Microscopic and spectroscopic analysis of multiple types of nanocrystal formation in a one pot seedless and surfactantless procedure.

Solid-state surface-enhanced Raman spectroscopic (SERS) substrates surmount the limitations of colloidal nanoparticles for many practical chemical and biomolecular sensors. The main bottom-up approaches adopted for SERS substrate fabrication include preparing plasmonic nanoparticles and their deposition to selected surfaces via chemical self-assembly, inkjet printing, spray coating, dip-coating, etc. In contrast, the top-down strategy is to create nanostructures on surfaces via different lithographic techniques (nanoimprint lithography, electron beam lithography), laser ablation, or chemical etching and then depositing a nanolayer of coinage metals. The ease and reproducibility of production, high enhancement, and uniformity of performance are the requirements for a reliable SERS substrate. This work describes an easy process for preparing SERS substrates from a less expensive and readily available material, brass. The treatment of brass with hydrochloric acid caused preferential etching of Zn from the surface, leaving a uniform Cu nanoporous substrate (Cu NPS ). The subsequent galvanic displacement of Cu NPS with AgNO 3 resulted in silver nanocrystal overgrowth, as evidenced by microscopic, spectroscopic, and elemental studies. The corresponding SERS studies with 4-mercaptophenylboronic acid (4-MPBA) as the probe molecule revealed ∼30 and ∼300 times improved performance compared to Cu NPS and the parent brass substrates, respectively. Further, we explored the possibility of sensing creatinine, the biomarker for kidney functioning. Creatinine followed a Freundlich type adsorption, and the SERS substrate developed herein exhibited a sensitivity down to 1.7 pg/mL.