We report a surprising discovery that Prussian blue (PB) can be employed as a highly sensitive and background-free resonant Raman reporter. Conventional Raman reporters show multiple spectral bands in the fingerprint region, which are generally overlapped with those from dominant endogenous biomolecules, and are thus difficult to be separated. Herein, we found that PB only possesses a strong and sharp single-band in the cellular Raman-silent region, where no Raman signals from biological species were observed. Therefore, the Raman spectra from PB and endogenous biomolecules are completely resolved without resorting to complicated spectral unmixing. Moreover, PB holds a strong UV-vis absorption band between 500 and 900 nm, which is resonant with the incident detection lasers, providing extremely high sensitivity. Through assembly of PB onto plasmonic cores, a new surface-enhanced resonance Raman scattering (SERRS) probe was achieved with a high signal-to-background ratio (SBR). We demonstrated the performance of the PB-based SERRS tags for high-sensitivity immunoassay and cancer cell imaging.

Single-molecule detection using surface-enhanced Raman spectroscopy (SERS) has attracted increasing attention in chemical and biomedical analysis. However, it remains a major challenge to probe single biomolecules by means of SERS hot spots owing to the small volume of hot spots and their random distribution on substrates. We here report an in situ hot-spot assembly method as a general strategy for probing single biomolecules. As a proof-of-concept, this proposed strategy was successfully used for the detection of single microRNA-21 (miRNA-21, a potential cancer biomarker) at the single-cell level, showing great capability in differentiating the expression of miRNA-21 in single cancer cells from normal cells. This approach was further extended to single-protein detection. The versatility of the strategy opens an exciting avenue for single-molecule detection of biomarkers of interest and thus holds great promise in a variety of biological and biomedical applications.

An interference-free surface-enhanced Raman scattering tag is constructed to profile the expression of cancer biomarkers at the single-cell level. The Raman tags present a strong and sharp peak in the cellular Raman-silent region, significantly diminishing the background interference. Moreover, the reporters are embedded in the layered gold nanoparticles, avoiding desorption and enzymatic degradation in physiological conditions.

In article number 1603340, by Dingbin Liu and co‐workers, an interference‐free surface‐enhanced Raman scattering tag is constructed to profile the expression of cancer biomarkers at the single‐cell level. The Raman tags present a strong and sharp peak in the cellular Raman‐silent region, significantly diminishing the background interference. Moreover, the reporters are embedded in layered gold nanoparticles, avoiding desorption and enzymatic degradation in physiological conditions.