<p>In this paper, we designed, built, characterized and demonstrated a cost-effective diffuse optical tomographic (DOT) system for imaging absorbing and fluorescent targets and fluorescence alteration induced by temperature change in a scattering medium. DOT based imaging in a scattering media (such as biological tissue) is highly desired because of its high sensitivity and non-invasive nature. Unfortunately, conventional methods require expensive devices, such as lasers, optical switches, scientific cameras or photon detectors and advanced electronic controlling systems and data acquisition tools. To lower the cost and provide a simple system that can be used by researchers, teachers, and students who have a limited budget, we investigated and tested a method that uses light-emitting diodes (LEDs), a mobile phone-based camera, and a low-cost microcontroller (an Uno R3 board) to achieve the goal with reasonable accuracy. This method includes a hardware system, a software system for hardware controlling, data acquisition and processing, and an imaging reconstruction algorithm. By combining these subsystems, we demonstrated the feasibility of 3-dimensional imaging of absorbing and fluorescence targets and temperature change-induced fluorescence in a scattering medium using a temperature-sensitive fluorophore.</p>