A droplet that dries into a ring can concentrate material at its edge. In a carbamazepine assay, the researchers used this effect to bring the drug into the area where they collected a Raman signal.
The team extracted carbamazepine from serum, deposited a drop on a silicon substrate carrying silver nanoparticles, and sampled three points around the dried ring. The nanoparticles enhanced the Raman signal. The placement of the laser, the surface preparation, and the handling of the serum matrix were therefore part of the method.
In simulated samples, the reported detection limit was 0.01 µg/mL. The evaluated calibration range in spiked serum was 2.5 to 40 µg/mL. A detectable signal at the lower value does not establish accurate quantitation there. When reviewing the assay, ask which concentrations were calibrated in serum and which findings were demonstrated in actual specimens.
Zhu and colleagues, Molecules (2023). Journal article · Full text.