A target-responsive and signal-amplified DNA hydrogel biosensor for visual and quantitative detection of aflatoxin B1

Source: Journal of Food and Drug Analysis, by Haojie Du; Haoyue Liu; Yongshuai Li; Shiyi Wei; Xinning Wang; Yunxuan Weng; Xiaoying Zhao (September 10, 2026). AI-generated summary by biochip.com, published September 23, 2026. Not independently reviewed.

Researchers at Beijing Technology and Business University have built a DNA hydrogel biosensor that turns the presence of aflatoxin B1 into a visible color signal. Aflatoxin B1, often shortened to AFB1, is a fungal toxin that can contaminate foods including grains, peanuts, milk, eggs, and animal feed. The sensor uses a soft sodium alginate gel held together by DNA strands that recognize AFB1, while trapped gold nanoparticles provide the visual readout. When AFB1 binds the DNA, it breaks apart the gel's crosslinks and releases the gold nanoparticles, producing a measurable signal. The team added an enzyme-driven recycling step designed to make one toxin-triggered event disrupt more of the gel network. In testing, the system measured AFB1 across a 0 to 50 micromolar range and reached a reported detection limit of 12.9 nanomolar. The device is aimed at rapid, on-site food safety screening, where conventional laboratory methods can be costly and slow. It is a substantive biosensing platform because the hydrogel itself combines molecular recognition, signal generation, and amplification in one portable format.

A gel designed to fall apart on command

A hydrogel is a water-rich network of polymers, much like a soft kitchen gelatin or contact lens. In this sensor, sodium alginate forms that network, but the crucial structural links come from specially designed DNA sequences called aptamers.

An aptamer is a short, single-stranded DNA molecule that folds into a shape able to bind a specific target. Here, the aptamer recognizes AFB1. It serves two jobs at once: it helps crosslink the hydrogel and gives the material its chemical selectivity.

How AFB1 produces a visible signal

The sensing process resembles a net held together by clips that release when they encounter the right molecule. In the intact state, aptamer crosslinkers connect modified polymer chains and keep gold nanoparticles, or AuNPs, enclosed within the hydrogel.

When AFB1 enters the system, it binds the aptamer. That interaction causes the aptamer crosslinker to dissociate from the network, weakening and ultimately disintegrating the gel. As the structure comes apart, it releases the gold nanoparticles, which act as a colorimetric reporter that can be visually observed and quantitatively measured.

Why gold nanoparticles are useful reporters

Gold nanoparticles are tiny particles of gold whose optical properties make them useful in color-based tests. Their role here is not to identify the toxin directly. Instead, they make the hydrogel's physical response easier to see.

This arrangement separates recognition from reporting. The aptamer supplies the molecular recognition step, while nanoparticle release translates that event into a signal. Such a design can be easier to interpret outside a specialized laboratory than an instrument-heavy analytical workflow, although the reported work does not establish performance in real food samples.

Amplifying a small molecular event

The team incorporated Exonuclease I, or Exo I, to amplify the response. Exo I is an enzyme that can cleave single-stranded DNA. In this design, it acts on the aptamer-target complex after AFB1 has initiated the process.

The practical idea is recycling. Rather than allowing an AFB1 molecule to trigger only one disruption event, cleavage of the complex can free the target to interact again, extending hydrogel disruption and releasing more nanoparticles. That amplification strategy is intended to improve sensitivity when toxin concentrations are low.

Measured detection performance

The researchers optimized the sodium alginate concentration and the hydrogel crosslinking conditions before evaluating the sensor. They reported a linear AFB1 detection range from 0 to 50 micromolar, meaning the measured response changed in a consistent relationship with toxin concentration over that interval.

The reported detection limit was 12.9 nanomolar. A detection limit describes the lowest concentration distinguishable from background under the study's test conditions. The sensor also showed high selectivity toward AFB1, indicating that its response was stronger for the intended toxin than for the other substances assessed by the team.

Why conventional testing remains difficult to replace

High-performance liquid chromatography and mass spectrometry are established methods for measuring aflatoxins. They offer strong reliability and selectivity, but they generally require costly equipment, trained operators, and time-consuming procedures.

A colorimetric hydrogel sensor addresses a different use case: screening where food is produced, stored, or handled. The goal is not simply to make a laboratory assay smaller. It is to create a material that converts toxin recognition into a readout that could support portable, on-site testing.

Why This Matters

AFB1 is a serious food safety concern because of its potent carcinogenicity and its potential presence throughout the food chain. Contamination can arise during agricultural production and storage, then persist in products consumed by people or used as feed for animals.

The platform demonstrates how a biosensor can integrate several functions into one material: a DNA recognition element, a hydrogel structure, a nanoparticle reporter, and enzymatic signal amplification. That integration is central to chip and sensing technology because it can reduce the number of separate instruments and processing steps needed to obtain a result.

What comes next for the platform

Before a hydrogel sensor like this could support routine food monitoring, it would need to perform reliably with complex real-world food matrices, where proteins, fats, pigments, and other chemicals may affect the signal. It would also need practical workflows for sample preparation, storage, calibration, and interpretation. Still, the work offers a clear design strategy: build a responsive material that physically changes when it encounters a toxin, then make that change easy to see.

Topics: Biosensors · Food & agriculture

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