Multimode Imaging in the Thermal Infrared for Chemical Contrast Enhancement. Part 2: Simulation Driven Design

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) detection limits for blood on fabric: Orientation and coating uniformity effects

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to analyze four types of forensically relevant fabrics coated with varying dilutions of blood. The blood was applied in two manners, dip coating with a smooth and uniform layer and drip coating with droplets from pipettes. Spectra of neat and dip coated fabrics were acquired using controlled orientations, and these were compared to spectra collected on samples with random orientations. The improved reproducibility seen in visual inspection of the spectra is confirmed by principal component and linear discriminant projections of the spectra, as well as by statistical hypothesis testing. Principal component regression (PCR), using the regions of the IR spectra associated with the amide A/B, I, II, and III vibrational bands (3500-2800, 1650, 1540, and 1350 cm^-1), was employed on the more uniform dip coated spectra to estimate limits of detection for blood on two of the four fabrics - acrylic and nylon. These results demonstrate that detection limits for blood on fabrics can be decreased significantly by controlling for the orientation and face of the fabric samples while collecting spectra. Limits of detection for acrylic and nylon were found to be 196 × and 227 × diluted blood, respectively.

Attenuated Total Reflection (ATR) Sampling in Infrared Spectroscopy of Heterogeneous Materials Requires Reproducible Pressure Control

Attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy, in which the sample is pressed against an internal reflection element, is a popular technique for rapid IR spectral collection. However, depending on the accessory design, the pressure applied to the sample is not always well controlled. While collecting data from fabrics with heterogeneous coatings, we have observed systematic pressure-dependent changes in spectra that can be eliminated by more reproducible pressure control. We also described a pressure sensor adapted to work with an ATR tower to enable more precise control of pressure during ATR sampling.

Identification of individual red blood cells by Raman microspectroscopy for forensic purposes: in search of a limit of detection

Traces of body fluids can be present at a variety of crime scenes. It is important that forensic investigators have a reliable and nondestructive method of identifying these traces. Of equal importance is establishing the limitations of any method in use, including its detection limit. We have previously reported on the use of Raman microspectroscopy and multivariate data analysis to identify and differentiate body fluids. While many studies use serial dilutions to establish limits of detection, we utilized a different approach and demonstrated that a single red blood cell is sufficient to be correctly identified as blood. The experimental Raman spectra of individual red blood cells were loaded into the previously reported models for body fluid identification, and all were correctly classified as peripheral blood. These results demonstrate that our model can be used to identify peripheral blood, even if there is only a single red blood cell present. Furthermore, a single red blood cell is 5000× smaller than the amount of peripheral blood required to perform DNA analysis in a modern crime laboratory. This means that if a bloodstain is large enough for DNA analysis, Raman microspectroscopy should be able to make a positive identification. Considering that the sample analysis reported here was carried out with a different instrument, not the one used for the previously reported method development, these results also represent a form of method validation. The model's ability to correctly classify spectra acquired on a different instrumental platform is crucial in preparing it for practical application. Graphical Abstract Peripheral blood is of great interest in forensic sciences. While many tests are available for the identification of peripheral blood at a crime scene, most are presumptive and destructive. Here we present results that show our new, nondestructive method can identify peripheral blood using as little as a single red blood cell.

An Improved-Efficiency Compact Lamp for the Thermal Infrared

A major type of infrared camera is sensitive to wavelengths in the 8-14 μm band and is mainly used for thermal imaging. Such cameras can also be used for general broadband infrared reflectance imaging when provided with a suitable light source. We report the design and properties of an infrared lamp using a heated alumina emitter suitable for active thermal infrared imaging, as well as comparisons to existing commercial light sources for this purpose. We find that the alumina lamp is a broadband non-blackbody source with a lower out-of-band emission intensity and therefore higher electrical efficiency for this application than existing commercial sources.

Chemical contrast observed in thermal images of blood-stained fabrics exposed to steam

Thermal imaging is not ordinarily a good way to visualize chemical contrast.

Tunable filter-based multispectral imaging for detection of blood stains on construction material substrates part 2: realization of rapid blood stain detection

Based on the blood stain detection method and criteria established in part 1 of this article, we combine and organize all necessary tasks to realize the multispectral imaging-based rapid blood stain detection system. To rapidly detect blood stains on the test surface, the developed system automatically captures the spectral images, extracts their spectral data, determines the positions of blood stains, and accurately highlights the positions of blood stains on the display. To achieve such a system, several tasks are newly introduced, including adjustment of camera exposure times to prevent image saturation or excessive darkness, the search for the sampled clean positions of the substrate to determine the substrate reflectance spectrum, and suitable detection procedures and proper arrangement of criteria to eliminate unnecessary calculations. Parallel processes between image capturing and blood stain identification help shorten the time for blood stain identifications despite a large amount of spectral data to be processed. The developed system can identify blood against several other reddish brown stains on several substrates. The measured average identification times on different test surfaces range from only 23.3 to 28.7 s, including the image capturing process.

Tunable filter-based multispectral imaging for detection of blood stains on construction material substrates. Part 1. Developing blood stain discrimination criteria

In this article, we establish blood stain detection criteria that are less substrate dependent for use in a liquid crystal tunable filter-based multispectral-imaging system. Kubelka-Munk (KM) theory is applied to transform the acquired stains' reflectance spectra into the less substrate dependent spectra. Chosen spectral parameters are extracted from the KM absorbance spectra of several stain samples on several substrates. Blood discrimination criteria based upon those spectral parameters are then established from empirical data, tested, and refined. In our newly invented method, instead of introducing conventional contrast enhancement on the blood stain image, blood stain determination is executed mathematically via Boolean logic, resulting in more discriminative blood stain identification. This proposed approach allows for nondestructive, quick, discriminative, and easy-to-improve presumptive blood stain detection. Experimental results confirm that our blood stain discrimination criteria can be used to locate blood stains on several construction materials with high precision. True positive rates (sensitivity) from 0.60 to 0.95 are achieved depending on blood stain faintness and substrate types. Also, true negative rates (specificity) between 0.55 and 0.96 and identification time of 4-5 min are accomplished, respectively. The established blood stain discrimination criteria will be incorporated in a real blood stain detection system in part 2 of this article, where system design and considerations as well as speed issues are discussed.