Dunn Darrell S, Sridhar Narasi, Miller Michael A, Price Kendra T, Pabalan Roberto, Abrajano Teofilo A
Southwest Research Institute, 6220 Culebra Road, San Antonio, Texas 78238, USA.
Appl Spectrosc. 2007 Jan;61(1):25-31. doi: 10.1366/000370207779701424.
Raman spectroscopy has been identified as a potentially useful tool to collect evidence of past or present life on extraterrestrial bodies. However, it is limited by its inherently low signal strength. In this investigation, laboratory tests were conducted using surface-enhanced Raman spectroscopy (SERS) in an "inverted" mode to detect the presence of organic compounds that may be similar to possible biomarkers present on Mars. SERS was used to overcome the inherently low signal intensity of Raman spectroscopy and was an effective method for detecting small concentrations of organic compounds on a number of surfaces. For small organic molecules, dissolution of the molecule to be analyzed in a suitable solvent and depositing it on a prepared SERS substrate for analysis is possible. However, for larger molecules, an "inverted" SERS (iSERS) technique was shown to be effective. In iSERS, nanoparticles of silver or gold were deposited on the mineral substrate/organic compound to be analyzed. Benzotriazole, benzoic acid, and phthalic acid were used as test organic analogs and the iSERS technique was able to detect femtomole levels of the analytes. The interference from various mineral substrates was also examined. Different methods of depositing silver particles were evaluated, including ion beam-assisted vapor deposition and deposition from aqueous colloidal suspensions.
拉曼光谱已被确定为一种潜在有用的工具，可用于收集外星天体上过去或现在存在生命的证据。然而，它受到其固有的低信号强度的限制。在本研究中，使用表面增强拉曼光谱（SERS）以“倒置”模式进行实验室测试，以检测可能与火星上可能存在的生物标志物相似的有机化合物的存在。SERS被用于克服拉曼光谱固有的低信号强度，并且是检测多种表面上低浓度有机化合物的有效方法。对于小有机分子，可以将待分析的分子溶解在合适的溶剂中，并将其沉积在制备好的SERS基底上进行分析。然而，对于较大的分子，“倒置”SERS（iSERS）技术被证明是有效的。在iSERS中，银或金的纳米颗粒被沉积在待分析的矿物基底/有机化合物上。苯并三唑、苯甲酸和邻苯二甲酸被用作测试有机类似物，iSERS技术能够检测到飞摩尔水平的分析物。还研究了各种矿物基底的干扰。评估了沉积银颗粒的不同方法，包括离子束辅助气相沉积和从水性胶体悬浮液中沉积。
