This paper describes the use of plasmonics-based nanoprobes that act as molecular sentinels for DNA diagnostics. The plasmonics nanoprobe comprises a metal nanoparticle and a stem-loop DNA molecule tagged with a Raman label. The nanoprobe utilizes the specificity and selectivity of the DNA hairpin probe sequence to detect a specific target DNA sequence of interest. In the absence of target DNA, the stem-loop configuration maintains the Raman label in proximity to the metal nanoparticle, inducing an intense surface-enhanced Raman scattering (SERS) effect that produces a strong Raman signal upon laser excitation. Upon hybridization of a complementary target DNA sequence to the nanoprobe, the stem-loop configuration is disrupted, causing the Raman label to physically separate from the metal nanoparticle, thus quenching the SERS signal. The usefulness and potential application of the plasmonics nanoprobe for diagnosis is demonstrated using the gag gene sequence of the human immunodeficiency virus type 1 (HIV-1). We successfully demonstrated the specificity and selectivity of the plasmonics nanoprobes to detect PCR amplicons of the HIV gene. The potential for combining the spectral selectivity and high sensitivity of the SERS process with inherent molecular specificity of DNA hairpins to diagnose molecular target sequences in homogeneous solutions is discussed.