This work is aimed at development of highly sensitive silicon (Si)-based sensors allowing for selective detection and analysis of liquid solution composition containing ammonia (NH3) and hydrochloric acid (HCl) in an indirect manner. To provide enhanced sensitivity, we use Si nanowires obtained with cryogenic plasma etching with high aspect ratio providing large adsorption surface area. The nanowires are placed on a contact platform and electrochemical impedance spectroscopy (EIS) is used to detect the analytes. For optimization of the sensor performance we develop three types of the sensor based on as-fabricated Si nanowires, nanowires treated with hydrofluoric acid (HF) and nanowires decorated with silver (Ag) NPs.