Atomic force microscopy as a biophysical tool for nanoscale forensic investigations

The atomic force microscope (AFM) has found its way to the arsenal of tools available to the forensic practitioner for the analysis of samples at the nano and microscales. As a non-destructive probing tool that requires minimal sample preparation, the AFM is very attractive, particularly in the case of minimal or precious sample. To date, the use of the AFM has primarily been in the arena of imaging where it has been complementary to other microscopic examination tools. Forensic applications in the visual examination of evidence such as blood stains, questioned documents, and hair samples have been reported. While a number of reviews have focused on the use of AFM as an imaging tool for forensic analyses, here we not only discuss these works, but also point to a versatile enhancement in the capabilities of this nanoscale tool – namely its use for force spectroscopy. In this mode, the AFM can determine elastic moduli, adhesion forces, energy dissipation, and the interaction forces between cognate ligands, that can be spatially mapped to provide a unique spatial visualization of properties. Our goals in this review are to provide a context for this capability of the AFM, explain its workings, cover some exemplary works pertaining to forensic sciences, and present a critical analysis on the advantages and disadvantages of this modality. Equipped with this high-resolution tool, imaging and biophysical analysis by the AFM can provide a unique complement to other tools available to the researcher for the analysis and characterization of forensic evidence.     

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.     

红外光谱结合化学计量学方法在激光打印原装黑色墨粉分析中的应用研究

目的 采用红外光谱比较分析不同原装黑色墨粉（31个样本）的差异,探讨化学计量学方法在墨粉种类识别中的适用性.方法 对打印样本纸张上的黑色墨粉进行烫熨提取后直接分析检测.IR分析条件：显微红外光谱仪,常温透射模式,扫描范围为4 000～400 cm-1,分辨率为16cm-1,累计扫描次数为64次.结果 墨粉树脂主要为聚苯乙烯/甲基丙烯酸甲酯和聚对苯二甲酸/环氧树脂.采用主成分析（Principal Component Analysis,PCA）与系统聚类法（Hierarchical Cluster Analysis,HCA）对不同种类墨粉进行聚类分析与建模预报.基于前两主成分得分值（53.3％）不同树脂成分的墨粉样本聚类效果明显,同时在第三个主成分方向上黑白与彩色激光墨粉样本获得良好区分.结论 红外光谱法结合化学计量学方法用于不同种类树脂及打印类型原装黑色墨粉的聚类分析与建模预报方法可行,结果准确可靠.     

氨基比林血痕预试验处理血痕后样本的DNA定量

目的：探讨氨基比林血痕预试验处理血痕后样本DNA含量的变化及对STR分型检测的影响。方法10名健康无关个体EDTA抗凝血液制成滤纸血痕,氨基比林血痕预试验检测,按试验后血样干燥保存时间分30 min、1 h、3 h、6 h、12 h、24 h共6个实验组,并采用磁珠法、QIAcube DNA纯化法、Chelex-100法三种方法提取样本DNA,应用荧光定量PCR检测样本DNA含量,PCR-STR荧光技术进行STR分型。结果提取方法相同时,氨基比林血痕预试验后血样随干燥保存时间的延长,样本DNA含量呈逐渐降低的趋势。保存时间相同时,不同DNA提取方法间,样本DNA含量差异也有统计学意义。90.56%样本均可获得16个STR基因座明确分型。结论氨基比林血痕预试验对血痕样本DNA有损伤,24 h内多可获有效STR分型。磁珠法提取样本DNA进行STR分型,效果最好。     

基于MRI的中国汉族成人颅面径线测量与分析

目的通过MRI和VGStudio MAX 2.2软件对中国汉族成人颅面相关径线进行测量,并分析其与性别、年龄、身高以及体重的关系。方法按颅面标志点设定4条径线。A径线：在正中矢状面上颏下点至头顶点的最大直线距离;B径线：在正中矢状面上发际点至后头点的最大直线距离;C径线：在水平面上左、右外眼点间的最大直线距离;D径线：在冠状面上左、右侧颧点间的最大直线距离;用VGStudio MAX 2.2软件对MRI图像数据进行三维重建,直接用软件的测量工具对颅面的相关径线进行测量,并用SPSS 16.0进行分析。结果 A、B、C、D径线的均值分别为（237.54±8.63）mm、（173.07±8.28）mm、（89.58±4.46）mm、（127.34±8.16）mm,与性别有着显著性差异（P〈0.01）;其中A、C、D径线与身高,A、D径线与体重,C径线与年龄,均存在明显的直线相关关系。结论中国汉族成人颅面径线A、B、C、D均存在明显的性别差异;且A、C、D径线与身高,A、D径线与体重,C径线与年龄,均存在明显的直线相关关系。     

Using Raman Spectroscopy to solve crime: inks, questioned documents and fraud

Raman microscopy is becoming a tool of major importance in forensic analysis, particularly of drugs and explosives. It is a non-invasive, non-destructive chemical probe allowing samples to be examined in their entirety without any preparation. This paper demonstrates the use of the technique as a general tool for inks analysis. Furthermore, it addresses two important issues that historically have been extremely difficult for the professional document examiner, namely, comparison of black ballpoint inks and the chronological sequencing of crossed ink lines. We show that Raman can successfully distinguish between a representative sample of commercially available black ballpoint inks. This data has been converted into a database for future reference. A method for chronological sequencing of crossed ink lines has been developed using confocal Raman microscopy. Case study work has shown the feasibility of this approach.     

Using Paint to Investigate Fires: An ATR‐IR Study of the Degradation of Paint Samples Upon Heating

Fire investigation is a challenging area for the forensic investigator. The aim of this work was to use spectral changes to paint samples to estimate the temperatures to which a paint has been heated. Five paint samples (one clay paint, two car paints, one metallic paint, and one matt emulsion) have been fully characterized by a combination of attenuated total reflectance Fourier transform infrared (ATR‐IR), Raman, X‐ray fluorescence spectroscopy and powder X‐ray diffraction. The thermal decomposition of these paints has been investigated by means of ATR‐IR and thermal gravimetric analysis. Clear temperature markers are observed in the ATR‐IR spectra namely: loss of ν(C = O) band, >300°C; appearance of water bands on cooling, >500°C; alterations to ν(Si–O) bands due to dehydration of silicate clays, >700°C; diminution of ν(CO₃) and δ(CO₃) modes of CaCO₃, >950°C. We suggest the possible use of portable ATR‐IR for nondestructive, in situ analysis of paints.     

The Identification of Spiromesifen,a Recently Introduced Pesticide,Using Approaches to Chemical Unknown Analysis

An unknown, viscous, opaque, white liquid with a strong, unpleasant odor was submitted with a request for identification. It was analyzed using infrared (IR) spectroscopy, gas chromatography–mass spectrometry, and X‐ray fluorescence spectroscopy. It was found to contain glycerin as well as another compound. IR and mass spectral data were readily obtained for this second component, but it was not easily identified as common instrument libraries had no matching spectra. After an extensive literature search, the unknown compound was identified as spiromesifen, a recently introduced pesticide. The IR spectrum and electron impact mass spectrum of spiromesifen are presented here as these are not available in the published literature. This case report also provides useful approaches for searching for and identifying an unknown compound when it is not found in a laboratory's spectral libraries.     

The Differentiation of Menstrual from Venous Blood and Other Body Fluids on Various Substrates Using ATR FT‐IR Spectroscopy

Crime scene investigators and laboratory analysts use chemical tests to detect and differentiate body fluids. Testing often requires a sample of the stain, and the chemicals may cause degradation of the fluid or interfere with subsequent tests. Colorimetric chemical tests do not differentiate between different types of the same fluid, such as venous and menstrual blood, and there is no presumptive test available to simultaneously differentiate several body fluids. In this study, we recorded ATR FT ‐IR spectra of venous and menstrual blood, semen, saliva, and breastmilk. Neat and simulated casework body fluid samples were analyzed on cotton, nylon, wood, paper, and glass substrates. Differences in fluid composition, including proteins and small molecules, resulted in spectral differences. Venous and menstrual blood is differentiated by the peak at 1039 cm^?1 attributed to phosphoric acid found in menstrual blood. Peak intensity is influenced by the porosity and weave of the substrate fabric.     

磁珠直接吸附法对体态检材游离DNA的提取

目的采用磁珠直接吸附法对人体尿液、唾液、血液3种体态生物检材中的游离DNA进行提取检验,为法医物证中游离DNA的研究及检验工作提供参考。方法对3种生物检材采取离心吸取上清液的方法分离游离DNA,然后采用磁珠直接吸附法进行提取纯化,Identifiler-Plus试剂盒进行复合扩增后常规STR检测。结果在3种检材中均检出了游离DNA,其中血液中游离DNA检出率为100%,唾液为90%,尿液为70%。结论人体体态生物检材中存在游离DNA,同时磁珠直接吸附法可高效、快捷的提取生物检材中的游离DNA。