Frequency domain fNIRS is a tissue optical measurement technique used to measure absolute haemoglobin concentrations in brain tissue. This work is intended to be the first step in the development of a wearable, low-cost FD-fNIRS device for neurofeedback applications. The system requirements were generated from a review of relevant literature. A simplified system architecture was developed based on the various instrumentation methodologies proposed by various authors. The functional blocks of this system were prototyped and their performance was evaluated. The developed VCSEL current source was found to have a span of 10uA which meets the design specifications. However, challenges exist in optimally biasing SiPM, which is susceptible to optical and electronic noise sources.