LASER BASED 14C COUNTING FOR BIOMEDICAL STUDIES

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 碳14同位素标记在生物和医学研究、医学诊断以及药物发现和开发中被广泛使用。然而，检测放射性同位素的方法取决于对核衰变事件的检测，这是一个低效的过程，因为样品中每43.5亿个14C原子每分钟只有一个衰变事件，需要使用高水平的放射性。该项目的目的是展示一种适用于常规实验室使用的示踪剂14C的原子计数装置，将14C视为一种“稳定的”同位素，减少大多数实验所需的剂量，并使新的研究类别成为可能。LARA将从对13CO2的分析扩展到对14CO2的类似分析。仪器的灵敏度将比闪烁(衰变)检测的灵敏度大几个数量级，并将与典型的串联式加速器质谱仪(AMS)竞争，后者已证明对阿托摩尔水平的灵敏度为皮摩尔。这种增强的灵敏度对于低剂量和小样本示踪研究、长期代谢研究和药代动力学研究非常重要，并正在被研究为蛋白质测序和显微成像研究的一种可能工具。14CO2的LARA设备预计将比具有类似能力的AMS要小得多，复杂得多，成本也低得多。它将表明，在14CO2中以独特的红外跃迁工作的密封红外激光器可以常规地用于探测含有二氧化碳的样品池。样品将在低压放电中进行优化，以检测低噪声的光电流效应。这种系统可以用来定量测量少量富含14C的二氧化碳样品。丰富样品的测量结果将量化实现最终灵敏度所需的改进。将开发技术以在皮摩尔和阿托摩尔水平上实现更高的灵敏度。技术将包括降低噪声的电子和数字算法，增强信号的气体混合变化和量子电子(激光)增强。它的进一步目标是建造常规实验室使用的原型仪器，并将技术转移到生物医学研究设施。 去年的重大进展导致超过了设计目标，实现了10-15个数量级的14C/12C比值的灵敏度，样品大小为5-10微克总碳。从生物医学AMS研究资源获得的校准样本已用于这些研究。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The use of isotopic labeling with carbon 14 is widespread in biological and medical research, medical diagnostics and drug discovery and development. However, methods to detect radioisotopes depend on the detection of a nuclear decay event, an inefficient process as there is only 1 decay event per minute for every 4.35 billion atoms of 14C present in a sample,requiring the use of high levels of radioactivity. The aim of this project is to demonstrate a device, suitable for routine laboratory use, for atom counting of the tracer 14C, treating 14C as a "stable" isotope, decreasing the dosage required for most experiments and making new classes of studies possible. LARA will be extended from analysis of 13CO2 to similar analysis of 14CO2. Instrumentation will have sensitivity orders of magnitude greater than possible with scintillation (decay) detection and will compete with typical tandem accelerator mass spectrometers (AMS) that have demonstrated sensitivity at the picomole to the attomole level. The enhanced sensitivity is important for low dose and small sample tracer studies, long-term metabolic studies, pharmacokinetics studies and is being studied as a possible tool for protein sequencing and micro-imaging studies. A 14CO2 LARA device is projected to be considerably smaller, less complex and much lower in cost than an AMS with comparable capability. It will be shown that a sealed infrared laser operating at a unique infrared transition in 14CO2, can be routinely used to probe a sample cell containing carbon dioxide. The sample will be in a low pressure electrical discharge optimized for low noise detection of the optogalvanic effect. Such a system can be used to quantitatively measure small samples of 14C-enriched carbon dioxide. Results of the measurements with enriched samples will quantify improvements required to achieve ultimate sensitivity. Techniques will be developed to achieve enhanced sensitivity at the picomole to attomole level. Techniques will include electronic and digital algorithms to lower noise, gas mixture variations to enhance signal and quantum electronic (laser) enhancements. It is further aimed to build prototype instruments for routine laboratory use and transfer the technology to biomedical research facilities. Major progress in the last year led to exceeding design goals and achieving sensitivity of order 10-15 14C/12C ratio with sample size of order 5 to 10 micrograms total carbon . Calibration samples obtained from the Research Resource for Biomedical AMS have been used in these studies.