Development of microfluidic analytical device for detection of sulfur-containing compounds using raman spectroscopy

Abstract

In this work, microfluidic systems coupled with Raman detection for analytical applications were developed using both off-chip and on-chip synthesized nanoporous Ag microstructures (np-AgMSs) as SERS substrates. Off-chip synthesized np-AgMSs were used as on-chip SERS substrates for determination of glutathione (GSH) using a reversed reporting technique. The np-AgMSs were drop casted onto the cross channel of a microfluidic device. R6G (a Raman reporter) interacted with the embedded np-AgMSs in the microchannel to form R6G-np-AgMSs which provided high SERS signal. Then, R6G in the R6G-np-AgMSs complex was replaced by GSH, causing the decrease in SERS signal which was related to the GSH concentration. A linear range of the method for determination of GSH was found to be 10-8-10-3 M with R2 = 0.9760 and the lowest of calibration curve was 10-8 M. The embedded np-AgMSs could be reused up to 3 cycles by chemical regeneration using NaBH4. In addition, np-AgMSs were also on-chip synthesized using Cl- induced precipitation of a silver ammine complex ([Ag(NH3)2]+) to form AgCl templates and followed with chemical reduction. By simply changing input reactant flow rates, four different structures of fabricated AgCl templates, including cubic, tetrahedron, tripod and tetrapod, were observed. The obtained AgCl templates were subsequently chemically reduced to form np-AgMSs. NaBH4 was found to be the best reducing agent to reduce AgCl templates because it retained the structure of the parent AgCl templates. SEM results showed that the interconnected grain size of np-AgMSs was in the range of 40-65 nm. Tetrapod np-AgMSs which provided the highest SERS signal were chosen as SERS substrates for on-chip quantitative determination of SCN-. A linear range of this approach for determination of SCN- was in the range of 1-20 µM with R2 = 0.9887. Calculated LOD and LOQ were 0.10 and 1.5 µM, respectively. For accuracy study, %recovery of spiked SCN- standard solutions was found to be in the range of 90-110%. In addition, %RSD of SERS signal for the detection of KSCN in saliva was less than 9% for both intraday and interday measurements. The developed SERS-microfluidic method for the determination of SCN- was found to be high accuracy and precision.