Trinitarian quantitative analysis of the continuous organic phase and built-in tags as internal standards for two-liquid interfacial surface-enhanced Raman spectroscopy

The reported IS mainly includes discrete surface-modified tags and isolated core-shell built-in tags, and our group previously proposed continuous phase organic solvents as the inherent IS. These different kinds of IS may generate different quantitative accuracies for SERS analysis but their comparison has not yet been determined, and it is a fundamental question that should be addressed but has long been ignored. Herein we determined the capability of the above three kinds of IS through trinitarian quantitation of two-liquid interfacial SERS signals by means of assembling three-dimensional liquid-like plasmonic arrays. Interestingly, no absolute advantage or disadvantage for each IS is observed, but it depends on the liquid phase that the analyte dissolves in. The signals from each IS all indicated superior stability, even under harsh conditions. The IS attached to the surface of the nanoparticles can sense the fluctuation of the microenvironment well, and shows superior ability in quantifying high-flow analytes, such as the quantitative analysis of biphasic-soluble molecule R6G. The organic solvent serves as the inherent IS of the liquid-liquid interface (LLI), avoiding the complicated procedure of introducing additional ISs, and is suitable for the quantitative analysis of water-soluble molecule MB. The target analyte TBZ which dissolved in the organic phase produces a stable signal itself without the need for additional ISs. This study provides a better understanding for ensuring the accuracy of quantitative detection of analytes under different solution conditions.