Strong infrared (IR) signals from metal nanoparticles-polyelectrolyte-germanium composites have been investigated in details using in situ attenuated total reflectance infrared (ATR-IR) spectroscopy and microscopy. Layer by layer method has been applied to build up the polyelectrolytes-nanoparticles multilayers. Different types of nanostructures have been synthesized and utilised to study the system in details. Strong IR signals from molecules, polyelectrolytes and water are observed when they are adsorbed on plasmonic metal nanoparticles surface. This enhancement depends on particles size, coverage and distance from particles surface. Strong signal originates from nanogaps. Furthermore enhancement has been found from the bottom of nanoparticles. Furthermore, a huge IR signal was observed from germanium-polyelectrolyte-metal nanoparticles composites upon visible light illumination. This IR signal is due to holes in the valence band of germanium semiconductor which reveals electron transfer from germanium to metal. This type of system can be applied as infrared modulator as well as for sensing.