The main sensors being explored for integration on the IMPACT chip are ISFET and Clark sensors for detection of pH and oxygen concentration.
Clark Oxygen sensor
The Clark sensor is a commonly used method of measuring oxygen and is therefore a candidate sensor for integration on the IMPACT chip. The Clark sensor works using an oxygen permeable membrane, which shields an electrode and small chamber of electrolyte. The oxygen diffuses through the membrane and reduces on the electrode surface, allowing oxygen levels to be measured. One of the challenges for the IMPACT project is to miniaturise and integrate this sensor onto the chip.
ISFET-based pH/O2 Sensors
The Ion Sensitive Field Effect Transistor (ISFET) is a chemical sensor which an also be used to measure pH. It can be made using the same design as a standard MOSFET. The ISFET can be made using standard industry fabrication process and is hence ideally suited for incorporation onto the IMPACT chip.
The ISFET can also become an oxygen sensor by placing oxygen transducing electrodes near the pH sensitive layer.
To enable the ISFET to be integrated with instrumentation, a CMOS compatible fabrication process is required. This takes advantage of the metallisation layers available in the standard CMOS process to bring the gate connection up to the surface of the integrated circuit.
Insulating the chip
Deploying on-chip sensors in the body requires the chip to be protected, while not interfering with the operation of the chip and its embedded sensors.
Hence, the IMPACT project is developing encapsulation which will prevent the system coming into contact with the body, except where required at the designated sensing areas. In order to minimise the final chip dimensions, this encapsulation must be both thin and robust in order to function as a stable barrier within the tumour environment over the course of the treatment. Clearly, this coating must also be biocompatible and minimise the effect of biofouling.
Data and Signal Processing
The data and signal processing strand of IMPACT is focused on the analysis of signals measured by the implantable chip system to help monitor the tumour and thus adapt cancer treatment to the individual patient.
The aim of IMPACT is to "personalise" the delivery of radiotherapy and to monitor its effect. To meet this objective IMPACT will deliver a platform consisting of a miniaturised and wireless implantable system that monitors and interprets biomarkers that are associated directly with cancer progression and cancer cell death (apoptosis) to optimise cancer treatment.
The platform developed will embed sensors monitoring different physiological parameters such as tissue acidity, hypoxia level (reduced supply in oxygen) and protease activity (using electrochemical biosensors). This strand of the project aims to translate the electrical signals produced by the chip into parameters (pH, oxygen concentration …) whose values and variations provide information about the local state of the tumour and the efficiency of the treatment.
By analysing how these key parameters interact and vary within the tumorous region and evolve during the treatment, we will be able to interpret the measured signals from which useful information will be extracted. As a consequence, this project will provide powerful tools enabling the patient treatment to be assessed and adapted if required (i.e. number and frequency of radiotherapy fractions) and thus improve patient outcome.