For the developement of bio-PIXE, two problems remain to be solved; one in accelerator availability and the other in data analysis. To improve the former, a method of applying baby cyclotrons to PIXE has been developed. To solve the latter, the computer program SAPIX for x-ray spectrum analysis ,which runs on ordinary personal computers and is fairly easy to operate has been developed. Examples of spectral fitting by the SAPIX and a description of the program are given. Further, the two-detector measuring system which we have employed for the simultaneous determination of all elements is reported.
Carbon nanotubes (CNTs) are promising materials for use in amperometric biosensors. The defect sites at their ends, and on their sidewalls, are considered to be edge plane-like defects and show high electrocatalytic activity toward several biological molecules. However, electrocatalytic activity toward H(2)O(2) has not been compared among bamboo-structured CNTs (BCNTs), which have many defect sites; hollow-structured CNTs (HCNTs), which have few defect sites; edge plane pyrolytic graphite (EPG); and traditional glassy carbon (GC). The advantages of using CNTs in electrodes for biosensors are still equivocal. To confirm the utility of CNTs, we analyzed the electrochemical performance of these four carbon electrodes. The slope of the calibration curve for H(2)O(2) at potentials of both +0.6 V and -0.1 V obtained with a BCNT paste electrode (BCNTPE) was more than 10 times greater than the slopes obtained with an HCNT paste electrode and a GC electrode, reflecting the BCNT's larger number of defect sites. Although the slope with the EPG electrode (EPGE) was about 40 times greater than that with BCNTPE at +0.6 V, the slopes with these two carbon electrodes were nearly equivalent at -0.1 V. EPGE demonstrated excessive electrochemical activity, detecting currents on the basis of consumption of oxygen and oxidation of ascorbic acid, even at -0.1 V. In contrast, BCNTPE could dominantly detect a cathodic current for H(2)O(2) at -0.1 V, even when interfering molecules were added. BCNTPE possesses appropriate electrochemical activity and is an effective electrode materials for developing interference-free oxidase-based biosensors operated by the application of an appropriate potential.
A new PIXE facility combined with a small cyclotron (alias Baby Cyclotron) established exclusively for medical use is described. Sufficient amount of 2.9-MeV protons can be extracted from the cyclotron by accelerating H2+-ions with acceleration parameters for 8.3-MeV deuterons. Some technical problems for applying the cyclotron to PIXE analysis, such as elimination of deuteron contamination from proton beams and radiation shielding of the PIXE room during radioisotope production in the cyclotron vault, are reported.
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