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Nanoscale resolution sub-surface fluorescence imaging with aperture Scanning Near-Field Optical Microscopy

F. Bonaccorso 1,4A. Mazzaglia 2L. Monsù Scolaro 3A. Valerio 5A. Rencurosi 6L. Lay 5U. Giorgianni 4N. Micali 1V. Villari 1O. M. Maragò 1Pietro G. Gucciardi 1

1. CNR Ist. Processi Chimico-Fisici sez. Messina (CNR-IPCF), Via La Farina 237, Messina 98123, Italy
2. ISMN-CNR, Dipartimento di Chimica Inorganica, Università de Messina, Salita Sperone 31, Messina 98166, Italy
3. Dipartimento di Chimica Inorganica, Università de Messina, Salita Sperone 31, Messina 98166, Italy
4. Dipartimento di Fisica della Materia, Università de Messina, Salita Sperone 31, Messina 98166, Italy
5. Dipartimento di Chimica Organica ed Industriale, Via G. Venezian 21, Milano 20133, Italy
6. ISTM-CNR, Via C. Colgi 19, Milano 20133, Italy

Abstract

In this paper, we demonstrate the capability of aperture scanning near-field optical microscopy (SNOM) to attain topography-free sub-surface fluorescence imaging with sub-diffraction resolution on supramolecular aggregates of amphiphilic b-cyclodextrins (CDs) and porphyrins. The system is prepared by mixing CD covalently tagged with a dansyl fluorescent group (SC6CDDns) and CD targeted by receptor specific group (SC6CDGal). Static and Dynamic Light Scattering show that the formed nanoaggregate is constituted by both SC6CDDns and SC6CDGal species. The mixed nanoaggregates (MixCDDansGal) can encapsulate cationic porphyrins (H2T4) in solution as shown by batochromic shift of H2T4 Soret band in UV-Visible spectra. Solutions of MixCDDansGal/H2T4 at 10:1 molar ratio have been cast onto glass substrates, evaporated overnight and analysed by SNOM. We have imaged localized porphyrin aggregates, fluorescing at lfluo ~ 660 nm, below the surface of mixed porphyrin-cyclodextrin micrometric vesicles, with 150 nm spatial resolution. Similarly, nano-bubbles have been localized below the surface of thin films of amphiphilic b-cyclodextrin, marked with dansyl fluorescent molecules (lfluo> 500 nm). Both commercial and homemade optical fiber probes have been used. SNOM subsurface imaging opens up fascinating possibilities for chemical and structural analysis at the nanometer scale of nanocomposite materials, bio-recognition of carriers including drugs and specific receptor protein or single fluorescent molecules embedded under transparent membranes.

 

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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium H, by Pietro G. Gucciardi
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-06-15 18:20
Revised:   2009-06-07 00:44