Limits...
Design and Fabrication of Fiber-Optic Nanoprobes for Optical Sensing

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.


SEM images of a silver- and b aluminum-coated nanofibers after plasma cleaning.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3211233&req=5

Figure 6: SEM images of a silver- and b aluminum-coated nanofibers after plasma cleaning.

Mentions: Aluminum is a desirable material to use because it has the highest extinction coefficient of all metals. Aluminum adheres to fibers more firmly than silver or gold so that no interface layer is required and general cleaning does not affect the coating. Figure 6 compares the nanofibers after argon plasma cleaning (Emitech K-1050X, 100 W, 5 min). Silver coatings are easily peeled off while aluminum coatings exhibit no changes under the same condition. Aluminum is inert toward corrosive agents since a protective oxide layer is formed readily upon contact to the air. However, it is difficult to evaporate aluminum as a thin film while maintaining smooth films with small grain sizes [19]. Grainy films contribute to the high background in near-field sensing. The grain diameter is highly and sensitively dependent on the deposition pressure. Below 5 × 10-6 torr, the size of the individual grains is smaller than 100 nm. There was a relationship between rate of metallic deposition and subsequent surface roughness, and studies revealed that higher coating rate (>10 nm/s) resulted in better smoothness and the film opacity required for our intended sensor applications.


Design and Fabrication of Fiber-Optic Nanoprobes for Optical Sensing
SEM images of a silver- and b aluminum-coated nanofibers after plasma cleaning.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: SEM images of a silver- and b aluminum-coated nanofibers after plasma cleaning.
Mentions: Aluminum is a desirable material to use because it has the highest extinction coefficient of all metals. Aluminum adheres to fibers more firmly than silver or gold so that no interface layer is required and general cleaning does not affect the coating. Figure 6 compares the nanofibers after argon plasma cleaning (Emitech K-1050X, 100 W, 5 min). Silver coatings are easily peeled off while aluminum coatings exhibit no changes under the same condition. Aluminum is inert toward corrosive agents since a protective oxide layer is formed readily upon contact to the air. However, it is difficult to evaporate aluminum as a thin film while maintaining smooth films with small grain sizes [19]. Grainy films contribute to the high background in near-field sensing. The grain diameter is highly and sensitively dependent on the deposition pressure. Below 5 × 10-6 torr, the size of the individual grains is smaller than 100 nm. There was a relationship between rate of metallic deposition and subsequent surface roughness, and studies revealed that higher coating rate (>10 nm/s) resulted in better smoothness and the film opacity required for our intended sensor applications.

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.