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Chapter 4 Methods for Examining Biological Evidence Prof. J. T. Spencer Adjunct Prof. T. L. Meeks
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Learning Goals and Objectives Biological evidence forms a critical core of forensic investigations. Accurate observations and measurements are key to analyzing these data…
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Learning Goals and Objectives How measurements are taken - units, accuracy and precision of measurements Limitations of our senses on our interpretation of the world around us What is electromagnetic radiation and how do we perceive it What is the SI system of measurement and how does it work How the uncertainty of a measurement is estimated and indicated
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Learning Goals and Objectives What is meant by the accuracy and precision of a measurement How a lens works to create a magnified image What are the basic principles of microscope operation That is meant by resolution, magnification, numerical aperture, and related terms
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Learning Goals and Objectives What are the main types of optical microscopy and how do they work How electron microscopy works What other types of microscopy are available and when they are used
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CHE 113 6 Matter; Measurement It probably comes as no surprise that accurate, reliable and meaningful observations and measurements are fundamental to all of forensic science. These observations can be either quantitative, involving detailed measurement, and qualitative, involving careful descriptions.
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CHE 113 7 Systems Systems Metric - base 10 Metric - base 10 SI- international scientific system SI- international scientific system – massKilogram – lengthMeter – timeSecond – electric currentAmpere – temperatureKelvin – lightLumen (Candela) – amountMole Factor label method for conversions Factor label method for conversions Measurement
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CHE 113 8 Prefixes Prefixes MegaM10 6 Kilok10 3 Decid10 -1 Centic10 -2 Millim10 -3 Micro 10 -6 Nanon10 -9 Measurement
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CHE 113 9 Matter; Measurement A B Which is True? A = B A > B A < B
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CHE 113 10 Matter; Measurement A B Which is True? A = B A > B A < B
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CHE 113 11 Matter; Measurement A B Which is True? A = B A > B A < B
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CHE 113 12 Uncertainty in Measurement Precision and Accuracy Precision and Accuracy Precision - how closely individual measurements agree Precision - how closely individual measurements agree Accuracy- how closely the measurements agree with the true value Accuracy- how closely the measurements agree with the true value Significant Figures Significant Figures All measurements are inaccurate intrinsically All measurements are inaccurate intrinsically measured quantities are reported such that the last figure is uncertain measured quantities are reported such that the last figure is uncertain
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CHE 113 13 Good Precision Poor Accuracy Good Precision Good Accuracy Poor Precision Poor Accuracy Uncertainty in Measurement
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CHE 113 14 Accuracy in Measurement
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Tools for Understanding Biological Evidence When doing observations and measurements, we perceive the world only indirectly through the facility of our senses of sight, touch, taste, hearing and smell…
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The Microscope Provides a direct image of a small object of interest Provides a direct image of a small object of interest spectroscopy gives an abstract representation which must be interpreted on the basis of a model or some assumptions spectroscopy gives an abstract representation which must be interpreted on the basis of a model or some assumptions A typical animal cell is 10-20 nm in diameter A typical animal cell is 10-20 nm in diameter 5x smaller than the smallest object that can be seen directly by the naked eye 5x smaller than the smallest object that can be seen directly by the naked eye
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The Microscope Produce a magnified image of a specimen Produce a magnified image of a specimen Separate the details in the image Separate the details in the image Render the details visible to the human eye or camera Render the details visible to the human eye or camera
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Microscopy History
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Lenses Refraction of a light ray as it passes through a prism
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Lenses Light passing through two “identical” prisms stacked base to base would intersect at point I Light passing through two “identical” prisms stacked base to base would intersect at point I produce a real image converging lens
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Focal Point & Focal Length The point at which parallel rays are converged to an image is the focal point of the lens The point at which parallel rays are converged to an image is the focal point of the lens The distance of this point from the lens is the focal length The distance of this point from the lens is the focal length
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Simple Magnifier Object O is placed close to the lens Object O is placed close to the lens rays converge but do not intersect rays converge but do not intersect real image not formed real image not formed The observer’s eye follows rays back to the point of apparent origin (I) The observer’s eye follows rays back to the point of apparent origin (I) (I) bigger than object (I) bigger than object
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The Compound Microscope Rays pass first through the objective lens forming a real, slightly enlarged, inverted image Rays pass first through the objective lens forming a real, slightly enlarged, inverted image The second lens (eyepiece) acts as a simple magnifier The second lens (eyepiece) acts as a simple magnifier
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Compound Microscope Both lenses produce magnification Both lenses produce magnification Overall magnification is found by multiplying the two magnifications Overall magnification is found by multiplying the two magnifications Magnification determined mainly by objective Magnification determined mainly by objective
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Limitations of Light Microscope Radiation of a given wavelength can’t be used to probe structural details much smaller than its own wavelength Radiation of a given wavelength can’t be used to probe structural details much smaller than its own wavelength Light Microscope Light Microscope limited to range of visible light limited to range of visible light 0.4 mm (violet) to 0.7 mm (deep red) 0.4 mm (violet) to 0.7 mm (deep red) bacteria & mitochondria (~0.5mm wide) smallest objects that can be seen clearly bacteria & mitochondria (~0.5mm wide) smallest objects that can be seen clearly
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The Comparison Microscope Two compound microscopes combined into one unit Two compound microscopes combined into one unit When viewer looks through the eyepiece, a field divided into two equal parts is observed When viewer looks through the eyepiece, a field divided into two equal parts is observed specimen on left scope on left side of field specimen on left scope on left side of field specimen on right scope on right side of field specimen on right scope on right side of field
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The Comparison Microscope Bullet comparisons Bullet comparisons Hair & Fiber comparisons Hair & Fiber comparisons Questioned documents Questioned documents
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Test Fire Reference Gun
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Use A Comparison Microscope
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Striations match
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Phase-Contrast Microscope A phase-contrast microscope splits a beam of light into 2 types of light, direct and refracted (reflected) and brings them together to form an image of the specimen. A phase-contrast microscope splits a beam of light into 2 types of light, direct and refracted (reflected) and brings them together to form an image of the specimen. Where they are "in-phase" the image is brighter, where they are "out of phase" the image is darker, and by amplifying these differences in the light, it enhances contrast Where they are "in-phase" the image is brighter, where they are "out of phase" the image is darker, and by amplifying these differences in the light, it enhances contrast It allows the detailed observation of living organisms, especially the internal structures. It allows the detailed observation of living organisms, especially the internal structures.
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Light confined to a single plane of oscillation is said to be polarized. Light confined to a single plane of oscillation is said to be polarized. Many crystals are birefringent (light is refracted into 2 separate rays). Many crystals are birefringent (light is refracted into 2 separate rays). Reduces glare by transmitting light in a vertical plane only. Reduces glare by transmitting light in a vertical plane only. Polarizing Microscope
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Why do molecules rotate polarized light? A molecule possessing nonsupeposable mirror images is termed chiral. Naturally occurring substances are often found as just one mirror image (enantiomer). Enantiomers are identical in physical properties and identical chemical properties when they react with nonchiral reagents; only in a chiral environment will the differences show. Enantiomers rotate of polarized light in different directions.
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Optical Activity Non-superimposable mirror images Non-superimposable mirror images Mirror Left Hand Right Hand
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Optical Isomers Amino Acids are Chiral Amino Acids are Chiral Mirror Plane Enantiomers alanine
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Polarizing Potato Starch
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In fluorescence microscopy, specimens are first stained with fluorochromes and then viewed through a compound microscope by using an ultraviolet (or near- ultraviolet) light source. In fluorescence microscopy, specimens are first stained with fluorochromes and then viewed through a compound microscope by using an ultraviolet (or near- ultraviolet) light source. The microorganisms appear as bright objects against a dark background. The microorganisms appear as bright objects against a dark background. Fluorescence microscopy is used primarily in a diagnostic procedure called fluorescent- antibody (FA) technique, or immunofluorescence. Fluorescence microscopy is used primarily in a diagnostic procedure called fluorescent- antibody (FA) technique, or immunofluorescence. This technique is especially useful in diagnosing syphilis & rabies. This technique is especially useful in diagnosing syphilis & rabies. Fluorescence Microscope
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Hand section of sugarcane vascular bundle viewed with fluorescence microscope Sugarcane vascular bundle viewed with traditional staining and transmitted light (Bright Field) microscopy Hand-section of Sugarcane stem with a vascular bundle Stained with Toluidine Blue & Viewed with Bright Field microscopy
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An egg that was stained with a dye that appears yellow in a fluorescence microscope. An unfertilized egg stained with a dye that appears red in a fluorescence microscope. The line indicates size (10 micrometers = 1/100 of a millimeter). The egg is about 100 micrometers in diameter, so about ten eggs would fit side by side on a pencil line.
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Stereoscopic Microscope Two separate monocular microscopes Two separate monocular microscopes Each has its own set of lenses Each has its own set of lenses Gives a 3D view Offers the largest stage for evidence
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Stereoscopic Microscope Using the Stereo MicroscopeUsing the Compound Microscope
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Stereoscopic Microscope Cell division in a frog's egg.
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FT-IR Microspectrophotometer
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Photocopier Toner Analysis important for establishing corroborative evidence linking documents to specific locations in forensic investigations of corporate crime important for establishing corroborative evidence linking documents to specific locations in forensic investigations of corporate crime Must be performed non-destructively Must be performed non-destructively can’t remove toner from paper can’t remove toner from paper physical size of specimen is very small physical size of specimen is very small microscope to find sample microscope to find sample FT-IR to analyze the sample FT-IR to analyze the sample
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Photocopier Toner Analysis
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Scanning Electron Microscope This scanning electron microscope has a magnification range from 15x to 200,000x and a resolution of 5 nanometers This scanning electron microscope has a magnification range from 15x to 200,000x and a resolution of 5 nanometers
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Range of Readily Resolvable Objects
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How the SEM Works
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Conventional light microscopes use a series of glass lenses to bend light waves and create a magnified image.
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The Scanning Electron Microscope creates the magnified images by using electrons instead of light waves The Scanning Electron Microscope creates the magnified images by using electrons instead of light waves
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The SEM shows very detailed 3-dimensional images at much higher magnifications than is possible with a light microscope. The images created without light waves are rendered black and white
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Samples have to be prepared carefully to withstand the vacuum inside the microscope
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Biological specimens are dried in a special manner that prevents them from shriveling. Biological specimens are dried in a special manner that prevents them from shriveling. Because the SEM illuminates them with electrons, they also have to be made to conduct electricity Because the SEM illuminates them with electrons, they also have to be made to conduct electricity
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How do you make a mosquito conductive? How do you make a mosquito conductive? SEM samples are coated with a very thin layer of gold by a machine called a sputter coater SEM samples are coated with a very thin layer of gold by a machine called a sputter coater
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The specimen is now prepared
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The sample is placed inside the microscope's vacuum column through an air-tight door
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Air is pumped out of the column Air is pumped out of the column An electron gun [at the top] emits a beam of high energy electrons. An electron gun [at the top] emits a beam of high energy electrons. travels downward through a series of magnetic lenses designed to focus the electrons to a very fine spot
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Near the bottom, a set of scanning coils moves the focused beam back and forth across the specimen, row by row Near the bottom, a set of scanning coils moves the focused beam back and forth across the specimen, row by row
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As the electron beam hits each spot on the sample, secondary electrons are knocked loose from its surface. As the electron beam hits each spot on the sample, secondary electrons are knocked loose from its surface. A detector counts these electrons and sends the signals to an amplifier A detector counts these electrons and sends the signals to an amplifier
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The final image is built up from the number of electrons emitted from each spot on the sample The final image is built up from the number of electrons emitted from each spot on the sample
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TEM Pictures Silver Nanoprisms Gold Nanoparticle
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Fiber Analysis
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Who am I?
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I’m a louse fly of a wallglider (an alpine bird)
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