1. Crisis: Entangled in the food chain - arsenic → Groundwater → rice
Arsenic, as the most common environmental toxic element and carcinogen worldwide, has entered the food chain through the "groundwater - farmland - rice" system, which has become a core issue threatening food safety and human health. Its toxicity and mobility are mainly determined by its chemical form, while biological transformation is the key to morphological change, which is particularly prominent in the coupling of arsenic pollution in groundwater and arsenic accumulation in rice.
The two form a risk chain of "polluted water sources - irrigation - crop absorption - dietary exposure", which not only leads to chronic diseases and cancer caused by direct consumption of polluted groundwater, but also exposes people who mainly consume rice to dual exposure of "drinking water + diet". Exposure during pregnancy can also affect fetal development, and the situation is particularly severe in high-risk overlapping areas such as South Asia and Southeast Asia.
2. Arsenic - highly toxic, carcinogenic, irreversible
The harm of arsenic pollution to public health shows the characteristics of "systemic, long-term latent and multi-system" : its early typical signal is skin lesion, manifested as abnormal pigmentation of the trunk and limbs and keratosis of the palms and soles, which usually appears after 10 to 20 years of exposure. Children, men and those with malnutrition are at higher risk. The most fatal long-term consequence is the induction of cancers in multiple organs such as the lungs, bladder and skin, with an incubation period of up to 40 years.
Arsenic exposure remains one of the main causes of cardiovascular diseases among people in contaminated areas. Exposure during pregnancy increases the risk of stillbirth. Early childhood (including intrauterine) exposure can lead to cognitive development disorders, and the mortality rates of cancer, lung diseases, etc. increase in adulthood. The arsenic exposure per unit body weight of infants and young children who mainly eat rice is three times that of adults. It can also cause numbness in hands and feet, gastrointestinal discomfort, diabetes and other multi-system damages. Patients often face social discrimination due to skin lesions.
3. Bottleneck: On-site arsenic monitoring - A complete blank
The lack of on-site monitoring means for arsenic pollution has become a key bottleneck restricting pollution prevention and control as well as health risk early warning. From a technical perspective, the current mainstream detection still highly relies on the "on-site sampling - laboratory analysis" model, which not only has a cumbersome process, takes a long time and is costly, but also the samples are prone to arsenic form transformation during transportation and storage, leading to distorted results. The current on-site rapid detection methods have obvious flaws: insufficient accuracy and the generation of highly toxic substances. On-site testing of agricultural products such as rice is still a blank. Laboratory testing requires complex pretreatment, and there is no mature on-site rapid quantitative technology in the market, making it difficult to cover the entire production and circulation process. At the practical level, many grassroots environmental protection departments in various places, due to a lack of funds and technology, have not been equipped with special arsenic monitoring devices, and some even have no arsenic monitoring capabilities at all. In developing countries and rural areas, this problem is even more prominent, making it difficult to detect the risk of arsenic pollution spread and exposure in a timely manner, posing a major hidden danger to public health security.
Existing biosensor technologies typically have the following inherent limitations:
1. Insufficient sensitivity and specificity: Although some existing arsenic biosensors can achieve a low detection limit in the laboratory, their sensitivity is easily disturbed when entering real environments containing organic matter and coexisting heavy metals, and their adaptability is insufficient.
2. High background noise (leakage expression) : Arsenic biosensors based on ArsR/Pars suppressed regulation systems generally have background leakage. Although it can be improved through component modification, it is easy to sacrifice signal strength or cause false positives, and the signal is blurred in low-concentration arsenic environments.
3. Lack of ecological relevance: Most arsenic biosensors are based on Escherichia coli as the chassis and constructed with model microbial elements. They have poor environmental adaptability and are difficult to accurately reflect the form and bioavailability of arsenic in real agricultural environments, resulting in a disconnection between "laboratory and field" performance.
4. Single function: The existing arsenic biosensors mostly only achieve the single function of "detection - signal output", lacking a collaborative interface with pollution remediation, and their long-term stability has not been resolved, making it difficult to meet the practical needs in the field.
What We Did
1. Break through the existing sensor "disconnection between laboratory and field"
We extracted the core component of the unique ArsR protein from the endophytic fungus CML2 of rice in an arsenic-contaminated environment. Its sensing characteristics can precisely match the actual demands of farmland ecological niches, making the detection results truly align with the practical significance of agricultural scenarios, thereby breaking the problem of the existing sensors being "disconnected from the laboratory and the field".
2. Solve the widespread problem of background leakage
In terms of technical performance, we rely on multiple rounds of DBTL cycles (design - build - Test - learn) to screen and optimize the promoter, balance the expression of ArsR, and innovatively introduce the split-GFP self-assembly module, fundamentally solving the background leakage problem that is common in inhibitory loops. It has opened up a brand-new path for achieving highly sensitive detection.
3. Build an integrated platform for "detection and repair"
We are currently building an optimized sensor in Escherichia coli, which is a necessary proof-of-concept and component debugging stage. The ultimate goal is to build an integrated "detection-repair" platform within the CML2 strain - by leveraging its natural colonization ability as an endomycete in rice, in the future, live bacterial agents that can not only monitor arsenic pollution in situ and in real time but also simultaneously carry out biological repair will be developed, truly achieving a functional leap from "diagnosis" to "treatment".
Project Introduction Video
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