Exploring the nanoscale engines that are transforming medicine, computing, and smart materials
Imagine machines so tiny that thousands could fit within the diameter of a human hair—molecular motors represent one of the most exciting frontiers in modern science.
These nanoscale devices, which convert various forms of energy into mechanical motion, are inspiring a new generation of materials and technologies. From light-activated systems that can precisely target cancer cells to molecular shuttles that move along tracks like miniature trains, these biological and synthetic engines are pushing the boundaries of what's possible at the nanoscale.
The development of artificial molecular machines earned the 2016 Nobel Prize in Chemistry, highlighting their transformative potential. As researchers continue to unravel the mysteries of these microscopic workhorses, they're paving the way for breakthroughs in medicine, computing, and smart materials that were once confined to the realm of science fiction.
Operating at molecular levels with unprecedented control
Activated by light, electricity, or chemical fuels
Revolutionizing targeted therapies and drug delivery
Molecular motors can be defined as supramolecular structures designed to perform specific functions through mechanical movements of their components when stimulated externally. In essence, they are molecules engineered to carry out tasks—making them the molecular equivalents of the machines we encounter in our daily lives, but operating at the atomic scale.
What makes these systems truly remarkable is their ability to convert energy into mechanical work, much like their macroscopic counterparts, but through nuclear rearrangements rather than moving parts.
These protein-based systems are found throughout biological organisms and are powered by ATP (adenosine triphosphate), the universal energy currency of cells. Prime examples include kinesin and myosin, which transport cargo within cells and enable muscle contraction.
Created in laboratories, these come in two main varieties: DNA-based motors that derive energy from DNA interactions, and chemical molecular motors that can be powered by light, electrical energy, or chemical reactions.
| Motor Type | Power Source | Key Features | Potential Applications |
|---|---|---|---|
| Natural Protein Motors | ATP hydrolysis | High efficiency, biological compatibility | Understanding cellular transport, biological inspiration |
| Synthetic Chemical Motors | Light, electricity, chemical fuels | Tunable properties, robust operation | Smart materials, nanofabrication |
| DNA-based Motors | DNA hybridization/dissociation | Programmable, self-assembling | Biosensing, programmed drug release |
| Hybrid Systems | Multiple sources (e.g., light + chemical) | Enhanced functionality, adaptive response | Complex nanomachines, environmental remediation |
The field of molecular motors has recently witnessed remarkable advances that are pushing the technology toward practical applications. One of the most significant challenges has been the reliance on ultraviolet light to power many synthetic molecular motors—a limitation that restricts their use in biological systems and other environments where UV light can cause damage.
In a groundbreaking development published in October 2025, researchers at Tianjin University demonstrated that molecular motors can run on gentler, visible light when paired with quantum dots and a helper molecule.
This innovative approach uses quantum dots—semiconductor nanocrystals that absorb visible light—as "light-harvesting antennas" that capture green, yellow, and even red photons and transfer their energy to the motors. The implications are profound: "Visible light is a clean and abundant energy source for molecular motors," notes Lili Hou, a corresponding author of the study. "Our strategy shows a way to run these motors across the visible range, opening opportunities for micropumps, microvalves, nanorobots, or even molecular surgery tools." 1
In another landmark study from the University of Warsaw, researchers designed a molecular motor whose direction of rotation can be controlled remotely using electric field pulses. Traditional molecular motors have their chirality—or "handedness"—permanently built into their structure, meaning a given motor will always rotate in one fixed direction.
The Warsaw team overcame this limitation by incorporating a special switching unit that changes the motor's chirality when triggered by a properly oriented electric field. This breakthrough opens new possibilities for precise molecular control, potentially enabling applications in molecular engineering, smart surfaces, and nanorobotics where the ability to program rotation direction could be used to create switchable materials or direct molecular assembly processes. 2
First synthetic molecular machine created
Opened the field of artificial molecular machinesNobel Prize in Chemistry for molecular machines
Recognized the transformative potential of the fieldVisible-light-powered motors using quantum dots
Overcame key limitation of UV light requirementElectric-field-switchable rotation direction
Enabled remote control of molecular motor directionOne of the most compelling recent experiments in molecular motors comes from researchers at the Japan Advanced Institute of Science and Technology (JAIST), who achieved the remarkable feat of directly observing molecular motors in real time. The team, led by Associate Professor Ken-ichi Shinohara, focused on a system called polypseudorotaxane, where ring-shaped α-cyclodextrin (α-CD) molecules shuttle back and forth along a poly(ethylene glycol) (PEG) polymer chain. While such systems have been studied for years, the specific structural changes behind their movement had remained unclear—until now. 3
| Parameter | PEG Chain Alone | PEG@α-CD Complex | Change |
|---|---|---|---|
| Average Length | 48.1 nm | 499.6 nm | ~10x increase |
| Flexibility | Highly flexible, spring-like | More rigid structure | Reduced flexibility |
| Observed Motion | Random coiling/uncoiling | Directed shuttling motion | Controlled mechanical action |
| Primary Motion Mechanism | Thermal fluctuations | α-CD ring movement | Energy-driven transport |
"The polypseudorotaxane exhibited shrinking and extending motions driven by the shuttling of α-CD rings along the polymer chain," as Dr. Shinohara explained. These movements primarily occurred in the exposed PEG segments, where repeated expansion and contraction were observed as the α-CD rings moved back and forth.
Building and studying molecular motors requires specialized materials and methods. Below is a guide to key research reagents and their functions in creating and operating these nanoscale machines:
| Reagent/Method | Function | Example Use Case |
|---|---|---|
| Poly(ethylene glycol) (PEG) | Polymer track for molecular shuttles | Serves as a "rail" for cyclodextrin rings to move along in polypseudorotaxane systems |
| α-Cyclodextrin (α-CD) | Ring-shaped component that moves along tracks | Acts as a molecular "shuttle" in PEG@α-CD systems |
| Quantum Dots | Light-harvesting antennas | Extend molecular motor operation to visible light spectrum |
| 9-Anthracenecarboxylic Acid | Mediator molecule | Transfers energy from quantum dots to molecular motors |
| Fast-Scanning Atomic Force Microscopy (FS-AFM) | High-resolution imaging technique | Visualizes molecular motion in real time at solid-liquid interfaces |
| Molecular Dynamics Simulations | Computational modeling | Predicts and explains molecular behavior and interactions |
As research progresses, molecular motors are poised to transition from fundamental studies to transformative technologies. One of the most promising avenues lies in biomedical applications. Researchers at Texas A&M University are pioneering the use of light-activated molecular motors for non-invasive cancer therapies. These nanometer-sized machines can enter cancer cells and, when triggered by light, apply mechanical forces from within to selectively disrupt cancerous activity.
"This could have relevance in diseases with existing chemical therapeutics that have unpleasant and often debilitating side effects or to treat diseases where existing drugs provide very limited efficacy, like many cancer and chronic diseases."
What makes this approach revolutionary is its fundamental operating principle. Unlike conventional treatments that rely on chemical agents acting from outside the cell, molecular motors apply mechanical forces from within the cell itself. "The most significant aspect of this work is the proof that internal mechanical forces, which are created by light-activated molecular machines, can specifically and effectively modulate cell behavior," explains Galvez-Aranda. 4
Surfaces that can change their properties on demand, such as switching between repelling and absorbing water in response to light.
Development of synthetic nano-robots or smart molecules that can perform tasks inside the human body.
Materials that can efficiently capture and convert light energy into mechanical work for solar energy applications.
Materials whose shape, stiffness, or other properties can be controlled through coordinated molecular motor action.
As Professor Jorge Seminario of Texas A&M notes, research groups are "deeply engaged in advancing both ab initio (first principles) and AI-driven computational methods to pioneer the next generation of materials discovery," highlighting how computational approaches are accelerating progress in this field. 5
Molecular motors represent a fascinating convergence of biology, chemistry, physics, and materials science—a field where fundamental discoveries are rapidly translating into transformative applications.
From the elegant efficiency of natural molecular machines that have evolved over billions of years to the creative design of synthetic systems that push the boundaries of human ingenuity, these nanoscale engines are expanding our understanding of what's possible at the smallest scales.
As research continues to overcome technical challenges—such as operating under biological conditions with visible light and achieving precise external control—we move closer to a future where molecular motors can routinely perform tasks inside our bodies, within advanced materials, and as part of the technological infrastructure that supports our daily lives.