Biophotonics_Concepts_to_Applications

result is a wavelength shift in the LSPR peak due to a change in the phase matching
condition, as shown by the red curve in Fig.11.4. This lab-on-fiber setup thus
enables highly sensitive biological, chemical, and physical sensing functions.

11.3 Microscope in a Needle

The desire to analyze abnormal growths located deep within tissue has resulted in a
number of minimally invasive needle-based optical imaging techniques. One
method is to place an opticalfiber inside of small gauge needles for optical imaging
within soft tissues or lesions [ 23 – 26 ]. This method enables confocalfluorescence
microendoscopy or OCT to be performed inside the body to locate and diagnose
very small tumor elements. The basic technology goal is to have microscope
imaging capabilities inside a standard hypodermic needle to do 3D scanning. Such
techniques avoid the need for more invasive surgery and allow a quicker patient
recovery from the examination process compared to a conventional biopsy.
One example is an ultrathin 30-gauge needle (310μm in diameter), which
encapsulates a SMF [ 23 – 25 ]. The optical elements in the needle consist of a
260-μm section of no-corefiber (NCF) and a 120-μm section of graded-index
(GRIN)fiber, which is spliced to a single-modefiber. Another piece of NCF, which
is polished at a 45° angle, follows the GRIN section. This angled NCF allows side
illumination and viewing through a miniature window in the side of the needle. The
output beam from the window is elliptical with a transverse resolution that is
smaller than 20μm at the full-width half-maximum level over a distance of about
740 μm in tissue. The peak resolutions typically are 8.8 and 16.2μm in the x- and
y-directions, respectively.

Reflectance

Wavelength (nm)

0.8

0.6

0.4

0.2

1350 1400 1450

Reflectance

without an

analyte

Reflectance

with an

analyte

Fig. 11.4 Example shift in
the surface plasmon resonant
peak due to a relative index
change at afiber tip covered
with a nanoarray pattern
[J. Biomed. Opt. 19(8),
080902 (Aug 28,
2014]. doi:10.1117/1.JBO.19.
8.080902)

332 11 Biophotonics Technology Applications