What is the Field of Biophysics?

Biophysics applies physics tools and concepts to living systems in three main ways: using physics instruments to measure biology more precisely, using biological systems to study fundamental physics phenomena that are otherwise hard to realize experimentally, and applying physics training to biomedical engineering problems. Medical physics, covering imaging and radiation therapy, is a related but distinct field.

Key Takeaways

• Optical tweezers, which use focused lasers, have been used to measure the force required for the motor protein kinesin to walk along a microtubule.
• Deoxyribonucleic acid (DNA) has become a standard model polymer for single-chain polymer physics experiments because it is large enough to see under a microscope, small enough for thermal effects to dominate its behavior, and monodisperse, meaning all chains are the same size.
• Bulk polymer physics theories were historically tested only through scattering or rheology experiments on many chains at once, not single chains.
• Medical physics covers two primary applications in routine clinical use: medical imaging and radiation therapy.
• Positron emission tomography (PET) scans rely on detecting antimatter to locate tumors.

What Is Biophysics?

The most literal answer, based on the name itself, is that biophysics combines biology and physics. That combination takes several distinct forms, each with a different relationship between the two fields. The sections below describe these forms separately, since they represent genuinely different kinds of work rather than a single unified discipline.

Using Physics to Make Better Biological Measurements

One of the most common areas of biophysics applies the precise measurement tools developed in physics to learn more about living systems at the cellular and molecular scale. This is the broadest branch of biophysics, and the one with the most direct overlap between biology and physics research.

Optical tweezers, which use focused laser beams, have been used to measure the force required for the motor protein kinesin to walk along a microtubule. Other examples include developing new fluorescence microscopy techniques to observe dynamics inside living cells, using atomic force microscopy to physically probe cells and observe their mechanical response, and firing lasers at photosynthetic organelles to track how light energy is transferred through them.

Using Biology to Study Fundamental Physics

Some physical phenomena are conceptually interesting but difficult to realize experimentally using conventional engineered systems. A subset of these phenomena can instead be found in biological systems. Life has been evolving for roughly a billion years, and in some cases biological structures already solve engineering problems that physicists would otherwise need to build from scratch.

DNA as a Model Polymer

A large body of theoretical work has gone into understanding the physics of gels, plastics, and other soft materials, based on the thermodynamic behavior of single polymer chains and the interactions between different parts of a chain. Experiments testing these theories historically relied on the bulk properties of many chains at once, measured through scattering or rheology experiments, rather than on single chains.

To test single-chain theories directly, researchers needed a polymer large enough to see under a microscope, small enough that thermal effects dominate its behavior, and monodisperse, meaning all chains are the same size. Deoxyribonucleic acid (DNA) satisfies all three properties. Over roughly the past twenty years, a field has developed around studying polymer physics using DNA, not because of its genetic sequence but because it functions as the best available model polymer.

Active Matter and Self-Propulsion

Active matter is another example drawn from biology. When a large number of particles interact without any internal energy source, they move around randomly, collide, and dissipate excess energy, behavior described by standard thermodynamics and statistical mechanics. When those particles can instead consume energy to propel themselves, their motion can no longer be explained by equilibrium thermodynamics alone, and distinct phenomena emerge as a result.

Researchers could attempt to engineer self-propelling particles from scratch to study these effects, but living organisms are already self-propelling, powered by adenosine triphosphate (ATP) metabolism. Physicists studying this branch of biophysics are often motivated less by any biological or medical application and more by the underlying physics itself being compelling on its own terms.

Physicists Working in Biomedical Engineering

A third branch of biophysics involves physicists applying their training directly to biomedical engineering problems, developing tools, devices, or analytical methods aimed at biomedical rather than purely physical questions.

Medical Physics

Medical physics is typically considered a separate field from biophysics, but the similarity in naming often causes the two to be grouped together. Medical physics has two main applications in routine clinical use: medical imaging and radiation therapy. Both draw on substantial physics expertise, and radiation-tissue interactions remain an active area of ongoing research within the field.

Positron emission tomography (PET) scans rely on detecting antimatter to locate tumors, one example of how deeply physics principles are embedded in modern diagnostic imaging.

Frequently Asked Questions

Is biophysics the same as biochemistry?

No. Biophysics and biochemistry are distinct fields that both study living systems but draw on different core tools and training. Biophysics centers on applying physics measurement techniques and physical theory to biological questions, while biochemistry approaches living systems primarily through chemistry.

Is medical physics part of biophysics?

Medical physics is typically considered a separate field from biophysics, though the similar names often lead people to group them together. Medical physics focuses specifically on medical imaging and radiation therapy rather than the broader range of biological systems studied in biophysics.

Why do physicists study DNA if they are not interested in genetics?

Physicists studying DNA as a model polymer are typically not interested in its genetic sequence at all. Instead, DNA is useful because it is large enough to observe under a microscope, small enough for thermal effects to dominate its behavior, and monodisperse, meaning every chain is the same size, making it an ideal physical model for testing single-chain polymer theory.

What is active matter?

Active matter refers to systems of particles that consume energy to propel themselves, rather than simply moving and colliding randomly while dissipating energy. Because these particles generate their own motion, their collective behavior cannot be fully explained by equilibrium thermodynamics, producing distinct physical phenomena that researchers can study using naturally self-propelling living organisms.

How do PET scans use antimatter?

Positron emission tomography (PET) scans detect antimatter particles as part of locating tumors in the body. This represents one way that fundamental physics principles are applied directly within routine medical imaging.

Glossary

• Optical tweezers: focused laser beams used to measure or exert tiny forces, such as the force required for kinesin to walk along a microtubule.
• Monodisperse: describes a population of polymer chains that are all the same size.
• Active matter: systems of particles that consume energy to propel themselves rather than moving through random collisions alone.
• Adenosine triphosphate (ATP): the molecule that powers self-propulsion in living organisms.
• Positron emission tomography (PET): a medical imaging technique that detects antimatter particles to locate tumors.