Abstract:
An infectious disease or disorder in a fluid, such as a mammalian blood sample, is detected by taking a transmission spectrum of a test sample in at least a portion of the ultraviolet-visible-near-infrared and comparing the spectrum with a standard sample spectrum. From the comparison it is then determined whether the fluid from the test sample contains an infectious disease or disorder, and an identity of the infectious disease or disorder is determined. Spectroscopic and multiwavelength turbidimetry techniques provide a rapid, inexpensive, and convenient means for diagnosis. The comparison and determination steps may be performed visually or by spectral deconvolution.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority from commonly owned provisional application Serial No. 60/217,742, filed Jul. 12, 2000, “Method for the Identification and Diagnosis of Infectious Diseases,” the disclosure of which is incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a spectroscopic system and methods for the identification and characterization of particles in a fluid, and, more particularly, to such systems and methods for the identification and characterization of particles in a bodily fluid.  
           [0004]    2. Description of Related Art  
           [0005]    A critical limitation in the area of disease identification, diagnosis, and prevention has been the lack of simple, rapid, and effective screening techniques. This problem is particularly acute in locations and/or situations where rapid analysis and diagnosis may involve decisions concerning life-threatening circumstances such as natural disasters or combat, and where the need for portable laboratories is accentuated by the remoteness of areas where diseases are endemic and where epidemics are generated. In addition, in the medical field there is a considerable need for the identification of markers that permit the diagnosis and treatment of diseases early in their development stage and thus avoid lengthy periods of incubation, which invariably worsen the condition of the patient.  
           [0006]    Typically, microorganisms and viruses of concern have sizes ranging between 0.5 and 20 μm and, in many cases, are present in fairly dilute concentrations. Although the analytical instrumentation used in medical and clinical laboratories has improved considerably over the past decade to the present, there are still no suitable techniques capable of detecting, classifying, and counting microorganisms in bodily fluids.  
           [0007]    Technology known in the art requires that the presence of target microorganisms be detected using microscopy and/or immunoassay techniques. These require a significant amount of time, trained technicians, and well-equipped laboratory facilities. The costs associated with current laboratory techniques for disease identification and diagnosis therefore further accentuate the need for the development of rapid screening methods.  
           [0008]    Another limitation of the currently employed technology is a lack of on-line capability and continuous measurement capabilities for the characterization of blood and other fluid components, as well as a lack of portable instrumentation capable of detecting, counting, and classifying specific blood and other fluid components. The problem of portable instrumentation and suitable methods of analysis and diagnosis is particularly relevant to the medical industry, where the need for rapid analysis and diagnosis often involves life-threatening situations. Although the analytical instrumentation used in medical and clinical laboratories has improved considerably over the past decade, there are still no suitable techniques capable of detecting, classifying, and counting on-line critical cell populations and/or pathogens in blood and other bodily fluids.  
           [0009]    Blood cell component counting technology known in the art uses, for example, red cell counts, platelet counts, and white cell counts as indicators of the state of disease. White blood cells can be difficult to count if they are present in small numbers. At present automated hematology analyzers that employ light scattering or impedance techniques are used, but these can introduce a high error rate when determining counts for low sample numbers. In cases of leukoreduced blood products with lower numbers of white blood cells, staining and microscopy or flow cytometry are typically used.  
           [0010]    As is known from spectroscopy theory, a measure of the absorption of the attenuation of light through a solution or a suspension is the extinction coefficient, which also provides a measure of the turbidity and transmission properties of a sample. Spectra in the visible region of the electromagnetic spectrum reflect the presence of metal ions and large conjugated aromatic structures and double-bond systems. In the near-ultraviolet (uv) region small conjugated ring systems affect absorption properties. However, suspensions of very large particles are powerful scatterers of radiation, and in the case of cells and microorganisms, the light scattering effect can be sufficiently strong to overwhelm absorption effects. It is therefore known to use uv/vis spectroscopy to monitor purity, concentration, and reaction rates of such large particles and their suspending media.  
           [0011]    Many attempts have been made to estimate the particle size distribution (PSD) and the chemical composition of suspended particles using optical spectral extinction (transmission) measurements. However, previously used techniques neglectthe effects of the chemical composition and require that either the form of the PSD be known a priori or that the shape of the PSD be assumed. One of the present inventors has applied standard regularization techniques to the solution of the transmission equation and has demonstrated correct PSDs of a large variety of polymer lattices, protein aggregates, silicon dioxide and alumina particles, and microorganisms.  
           [0012]    It has also been known to use the complementary information available from simultaneous absorption and light scattering measurements at multiple angles for the characterization of the composition and molecular weight and shape of macromolecules and suspended particles (Garcia-Rubio, 1993; and U.S. Pat. No. 5,808,738, the disclosure of which is incorporated herein by reference).  
           [0013]    Interferometric techniques are known in the art for cell classification (Cabib et al., U.S. Pat. Nos. 5,991,028 and 5,784,162) which use fluorescence microscopy with stained cells. Fluorescence and reflection spectroscopy can also be used to characterize a material by sensing a single wavelength (Lemelson, U.S. Pat. Nos. 5,995,866; 5,735,276; and 5,948,272), which can detect organisms in a bodily fluid. Electroluminescence may also be used to detect an analyte in a sample (Massey et al., U.S. Pat. No. 5,935,779). Cell counting may be accomplished by vibrational spectroscopy (Zakim et al., U.S. Pat. No. 5,733,739). Infrared techniques can detect cellular abnormalities (Cohenford et al., U.S. Pat. Nos. 6,146,897 and 5,976,885; Sodickson et al., U.S. Pat. No. 6,028,311).  
           [0014]    One of the present inventors previously developed ultraviolet-visible spectroscopic techniques for detecting and classifying microorganisms in water (Garcia-Rubio, U.S. Pat. No. 5,616,457), for characterizing blood and blood types (Garcia-Rubio, U.S. Pat. No. 5,589,932), and, as mentioned above, for characterizing particles with a multiangle-multiwavelength system (Garcia-Rubio et al., U.S. Pat. No. 5,808,738). The disclosures of these patents are incorporated herein by reference.  
         SUMMARY OF THE INVENTION  
         [0015]    It is therefore an object of the present invention to provide a system and method for identifying and diagnosing an infectious disease.  
           [0016]    It is a further object to provide such a system and method for identifying and diagnosing such an infectious disease in the bloodstream.  
           [0017]    It is another object to provide such a system and method for identifying and diagnosing such an infectious disease in another bodily fluid.  
           [0018]    It is an additional object to provide such a system and method for identifying and diagnosing a blood disease.  
           [0019]    It is yet a further object to provide such a system and method for identifying and diagnosing a disease that affects the size, shape, and/or chemical composition of a particulate or other component in a bodily fluid.  
           [0020]    It is yet another object to provide such a system and method that are operable in a remote location.  
           [0021]    These and other objects are achieved by the present invention, a method for detecting a presence of and identifying an infectious disease or disorder in a mammalian blood sample. Herein the word disorder is intended in its broadest sense, that is, as any abnormality detectable over a known range of characteristics of the measured particulates or suspending medium.  
           [0022]    The method comprises the steps of taking a multiwavelength spectroscopy measurement, typically a transmission spectrum of a test blood sample in at least a portion of the ultraviolet-visible-near-infrared range of the electromagnetic spectrum and comparing the spectrum with a standard blood sample spectrum known to be free from the infectious disease or disorder. From the comparison it is then determined whether the blood from the test sample contains the infectious disease or disorder, and an identity of the infectious disease or disorder is determined.  
           [0023]    Spectroscopic and multiwavelength turbidimetry techniques provide a rapid, inexpensive, and convenient means for diagnosis. As a first embodiment, the comparison and determination steps may be performed visually, since the signatures of certain diseases and disorders are so strong; in another embodiment it has been found that the spectral deconvolution of the turbidimetric spectra can provide additional and more detailed qualitative and quantitative information. Both embodiments of the invention can rapidly and inexpensively achieve disease diagnosis in remote locations and at a natural disaster, epidemic, or combat site.  
           [0024]    In a particular subembodiment, a change in a blood particle or other component caused by an infectious agent or disorder is detected spectroscopically. Such a change may comprise, for example, a shape change, such as occurs with sickle cell anemia, or a lysis, for example, of a red blood cell, which releases free hemoglobin and bilirubin into the blood plasma.  
           [0025]    In another subembodiment the test sample may comprise another bodily fluid for detecting a presence of an infectious disease or disorder.  
           [0026]    The method is based on multiwavelength spectroscopy measurements and the interpretation of the absorption and scattering properties of single particles from a plurality of populations and their suspending media. The spectroscopy measurements may comprise transmission, reflectance, and multiangle multiwavelength, using either polarized or unpolarized light, in the uv-vis-near-infrared portions of the electromagnetic spectrum. Unlike microscopy measurements, the samples typically comprise cells in the range of 10 6  particles. The analytical method yields such information as, but not intended to be limited to, particle counts, compositional analysis, size, and shape of the particulates and the suspending media.  
           [0027]    The invention is believed to provide a multiplicity of improvements over the prior art in achieving a rapid, inexpensive, and convenient means for characterization and detection of particulates in a bodily fluid, including characterization of such particulates as, but not intended to be limited to, cell shapes, blood antigens, microorganisms, and viruses. The rapidity and portability of the system of the invention permits its use in critical conditions such as epidemics and combat and also in remote and/or technology-disadvantaged locations.  
           [0028]    The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]    [0029]FIG. 1 is a flow chart of the method of the present invention.  
         [0030]    [0030]FIG. 2 is an exemplary optical density spectrum for normal and sickle cell red blood cells.  
         [0031]    [0031]FIG. 3 is an exemplary optical density spectrum for normal and dengue fever patients.  
         [0032]    [0032]FIG. 4 is an exemplary optical density spectrum for normal and malarial patients.  
         [0033]    [0033]FIG. 5 is an exemplary optical density spectrum for normal and treated malarial patients.  
         [0034]    [0034]FIG. 6 is an exemplary optical density spectrum for normal, aged, sickle cell, and malarial patients. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    A description of the preferred embodiments of the present invention will now be presented with reference to FIGS.  1 - 6 .  
         [0036]    The system of the present invention comprises any of known standard spectrometers, such as a portable fiber optics-based spectrophotometer for laboratory testing, in situ measurements, and field applications. The spectrophotometer should be capable of recording the transmission, reflectance, or angular backscaftering spectra of blood and other bodily fluids, neat, in solution, and in situ, in any combination or portion of the ultraviolet, visible, and near-infrared portions of the electromagnetic spectrum, preferably with a resolution of at least 2 nm. Recent developments in miniature spectrometer technology permit the use of portable multiprobe integrated systems for rapid blood characterization and diagnosis within the scope of the present invention.  
         [0037]    An exemplary method of analyzing a fluid sample for the presence of particulates, their characteristics, and that of the suspending medium is shown in the flow chart of FIG. 1. A sample, such as a blood sample, is taken (block  100 ) and diluted (when appropriate) (block  101 ) to a concentration level for spectrophotometer linearity, typically 4000 cells per microliter for whole blood. This number is not intended as a limitation, and it will be understood by one of skill in the art that such values are likely to change with the introduction and alteration of technology in the field. An exemplary figure for use at present comprises 1.5 Au.  
         [0038]    A exemplary blood dilution protocol is followed for the detection of, for example, a tropical disease, which comprises drawing a whole blood sample into an anticoagulant and diluting substantially 1:1000 with physiological saline. One dilution tube for each whole blood sample that is to be analyzed is prepared by pipetting 3 mL of saline into the tube and adding 3 μL blood, after wiping the outside of the pipette tip to remove excess whole blood. The sample is mixed by inverting the cuvette gently three times. If dilution tubes are not available, the whole blood can be diluted directly into a cuvette by adding 2 μL whole blood into 2 mL saline in the cuvette. Alternatively, the sample can be placed in a thin measurement cell such that the complete transmission spectrum can be recorded in accordance with known spectroscopy practices.  
         [0039]    If the diluted sample is above 1.5 absorbance units in the spectral region measured from 240 to 800 nm, an additional 0.5 mL saline should be added directly to the cuvette and mixed by inverting gently three times. If the spectrum is still too strong, repeat the saline addition until the spectrum is below 1.5 absorbance units. Alternatively, if the spectrum is too concentrated (above 1.5 absorbance units), a new whole blood dilution can be prepared by using less whole blood (e.g., 2 μL whole blood into 3 mL saline).  
         [0040]    If the diluted blood sample is below 0.2 absorbance units in the spectral region measured from 240 to 800 nm, prepare a new whole blood dilution using more whole blood (e.g., 4 μL whole blood in 3 mL saline). Similar effects can be accomplished by adjusting the path length of the measurement cell in accordance with standard spectroscopy practices.  
         [0041]    In a particular embodiment, the cuvette should be rinsed five times with deionized water before measuring the spectrum of another diluted blood sample.  
         [0042]    After all the samples have been analyzed each day, the cuvette should be cleaned by filling it with a dilute soap solution and sonicating for 10 min. After sonication, rinse the cuvette ten times with deionized water to remove residual soap. The cuvette should be stored with deionized water in it.  
         [0043]    A transmission spectrum of the sample properly diluted relative to the path length used sample is taken (block  102 ) with the spectrophotometer, and the data collected are sent to a processor (block  103 ), wherein standard data from normal controls are resident and may be accessed (block  104 ). The test and standard data are then normalized (block  105 ) so that they may be more easily compared. In some cases normalization may not a necessity. The differences are significant enough without normalization.  
         [0044]    If the characteristic being examined for has a sufficiently strong signature within the spectrum (block  106 ), the spectra may be co-plotted (block  107 ) and a visual determination made (block  108 ) for the presence of the characteristic. The disease-specific spectral features arise from changes in the size, shape, and chemical composition of the major blood components (blood cells and plasma) caused by the pathogen.  
         [0045]    If the characteristic does not have strong signal, or if particular features are desired to be calculated, such as particle size distribution, size, shape, or chemical composition (block  106 ), spectral deconvolution is performed (block  109 ), an analysis of the deconvoluted data performed (block  110 ), and the characteristic of the particulate(s) determined (block  111 ). This information is used to define elements of classification for the quantification of chemical species, cell enumeration, and the identification of viruses, bacteria, or protozoa of interest, for example, although these are not intended as limitations.  
         [0046]    The deconvolution may be accomplished by, for example, calibration based on correlation or with the use of theoretical models based on theories of absorption and scattering of electromagnetic radiation. References authored by some of the present inventors contain disclosure on the analysis of multiwavelength spectroscopic data, and these references are incorporate herein by reference (Brandolin et al., 1991; Chang et al., 1993; Elicabe et al., 1988, 1990; Garcia-Rubio et al., 1984, 1985, 1987, 1989, 1992, 1993, 1994, 1999; Marquez et al., 1993; Mattley et al., 2000).  
         [0047]    As examples, samples may be analyzed for the concentration of several types of hemoglobin, the level of oxygenation, bilirubin, and total hematocrit. It is also possible to identify and classify blood types using their spectral signature and to detect free hemoglobin and other particles present in blood such as abnormal sickling hemoglobin and Plasmodium sp. It will also be possible, it is believed, to detect markers of other diseases such as HIV and HBV.  
         [0048]    The uv-vis transmission spectra of a large variety of blood samples of different types have been spectroscopically investigated. These spectra have shown that the uv-vis portion of the spectrum contains sufficient information for the statistical identification and classification of blood types and the subsequent identification of blood diseases and the presence of foreign microorganisms. In addition, the spectra establish the reproducibility of the method, permit identification of spectral features associated with healthy blood, and establish appropriate controls for comparison purposes.  
         [0049]    Sample spectra of several blood diseases are shown in FIGS.  2 - 6 , with contrasting spectra for normal controls. Tables 1 and 2 provide accompanying diagnosis data provided by the Laboratorio Regional de Apoyo Epidemiologica, Valencia, Venezuela, where the malaria and dengue fever data were obtained.  
                                         TABLE 1                           Malaria Patient Information            Malaria       Symptoms                   Patient   Species   Noted   Diagnosed   Treated   Spectroscopy               1   F   day 1   day 10   7 days   day 17       2   F   day 1   no data   no data   day 17       3   V   day 1   day 4   4 days   day 17       4   Suspected   no data   no data   no data   day 17                  
 
         [0050]    [0050]                                         TABLE 2                           Dengue Fever Patient Information            Dengue           Clinic   Laboratory           Fever   Type   Symptoms   Diagnosis   Diagnosis   Spectroscopy               1   H   day 1   day 5   no data   day 21       2   C   day 1   day 2   day 4   day 7       3   C   day 1   day 3   day 6   day 19       4   C   day 1   day 3   no data   day 30                    
         [0051]    In FIG. 2 are uv-vis spectra of two replicate measurements of normal (N) whole blood together with measurements of whole blood containing sickle cells (SC) from two different patients. Dramatic differences may be noted in the spectral region between 220 and 600 nm, where the main chromophoric groups in blood, including nucleic acids, proteins, and liganded metals, are known to absorb. The spectral differences between 600 and 900 nm are also significant in that they reflect changes in the scattering characteristics (size and shape) of the cells. Thus this region of the electromagnetic spectrum is particularly suitable for the detection and identification of particulate(s) with a high degree of specificity.  
         [0052]    In FIG. 3 spectra of normal (N) whole blood and whole blood from dengue fever patients are shown. The dengue fever patients include hemorrhagic (H), classical acute phase (CAP), and classical (C). Again dramatic differences are shown across the uv-vis spectrum, and there are clear similarities in the absorption and scattering characteristics of the spectra from dengue fever patients&#39; blood. One may also distinguish a patient in the acute phase of the disease.  
         [0053]    In FIG. 4 are shown spectra of normal (N) whole blood, aged normal (NA) whole blood, and blood from malarial patients. Dramatic differences in the spectral region between 250 and 600 nm are shown; as above, the changes in the 600-900 nm range are significant in that they reflect changes in the scattering characteristics of the cells. In malarial patients this is to be expected, since it is known that malarial parasites host in red blood cells. There are also clear spectral differences between the two types of malarial parasites, Vivax (V) and Falciparum (F). It is also notable that the age of the blood sample has a clearly discernible effect on the spectra.  
         [0054]    From FIGS.  2 - 4  it may be seen that the system and method of the present invention are capable of identifying and classifying blood-borne diseases. A penetration level, that is, a level of infection, may also be deduced from the magnitude of the signature, which can be seen in FIG. 2, as an example.  
         [0055]    The effect of treatment on the spectrum of whole blood for malarial patients is shown in FIG. 5. The spectra include normal (N), Falciparum treated 7 days (F7), Vivax treated 4 days (V4), suspected malaria and amebiasis treated for 5 days with antibiotics (MA5). Referring back to FIGS. 3 and 4, it may be seen that, as the disease is treated, the spectral characteristics of the blood begin to approach those of normal whole blood. Thus it may be seen that the present invention can be used to monitor both the extent of the disease and the progress of the treatment.  
         [0056]    Representative samples of fresh healthy whole blood (N), healthy blood aged 6 days (NA), whole blood containing sickle cells (SC), and whole blood from individuals diagnosed with Vivax malaria (V), and dengue fever in the classical acute phase (CAP) are plotted together in FIG. 6 for comparison.  
         [0057]    It should be noted that the system and method can also be applied to other bodily fluids or tissues in the diagnosis of syphilis, gonorrhea, HIV, tuberculosis, and onchocerciasis, and for the characterization of micrometer- and submicrometer-sized particles such as may be present in blood and other bodily fluids, such as, but not intended to be limited to, mucus, urine, tear fluid, spinal fluid, menstrual fluid, and amniotic fluid. In spinal fluid, for example, meningitis, both viral and bacterial, would be easily detectable; in urine, microalbuminemia or hyperproteinurea can be detected to suggest a diagnosis of kidney disease.  
         [0058]    It is believed that the present invention provides a maximum amount of information and also the greatest sensitivity of detection and identification. Samples in a range of 10 6  particles are being examined simultaneously, and are not merely being counted, as with microscopic methods.  
         [0059]    Another advantage of the present invention is speed of analysis. Blood testing by microscopy typically entails a one-week waiting time and requires a trained microscopist to interpret the data. The present invention provides an immediate analysis, which means that treatment can begin immediately, and the patient does not have to make a return trip to the doctor&#39;s office. Further, the speed of analysis permits on-site use in remote locations and in critical situations such as combat and in an epidemic.  
         [0060]    A further advantage of the present invention is the cost. Whereas testing for some disorders or diseases can cost approximately $700, it is believed that the present invention can decrease this amount by two orders of magnitude, owing to lower equipment investment and elimination of the need for highly trained personnel. A laptop computer can accommodate the software required for the system, and a fiber-optic spectrometer is sufficient for data collection. This enables on-site analysis in remote, underdeveloped areas.  
         [0061]    In another embodiment of the present invention, the technique of uv-vis spectroscopy is applicable to noninvasive measurements, wherein the absorption, scattering, and polarization properties of the bodily fluid may be studied through the skin.  
         [0062]    In yet another embodiment, commercially available metallic beads can be coated with a substance, which will aggregate together if an antibody to the substance exists in the system. Such an aggregation is easily detected with the system and method of the present invention, which can thus be used to test with an immobilized reagent.  
         [0063]    In the foregoing description, certain terms have been used for brevity, clarity, and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such words are used for description purposes herein and are intended to be broadly construed. Moreover, the embodiments of the apparatus illustrated and described herein are by way of example, and the scope of the invention is not limited to the exact details of construction.  
         [0064]    Having now described the invention, the construction, the operation and use of preferred embodiment thereof, and the advantageous new and useful results obtained thereby, the new and useful constructions, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.  
       References  
       [0065]    Brandolin, A., L. H. Garcia-Rubio, T. Provder, M. E. Kohler, and C. Kuo, “Latex Particle Size Distribution from Turbidimetry Using Inversion Techniques, Experimental Validation,” ACS Symposium Series No. 472, Chap. 2, 1991.  
         [0066]    Elicabe, G., and L. H. Garcia-Rubio, “Latex Particle Size Distribution from Turbidimetry using a Combination of Regularization Techniques and Generalized Cross Validation,”  Advances in Chemistry Series  Vol. 227, Chap. 6, ACS, Washington D.C., 1990.  
         [0067]    Garcia-Rubio, L. H., “The Effect of the Molecular Size on the Absorption Spectra of Macromolecules,”  Macromolecules  20, 3070, 1987.  
         [0068]    Garcia-Rubio, L. H., “Determination of the Absorption Coefficient of Proteins in the Presence of Protein Aggregates using Turbimetry,”  Chem. Eng. Comm.  80, 193, 1989.  
         [0069]    Garcia-Rubio, L. H., “Refractive Index Effects on the Absorption Spectra of Macromolecules,”  Macromolecules  25, 2608-13, 1992.  
         [0070]    Garcia-Rubio, L. H., C. A. Garcia, and S. Grossman, “Spectroscopy Characterization of Proteins: Use of Model Molecules for Porcine Somatotropin Analysis,”  Chem. Eng. Comm.,  122, 85-101, 1993.  
         [0071]    Garcia-Rubio, L. H., and N. Ro, “Detailed Copolymer Characterization using Ultraviolet Spectroscopy,”  Can. J. Chem.  63, 253, 1985.  
         [0072]    Garcia-Rubio, L. H., N. Ro, and R. D. Patel, “UV Analysis of Benzoyl Peroxide Initiated Polymerizations and Copolymerizations,”  Macromolecules  17, 1998, 1984.  
         [0073]    Garcia-Rubio, L. H., J. D. Rose, M. C. Callahan, and R. Robertson, “Combined Absorption and Light Scattering Methods for the Characterization and Detection of Cryptosporidium,” submitted.  
         [0074]    Koumarioti, I., L. Davis, S. Chang, and L. H. Garcia-Rubio, “Spectroscopy Analysis of Particle Suspensions,”  Development of Non - Renewable Resources: Challenges and Solutions , Eds, H. El-Shall, A. Ismail, and B. Moudgil. United Engineeering Foundation, Inc., New York, pp 83-93, 1999.  
         [0075]    Marquez, E., V. R. Bhethanabotla, and L. H. Garcia-Rubio,  Macromolecules  26, 479, 1993.  
         [0076]    Mattley, Y., G. Leparc, R. Potter, and L. H. Garcia-Rubio, “Light Scattering and Absorption Model for the Quantitative Interpretation of Human Platelet Spectral Data,”  Photochem. Photobiol.  71(5), 610-19, 2000.  
         [0077]    Throckmorton, J. F., R. Potter, and L. H. Garcia-Rubio, “Determining a UV/VIS Model for Tyrosine: Use of Model Molecules for the Spectroscopy Characterization of Proteins,” Presented at the 5th Symposium: Technologies on Protein Studies and Purification, Grenoble, France, Mar. 17th-19th, 1992.