<p>Single molecule Raman spectroscopy using isolated, circular ~ 110 nm diameter, multilayer insulator-metal-insulator-metal (MIM<sup>+</sup>) disk enhancement structures fabricated with 355 nm interferometric lithography in a 2D 400 nm period array is reported. Adenine and cytosine are selected as a bi-analyte pair, with comparable strength Raman lines arising from ring breathing modes in close proximity (A: 743 cm<sup>-1</sup> shift and C: 807 cm<sup>-1</sup> shift). Samples are soaked in 1:2 A:C mixtures diluted in water to ~ 1x10<sup>-3</sup> to 5x10<sup>-4</sup> of a monolayer coverage. Raman spectra are obtained with 633 nm excitation. The spectra show truncated Pareto distribution statistics with individual spectra showing: only A; only C; and A &amp; C features demonstrating single molecule sensitivity. Over 90% of the spectra are null spectra without either A or C features. Importantly, the enhancement structures are isolated from each other, no close approach is required as in the case of spherical nanoparticles where ~ 1 nm gap modes are responsible for the large enhancement required for non-resonant single molecule sensitivity. These enhancement structures are readily fabricated by volume manufacturing lithography (optical and nanoimprint).</p>

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Bi-analyte demonstration of non-resonant, single-molecule SERS with isolated lithographic enhancement structures

  • Xin Jin,
  • Hui Xia,
  • S. R. J. Brueck

摘要

Single molecule Raman spectroscopy using isolated, circular ~ 110 nm diameter, multilayer insulator-metal-insulator-metal (MIM+) disk enhancement structures fabricated with 355 nm interferometric lithography in a 2D 400 nm period array is reported. Adenine and cytosine are selected as a bi-analyte pair, with comparable strength Raman lines arising from ring breathing modes in close proximity (A: 743 cm-1 shift and C: 807 cm-1 shift). Samples are soaked in 1:2 A:C mixtures diluted in water to ~ 1x10-3 to 5x10-4 of a monolayer coverage. Raman spectra are obtained with 633 nm excitation. The spectra show truncated Pareto distribution statistics with individual spectra showing: only A; only C; and A & C features demonstrating single molecule sensitivity. Over 90% of the spectra are null spectra without either A or C features. Importantly, the enhancement structures are isolated from each other, no close approach is required as in the case of spherical nanoparticles where ~ 1 nm gap modes are responsible for the large enhancement required for non-resonant single molecule sensitivity. These enhancement structures are readily fabricated by volume manufacturing lithography (optical and nanoimprint).