Sviluppo di un modulo di rilevazione in CdTe per spettroscopia X ad alta energia

Golden nanoparticles (GNPs) have aroused considerable interest in biomedical applica-tions in recent years thanks to the remarkable potential offered in the field of cancer therapy. Biologists and tissue engineers have been able to develop 3D tumor models (tumoroids) through the use of engineered cellular tissues that mimic the microenviron-ment of a solid tumor mass and which offer the possibility to quantify and optimize the targeting efficiency of nanoparticles under controlled cellular conditions. In this context, there is a need for a non-destructive in vivo measurement of the gold na-noparticles concentration within the tumoroid to evaluate and determine the absorption of nanoparticles. Analysis techniques based on the measurement of the characteristic photons of gold (e.g. X-Ray Fluorescence XRF) can be advantageously employed in this field due to its sensitivity and specificity. One of the research lines is to focus on the de-tection of the gold L-lines (9-13keV). In this case a L-XRF detection system based on an SDD (Silicon Drift Detector) offers excellent performance in detecting gold concentra-tions located in shallow tumor sites of few millimeters, but is ineffective in the real case of gold concentrations located at higher depths due to the low X-ray energies. A more ambitious and effective approach is to detect the gold K-lines which are at higher energy (66-69keV). Cadmium Telluride detectors (CdTe) are a possible alternative to the most common HPGe detectors within K-XRF detection system. The potentialities in using a CdTe detector derive mainly from its greater detection efficiency at gold K-fluorescence emissions and the ability to operate at room temperature in a compact and lightweight apparatus. My thesis activity at the “Imaging Detectors and Low Noise Electronics Laboratory” at the Department of Electronics, Information and Bioengineering of the Politecnico di Mi-lano was then focused on the development of a custom CdTe detection module expressly designed for high energy X-ray spectroscopy of gold NPs. The following thesis consists of six chapters. The first chapter provides a general introduction of nanoparticles in biomedical applica-tions. Specifically, the potentialities offered in the visualization and therapy of tumor tis-sues and the main detection techniques are presented. In the second chapter, the use of CdTe detector inside a gold K-XRF spectroscopy sys-tem is analyzed. The typical properties of the semiconductor are then exposed and a comparison is made with silicon and germanium detector materials. The latter part of the chapter focuses on the performance optimization in terms of FWHM in energy and ENC (Equivalent Noise Charge) for several input transistors of the charge preamplifier. The third chapter deals with the various phases of design and development of the CdTe detection module. This chapter describes the considerations made during the design phase of the charge preamplifier and the Detector and Power boards. In addition, the de-sign of the outer mechanical box is shown and illustrated. The next chapter, the fourth, shows the results of the preliminary tests carried out on the high speed charge preamplifier and on the DC-DC high voltage output control electron-ics. Then the I-V characterization of the In-Schottky CdTe detector is reported. In the fifth chapter, the first spectroscopic measurements obtained in the laboratory with the radioactive sources of Am241, Fe55 and Ba133 are shown. The sixth and final chapter closes the thesis with the conclusions on the CdTe detection module and future perspectives.

L’attività di tesi da me svolta presso il laboratorio di Imaging Detectors and Low Noise Electronics Laboratory del Dipartimento di Elettronica, Informazione e Bioingegneria del Politecnico di Milano si è incentrata sullo sviluppo di un modulo di rivelazione spe-rimentale in CdTe per spettroscopia X ad alta energia. La seguente tesi consta di sei ca-pitoli. Nel primo capitolo viene offerta una descrizione generale delle nanoparticelle nell’ambito delle applicazioni biomediche. Nello specifico vengono presentate le potenzialità offerte nella visualizzazione e nella terapia di tessuti tumorali e le principali tecniche di rivelazione. Nel secondo capitolo viene analizzato l’utilizzo di un rivelatore in CdTe all’interno di un sistema di spettroscopia K-XRF dell’oro. Vengono quindi esposte le proprietà tipiche del semiconduttore e viene eseguito un confronto con i rivelatori in Silicio ed in Germanio. In chiusura del capitolo viene posta l’attenzione sulle prestazioni ottenibili in termini di FWHM e ENC per diversi transistori di ingresso del preamplificatore di carica. Il terzo capitolo tratta le varie fasi di progetto e di sviluppo del modulo di rivelazione in CdTe. In questo capitolo vengono descritte le considerazioni effettuate in fase di proget-to del preamplificatore di carica e delle schede di Detector Board e di Power Board. I-noltre viene esposto ed illustrato il disegno della scatola meccanica esterna. Nel capitolo successivo, il quarto, sono riportati i risultati dei test preliminari effettuati sul preamplificatore di carica a larga banda realizzato e sull’elettronica di controllo dell’uscita ad alta tensione del convertitore DC-DC. Viene poi riportata la caratterizza-zione I-V del rivelatore. Nel quinto capitolo vengono mostrate le prime misure spettroscopiche ottenute in labo-ratorio con le sorgenti radioattive di Am241, Fe55 e di Ba133. Il sesto e ultimo capitolo chiude la tesi con le conclusioni sul modulo di rivelazione rea-lizzato e le prospettive future.