High-throughput HPLC-SERS capable of generating a spectrum from individual eluent droplets based on a superhydrophobic SERS array.

We have developed a protocol for a high-throughput high-performance liquid chromatography-surface enhanced Raman spectroscopy (HPLC-SERS), whereby a 15 μL eluent droplet was captured every second and a series of SERS spectra was obtained to show a time course in the chemical composition within the eluent. To accomplish this, we prepared arrays of SERS spots based on metal film on nanosphere (MFON). Fifty of these spots 3 mm in diameter were formed in a 5 by 10 array format on a special glass slide covered by a hydrophobic coating. In a second version, the SERS spot size was reduced to 1 mm, surrounded by a superhydrophobic area with a contact angle greater than 120 degrees. Here, 2 μL of the eluent droplet was placed on each spot. Heating of the array substrate allowed complete evaporation of the droplet under 3 min, without the adverse coffee ring effect. We demonstrated the utility of such a setup by injecting 1 mM adenine into a portable HPLC instrument and capturing the time course of SERS spectra. We characterize our MFON SERS spots in terms of its dependence on the concentration and incubation time as well as a two-dimensional SERS imaging showing the uniformity in the signal intensity.