1.Key Labortory of Drug Preventation and Control Technology of Zhejiang Province, Hangzhou 310053, China 2.Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China 3.Department of Chemial Engineering, Massachusettes Institute of Technology, MA 02139, USA 4.School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
Fund Project:Project supported by the National Key R&D Program of China (Grant Nos. 2017YFC0110301, 2016YFC0800906), the National Natural Science Foundation of China (Grant No. 61575219), the Natural Science Foundation of Zhejiang Province, China (Grant No. LQ16B050002), the Technology Research Program of Ministry of Public Security, China (Grant No. 2016JSYJA32), and the Youth Innovation Promotion Association, CAS (Grant No. 2018007).
Received Date:30 January 2019
Accepted Date:28 February 2019
Available Online:01 March 2019
Published Online:20 March 2019
Abstract:Developing on advanced light sources, especially those applied in the areas of spectral imaging and mass spectrometry imaging, has made the trace analysis feasible and more reliable. These techniques show great potentials in various fields including forensic science, environment, food, pharmaceuticals, archaeology, etc. In many cases of trace analysis, it is expected to obtain both the spatial distributions and chemical compositions of the target objects. Through the combination of imaging technology with optical spectroscopy and mass spectrometry, it is possible to detect the trace chemicals on the surface of various materials as well as their spatial distributions, thus improving the accuracy of detection and the range of application. Moreover, trace analysis based on such methods can reduce or even avoid the use of special chemical reagents, and is compatible with the traditional chemical detection methods. In the paper, we focus on fingerprint visualization and analysis, as a typical trace analysis issue, to discuss the recent progress of the applicable chemical imaging technologies based on the advanced light sources. The effect of latent fingerprint development depends on not only features of fingerprint carrying object, but also the characteristics of fingerprint residues. In this paper, we provide an overview of two technical approaches: specific component targeted chemical imaging and nondirective chemical imaging. We describe the major technologies involved in this field, including visible-near infrared chemical imaging, mid-infrared chemical imaging, Raman imaging, and mass spectrometry imaging. Keywords:trace analysis/ spectral imaging/ mass spectrometry imaging/ fingerprint
红外光谱(这里主要指长波近红外至中红外区)作为一种分子振动光谱, 被广泛用于化学分析. 带有阵列检测器的红外光谱仪可同时采集检测范围内不同位点的数千个波长处的红外光谱数据, 不仅可以获取检测对象的特征化学信息, 还能获得化学信息的空间分布. 不仅汗液、油脂等内源性组分在红外光区具有特征吸收(图3(b)), 许多外源性组分也具有特征吸收. Ossa等[22]利用近红外光谱成像技术原位识别多种爆炸物成分, 并实现指纹图像提取. Banas等[23]利用傅里叶变换红外光谱(Fourier transform infrared spectroscopy, FT-IR)技术检测潜到微量爆炸物、阿司匹林等外源成分. 然而, 由于指印遗留物的含量相对基质来说往往很低, 指纹显现的关键难点在于检测灵敏度和背景干扰问题. 对此, 现有研究主要体现了三种不同的技术路线. 图 3 基于焦平面阵列红外光谱的指纹成像[29] (a)检测区域的亮场光学图像; (b)汗腺、皮脂腺分泌物和皮肤脱落物的FT-IR光谱; (c)指印物质组分的空间分布图像; (d)基于汗腺分泌物的O—H键弯曲振动吸收带(1520—1719 cm–1)、皮脂腺分泌物的C=O键吸收带(1713—1773 cm–1)和和皮肤脱落物的酰胺II带(1507—1548 cm–1)产生的指印物质空间分布图像 Figure3. Fingerprint image investigated with FT-IR focal plane array imaging[29]: (a) Bright field optical image of the area investigated with FT-IR focal plane array imaging; (b) FT-IR spectra of eccrine, sebaceoussecretions and skin debris obtained using the conventional FT-IR spectroscopy; (c) the composite distribution map; (d) individual false colour images were generated by integrating over the O—H bending band for the eccrine material (1520?1719 cm–1), the C=O band for the sebaceous material (1713?1773 cm–1) and the amide II band (1507?1548 cm–1) for skin debris.
拉曼光谱是一种光散射技术, 主要采用紫外、可见和近红外激光器作为激发光源, 基于分子振动探测分子结构信息. 与红外光谱相比, 拉曼光谱具有非接触式检测的优点. 许多研究应用拉曼光谱检验药物、爆炸物等外源性手印遗留物质. Day等[33]利用傅里叶变换拉曼光谱检测遗留在钢片表面的油脂和汗潜手印上沾附的盐酸可卡因、硝基安定、滑石粉. 经超级胶熏显处理后的手印也能检测到目标组分[34]. 结合成像技术, 可进一步获取基于指印物质组分的指纹图像. 例如, 利用胶带提取转移指印物质(含若干外源药物组分)到载玻片上进行扫描检验. 结合拉曼光谱成像与变量统计方法, 分析出各个组分及其空间分布[35]. Emmons等[36]将沾附有多种爆炸物成分的手印遗留于铝包覆的载玻片上, 通过拉曼光谱成像获得指纹图像信息、爆炸物组分信息及其分布. 该课题组进一步研究了指印遗留于具有拉曼散射信号的客体上的情形. 结合背景扣除算法, 也检测到了附着于聚苯乙烯、聚碳酸酯、漆层表面的微量爆炸物成分[37]. 由于拉曼光谱信号强度相对较低, 需要较长的时间完成成像操作, 长时间聚焦条件下激发光能量可能对检材产生不利影响. 为此, 有研究通过改进样品制备, 获得基于金属电介质纳米颗粒基质的表面增强拉曼光谱, 得到高灵敏度的光谱信息[38]. 但是, 这种方法需要对手印样品进行处理, 使其表面吸附特殊金属颗粒, 对样本造成不可逆改变. 基于同步超快激光脉冲的受激拉曼散射显微成像技术进一步拓宽了拉曼光谱的适用性. Figueroa等[39]利用该技术实现了基于内源性或外源性手印组分的指纹成像. 发现该技术提高了光谱采集速度、检测灵敏度、空间分辨率和穿透深度, 从而释放了拉曼光谱作为一种无标记检验方法的应用潜力(图4). 图 4 利用受激拉曼散射显微成像实现潜指纹的无标记化学成像[39] (a) 2850 cm–1和1067 cm–1波段融合图像; (b)潜指纹中KNO3的受激拉曼光谱; (c) 2850 cm–1和1639 cm–1波段融合图像; (d)苯甲酸的受激拉曼光谱 Figure4. Label-free chemical imaging of latent fingerprints with stimulated Raman scattering microscopy[39]: (a) Image of merged channels from 2850 cm–1 and 1067 cm–1; (b) SRS spectrum of pure KNO3 on the LFP; (c) image of merged channels from 2850 cm–1 and 1639 cm–1; (b) SRS spectrum of benzoic acid.
23.4.质谱成像 -->
3.4.质谱成像
质谱技术可以更为精准地确定分子水平的化学组成信息[40,41]. 利用检测目标物离子化产生的指定质荷比化合物的离子密度图可以显现基于检测目标分子组成的指纹图像. 该技术有望在定性分析爆炸物、药品、人体代谢产物等痕量(微量)物质方面起到十分关键的作用. 例如, Tang等[41]通过在指纹上喷镀一层金纳米颗粒, 利用表面等离子共振和激光解吸/电离技术(laser desorption ionization mass spectrometry, LDI MS)获取基于不同脂肪酸成分的指纹图像. Cheng等[42]通过在指纹表面喷溅包覆银-金合金纳米颗粒, 利用表面辅助激光解吸/离子化质谱(surface-assisted laser desorption/ionization-mass spectrometry, SALDI-MS)获取手印组分信息(如脂肪酸)及基于去质子化脂肪酸的指纹图像信息. Hinners等[43]对指印进行银纳米颗粒喷溅, 利用基质辅助激光解吸电离质谱成像(matrix-assisted laser desorption/ionization mass spectrometry imaging, MALDI MSI)技术分析手印中的外源物质(如防晒霜、酒、食用油、柑橘类水果). Kaplan-Sandquist等[44,45]利用基质辅助激光解吸电离飞行时间质谱成像(matrix-assisted laser desorption/ionization time of flight mass spectrometry imaging, MALDI/TOF MSI), 分析指印中的药物、爆炸物成分. 遗留在铝包覆的载玻片的手印, 通过粉末刷显、${\text{α}}$-氰基-4-羟基肉桂酸喷雾处理(MALDI基质喷雾)等方法进行预处理, 然后采用MALDI/TOF MSI进行化学成分分析. 图5展示了经粉末刷显处理后利用MALDI/TOF MSI检出潜指纹中的伪麻黄碱以及指纹成像效果[45]. 图 5 利用MALDI/TOF MSI检出伪麻黄碱和指纹图像[45] (a)总离子流图像; (b)质荷比166的提取离子图; (c)总离子流和提取离子的叠加图; (d)标记区域质谱数据; 潜指纹经粉末刷显处理 Figure5. Pseudoephedrine residue detection and fingerprint imaging using MLDI/TOF MSI[45]: (a) Total ion current image; (b) extracted ion image for m/z 166; (c) superimposed image of TIC and extracted ion image; (d) the corresponding mass spectra of the highlighted areas. Fingerprints were developed with fingerprint powder.