Chemistry: analytical and immunological testing – Involving an insoluble carrier for immobilizing immunochemicals
Reexamination Certificate
2000-06-13
2003-05-06
Chin, Christopher L. (Department: 1641)
Chemistry: analytical and immunological testing
Involving an insoluble carrier for immobilizing immunochemicals
C385S012000, C385S123000, C422S051000, C422S083000, C422S082050, C422S082080, C422S082110, C427S002110, C427S002120, C427S002130, C427S162000, C427S163100, C427S163200, C435S004000, C435S005000, C435S006120, C435S007400, C435S007320, C435S287100, C435S287200, C435S288700, C435S808000, C436S164000, C436S172000, C436S527000, C436S805000
Reexamination Certificate
active
06558958
ABSTRACT:
FIELD OF THE INVENTION
The current invention relates to a global class of optical sensors that use evanescent fields to excite fluorescence from species bound to a waveguide fiber surface during assay performed in the gas phase, liquid solution, or solid environment.
DESCRIPTION OF RELATED ART
The evanescent field associated with an electromagnetic field propagating in an optical waveguide typically penetrates from a few nanometers to several hundred nanometers into the medium surrounding the optical waveguide. This evanescent field can excite fluorescent materials, such as fluorophores, which will fluoresce when they are bound by molecules on or very close to the optical waveguide surface. This fluorescence can lead to an efficient and selective immunoassay or hybridization assay. For an archetypal immunoassay sensor, biological recognition (binding) of an antigen by antibodies attached to the waveguide surface with concomitant displacement of fluorescent-labeled antigen is measured as a change in fluorescence. An oligonucleotide (either RNA or DNA), to which is attached a suitable fluorophore, is recognized by a complementary oligonucleotide (either RNA or DNA).
For a hybridization assay sensor, biological recognition (binding) of an oligonucleotide is measured as a change in fluorescence. A suitable fluorophore is attached to the oligonucleotide by a complementary oligonucleotide (either RNA or DNA) that in turn is attached to the waveguide surface, with a concomitant enhancement of fluorescence.
The use of optical fibers in certain geometrical configurations for immunoassay sensors is also known. One such use of optical fibers is as waveguides that capture and conduct fluorescent radiation emitted by molecules near the optical fiber surface. However, waveguide-binding sensors of this sort that are known for use in assays of aqueous fluids have demonstrated inadequate sensitivity. Specifically, poor sensor performance is attributed at least in part to the small size of the sample being analyzed, which is typically a few monolayers deep, and to the small active surface area of the optical waveguide. These factors limit the number of fluorophores that may be excited. More serious sensor performance degradation is attributable to the effects of a weak evanescent wave that fails to excite enough fluorophores to produce detectable levels of fluorescence. In addition, the past geometries used provide inadequate coupling of the fluorescence into the waveguide for subsequent detection.
Increasing the strength of the evanescent wave penetrating into a fluid sample to be assayed increases the amount of fluorescence, thereby increasing sensor sensitivity. Each mode (low and high order) propagating in the fiber has a portion of its power in the evanescent wave. Higher order modes have a larger percentage of their power in the evanescent wave and thus make a larger contribution to power in the evanescent wave. However, these higher order modes are weakly guided and lossy and can easily leak at a discontinuity or a bending point along the waveguide. In addition, the light distribution among the many modes of a multimode fiber is a very sensitive function of the specific optical arrangement of the fiber and effects on it produced by its environment. Even small bending or other mechanical effects on the fiber change the modal intensity distribution. These effects make an evanescent field sensor based on multimode fibers noisy and less sensitive.
The use of some types of tapered optical fiber to increase the sensitivity of fiber-optic assay systems is known. For example, it is known to use optical fibers as sensors in conjunction with assays.
Evanescent sensors using acid-etched multimode fiber probes are known. Higher-order modes in these fibers have the advantage of a large number of reflections per unit length and, thus, a long interaction length with the external medium and weaker evanescent field interaction to minimize photobleaching in situations where this might be a problem. However, the use of multimode fibers has a number of disadvantages. In a multimode sensor arrangement, the lower-order modes are confined to the central core region, limiting their interaction with the surroundings. This means that the total fraction of power that interacts with the external medium depends on the distribution of modal excitations and the fraction of each mode outside the core. Also, sensors made of multimode fibers are not easily compatible with many in-line fiber components, such as fiber directional couplers, isolators, and fiber Bragg grating filters.
Tapered multimode fibers may be produced in a known way using concentrated hydrofluoric acid (HF) solution. The method involves a multi-step procedure and requires a high-precision, computer-controlled stage to lower the fiber into the acid bath over a number of time intervals. This is a time-consuming and potentially non-reproducible procedure. In the procedure, the plastic cladding of the fiber is mechanically removed. This introduces a step discontinuity between the cladded and uncladded section of the fiber. Consequently, a combination tapering procedure is required to minimize V-number mismatch and prevent excess loss of returned fluorescence radiation through the tapered fiber. Such a procedure is potentially dangerous because of the use of hazardous chemicals such as concentrated HF acid. The tapering operation must be performed under a fume hood in a clean-room environment by well trained technicians.
Use of a single-mode fiber for sensing can avoid negative aspects of multimode fibers while having advantages such as light launched into the fiber exciting only the fundamental mode, which interacts with the surrounding area in the tapering region.
Optical fibers can also be tapered by heating and drawing, whereby both the core and cladding outer diameters are decreased and ultimately merge. One such tapered optical fiber is used in microscopy applications. The tapered fiber tip is short, has an extremely small diameter (a few tens of nanometers), and has a metal coating applied over the end of the tip.
When an optical fiber is tapered by heating and drawing, both the core diameter and the cladding outer diameter are decreased. The fractional change in the core diameter is approximately equal to the fractional change in the cladding outer diameter. In other words, the cross section of the fiber changes in scale only. Significantly, the angle at which the core is tapered is substantially smaller than the taper angle &bgr;, which is defined as the angle at which the drawn fiber is tapered. In one known example, the tangent of the core is only 3/125, or 2.4%, times the tangent of the taper angle &bgr;. For this reason, even for relatively large values of &bgr; such as 30° or greater, the core will have an adiabatic taper, as discussed below. When a fiber is drawn to a diameter comparable to, or smaller than, a wavelength, the boundary between core and cladding glass disappears and the structure becomes one of a glass core/fluid cladding.
In an untapered fiber, the electric component of the dielectric mode is largely confined to the core and falls to a very small amplitude, typically less than 10
−10
times the peak amplitude, near the cladding outer surface. That is not necessarily the case in a tapered fiber. As a guided light wave propagates into the taper region, it encounters a progressively narrowing core. Eventually, the core becomes too small to substantially confine the guided mode. Instead, the light is guided by the interface between the cladding and the surrounding material, which may be air or a liquid. The core will generally be tapered at a small enough angle for the guide change to be adiabatic. By the term “adiabatic” it is meant that substantially all of the energy of the initial fundamental guided mode remains concentrated in a single mode, and is not coupled into other modes, particularly radiation modes, which lead to a loss of energy from the waveguide.
One potential disadvantage of fluorosensors is their use of f
Davis Christopher C.
Fielding Alexander J.
Pilevar Saeed
Portugal Frank
Chin Christopher L.
Millen White Zelano & Branigan P.C.
University of Maryland
LandOfFree
Optical fiber evanescent field excited fluorosensor and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical fiber evanescent field excited fluorosensor and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical fiber evanescent field excited fluorosensor and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3084382