Three Steps of Hierarchical Self Assembly Toward a Stable and Efficient Surface Enhanced Raman Spectroscopy Platform

Abstract

We report an innovative application of a true “bottom-up” approach for preparation of functional material. Three consecutive self-assembly steps were utilized for formation of a complex surface enhanced Raman spectroscopy (SERS) platform. First the Langmuir–Blodgett technique was used to deposit gold nanoparticles on a solid substrate. Thus prepared surfaces were afterward used as substrates in the chemical vapor deposition process of gallium nitride (GaN) nanowire growth. On such scaffolding, a third step of material fabrication was performed. Gold microflowers (Au MFs) deposited from solution preferably appeared at the top of the GaN nanowires and not in the cavities in between. The obtained morphology of the final material was controlled at each step of the preparation process to tailor its properties for desired purposes. Prepared surfaces were tested as SERS platforms. The enhancement factor was around 107 in case of p-mercaptobenzoic acid (p-MBA). The platforms were also suitable for biological and biomedical applications. We demonstrated the label free detection of DNA. The substrates gave reproducible SERS spectra both across a single platform and between different platforms. The average spectral correlation coefficients (Γ) was 0.87. Moreover, the obtained material proved to be very stable. The presented complex structure demonstrated therefore had the advantages of the two surface functionalization concepts it comprised: (1) GaN nanowire growth and (2) Au MF deposition, eliminating their major drawbacks. Presented material combined high SERS enhancement factor of Au MFs deposited on a flat surface and good durability of microflowers deposited on a surface completely covered with nanowires, which were almost SERS inactive. The final product provided truly exceptional stability and repeatability of SERS results, maintaining an enhancement factor comparable to the best commercially available platforms.