Photodynamic therapy (PDT) is a promising treatment for numerous kinds of cancer. A potential advantage of PDT compared to other cancer treatments like radiotherapy and chemotherapy is its selectivity. PDT is based on a photosensitive substance that is administered to a patient. The substance has selective uptake by cancerous tissue and when illuminated with a certain wavelength it destroys the tissue in close proximity. Metronomic PDT is a new proposed technique for treating patients with cancer. For this technique a new kind of light source is needed. The purpose of this thesis is to develop the light source needed for this technique. This light source also needs to monitor the treatment and should be controlled and powered from the outside. An optode chip has been developed which carries one or two LEDs used as light source and up to four photodiodes. The photodiodes were designed after Monte Carlo simulations to get an indication of the amount of incident light. The readout of the photodiodes consists of a transimpedance amplifier and an A/D converter. The LED is driven with pulse width modulation to adjust intensity. The communication is implemented with a Radio Frequency Identification technique. The power for the implant is provided by an inductive power link that was designed for low power dissipation in the coil. The power is buffered in a capacitor in case the coupling of the two coils is lost. It also allows the field to be switched off during measurement. The whole implant is controlled with a microcontroller, which has PWM and A/D conversion on chip. The several devices are soldered on a flexible printed circuit board. The flexible PCB was shaped in such a way that the coils for communication and power could be big enough to get a reasonable coupling and was designed for an animal model. The big part is placed on the shoulders of the rat, the optode is attached to the head of the rat. The electronic components are encapsulated with medical grade silicone. The optode chip is mounted with bond wires on the flexible circuit board and is encapsulated with a biocompatible polymer. The main function of the implant, illuminate a specific volume with a specific wavelength, was successfully implanted. The fluence rate monitoring and temperature monitoring were also successfully implemented. The monitoring of the amount of photosensitizer and oxygen was not implemented but experiments can be done with the current optode chip. The total system has been successfully tested outside the animal. The first animal test is planned in the near future. In the future the whole system needs to be developed further, the several discrete components on the implant need to be implemented on chip. A system with multiple optodes needs to be developed.