Real time β-imaging with silicon hybrid pixel detectors: kinetic measurements with C-14 amino acids and P-32 nucleotides

We present some additional results obtained with the BETAview system, a digital system for real time β-imaging based on semiconductor pixel detectors and on a single photon counting read-out chip. We describe the system assembled with a Si detector, 300-μm thick, segmented into 64 ×64 square pixels with 170-μm pitch. The solid-state pixel array detector is bump-bonded pixel by pixel to a low threshold, single particle counting electronics, the photon counting chip (PCC) developed by the Medipix1 Collaboration for biomedical applications. Each cell (corresponding to a detector pixel) of the front-end chip has a maximum count rate of 2 MHz, a minimum nominal threshold of 1400 e^- (corresponding about 5 keV in Si), and contains a 15-bit counter. The detector sensitive area is about 1 cm², but several detectors could be assembled in arrays. The measured background counts were about 3.5×10^-2 cps/cm², which implies a very high sensitivity of the device. The detection threshold used in this experiment was ∼15 keV. We show the results obtained in the real-time monitoring of two biological dynamic processes: an amino acid uptake by living cells and the thermal denaturation process of oligonucleotides. Specifically, we have followed over time the accumulation of a marked amino acid ([¹⁴C]L-Leucine) into Octopus vulgaris eggs cells. The results, described in Section III-B, show that after about 20 min from the beginning of the uptake process, the radioactively marked eggs become clearly visible over the background culture radioactive medium. In Sections III-C and III-D, we also describe the successful performance of the β-imaging system in genetic studies involving the real time reconstruction of denaturation and kinetics curves for two different ³²P-radiolabeled nucleotides.