Herein, for the first time, we introduce a new synthetic strategy for the synthesis of stable dual light emitting gold quantum cluster‐graphene quantum dot (AuQC@GQD) nanocomposite using a single protein, gluten as the raw material. Hydrothermal treatment of wheat gluten protein resulted in the development of a stable blue‐green emitting graphene quantum dot (GQD), which was further conjugated with gluten and used for the synthesis of gold quantum clusters (AuQC). Moreover, the gluten conjugated GQD acted as a reducing agent for the fast formation of red emitting AuQC. The resulted AuQC@GQD were characterized by various spectroscopic and microscopic techniques. We further explore the use of AuQC@GQD as a probe for ratiometric detection of mercury (Hg2+). The sensor exhibited a good linear relationship in the Hg2+ concentration range from 0.1 to 35.8 ppm with a detection limit of about 0.1 ppm. Moreover, AuQC@GQD were effectively incorporated into electrospun polyvinyl alcohol (PVA) nanofibers for visual colorimetric sensing. We have monitored the visual fluorescent response of AuQC@GQD‐PVA mat to Hg2+, and the observed change of color under UV irradiation indicates the utility of the AuQC@GQD‐PVA nanofibers for on‐site detection of Hg2+. In addition, the formed AuQC@GQD can able to produces white light emission at a particular composition of HAuCl4 and GQD under UV irradiation, which can further extend its applicability in the field of optoelectronics.