A new sensitivity organic vertical nano-junctions (VNJ) sensor for ammonia detection and its readout system are presented in this study. The designed ammonia sensor, VNJP3HT diode, is a simple structure with real-time response, high reproducibility and low-cost sensor. Along with the designed sensor, a precision and robust readout circuit is designed and successfully implemented as the proposed chip in this study. To utilize for a novel organic bio-chip, a particular readout system is presented that can acquire signal, compute and display concentration values of ammonia without using microcontroller. The chip is fabricated by the TSMC 0.18-μm 1P6M 3.3V mixedsignal CMOS process technique for verification. Experiment results show that the average resolution is 70.48mV/log(ppm) in a short transient time response, 50 seconds, as compared to prior study, 200 seconds. Error rate, average noise and detection rate reliability are 2.86%, 123 μVrms, and 99.6%, respectively. This chip could be suitable for application in cars, cell phones, watches, etc.