We demonstrate an ultracompact integrated silicon-based plasmonic sensor for lab-on-chip applications in the mid-infrared (MIR) spectral range. Our sensor possesses desirable features such as design simplicity and very high sensitivity. The sensor is designed using a platform for plasmonic effects in the MIR using highly doped silicon. This platform is exploited to create a metal-less plasmonic slot waveguide in the MIR range. This plasmonic waveguide is highly sensitive to any environmental change. Full wave electromagnetic simulations were carried out to design and optimize the structure. The proposed sensor covers a large wavelength span in the MIR range. High spectral sensitivity of 5000 nm/RIU was achieved for our sensor device. Further development of the structure was conducted to extend the sensor operation to multigas sensing.