Plasmonics-active nanoprobes are provided for detection of target biomolecules including nucleic acids, proteins, and small molecules. The nucleic acids that can be detected include RNA, DNA, mRNA, microRNA, and small nucleotide polymorphisms (SNPs). The nanoproprobes can be used in vito in sensitive detection methods for diagnosis of diseases and disorders including cancer. Multiplexing can be performed using the nanoprobes such that multiple targets can be detected simultaneously in a single sample. The methods of use of the nanoprobes include detection by a visible color change. The nanoprobes can be used in vivo for treatment of undesireable cells in a subject.