The present invention relates to compositions and methods for detection and quantification of individual target molecules in biomolecular samples. In particular, the invention relates to improved, stable nanoreporter probes that are capable of binding to and identifying target molecules based on the probes' uniquely detectable signal. Methods for identifying target-specific sequences for inclusion in the probes are also provided, as are methods of making and using such probes. Polynucleotide sequences of certain nanoreporter components are also provided. The probes can be used in diagnostic, prognostic, quality control and screening applications.