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Design and Fabrication of Fiber-Optic Nanoprobes for Optical Sensing

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ABSTRACT

This paper describes the design and fabrication of fiber-optic nanoprobes developed for optical detection in single living cells. It is critical to fabricate probes with well-controlled nanoapertures for optimized spatial resolution and optical transmission. The detection sensitivity of fiber-optic nanoprobe depends mainly on the extremely small excitation volume that is determined by the aperture sizes and penetration depths. We investigate the angle dependence of the aperture in shadow evaporation of the metal coating onto the tip wall. It was found that nanoaperture diameters of approximately 50 nm can be achieved using a 25° tilt angle. On the other hand, the aperture size is sensitive to the subtle change of the metal evaporation angle and could be blocked by irregular metal grains. Through focused ion beam (FIB) milling, optical nanoprobes with well-defined aperture size as small as 200 nm can be obtained. Finally, we illustrate the use of the nanoprobes by detecting a fluorescent species, benzo[a]pyrene tetrol (BPT), in single living cells. A quantitative estimation of the numbers of BPT molecules detected using fiber-optic nanoprobes for BPT solutions shows that the limit of detection was approximately 100 molecules.

No MeSH data available.


Instrumental system for fluorescence measurements using nanoprobes.
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Figure 2: Instrumental system for fluorescence measurements using nanoprobes.

Mentions: The optical measurement system used for nanoprobe is schematically illustrated in Figure 2. For nanoprobe measurements, the 325 nm line of a HeCd laser (CVI Melles Griot, 15 mW laser power) was focused onto a 400 μm delivery fiber. A tapered fiber was coupled to the delivery fiber through a capillary tubing and was secured to the micromanipulators (Narishige MLW-3) on a Zeiss Axiovert 200M microscope (Zeiss). The fluorescence emitted from the region beyond the aperture was collected by the microscope objective and passed through a bandpass filter (386 nm) and then focused onto a photomultiplier tube (PMT, Hamamatsu, HC125-2) for detection. The output from the PMT was recorded on a universal counter (Agilent 53131A), and a personal computer (PC) was used for further data treatment.


Design and Fabrication of Fiber-Optic Nanoprobes for Optical Sensing
Instrumental system for fluorescence measurements using nanoprobes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211233&req=5

Figure 2: Instrumental system for fluorescence measurements using nanoprobes.
Mentions: The optical measurement system used for nanoprobe is schematically illustrated in Figure 2. For nanoprobe measurements, the 325 nm line of a HeCd laser (CVI Melles Griot, 15 mW laser power) was focused onto a 400 μm delivery fiber. A tapered fiber was coupled to the delivery fiber through a capillary tubing and was secured to the micromanipulators (Narishige MLW-3) on a Zeiss Axiovert 200M microscope (Zeiss). The fluorescence emitted from the region beyond the aperture was collected by the microscope objective and passed through a bandpass filter (386 nm) and then focused onto a photomultiplier tube (PMT, Hamamatsu, HC125-2) for detection. The output from the PMT was recorded on a universal counter (Agilent 53131A), and a personal computer (PC) was used for further data treatment.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

This paper describes the design and fabrication of fiber-optic nanoprobes developed for optical detection in single living cells. It is critical to fabricate probes with well-controlled nanoapertures for optimized spatial resolution and optical transmission. The detection sensitivity of fiber-optic nanoprobe depends mainly on the extremely small excitation volume that is determined by the aperture sizes and penetration depths. We investigate the angle dependence of the aperture in shadow evaporation of the metal coating onto the tip wall. It was found that nanoaperture diameters of approximately 50 nm can be achieved using a 25° tilt angle. On the other hand, the aperture size is sensitive to the subtle change of the metal evaporation angle and could be blocked by irregular metal grains. Through focused ion beam (FIB) milling, optical nanoprobes with well-defined aperture size as small as 200 nm can be obtained. Finally, we illustrate the use of the nanoprobes by detecting a fluorescent species, benzo[a]pyrene tetrol (BPT), in single living cells. A quantitative estimation of the numbers of BPT molecules detected using fiber-optic nanoprobes for BPT solutions shows that the limit of detection was approximately 100 molecules.

No MeSH data available.