Tunable Coffee Ring Formation on Polycarbonate NanofiberFilm for Sensitive SERS Detection of Phenylalanine in Urine

摘要

A new method based on the coffee ring effect was developed for improving the sensitivity, simplicity, and robustness of surface-enhanced Raman scattering (SERS) in determining trace levels of analytes. In this method, a polyvinylpyrrolidone (PVP)-stabilized silver colloidal (AgC) solution was first prepared and mixed with a sample solution. Following deposition of the mixture solution on a solid substrate with a rough surface, a coffee ring was formed once the solvent had evaporated. The formation of a coffee ring not only concentrated the analyte but also reduced the space between silver nanoparticles (AgNPs) to strengthen the hotspot effect, thereby considerably improving SERS sensitivity. To strengthen the coffee ring effect further, the surface roughness of the solid support and PVP content of the AgC solution were investigated. The results indicated that an increase in surface roughness reduced the size of the coffee rings, whereas the addition of PVP not only stabilized the AgNPs but also improved the compactness of the coffee rings. When applying the proposed method to determinethe phenylalanine (Phe) level in urine for rapid screening of thephenylketonuria disorder, strong chemical interference from uric acid(UA), which is a major component in urine, was observed. To minimizethe interference from UA, ZnO powder was applied to the urine sampleto adsorb UA prior to SERS detection. After cleaning by using ZnO,the SERS signals of Phe were revealed for quantitative purposes. Underthe optimized conditions, both the sensitivity and reproducibilityof SERS measurement considerably improved. Quantitative analyses revealedthat the developed method is highly feasible for the rapid determinationof Phe in real samples.