A tribute to the visionary scientist who transformed DNA into a switchable circuit and opened new frontiers in molecular electronics
Imagine a world where the very molecules of life can be harnessed as tiny electronic components, where DNA becomes a switchable circuit, and diseases are detected by sensors a thousand times smaller than a human hair. This isn't science fiction—it was the revolutionary world of Professor Nongjian "NJ" Tao, a visionary scientist who dedicated his career to the electrifying intersection of biology and nanotechnology. At his laboratory in Arizona State University, Tao and his teams performed what seemed like molecular magic: they made DNA dance to an electrical tune, transforming our understanding of how electrons move through the building blocks of life 2 6 .
To appreciate Tao's breakthroughs, we first need to understand a fundamental question: how do electrons—the carriers of electrical energy—move through molecules? For decades, scientists had debated whether electrons traveled through DNA and other biological molecules like waves or like particles.
"Think of trying to cross a river," explained Limin Xiang, a postdoctoral researcher in Tao's lab. "You can either walk across quickly on a bridge or try to hop from one rock to another. The electrons in DNA behave in similar ways." 7
Electrons flow smoothly and efficiently, much like water flowing through a pipe. This coherent transport is characteristic of metals and allows for fast, efficient conduction.
Electrons jump disjointedly from one position to another, similar to crossing a river by leaping between stones. This "incoherent transport" is less efficient but common in semiconductor materials 7 .
What made Tao's work revolutionary was his discovery that we could intentionally tune DNA to favor one type of transport over the other—essentially giving scientists a dial to control how electricity flows through biology's most important molecule 7 .
In 2017, Tao's team announced a breathtaking achievement: the first controllable DNA switch that could regulate the flow of electricity within a single molecule 6 . This wasn't just an incremental advance—it was the molecular equivalent of inventing the light switch, only on a scale a thousand times smaller than a human hair.
They replaced one of DNA's standard chemical letters (A, C, T, or G) with a three-ringed carbon structure called anthraquinone (Aq) 6 .
Anthraquinone contains what chemists call a "redox group"—a component that can reversibly gain or lose electrons. When sandwiched between DNA's iconic double-helix structure, this modification gave DNA a newfound ability to turn electrical flow on and off 6 .
By carefully adjusting the electrical field around the modified DNA, the team could precisely control whether the molecule was in a high-conductance ("on") or low-conductance ("off") state 6 .
"It has been established that charge transport is possible in DNA, but for a useful device, one wants to be able to turn the charge transport on and off. We achieved this goal by chemically modifying DNA." 6
| Discovery | Year | Significance | Application Potential |
|---|---|---|---|
| Controllable DNA switch | 2017 | First molecular switch to regulate electricity in DNA | Disease detection, renewable energy studies 6 |
| Sequence-dependent charge transport | 2016 | Demonstrated DNA sequence tunes electron flow | Engineering DNA-based nanowires 7 |
| Odd-even conductance effect | 2016 | Found conductivity varies with patterned G-blocks | Precise molecular circuit design 7 |
Tao's most influential contribution to molecular electronics wasn't a single discovery, but rather a revolutionary method that enabled an entire field of research: the scanning tunneling microscope break junction (STM-BJ) technique 1 2 .
Before Tao's innovation, scientists struggled to reliably measure the electrical properties of single molecules. The challenge was akin to trying to measure the conductivity of a single strand of hair by connecting it to two enormous electrical pads—the scale difference made meaningful measurements nearly impossible.
This technique transformed the field because it allowed for the collection of large enough datasets for robust statistical analysis, providing far more reliable values for molecular conductance measurements than previous low-throughput approaches 1 .
| Molecule | Resistance (megohms) | Molecular Description |
|---|---|---|
| Hexanedithiol | 10.5 ± 0.5 | 6-carbon chain with sulfur end groups |
| Octanedithiol | 51 ± 5 | 8-carbon chain with sulfur end groups |
| Decanedithiol | 630 ± 50 | 10-carbon chain with sulfur end groups |
| 4,4' bipyridine | 1.3 ± 0.1 | Nitrogen-containing aromatic compound |
The data revealed another crucial pattern: the resistance increased exponentially with the length of the molecular chain, with a characteristic "tunneling decay constant" of approximately 1.0 per carbon atom for N-alkanedithiols . This quantitative relationship provided fundamental insights into how easily electrons can tunnel through molecular frameworks.
Tao's groundbreaking work was made possible by both sophisticated instruments and chemical ingenuity. Here are the key tools that formed the backbone of his research:
| Tool/Technique | Function | Significance in Tao's Work |
|---|---|---|
| Scanning Tunneling Microscope (STM) | Probes surfaces at atomic resolution | Core instrument for break junction experiments 2 |
| Atomic Force Microscope (AFM) | Measures topography and forces at nanoscale | Studied molecules in electrochemical environments 2 |
| Surface Plasmon Resonance (SPR) | Detects molecular interactions via light reflection | Enabled highly sensitive chemical and biological sensing 2 |
| Anthraquinone modification | Chemical DNA alteration | Created the first controllable DNA switch 6 |
| Gold electrodes | Molecular-scale electrical contacts | Provided junctions for measuring single molecules |
Nongjian Tao's impact extended far beyond academic publications. A truly prolific innovator, he published over 350 research papers that had been cited nearly 30,000 times by the time of his passing, achieving an exceptional h-index of 90 3 9 . He was awarded 26 U.S. patents, with most utilized in commercial products 3 .
Perhaps most telling of Tao's practical impact were the two companies he co-founded based on his inventions:
Even in his final years, Tao continued pushing boundaries. In 2023, a project he contributed to received a $1 million grant to develop low-cost mass measurement techniques for single molecules—research with potential applications in pharmaceutical drug screening, food safety, and clinical diagnosis 5 .
Nongjian Tao's work fundamentally changed our relationship with the molecular world, transforming DNA from solely a biological blueprint into a potential component for tomorrow's technologies. His research provided the tools and understanding to begin harnessing the natural molecular machinery of life for human innovation.
"You could say we are engineering the wave-like personality of the electron." 7
The controllable DNA switches and precise molecular measurement techniques Tao developed continue to inspire new generations of scientists working at the intersection of biology and technology. As we look toward a future of ever-smaller electronic devices, more precise medical diagnostics, and novel renewable energy solutions, we're building upon the foundation laid by this remarkable molecular maestro.
Through his lasting contributions to science, Nongjian Tao ensured that those electrons would continue moving purposefully through molecules, powering innovations that will enhance our lives for decades to come.