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Breaking the diffusion limit with super-hydrophobic delivery of molecules to plasmonic nanofocusing SERS structures


The detection of a few molecules in a highly diluted solution is of paramount interest in fields including biomedicine, safety and eco-pollution in relation to rare and dangerous chemicals. Nanosensors based on plasmonics are promising devices in this regard, in that they combine the features of high sensitivity, label-free detection and miniaturization. However, plasmonic-based nanosensors, in common with general sensors with sensitive areas on the scale of nanometres, cannot be used directly to detect molecules dissolved in femto- or attomolar solutions. In other words, they are diffusion-limited and their detection times become impractical at such concentrations. In this Article, we demonstrate, by combining super-hydrophobic artificial surfaces and nanoplasmonic structures, that few molecules can be localized and detected even at attomolar (10−18 mol l−1) concentration. Moreover, the detection can be combined with fluorescence and Raman spectroscopy, such that the chemical signature of the molecules can be clearly determined.

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Figure 1: High contact angle and evaporation process.
Figure 2: Architecture of the four different devices fabricated in this work.
Figure 3: Localization and spectroscopic measurements.
Figure 4: Single lambda-DNA localization and detection from a 10 aM solution.
Figure 5: Super-hydrophobic nanostructure.
Figure 6: Super-hydrophobic device with embedded plasmonic nanostructure.


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The authors thank L. Fruk (Karlsruhe Institute of Technology) for discussions and suggestions on biological aspects of this work, and R. La Rocca, R. Tallerico and A. Nicastri (BIONEM University of Magna Graecia) for sample preparation. This work was funded under European Project SMD FP7-NMP 2800-SMALL-2 (proposal no. CP-FP 229375-2), Project NANOANTENNA FP7-HEALTH-2009 (grant agreement no. 241818), Italian project FIRB ‘Rete Nazionale di Ricerca sulle Nanoscienze ItalNanoNet’ (cod. RBPR05JH2P_010).

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F.D.A. conducted FIB milling, electron-beam deposition and numerical simulations. F.G. carried out micropillar fabrication, super-hydrophobic measurements and modelling. F.M. prepared samples and carried out evaporation and sputtering. G.D. and P.C. conducted Raman measurements. M.M. carried out DNA deposition and protocol optimization. M.L.C. carried out electroless deposition and protocol optimization. G.C., A.A., L.T. and A.T. were involved in super-hydrophobic characterization. C.L. carried out fluorescence measurements. R.P.Z. conducted electromagnetic modeling. G.P. was responsible for superhydrophobic and microfluidic design. G.C. carried out the biological overview and protein evaluation. R.C. was responsible for project planning. E.D.F. was proposer and project coordinator.

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Correspondence to E. Di Fabrizio.

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The authors declare no competing financial interests.

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De Angelis, F., Gentile, F., Mecarini, F. et al. Breaking the diffusion limit with super-hydrophobic delivery of molecules to plasmonic nanofocusing SERS structures. Nature Photon 5, 682–687 (2011).

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