Optical sensing devices based on heterojunction structures are gaining a lot of attention due to their promising applications in various sectors. Therefore, this study presents a highly efficient infrared (IR) optical sensor based on a TiO2/RGO/SiNWs heterojunction structure on a silicon chip. Silicon nanowires (SiNWs) were synthesized using the metal-assisted chemical etching (MACE) method, while reduced graphene oxide (RGO) nanosheets were prepared via chemical vapor deposition (CVD) technique. The resulting heterojunction structure exhibited strong light absorption (>90%) due to the surface plasmon resonance effect, leading to significant charge carrier generation. The junction is capable to separate out the charge carriers, generating a photovoltage of approximately ~ 100 mV and a photocurrent of ~ 40 μA, thereby resulting in a highly efficient self-biased IR sensor operable under ambient room conditions. The sensor demonstrated excellent performance (an approximately 47% change in resistance), including a high responsivity of ~ 17 mA/W, detectivity of 2.3 × 1010 Jones, and fast response and recovery times of 0.3 s and 0.35 s, respectively. Additionally, the device showed stable operation over multiple ON/OFF cycles, confirming its reliability. These findings indicate that the developed heterojunction-based IR sensor is a promising, low-cost, consistent, and self-powered solution for advanced optical sensing applications.