Self-assembly of gold nanoparticles by chitosan for improved epinephrine detection using a portable surface enhanced Raman scattering device.

Surface enhanced Raman scattering (SERS) has become widely used for identification, quantification and providing structural information about molecular structure in low concentrations as it allows signal Raman enhancement using metallic nanoparticles (NPs). Controlling interaction between analyte and NPs is a major point for the optimization of signal exaltation in SERS analysis. The objective of this study is the improvement and the control of SERS analysis by aggregation/self-assembly optimization of AuNPs using quaternized chitosan. The interest of this approach is to allow stable and reliable measurements with a simple and low cost approach compatible with a massive use in the field. In this work, we used design of experiments by Box-Behnken design to fix optimized conditions to increase signal sensibility of epinephrine water solutions. We also tested SERS signal stability in isotonic sodium chloride 0.9% and glucose 5% matrices. Our results demonstrate that globally neutral AuNPs aggregates were stabilized at a nanometric size by the subsequent addition of polyelectrolyte chains and allows for significant Raman signal enhancement of epinephrine. We succeed to prepare the SERS active material and measure a stable signal of epinephrine at a concentration as down as 0.1 μg mL in less than 5 min. The signal remained stable and exploitable for at least 2 h. Our results reveal a strong correlation between intensity and logarithm of the concentration (concentration before dilution from 0.1 to 10 μg mL) suggesting a possible quantification. Furthermore, the signal of epinephrine at 10 μg mL were also exploitable and stable in complex media as isotonic sodium chloride 0.9% and glucose 5%. This represents a particularly interesting application that would allow direct analysis of drugs complex media and open the way to analysis in biological samples.