• blood pH sensor
• ECC
• fluorescence
• HPTS
• optical Sensor

Durante trattamenti in circolazione extracorporea (ECC), ottenere una misura precisa, sicura, in real-time e non invasiva del pH del sangue rappresenta ancora oggi una sfida tecnologica irrisolta. Questo lavoro di tesi è focalizzato sullo sviluppo e verifica sperimentale di un sensore ottico di pH sanguineo che rispetta questi requisiti. La misura si basa sull'analisi raziometrica del segnale di luce emesso dal fluoroforo HPTS a diretto contatto con il sangue. L'HPTS, quando eccitato a due precise lunghezze d'onda, risponde in maniera differenziata in funzione del pH. Il sistema di misura è in grado di stimare accuratamente il pH sia in PBS che su sangue bovino, con un’eccellente risposta dinamica e stabilità nel tempo elevata. Sulla base di test effettuati in PBS i parametri del sistema vengono ottimizzati rispetto al rapporto segnale rumore e stabilità nel tempo. Poiché il sensore mostra una non trascurabile dipendenza dalla temperatura, viene proposto un modello di correzione. Infine, viene indagata la possibilità di un miglioramento della sensibilità del sensore, modificando le regioni spettrali analizzate dal sistema.

The pH of human blood is physiologically bounded in the range 7.35 - 7.45 and even small modification of its value may be extremely harmful for the subject’s health. Extracorporeal circulation (ECC) treatments encompass a set of different medical procedures where blood is forced to circulate outside the patient’s body with high risks of pH variations due to physical or chemical contamination. At present, there is no device on the market capable of measuring the blood pH during ECC with a safe, reliable, non-invasive and real-time procedure. Hence, such device would realize a great improvement in the monitoring of patient health status during this type of highly invasive procedures. An innovative measuring instrument that could overcome current technical limitations was recently proposed and developed. The working principle of the sensing element is the pH-sensitive fluorescence emission of a fluorophore material (HPTS) deposited on a disposable cuvette and in contact with the blood flowing in the extracorporeal system. The pH is estimated through a ratiometric signal obtained from the ratio of the normalized fluorescence emitted signals at two different excitation wavelengths, namely of 465 and 405 nm. The pH around the physiological interval has a linear relation with the ratiometric signal. The interrogation system is an optoelectronic device that properly generates and acquires the optical signals through a NI Data Acquisition Board (DAQ) connected to a PC. This work is focused on a deeper characterization of sensor performances and investigation of its possible improvements. In order to reach these aims a wide database of tests executed with different boundary conditions has been considered and a wide range of experimental activities have been performed in ECC equivalent environment with PBS and in relevant condition with Bovine Blood. A specific analysis on the signal to noise ratio and the long-term photostability of the sensor in PBS was carried out. This analysis was used to optimize the adjustable parameters of the device in order to obtain a measure with estimation errors not exceeding the clinically significance level. The performance of the measuring system has been characterized also with respect to the dynamic response and the temperature dependence by processing the data acquired during bovine blood ECC. A model for the temperature compensation was proposed. The sensor was able to effectively measure the blood-pH for several hours with limited errors. The behavior of the emission upon excitation at 405 nm is different respect to PBS and with low pH sensitivity. Both in PBS and Blood environment the sensor exhibits excellent dynamic response, good accuracy and stability for tests in PBS long up to 24 hours. The proposed method for the temperature compensation was demonstrated to work efficiently in blood upon variations of its temperature up to 8°C. Moreover, different calibration solutions for the estimation of model parameters related to the disposable sensor were proposed. Besides, the robustness of the measurement against pH variations along acquisition lasting many hours were investigated. Finally, with the purpose of increasing the sensitivity of the sensor the optical head was modified with the substitution of the 405nm source with 375nm LED associated to a higher fluorescence emission.