Large‐Scale, Ultrasensitive, Highly Reproducible and Reusable Smart SERS Platform Based on PNIPAm‐Grafted Gold Grating

The design of the smart plasmonic sensor, based on the periodical gold gratings grafted with PNIPAm was proposed and realized. Periodical gold structure was created on the polymer backing modified by excimer laser (1x2 cm2 modified area) and subsequently covered by thin gold film. In the next step 7 nm thick PNIPAm layer was grafted to gold surface through two step procedure: covalent attachment of 4-carboxybenzil groups followed by carboxyl groups activation and their coupling with amino-terminated PNIPAm. Surface properties of the prepared structure and their switchable behaviour were investigated using refractometry, wettability measurements, AFM in water medium, cyclic voltammetry, pH and temperature-dependent z-potential. The structure enables effective entrapping and SERS detection of azo dyes, significant reduction of minimal detectable concentration of target molecules and detection limit down to femtomolar concentrations. Excitation of plasmons on well ordered surface structure also shows excellent reproducibility of SERS system along the particular sample surface and between different samples too. Additionally, the reversible switching of wettability under repeated temperature changes on gold plasmonic platform allows multiple use of the developed system.