Laser-based radiocarbon detection in the laboratory: How soon?

Research over the past 25 years and the use of accelerator mass spectrometry (AMS) have demonstrated benefits of single-atom counting of ¹⁴ C compared with scintillation monitoring of ¹⁴ C radioactive decay for a multitude of applications in drug development studies. These include pharmacokinetics and metabolism studies, microdosing studies, and quantification of DNA adducts. In the last decade, the possibility of single-atom counting using lasers has been demonstrated, providing the possibility of simplified laboratory-based systems, which can equal or excel AMS sensitivity and provide scintillation system convenience without high levels of radioactivity. To achieve the required sensitivity, optical storage cavities have been used to enhance the laser interaction of the low densities of radiocarbon present. Two types of laser technologies have been used-cavity ring-down spectroscopy (CRDS) and intracavity opto-galvanic spectroscopy (ICOGS). Problems to be overcome to achieve routine use have included separation of the ¹⁴ C signal from backgrounds, achievement of acceptable precision and accuracy, reduction of measurement times for small samples, and improvement in the ease of use for the operator. Both technologies have achieved impressive results to date using samples of order 1 mg with CRDS and 10 μg with ICOGS. Commercial development is the next step.