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

Abstract

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 determine the phenylalanine (Phe) level in urine for rapid screening of the phenylketonuria disorder, strong chemical interference from uric acid (UA), which is a major component in urine, was observed. To minimize the interference from UA, ZnO powder was applied to the urine sample to adsorb UA prior to SERS detection. After cleaning by using ZnO, the SERS signals of Phe were revealed for quantitative purposes. Under the optimized conditions, both the sensitivity and reproducibility of SERS measurement considerably improved. Quantitative analyses revealed that the developed method is highly feasible for the rapid determination of Phe in real samples.

Capture of Phenylalanine and Phenylalanine-Terminated Peptides Using a Supramolecular Macrocycle for Surface-Enhanced Raman Scattering Detection

“…This value is reasonable compared to studies under similar conditions. 16,41

Figure 2.(a) Raman of Phe (bottom) and SERS of Phe (top). The most intense peaks in the spectra persist with slight shifts from Raman to SERS from 1004 cm −1 to 1002 cm −1 and 1030 cm −1 to 1031 cm −1 .

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“…SERS methods of Phe detection, however, have mainly relied on direct adsorption of Phe to a noble metal substrate with no surface ligand. 16,17 The use of a capture agent with Phe affinity should afford enhanced SERS sensitivity in detecting this analyte.…”

A Review on Electrochemical Sensors and Biosensors Used in Phenylalanine Electroanalysis

“…In determining the essential amino acid Phe, optical methods were used, respectively: colorimetry [22,23]. UV and IR spectrophotometry [24], fluorescence [25][26][27][28][29], enhanced fluorescence [30], chemiluminescence [31][32][33]; separation methods, such as: gas chromatography [34], capillary electrophoresis, HPLC-high performance liquid chromatography [22,[35][36][37][38][39][40][41][42][43][44]; spectroscopic methods: Raman spectroscopy [45,46], laser-assisted spectroscopy [47], UV-Vis spectroscopy and chemometry [48]; UV−Vis and surface-enhanced Raman scattering [49], nuclear magnetic resonance [50] and circular dichroism spectroscopy [51]; mass spectrometry [22,34,41,52], fluorimetry [53].…”

Two-Dimensional Self-Assembly of Au@Ag Core–Shell Nanocubes with Different Permutations for Ultrasensitive SERS Measurements

“…This substrate possesses great potential in sensing and detection due to the advantages mentioned above. There are also related articles that studied the factors affecting the SERS activity of the coffee ring lining obtained after the colloidal natural evaporation . Meanwhile, Zhang made a detailed study on the SERS activity of the substrate obtained by electrostatic self-assembly, which was a good comparison and proof for the SERS detection results obtained in this paper.…”