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Bismuthene, a two-dimensional nanostructured material derived from the environmentally friendly and nontoxic element bismuth, holds significant potential for sustainable electrocatalytic applications. However, the large-scale application of bismuthene is hindered by the absence of a high-throughput method for synthesizing solution-processable bismuthene nanosheets, which are essential for the straightforward and low-cost fabrication of bismuthene-based nanostructure devices. This study introduces a simple solvothermal method for synthesizing bismuthene nanosheets, using hexamethylenetetramine (HMTA) as a structure-directing agent and in situ-generated hydrogen (H₂) from the alkaline hydrolysis of NaBH4 as the reducing agent. The structural and electron transfer properties were characterized by using microscopic, spectroscopic, and electrochemical analyses. To demonstrate the electrocatalytic application potential, a bismuthene-modified screen-printed carbon nanotube electrode was fabricated as a nanosensor for the quantitative detection of heavy metal ions in contaminated water. The nanosensor exhibited a wide linear concentration range and low detection limits of 0.1 and 0.16 ppb (μg/L) for Cd and Pb, respectively. Additionally, the sensor was integrated with a microfluidic flow cell, demonstrating its applicability for the flow-through analysis of Cd and Pb ions. The nanosensor showed high selectivity for Cd and Pb ions in the presence of other metal ions with excellent repeatability and sensor-to-sensor reproducibility, evidenced by a relative standard deviation of 2% and 10%, respectively.