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Nerve agents such as VX, Tabun (GA), and Cyclosarin (GF) are lethal even in trace amounts. Their lethality in addition to being difficult to detect makes nerve agents a significant global security problem. To address this problem, surface-enhanced Raman spectroscopy (SERS) has in recent years shown to be a promising technique for rapid and non-destructive field detection of various harmful substances. However, the application of SERS to nerve agents has so far been limited by their inherently poor Raman scattering cross-section, with nerve agents such as GF being particularly difficult to detect. In this work, we present a novel custom-designed Raman probe molecule: 4-Thiophene Pyridine Amido Oxime (TPAO), which enables selective detection and discrimination of live nerve agents in liquid media at trace concentrations, even using portable Raman instruments with limited spectral resolution. We report a detection limit for GF downward 1 ppm, much lower than that found in previous studies. We further find that TPAO allows us to detect VX and GA at 1.1 and 2.1 ppm, respectively, in line with or slightly surpassing previous benchmarks. To demonstrate the specificity with which TPAO can be used to sense and discriminate between nerve agents, we use principal component analysis to quantify spectral differences between nerve agents and simulants. Lastly, we show the robustness of TPAO, demonstrating its ability to detect nerve agents in complex backgrounds and after rinsing procedures. Altogether, this work represents a significant step forward towards achieving rapid and selective field detection of live nerve agents using SERS.