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In this work, we propose the preparation and investigation of advanced microfluidic surface-enhanced Raman spectroscopy (SERS) chip with a design allowing high SERS enhancement and analysis reproducibility. The proposed chip implements the creation of periodical metal structure (grating) inside the microfluidic chip and further immobilization of gold multibranched nanoparticles (AuMs) with shaped edges on the grating surface. Such an approach allows achieving plasmonic coupling between the surface plasmon polariton wave, excited on the Au grating, and localized surface plasmon, excited on sharped edges of AuMs. As a result, a high enhancement of electric field in the space between AuMs was achieved, which results in the high SERS enhancement factor, confirmed by both, theoretical calculation and experimental measurements with a typical SERS analyte—R6G. In particular, it is possible to detect a vanishingly small concentration of R6G using the proposed plasmonic coupling, which sensitivity significantly exceeds previously reported limits in the case of microfluidic SERS measurements. We also observed the dependency of SERS intensity on the microfluidic flow rate and demonstrated the perfect reliability of the SERS signal, measured in the microfluidic regimes under constant flow rate.

Creation of SERS substrate with the large active area and homogeneous distribution of hot spots is now one of the most important tasks in the field of SERS practical implementation. This problem has been solved by various techniques, but the most applicable of them are expensive due to highly technical nature. In this work, a simple alternative approach based on thermal annealing of sputtered Au layer has been proposed. Usually, the thermal annealing of the thin Au layer leads to the formation of gold clusters array with high plasmon efficiency but with too wide size distribution and highly disordered arrangement. To overcome this drawback the previous soaking of Au layer in the poly(vinylpyrrolidone) (PVP) solution was proposed, with the aim to affect clusters formation and achieve the more homogeneous distribution of created hot spots array. Annealed Au and Au-PVP thin layers were characterized by AFM, XRD, XPS, UV–Vis and Raman spectroscopy techniques. Present results indicate that the PVP treatment before thermal treatment significantly affect the growth of the clusters and provide the perspective way for increasing of SERS efficiency and reproducibility.

Colloid lithography represents a simple and efficient method for creation of a large-scale template for subsequent surface patterning, deposition of regular metal nanostructures, or periodical surface structures. However, this method is significantly restricted by its ability to create only a limited number of structures with confined geometry and symmetry features. To overcome this limitation, different techniques, such as plasma treatment or tilting angle metal deposition, have been proposed. In this paper, an alternative method based on the vapor annealing of ordered single polystyrene (PS) microspheres layer, followed by the surface grafting with arenediazonium tosylates is proposed. Application of vapor treatment before surface grafting allows effective control of the area screened by PS microspheres. Pristine and vapor-annealed microsphere arrays on the gold substrate were electrochemically modified using ADTs. Subsequent removal of the PS microsphere mask enabled to prepare well-defined nanostructures with controllable surface features. In particular, prepared periodic arrangements were achieved by the grafting of OFGs to the empty interspaces between nanopore arrays. The process of sample preparation was controlled, and the properties of prepared structures were characterized by various techniques, including atomic force microscopy (AFM), conductive AFM, scanning electron microscopy energy-dispersive X-ray spectrometry, Raman spectroscopy, and voltammetry.