Multiple biomarker detection is crucial for early clinical diagnosis, and it is significant to achieve the simultaneous detection of multiple biomarkers with the same nanomaterial. In this work, the hairpin DNA strands were selectively modified on the surface of gold nanorods (AuNRs) to construct two kinds of nanoprobes by rational design. When in the presence of dual microRNAs, AuNRs were assembled to form end-to-end (ETE) and side-by-side (SBS) dimers. Compared with a single AuNR, the dark-field scattering intensity and red color percentage variation of dimers were extremely distinguished, which could be developed for dual microRNA detection by combining the red color percentage and scattering intensity with the data processing method of principal component analysis to construct a two-dimensional analysis method. Especially, the fraction of AuNR dimers presented a linear relationship with the amount of microRNAs. Based on this, microRNA-21 and microRNA Let-7a in breast cancer cells were detected with the detection limits of 1.72 and 0.53 fM, respectively. This method not only achieved the sensitive detection of dual microRNAs in human serum but also realized the high-resolution intracellular imaging, which developed a new way for the oriented assembly of nanomaterials and biological detection in living cells.

Ascorbic acid (AA) has been widely used to improve human health since it was first found, such as resisting scurvy, enhancing immunity, and preventing arteriosclerosis. Moreover, it plays a very important role in the anti-oxidation process in the human body. Therefore, it is of great significance to develop sensitive and accurate detection methods. In this work, silver-coated gold nanorods (Au@Ag NRs) acted as the optical probe, which could be etched with hydroxyl radicals (·OH) from the Fenton reaction between H2O2 and Fe2+, leading to the blue shift of longitudinal localized surface plasmon resonance absorption. However, as a free radical scavenger, AA was able to inhibit the Fenton reaction, resulting in a red shift of plasmon resonance absorption. Based on the change in longitudinal plasma resonance absorption of silver-coated gold nanorods, a linear relationship between the maximum longitudinal absorption wavelength and the concentration of AA was established in the range of 2.5–17.5 μM with a limit of detection (LOD) of 0.48 μM and a limit of quantitation (LOQ) of 1.61 μM, which was feasible to detect AA in tablets.

Anisotropic nanomaterials, such as gold nanorods (AuNRs), could be employed as an orientation platform due to their polarization-dependent surface plasmon resonance. However, a variety of factors would affect the dark-field light scattering imaging of anisotropic nanomaterials, resulting in an unstable signal, which is not advantageous to its further application. In this work, the localized surface plasmon resonance properties of a few AuNRs at different angles were excited by polarization with a conventional dark-field microscope, in which it was found that the ratio of AuNRs’ light scattering intensity at different polarization angles (I) to that without a polarizer (I 0) reflected the orientation information of AuNRs. Furthermore, the light scattering signal ratio between the parallel polarization (I p) and that without a polarizer (I 0) was closely related with the aspect ratio of AuNRs, which could not be affected by external conditions. To verify this concept, a highly sensitive and selective assay of the alkaline phosphatase activity in human serum was successfully developed based on the chemical etching of AuNRs, resulting in a lower aspect ratio and a lesser I p/I 0. This result holds great promise for polarization-dependent colorimetric nanomaterials and single-particle tracers in living cells.