An open-source, low noise, low cost, and tunable transimpedance amplifier is presented. The compact circuit board requires few parts and costs less than $65 USD. The transimpedance amplifier is intended for low-light detection and operation with commercial photomultiplier tubes (PMTs). It provides a much more cost-effective acquisition tool compared to competitive products on the market. The system can easily be assembled and modified to suit specific current sensing applications. The amplifier features two variable gains and an adjustable DC offset to optimize dynamic range and suppress potential bias in the signal. With a target bandwidth of DC to 2 Hz and fourth-order Sallen-Key cutoff, the design is ideally suited for various applications in the field of analytical chemistry and biology, such as laser-induced fluorescence detection or chemiluminescence measurements.