Manufacturing, designing and developing economic but highly efficient bifunctional catalysts for water splitting technology have become necessary for the large-scale commercialization of regenerative fuel cells. In this work, for the first time, uniformly sized molybdenum/tungsten diselenide and cadmium disulfide nanohybrid quantum dots (MoSe₂:CdS and WSe₂:CdS NHDs) have been synthesized by a simple hydrothermal technique. The highly exfoliated and defect-abundant nanostructure possess abundant active sites and therefore shows bifunctional behavior with high catalytic activity towards the oxygen reduction/evolution reactions (ORR/OER). The WSe₂:CdS NHDs exhibit a small onset potential of +1.1 V vs. RHE and −0.26 V with a small Tafel slope of 49 mV dec⁻¹ and 27 mV dec⁻¹ for OER and ORR, respectively. Moreover, having a quantum sized structure along with CdS also made the NHDs a promising and biocompatible fluorescent probe for metal ion (Pb²⁺) analysis. The PL emission from NHDs is of high energy and is more intense than the bare NDs, with a very good quantum yield of 87%. The prepared NHDs show a highly stable fluorescence and NHDs coated paper strips were successfully implemented for trace level (20.0 μg L⁻¹) analysis of Pb²⁺ in real samples (human blood, urine, and polluted water). However, the NHDs were also employed for ultra-trace level (500.0 ng L⁻¹) detection of Pb²⁺, which confirm the highly selective, sensitive and multi-functional behavior of the prepared NHDs. Therefore, it is envisaged that this work may provide a simple route to synthesize multi-talented 2D layered nanodots suitabile for imaging, sensing, and other energy-related technologies.