Study on SERS substrate preparation of rice flower type silver/titanium nitride thin films and detection of Rhodamine 6G

Objective Rhodamine 6G (R6G), also known as Rose Red 6G, is a fluorescent dye with water solubility and is often used in optics, laser optics, dyes and other fields. It is very toxic to humans, and there is a risk of cancer from long-term exposure or use of rhodamine, so it is included in illegal additives. However, due to its low price and good coloring properties, it is often used by unscrupulous businessmen in textiles, medicine, food, etc. The current methods for detecting rhodamine are mainly high performance liquid chromatography and liquid chromatography-tandem mass spectrometry. However, the operation process is tedious and the cost is high. Therefore, it is necessary to design a new method for the rapid detection of rhodamine 6G.

Methods The performance of the substrate and the minimum detection limit of rhodamine 6G were investigated. The finite element method was used to simulate the milky substrate, and a milky silver/titanium nitride composite SERS substrate was designed and Raman detected for rhodamine 6G using electrochemical deposition method.

Results and Discussions  In order to obtain the SERS enhancement effect of silver nanosubstrates with different morphological rice flower type structures and thus optimize the SERS substrate design, the electric field intensity simulation experiments were performed by the finite element method to simulate the changes of field intensity under different central sphere radius r, rice flower petal axes a, b, c, and central sphere and petal spacing d. The SERS enhancement factor was calculated. Subsequently, the substrates were prepared by electrochemical deposition and the effects of voltage value and the concentration ratios of trisodium citrate and AgNO₃ on the substrate structure and properties were investigated, so as to prepare the rice flower type silver/titanium nitride thin film substrate with the closest morphology to the idealized physical model. It was then used for trace detection of rhodamine 6G (R6G) to investigate the Raman enhancement effect of this substrate as well as its stability. The experimental results show that the obtained rice flower type TiN-Ag composite SERS substrate is closest to the idealized model simulation morphology when the deposition voltage is 2 V and the concentration ratio of trisodium citrate to AgNO₃ is 1∶1. The optimal enhancement factor of this substrate was calculated to be 10¹⁵, and the detection limit of rhodamine 6G was up to 10⁻¹³ mol/L.

Conclusions Based on the finite element method simulation, the field strength of the rice flower structure substrate was compared under the conditions of different radius of the central sphere, rice flower petal axis and spacing between the central sphere and petal, and the best enhancement factor of the rice flower silver/titanium nitride thin film substrate was obtained as 10¹⁵. The rice flower TiN-Ag composite SERS substrate was obtained with the closest morphology to the rationalization model simulation and the lowest detection concentration of rhodamine 6G of 10⁻¹³ mol/L by comparative experiments when the deposition voltage was 2 V and the concentration ratio of AgNO₃ was 1∶1.