animals, humans, or plants. Such tests allow the observation of the condition,
the temporal changes, or the effects of an experiment on biological components
within a living entity in its natural surroundings.- In vitro: The term in vitro (Latin for“within the glass”) refers to tests done in a
laboratory setting on biological components that have been extracted from a
living organism. These tests often are made using containers such as glass test
tubes,flasks, and petri dishes. Thus the evaluations are done on microorganisms,
cells, molecules, or tissue samples outside of their normal biological
environment. - Ex vivo: The term ex vivo (Latin for“from the living”) refers to procedures that
typically involve taking living cells, tissues, or an organ from an organism and
examining, modifying, or repairing these biological components in a controlled
environment under sterile conditions with minimal alteration of the natural
conditions from which the samples originated.
There are several aspects of light that make it a powerful tool in the life sciences
and medicine. - The use of photonics techniques in biophotonics research allows contactless
measurements to be made on a tissue sample or within a cell or molecule with
no or minimal disturbance of the biological activity. In addition, many either
contactless or minimally invasive biomedical procedures can be carried out in a
clinical environment. For example, a light source and a camera can be posi-
tioned close to the biological tissue of an evaluation or treatment site for in vivo
contactless procedures. In addition, a thin opticalfiber probe and associated
miniaturized surgical instruments can be inserted through a natural body
opening or through one or more minor incisions in the body for minimally
invasive procedures. A generic example of a minimally invasive procedure is
shown in Fig.1.3. - A large selection of ultrasensitive photonics and biophotonics detection
instruments can be used over spatial scales covering six orders of magnitude
from fractions of a nanometer to centimeters. Table1.1shows examples of the
sizes of some biological components and measurement aids. The biological
components that can be observed, treated, or manipulated vary from micro-
scopic nanometer-sized molecules to macroscopic tissue samples. - As Table1.2shows, the measurement time scales for life sciences research
techniques and for biomedical processes can vary from femtoseconds (10−^15 s)
to hours (10^3 s). Such a broad temporal range can be satisfied by a variety of
photonics devices. For example, as Chap. 4 describes, ultrafast lasers that can
emit short pulse durations (e.g., a few femtoseconds) are available for use in
applications such asfluorescence spectroscopy where the pulse width needs to
be shorter than the desired time-resolution measurement. At the other time
extreme, highly stable lasers are available for processes in which a relatively
constant light output is required for measurements and monitoring of processes
that take place over periods of several hours.
4 1 Overview of Biophotonics