Surface functional groups on carbon dots (CDs) play a critical role in defining their photoluminescence properties and functionalities. A new kind of organosilane-functionalized CDs (OS-CDs) were formed by a low temperature (150°C) solvothermal synthesis of citric acid in N-(β-aminoethyl)-γ-aminopropylmethyl-dimethoxysilane (AEAPMS). Uniquely, the as-synthesized OS-CDs have dual long chain functional groups with both NH2 and Si(OCH3)3 as terminal moieties. Double sided anchoring of AEAPMS on CDs occurs, facilitated by the water produced (and confined at the interface between CDs and solvent) when citric acid condenses into the carbon core. The resultant OS-CDs are multi-solvent dispersible, and more significantly, they exhibit excellent selectivity and sensitivity to Hg(2+) with a linear detection range of 0-50nM and detection limit of 1.35nM. The sensitivity and selectivity to Hg(2+) is preserved in highly complex fluids with a detection limit of 1.7nM in spiked 1M NaCl solution and a detection limit of 50nM in municipal wastewater effluent. The results show that the OS-CDs synthesised by the solvothermal method in AEAPMS may be used as an effective Hg(2+) sensor in practical situations.