LASER BASED 14C COUNTING FOR BIOMEDICAL STUDIES

该子项目是利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得主要资金， 因此可以在其他CRISP条目中表示。列出的机构是 中心，不一定是研究者的机构。 碳14同位素标记广泛应用于生物学和医学研究、医学诊断以及药物发现和开发。然而，检测放射性同位素的方法依赖于核衰变事件的检测，这是一个效率低下的过程，因为对于样品中存在的每43.5亿个14 C原子，每分钟只有一个衰变事件，需要使用高水平的放射性。 该项目的目的是演示一种适合于实验室日常使用的装置，用于示踪剂14 C的原子计数，将14 C作为“稳定”同位素处理，减少大多数实验所需的剂量，并使新类别的研究成为可能。LARA将从13 CO2的分析扩展到14 CO2的类似分析。仪器的灵敏度将比闪烁（衰变）检测的灵敏度高出几个数量级，并将与典型的串联加速器质谱仪（AMS）竞争，后者已证明灵敏度在皮摩尔到阿托摩尔水平。增强的灵敏度对于低剂量和小样本示踪剂研究、长期代谢研究、药代动力学研究是重要的，并且正在作为蛋白质测序和显微成像研究的可能工具进行研究。预计14 CO2 LARA装置将比具有类似能力的AMS装置小得多，不那么复杂，成本也低得多。它将表明，密封的红外激光器在14 CO2中的独特的红外转换操作，可以常规地用于探测含有二氧化碳的样品池。样品将处于低压放电中，该低压放电针对光电流效应的低噪声检测进行了优化。这种系统可用于定量测量富含14 C的二氧化碳的小样品。富集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，以提高皮摩尔至阿托摩尔水平的灵敏度。技术将包括电子和数字算法，以降低噪音，气体混合物的变化，以提高信号和量子电子（激光）的增强。该项目的另一个目标是建立实验室日常使用的原型仪器，并将技术转让给生物医学研究设施。 去年取得的重大进展超过了设计目标，实现了10-15级14 C/12 C比的灵敏度，样品量为5至10微克总碳。 这些研究中使用了从生物医学AMS研究资源获得的校准样品。

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.