Harvard Turns a Silicon Chip Into a DNA Writing Machine

A silicon chip that has spent decades powering computers has just been given a strikingly different job: writing DNA. In a study published this week in Nature Electronics, a Harvard-led team unveiled a device that can synthesize 64 different DNA sequences at the same time using water and enzymes instead of the hazardous chemicals normally required.

The advance, from the lab of Donhee Ham at Harvard's John A. Paulson School of Engineering and Applied Sciences, represents a significant leap for a cleaner method of manufacturing custom DNA — a workhorse ingredient of modern medicine, diagnostics, cancer research and genome engineering.

Most synthetic DNA today is made using a decades-old process called phosphoramidite chemistry, which can produce millions of sequences in parallel but relies on aggressive organic solvents. Because of that, it typically happens inside specialized centralized facilities with dedicated waste-handling infrastructure. Enzymatic DNA synthesis — the water-based approach used in living cells — has long promised a gentler alternative, but until now it has lagged badly on throughput. Previous demonstrations of enzymatic chips maxed out at roughly a dozen sequences at once.

The Harvard team blew past that ceiling. Their chip successfully assembled 64 different DNA sequences in parallel, each as long as 39 nucleotides, all in an aqueous environment.

Here is how it works. DNA is assembled one nucleotide at a time. After each nucleotide is added, a temporary blocking group prevents the strand from growing further. To attach the next building block, that blocker has to be removed through "deprotection" — a small chemical unlocking step that happens when the surrounding water briefly becomes more acidic. Producing many different sequences at once means being able to lower the pH only at very specific locations on the chip during each cycle.

That is what the Harvard chip does. Its surface holds 64 synthesis sites, each surrounded by two concentric ring electrodes with DNA molecules anchored in the middle. When a site is activated, the inner electrode releases a burst of protons that acidify just that tiny patch of water. The outer electrode simultaneously mops up any acid that starts drifting outward, keeping the reaction pinned to a single spot. Repeating that cycle nucleotide by nucleotide lets the chip independently grow 64 unique strands across its surface.

One of the most charming details of the story is where the chip came from. It was not originally designed to make DNA at all. Jeffrey Abbott, a former PhD student in Ham's lab, originally built its silicon electronics to record electrical activity from large populations of neurons. The team eventually wondered whether the same fine-tuned current control they were using to poke holes in cell membranes could be redirected to steer chemistry on a molecular level. It worked.

"A defining feature of the chip was precision current injection, which we used to permeabilize neuronal membranes for intracellular access," Ham said. "At a certain point, we wondered whether that same current control could be redirected from cells to molecules, replacing the neuron-facing electrodes with ring-electrode pairs that could localize pH for DNA synthesis."

Water-based synthesis matters for more than just laboratory aesthetics. Reducing reliance on hazardous solvents lowers waste, cuts the environmental footprint of large-scale DNA production and could eventually enable smaller, safer synthesis units to be deployed outside of centralized facilities — inside hospitals, university labs or even remote research stations.

As a bonus demonstration, the team used the 64 synthesized sequences to encode 169 bytes of text — a nod to the long-term prospect of DNA-based data storage, which could one day pack enormous amounts of information into vanishingly small volumes. That application will require synthesis at a scale orders of magnitude beyond what today's chips can do, but the researchers argue that a scalable, water-based approach is exactly the direction such an industry would need.

"DNA data storage asks DNA synthesis to operate at a scale far beyond today's needs," said co-first author Woo-Bin Jung, now an assistant professor at POSTECH in South Korea. "That is why enzymatic synthesis in water can matter. If far more than 64 sequences can be synthesized in parallel, it could offer an environmentally friendly route toward writing DNA at very large scale."

The next step, the researchers say, is chemistry — refining the enzymes and reaction conditions so that longer, higher-fidelity sequences can be produced even more efficiently. But the core insight is already established: a general-purpose silicon platform, tweaked with the right electrodes, can double as one of the cleanest DNA factories ever built.