biosensors can manipulate and analyzefluid samples in volumes on the order of
microliters as the liquids pass through micrometer-sized channels. Lab-on-fiber
technology envisions the creation of multiple sensing and analysis functions
through the integration onto a singlefiber segment of miniaturized photonic devices
such as nanoparticle SPR sensors deposited on afiber tip,fiber Bragg gratings
combined with high-index surface coatings, and various types of opticalfilters.
Further miniaturizations have resulted in concepts such as the so-called
microscope-in-a-needle.Microscope-in-a-needleimplementations involve the use
of a highly sensitive, ultrathin, side-viewing 30-gauge OCT needle probe. As is
described in Sect.11.3, the basic goal of this technology is to incorporate micro-
scope capabilities inside a standard hypodermic needle to enable 3D scanning of
malignant tissue deep within the body.
Clinical techniques that exhibit a high sensitivity to specific allergens, a large
dynamic range to detect various biomarker concentrations, and the ability to assess
multiple biomarkers are in high demand for disease diagnostics. Of particular
interest is the ability to detect and analyze natural nanoparticles such as viruses and
pollutants. A method for detecting single nanoscale particles named interferometric
reflectance imaging sensor is described in Sect.11.4.
An innovative application of biophotonics techniques in the area of neuroscience
is given in Sect.11.5. These pursuits are referred to asneurophotonics, which
attempts to explore and understand the mechanisms of neuronal activity in organs
such as the brain and the heart. A major goal is to develop photonics-based methods
to control specific classes of excitable neural cells in order to determine the causes
and effects of various diseases caused by malfunctions in these cells.
11.1 Optical Manipulation
The advent of the laser in 1960 led to renewed interest in the centuries old concept
that light can exert forces. Experimental studies on radiation pressure in the 1970s
opened up a newfield of exploring biological materials and functions at the
microscopic level. This activity led to the concepts ofoptical tweezersandoptical
trappingfor the controlled grasping, holding, and manipulation of microscopic
particles. These techniques use a non-contact force for manipulation of cells and
single molecules down to the nanoscale level with forces ranging between 0.1– 200
pN and can be used in a liquid environment [ 1 – 7 ].
Example 11.1(a) What is a pN force? (b) What are force levels on a
molecular scale?Solution: (a) Newton’s second law of motion states that F = ma, where F is
the force in units of newtons (designated by N) applied on an object of mass
m (in kilograms) anda is the acceleration of the object (in m/s^2 ). Thus,
1N=1kgm/s^2. As an example, if a = g = 9.8 m/s^2 is the acceleration of324 11 Biophotonics Technology Applications