This paper presents a low-cost, portable, and highly selective 3D-printed gas detector for sensing different volatile organic compounds (VOCs) and identifying their concentrations. A 3D-printed microfluidic platform is fabricated by integrating a chemoresistor into a microfluidic channel providing a powerful tool for analyzing the kinetic response of the device to the diffused gas along the channel. Here, the effects of different channel’s coating materials and dimensions on the diffusion-physisorption of gas molecules are studied based on the diagnostic power as well as the speed of the sensor recovery. This study is resulted in identifying an optimum channel coating and geometry, the combination of which provides high selectivity in differentiating a range of different VOCs as compared to previous microfluidic-based gas detectors. The proposed gas detector also shows a faster recovery time (150 s) compared to those obtained by systems presented in previous studies (10 min). A new feature extraction method is used to quantify the concentration of the analyte. The innovative sensing technology proposed here will advance the state-of-the-art gas analysis methods by providing real-time sensing with higher selectivity and drastically decreased recovery time.