β‑Lactoglobulin Amyloid Fibrils-Poly(vinyl alcohol)-AgNPs Hydrogel as a Surface-Enhanced Raman Substrate for All-in-One Rapid Separation, Enrichment, and Detection of Small Molecules in Food Samples

A β-lactoglobulin amyloid fibrils-poly(vinyl alcohol)-Ag
nanoparticles (β-LAFs-PVA-AgNPs) hydrogel was prepared as a
surface-enhanced Raman scattering (SERS) substrate based on poly(vinyl
alcohol) (PVA) with adsorbent β-lactoglobulin amyloid fibrils
(β-LAFs) structured into the network structure of the hydrogel
using the immersion reduction method. Due to the high swelling and
contraction properties of the hydrogel in different states and the
“sieving” nature of its network cavities, small molecular
target analytes can more easily enter the space-confined hydrogel
and rapidly bind with the amide bonds of the protein structure. During
the contraction process of the hydrogel, the target analytes are enriched,
and the Ag nanoparticles (AgNPs) come closer together to form Raman
“hot spots”, generating stronger SERS signals. The SERS
performance of this hydrogel was evaluated using thiram and ibuprofen
as target molecules. The results showed high detection sensitivity
with limits of 37.1 μg/L for thiram and 85.6 μg/L for
ibuprofen, respectively, and the entire sample pretreatment and detection
process is completed within 11 min. The substrate also demonstrated
excellent selectivity, uniformity, stability, and reproducibility.
When applied to detect thiram in fruits and vegetables and ibuprofen
in herbal tea, the recovery rates ranged from 90.1% to 114.7%, with
the relative standard deviations (RSDs) of 0.61% to 5.8%. The SERS
results matched those from HPLC analysis. This method offers simple
and rapid sample pretreatment, high sensitivity, strong adsorption
capacity for organic pollutants, and good selectivity, making it a
promising candidate for on-site rapid detection applications.