Chemically etched plastic optical fiber probe for near-field scanning optical microscopy in liquids

Giovanni Dietler, Kanat Dukenbayev, Anton Smirnov
SPIE-INT SOC OPTICAL ENGINEERING, 2019
Article de conférence

Résumé

Some preliminary results and experimental details of Near-field Scanning Optical Microscopy (NSOM) operation in liquids have been reported by us earlier(1-4). Here we present the first use of custom made polystyrene/poly (methyl methacrylate) (PMMA) optical fibers to assemble new NSOM probe/sensor for operation in liquids. Assembled NSOM probe has quite large quality factor Q ranging 2000-6000 in air(1), and 300-900 when immersed 0.2-0.3 mm deep into the water. Such montage demonstrates high mechanical durability permitting to scan different samples during many hours or even days, and overall low cost in comparison with NSOM probes based on glass optical fibers. A specially prepared optical fiber with 125 mu m diameter (from Paradigm Optics Company, USA) (polystyrene core diameter is 0.85 mu m, n(core) = 1.59 and PMMA cladding, n(core) = 1.49) was chemically etched using a 9: 1 mixture of dichloromethane and ethyl acetate(2). As result of the etching, a smooth and sharp tip is formed with a typical radius of the curvature equal to 50 - 170 nm. For completeness, earlier unpublished images of living Picocyanobacteria bacteria obtained using glass fiber-made NSOM probes are also presented.

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https://infoscience.epfl.ch/record/268206?ln=fr

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Near-field scanning optical microscopy using polymethylmethacrylate optical fiber probes

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We report the first use of polymethylmethacrylate (PMMA) optical fiber-made probes for scanning near-field optical microscopy (SNOM). The sharp tips were prepared by chemical etching of the fibers in ethyl acetate, and the probes were prepared by proper gluing of sharpened fibers onto the tuning fork in the conditions of the double resonance (working frequency of a tuning fork coincides with the resonance frequency of dithering of the free-standing part of the fiber) reported earlier for the case of glass fibers. Quality factors of the probes in the range 2000–6000 were obtained, which enables the realization of an excellent topographical resolution including state-of-art imaging of single DNA molecules. Near-field optical performance of the microscope is illustrated by the Photon Scanning Tunneling Microscope images of fluorescent beads with a diameter of 100 nm. The preparation of these plastic fiber probes proved to be easy, needs no hazardous material and/or procedures, and typical lifetime of a probe essentially exceeds that characteristic for the glass fiber probe.

Elsevier2010

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The aim of the present PhD thesis is the elaboration of new, home-made Scanning Near-field Optical Microscope (SNOM or NSOM), and the demonstration of its great potential for high-resolution topography and fluorescence investigations of soft and solid samples, as well as the possibility to work in air and liquid environments showing high-resolution topographical and fluorescence abilities to investigate soft and solid samples. The first chapter starts from with the description of the general idea of SNOM and with a brief introduction into to the history and theory of optical image formation, and leading to the resolution limits in conventional optical microscopy. The following section will discuss about the different state-of-the-art different SNOM configurations and theirs peculiarities. The second chapter discusses the SNOM instrumentation and its operation in liquid. The central idea of the proposed approach is the application of the "joint recipient principle" method. Then we will describe the double-resonance principle of the SNOM sensor, and the preparation of glass optical fibers by chemical etching. In addition, the description of the important technical components (lasers, filter and so on) for the SNOM experiment concludes this chapter. The third chapter focus is on the time-gated pulse excitation and optical signal detection of SNOM images. The technical configuration of the SNOM is presented in more details. The fourth chapter starts from with a broad overview of living bacteria Escherichia coli (E.coli) and of the Green Synechococcus – type of Picocyanobacteria cell lines, and presents the distinctive advantages for of the SNOM investigations working in native physiological conditions. The following sections emphasize our obtained high-resolution experimental SNOM result measurements, then followed a discussion of the results follows. The sample preparation and deposition procedures of the living cells for the scanning will are also discussed in this chapter. The chapter five introduces our recently developed SNOM sensor, based on polymethylmethacrylate (PMMA) plastic optical fiber. The chemical preparation of sharp (>100 nm) tips, and its significant advantages will be illustrated by experimental results.

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Nowadays, sharpened glass fiber - made probes attached to a quartz tuning fork (TF) and exploiting the shear force - based feedback are by far the most popular in the field of SNOM. These probes are expensive, very fragile and their fabrication is difficult, hard to control and in many cases a hazardous process. Here we are presenting the first SNOM probes made from plastic optical fibers with a small, submicron size, core diameter. The sharp tips were prepared by chemical etching of the fibers in dichloromethane - ethyl acetate solution, and the probes were prepared by proper gluing of sharpened fibers onto the TF. These probes demonstrate excellent performance in both topographical and optical channels after intense use.

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