Submicroscopic refers to objects or structures that are too small to be seen with a standard light microscope. This realm exists beyond the limits of visible light, encompassing entities whose dimensions are far smaller than the wavelength of light itself. Understanding this unseen world is fundamental to comprehending the intricate workings of matter and life.
Understanding the Scale
The world can be categorized by scale: macroscopic objects are those large enough to be seen with the naked eye, such as a human or a table. Microscopic objects, conversely, require a light microscope for visualization, typically ranging from a few micrometers to a millimeter in size. Submicroscopic entities are even smaller, existing below the resolution capabilities of light microscopes, often measured in nanometers, which are billionths of a meter. Traditional light microscopes are limited because visible light has a wavelength between approximately 400 and 700 nanometers.
Common Examples
Numerous common entities fall into the submicroscopic category. Atoms, the basic building blocks of all matter, are typically around 0.1 to 0.5 nanometers in diameter. Molecules also exist at this minuscule scale, with their sizes varying depending on the number and arrangement of atoms. Viruses are complex biological structures, typically ranging from 20 to 400 nanometers, placing them firmly within the submicroscopic domain.
Visualizing the Invisible
To study submicroscopic structures, scientists employ advanced technologies that bypass the limitations of visible light.
Electron Microscopes
Electron microscopes, such as the Transmission Electron Microscope (TEM) and the Scanning Electron Microscope (SEM), utilize beams of electrons instead of light. TEMs pass electrons through an ultra-thin sample to reveal its internal structure and composition, providing details down to 0.1 nanometers. SEMs scan a focused electron beam across a sample’s surface, detecting scattered electrons to create detailed images of its topography and surface composition.
Scanning Probe Microscopes
Scanning probe microscopes offer another approach to “seeing” the submicroscopic world by using a physical probe to interact with a sample’s surface. The Scanning Tunneling Microscope (STM), for instance, uses an atomically sharp conductive tip brought very close to a conductive sample. A small electrical current, known as a tunneling current, flows between the tip and the sample, and by keeping this current constant as the tip scans, an image of the surface’s electron density is created. The Atomic Force Microscope (AFM) overcomes the STM’s conductivity requirement by using a sharp tip on a flexible cantilever that physically interacts with the sample’s surface, measuring the minute forces between the tip and the sample. The deflection of the cantilever is then translated into a topographic image of the surface.