigen on external mass transfer-limited binding kinetics to divalent antibody for biosensor applications to polycyclic-aromatic systems. Both cases are considered wherein the antigen is in solution and the antibody is either covalently or noncovalently attached to a cylindrical fiber-optic biosensor, and the antibody is in solution and the antigen is attached to the surface. Both single-step and dual-step binding processes are considered. The rate of attachment of antigen to antibody (or vice versa) is linear for the valencies (or reaction orders) analyzed in the time frame (100 min) considered. The rate of attainment of saturation levels of antigen or antibody in solution close to the surface is very rapid (within 20 min). An increase in the valency of the antigen in solution has the effect of decreasing the order of reaction (for valency, v > or = 1). An increase in the number of steps increases the order of reaction, as expected. An increase in the valency of the antigen in solution decreases the saturation level of the antigen close to the surface and the rate of antigen attachment to the antibody on the surface for all Damkohler numbers. A decrease in the diffusional limitations decreases the effect of valency (or reaction order) on saturation levels of Cs/C0. Nondimensional plots presented in the analysis help extend the analysis to different antigen-antibody systems. An increase in the valency of the antibody in solution has the effect of increasing the order of reaction (for v > 2). The effects in this case are reverse to those described earlier. For valency greater than 2, the reaction order is dependent on the antigen valency, whether it is in solution or immobilized on the surface. The general analysis presented here should be applicable to most surface reactions that involve ligand-receptor binding wherein multiple-binding sites are involved on either the receptor or the ligand.

Fibre-optic-based fluoroimmunosensors

Remote sensing of chemicals can be performed using fibre optic chemical sensors that use immunochemical reagent phases. Exploiting the specificity of antibody-antigen interactions and the sensitivity of laser-excited fluorimetry, highly selective measurements of ultra-trace levels of chemicals can be performed remotely and in situ via fluoroimmunoassay techniques. In this work, heterogeneous assay protocols using immunobeads are implemented. A passive sensor that samples analyte by diffusion through a permeable membrane and is capable of a single analysis is described and used for the measurement of a naturally fluorescent compound. Subsequently, a regenerable sensor that can perform assay procedures in a repetitive fashion is described and characterized. The versatility of this sensor for performing remote measurements using a variety of established fluoroimmunoassay methodologies is discussed.

ATSDR evaluation of health effects of chemicals. IV. Polycyclic aromatic hydrocarbons (PAHs): understanding a complex problem

Polycyclic Aromatic Hydrocarbons (PAHs) are a group of chemicals that are formed during the incomplete burning of coal, oil, gas, wood, garbage, or other organic substances, such as tobacco and charbroiled meat. There are more than 100 PAHs. PAHs generally occur as complex mixtures (for example, as part of products such as soot), not as single compounds. PAHs are found throughout the environment in the air, water, and soil. As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals, including PAHs (ATSDR, 1995), found at facilities on the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) and which pose the most significant potential threat to human health, as determined by ATSDR and the Environmental Protection Agency (EPA). These profiles include information on health effects of chemicals from different routes and durations of exposure, their potential for exposure, regulations and advisories, and the adequacy of the existing database. Assessing the health effects of PAHs is a major challenge because environmental exposures to these chemicals are usually to complex mixtures of PAHs with other chemicals. The biological consequences of human exposure to mixtures of PAHs depend on the toxicity, carcinogenic and noncarcinogenic, of the individual components of the mixture, the types of interactions among them, and confounding factors that are not thoroughly understood. Also identified are components of exposure and health effects research needed on PAHs that will allow estimation of realistic human health risks posed by exposures to PAHs. The exposure assessment component of research should focus on (1) development of reliable analytical methods for the determination of bioavailable PAHs following ingestion, (2) estimation of bioavailable PAHs from environmental media, particularly the determination of particle-bound PAHs, (3) data on ambient levels of PAHs metabolites in tissues/fluids of control populations, and (4) the need for a critical evaluation of current levels of PAHs found in environmental media including data from hazardous waste sites. The health effects component should focus on obtaining information on (1) the health effects of mixtures of PAHs particularly their noncarcinogenic effects in humans, and (2) their toxicokinetics. This report provides excerpts from the toxicological profile of PAHs (ATSDR, 1995) that contains more detailed information.

Construction and evaluation of a self-luminescent biosensor

The genes encoding bioluminescence (lux genes), derived from the marine bacterium V. fischeri, have been fused next to the genes encoding mercury detoxification (mer genes), derived from a clinical isolate of S. marcescens. The fusion has been made so that the expression of the light genes comes under the control of the mer regulatory gene and promoter. These genetic elements activate the expression of the light genes in the presence of mercury. The light can readily be collected and quantitated, resulting in a biosensor for the detection of mercury.