Analytical Chemistry in Forensic Science spectral imaging

Transcription

1 Analytical Chemistry in Forensic Science spectral imaging W.T. Chan Department of Chemistry University of Hong Kong June 4, 2015

2 Plan of presentation Overview of chemical analysis in forensic science Principles spectral imaging Applications in questioned document examination, blood stains identification, fingerprinting, remote sensing of mass graves

3 Basic Services of the Crime Laboratory Forensic Science Division, HK Government Laboratory Criminalistics and Quality Management Group Biochemical Sciences Sections A & B Chemical Sciences Section DNA Database Section Parentage Testing Section Physical Sciences Section Scene of Crime and Quality Management Section Drugs, Toxicology and Documents Group Controlled Drugs Sections A & B Forensic Toxicology Sections A & B Questioned Documents Section

4 Locard s Exchange Principle: Every contact leaves a trace Edmond Locard ( ) "Sherlock Holmes of France"

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6 Flow of forensic investigation: Document forgery Is there a crime committed? Crime scene investigation Collection of Physical evidence Exemplar Analysis of the evidence Report Analysis Results Inferences Confidence level

7 Spectroscopic methods of physical evidence examination X-ray fluorescence Energy Dispersive X-ray analysis (EDAX) UV-visible absorption spectrophotometry Infrared spectrophotometry Fluorescence Thermoluminescence Atomic absorption and emission spectroscopy Atomic mass spectrometry (ICP-MS) Molecular mass spectrometry

8 Molecular absorption electronic, vibrational, and rotational transitions broadband spectrum IR VIS UV Absorption spectrum Apparent color white light Spectrum of transmitted or reflected light K 2 Cr 2 O 7 energy bromophenol Blue l 1 l 4 l 1 l 5 l 1 l 5 0 Sample color is the complementary color (photons that are not absorbed) phenolphthalein

9 Molecular Fluorescence Fluorescence is relatively rare the molecule must absorb and emit a photon in sequence, but is highly selective and sensitive.

10 Imaging taking photos of the crime scene or the evidence Digital photos are now admissible in court Documentation of the crime scene Documentation of the physical evidence Digital image analysis Spectral imaging

11 Spectral imaging R G B

12 Infrared reflectance Canon 400D George Chan 2014

13 Infrared Reflectance and Infrared Luminescence Altered date on a contract Optical image IR reflectance IR luminescence Infrared Reflectance Infrared Luminescence

14 Infrared Imaging (Reflectance) Christ Driving the Traders from the Temple

15 Infrared Imaging (Reflectance) Many pigments are transparent to IR light Infrared can penetrate through the top color layers The underdrawing becomes visible The painting s underdrawing with the pig still visible in the sack.

16 Latent Fingerprints infrared reflectance using specific wavelength Wavenumber cm -1 Assignment 1016 Asymmetric O C C stretch, ester 1248 Asymmetric O C O stretch, ester 1456 CH 2 scissors 1552 N H bend combined with C N stretch, protein amide 1656 C = O stretch, protein amide 1744 C = O stretch, saturated ester 2856 Methylene C H stretch 2920 Methyl C H stretch

17 Black plastic garbage bag fingerprint is vague Band intensity image (ester band 1016 cm -1 )

18 Sequence of intersecting lines Ballpoint pen writing under or above laser printing?

19 laser printing Ballpoint pen ink under or above laser printing? visible image of intersection Ballpoint pen ink is under laser printing ballpoint pen ink infrared spectra infrared spectral images J Forensic Sci, November 2008, Vol. 53, No. 6,

20 Excitation Red 640 nm Imaging 780 nm (long-pass filter) Spirulina Fluorescence comparison of chlorophyllcontaining compounds (clockwise from top left: spirulina, wheatgrass, spinach, kale, lime, chlorella, broccoli, moringa powders)

21 IR fluorescence fingerprint powder (Spirulina) White light imaging IR imaging (850 nm long-pass filter)

22 Mass spectrometry Nature Reviews Cancer 10, (September 2010) doi: /nrc2917 Matrix-assisted laser desorption ionization (MALDI)-time-offlight (TOF) imaging mass spectrometer (IMS)

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24 1.28 mm Upper right corner Color-changing pattern Top edge near the middle Middle BEARER Bauhinia petal (top) Bauhinia petal (middle) 100 dollar mark (back side) 100 dollar mark (back side) Bottom edge (middle back side)

25 Anal. Chem. 2011, 83,

26 Imaging mass spectrometry analysis of questioned documents

27 HYPERSPECTRAL IMAGING (HSI)

28 hyperman superman ultraman hyper excessive, greatly exceeding norms (hypersonic highly supersonic, Mach 5) super exceeding norms (superhuman) ultra on the far side (ulrtraviolet)

29 Hyperspectral imaging (HSI) is superior to multi-spectral imaging in discriminating multiple chemical species, particularly when their spectra are partially overlapped spectral bands are captured in a spectrum

30 Datacube acquisition strategies

31 Push Broom Scanner imaging optics scan direction x y

32 Push Broom Spectrometry intensity 2-dimensional array detector current scan line dispersing optics x imaging optics scan direction data cube x y

33 HSI identifies chemicals by statistical analysis, e.g., principal component analysis (PCA), of the molecular spectra Pain killers Blood stains Gel Pen Inks

34 HSI for blood stains identification

35 HSI image four stains, (A) red ballpoint pen, (B) coffee stain, (C) brown sugar stain and (D) blood stain deposited on dark grey cotton HSI image colour image of 4 stains: (A) Cranberry tea, (B) red nail polish, (C) fake blood and (D) blood stain

36 Paracet Ibux Paracet Ibux Pamol Smelt Aspirin Pamol Smelt Aspirin

37 PryJector Push-broom system Continuously scanning HSI image of chemicals is computed and projected on-the-fly as false-colored images onto the surface Projected image is registered to the original features on the surface

38 Principal Component Analysis of four pharmaceuticals. The five classes are : Paracet, Ibux, Pamol Smelt, Aspirin, and background

39 Bone fragments in a complex mixture (a pile of sand, stones and tree fragments) are highlighted by a projector which continuously updates the chemical image of a surface using a line scanning hyperspectral camera

40 Mass grave remote sensing Empty refilled grave Infrared photograph of the experimental site. Airborne hyperspectral image of the experimental site, 4.7 m spatial resolution.

41 1 month after burial: No vegetation over both graves 5 months after burial: Less vegetation over mass grave due to toxic decomposition products 16 months after burial: The effects of toxic decomposition products on plant growth is still detectable Solid lines = mean; dotted lines = standard deviation

42 Summary Spectral imaging is based on absorption spectroscopy (reflectance), luminescence, and mass spectrometry Spectral imaging provides information on the chemical species of the evidence Hyperspectral imaging can differentiate chemical species that have partially overlapped molecular spectra

43 Thank You! Questions and Comments?