Date/Time: 04-05-2018 - Thursday - 05:00 PM - 07:00 PM
Bharath Bangalore Rajeeva1 Zilong Wu1 Andrew Briggs1 Palash Acharya1 Vaibhav Bahadur1 Seth Bank1 Yuebing Zheng1

1, University of Texas at Austin, Austin, Texas, United States

The incorporation of direct-write printing toward realization of optically active structures has been a limiting factor toward wide-spread incorporation of the technology. Specifically, compatibility and integration of the printing process with spatially constrained microfluidic devices is essential for point-of-care (POC) sensing and diagnostics. However, the current approaches are bound by resolution, accessibility and multi-step fabrication constraints. In this work, we develop a plasmonic bubble based approach, wherein arrays of Ag rings are fabricated from a precursor Ag ink in a single-step. A 532nm continuous-wave laser is focused on the gold nanoisland (AuNI) substrate with diamminesilver (I) acetate precursor ink covering the substrate. The array pattering is achieved via intermittent laser exposure (<200 ms) and stage translation. Using the above “point-and-shoot” approach, we fabricate optically active Ag rings with tunable diameters between 1-2 µm and a lattice spacing of 3mm. The thermally reduced Ag from the precursor is immobilized along the bubble/water interface to yield instantaneous ring morphology. Analytical modelling of the fabrication process substantiates the realization of the ring geometry. The hybrid Ag ring/AuNI substrate exhibits plasmonic resonances in the mid-IR and visible regime. Finite-difference time-domain (FDTD) simulated electric-field distribution at a single Ag ring establishes that the resonance in the mid-IR regime arises from the dipolar plasmon mode of the Ag ring. The visible component of the hybrid substrate arises from the AuNI particles. We show simultaneous surface-enhanced infrared spectroscopy (SEIRS) of 2, 4, 6 – trinitrotoluene (TNT) and surface-enhanced Raman spectroscopy (SERS) of rhodamine 6G (R6G) to demonstrate the dual-mode applicability. The aromatic (3.43 µm) and aliphatic (3.51 µm) C-H stretch bands of TNT on the Ag ring-AuNI substrate are enhanced via SEIRS. Further, we measured the SERS spectra of R6G molecules drop-casted on the Ag ring-AuNI substrate and also within a microfluidic chamber. The SERS signal is enhanced due to the high E-field enhancement at the Ag-ring/AuNI interface, which arises from the intense hot spots at the multiple Ag-Au junctions with the sub-20 nm gaps. Similar fabrication and sensing characteristics along with high stability under various flow conditions are realized within a spatially-constrained microfluidic channel. With simplicity, high efficiency and integrability in fabrication of micro/nanostructures, “point-and-shoot” approach enables realization of device miniaturization, portability and multi-functionality.

Meeting Program

5:00 PM–7:00 PM Apr 5, 2018

PCC North, 300 Level, Exhibit Hall C-E