Poly(diacetylene) Monolayers Studied with a Fluorescence Scanning Near-Field Optical Microscope

Abstract

A novel and powerful method to study the optical properties of thin lipid films which a resolution superior to confocal microscopy is presented. With a scanning near-field optical microscope, fluorescence images of a Langmuir-Blodgett film of diethylene glycol diamine pentacosadiynoic amide are obtained with a lateral resolution of 100 nm. Simultaneously a force image is measured that gives the topography. Therefore it is possible to correlate a high-resolution fluorescence micrograph with the topological structure of the polymer film. Polymer domains that do not fluoresce are visible in the force image, while polarization dependence, an optical property not afforded by atomic force microscopy, is clearly demonstrated with a high resolution in the near-field optical image. This combination of fluorescence scanning near field optical microscopy and force microscopy provides additional information on the structure of the polymer film that can be valuable in the research of Langmuir-Blodgett films.

Probing single molecule orientations in model lipid membranes with near-field scanning optical microscopy

“…2, the simultaneous near-field topography measurements add an important dimension by providing a consistent and complementary view of sample properties that is particularly informative when combined with the near-field fluorescence measurements. 39,40,42 Comparing the near-field force and fluorescence images shown in Figs. 2͑A͒ and 2͑B͒ confirms that the fluorescent probe molecule TRITC-DHPE partitions into the less or- dered LE lipid phase, which is characterized by regions of reduced height in the force image and bright regions in the fluorescence image.…”

“…38 Recently, our group and others have illustrated the utility of NSOM for these types of measurements, which has resulted in the observation of new structures and processes at the submicron level. 31,[39][40][41][42][43][44] The capabilities of NSOM are often complimentary with other high resolution techniques. For studies on model lipid membranes, the simultaneously collected near-field fluorescence and force information provide a unique window into the phase partitioning and effects of constituents on membrane structure.…”

Multi-detection and polarisation contrast in scanning near-field optical microscopy in reflection

“…Finally the bright field image correlates strongly to the shear force image: on the glass areas the shear force feedback keeps the tip further from the surface resulting in reduced reflected light compared to the LB-film domains. The LB film absorbs about 10% of the light in transmission [13]; however, in bright field reflection this is not observed due to the dominant effect of topography and shear force regulation.…”

“…A monolayer with a thickness of 6 nm was transferred onto an object glass slide by use of Langmuir-Blodgett techniques. The film consists of domains, varying from nanometers to several square micrometers in size [13,22]. All polymerised domains absorb in the green and fluoresce in the red.…”

“…Especially near-field fluorescence, as first demonstrated by Betzig et al [11], is promising due to the combination of high sensitivity, strong background suppression and chemical specificity. Recently important progress in transmission near-field fluorescent microscopy of chemical and biological systems has been achieved [12][13][14][15], ultimately leading to single molecular detection and spectroscopy [16][17][18][19].…”