Quantification of trace chemicals in unknown complex systems by SERS.

The chemical quantitative analysis at trace level has been widely explored by means of various techniques. While it still remains challenging to achieve ultrasensitive but facile, rapid, and inexpensive detection methods. In this paper, the possibility of employing surface-enhanced Raman scattering technique on a portable Raman system for rapid and accurate quantitative analysis of target chemicals in unknown systems was investigated. This detection approach contains 3 steps: (1) adding target chemicals with different amount to the initial unknown solution, leading to new solutions with target molecules of various concentrations; (2) Obtaining different samples' SERS spectra and capturing featured SERS peaks whose intensity grew up with the addition of target chemicals; (3) examining the relationship between featured peak intensity increment after adding target chemicals and its corresponding addition amount, and thus we could perform quantitative analysis of the chemical in an unknown solution and obtain its initial concentration. The validity of this method was systematically demonstrated by estimating the concentrations of 2-Naphthalenethiol (2-NaT) and 4-Mercaptopyridine (4-MPY) both in their single-component solutions and binary solutions, respectively. Predictions are close to their real values. Furthermore, we successfully predicted the concentrations of malachite green (MG) in fish water and benzidine in ground water. This study clearly demonstrates an accurate and facile approach to calculate the concentration of target chemicals in unknown systems, which fully exploit the potential of SERS quantitative analysis.