IIT Jodhpur fabricates highly sensitive device to detect lead

 

In news:

• A highly sensitive, portable device that can detect the presence of lead in water even when present in extremely small amount of 0.018 parts per billion (ppb) has been fabricated by a team of researchers from the Indian Institute of Technology (IIT) Jodhpur.

 

Important facts:

• The sensor is highly specific to lead even in the presence of other metals.
• The World Health Organisation limit for lead in drinking water is 5 ppb.
• The sensor can be reused multiple times.
• The results were published in the journal IEEE Electron Device Letters.
• The research was done in collaboration with the Singapore-based Agency for Science, Technology and Research.

 

Fabricating the sensor:

• The sensor is fabricated using silicon wafer as the base material. However, the crystal structure of silica and gallium nitride/aluminium gallium nitride is different and so they experience stress when grown on silicon.
• The thermal expansion of silicon and gallium nitride is different.  As the layers are grown at 1,000 degree C, it causes stress on the grown material.
• To produce a layer of gallium nitride that is stress-free, the researchers produced a stack of five layers of gallium nitride and aluminium gallium nitride on the silicon wafer base (with the percentage of aluminium in gallium nitride reducing from 100% to 0%).
• This helped in producing an almost defect-free gallium nitride layer at the top. A layer of AlGaN is then grown on the defect-free gallium nitride.
• The researchers then fabricated the source and drain terminals that allow the electrons to flow and then used a gate (akin to a valve) to regulate the flow of electrons.
• At the junction of the top layers of GaN and AlGaN, a two-dimensional electron gas is formed naturally, which is the conducting layer that moves the electrons from the source to the drain.
• Finally, the gate was functionalised to facilitate lead ion adsorption. When lead ions get adsorbed on the gate, the rate of flow of electrons increases leading to increased current flow.
•  The amount of increase in current depends on the amount of lead ions that get adsorbed.
• There is a slight increase in current even when lead concentration in water is as low as 0.01 ppb. The increase is more at higher lead concentration
• The sensor shows good agreement with the results from standard techniques used for lead detection.

 

Developing more sensors

• Researchers are fabricating an array of devices on a single chip to detect different heavy metal ions. We have already developed a cadmium ion sensor.
• The cadmium sensor has higher sensitivity (0.255 ppb) than other electrochemical approaches and can detect cadmium in about 3 seconds.
• The results of cadmium sensor werepublished in April 2019 in the journal IEEE Electron Device Letters.

 

 

Additional Information:

 

What is Lead?

• Lead is a naturally occurring toxic metal found in the Earth’s crust. Its widespread use has resulted in extensive environmental contamination, human exposure and significant public health problems in many parts of the world.
•  Water is rarely an important source of lead exposure except where lead pipes, for instance in old buildings, are common.
• People are exposed to lead through the air they breathe, through water and through food/ingestion. Toxic effects are usually due to long term exposure. 

 

Key facts related to Lead

• Lead is a cumulative toxicant that affects multiple body systems and is particularly harmful to young children.
• Lead in the body is distributed to the brain, liver, kidney and bones. It is stored in the teeth and bones, where it accumulates over time. Human exposure is usually assessed through the measurement of lead in blood.
• Lead in bone is released into blood during pregnancy and becomes a source of exposure to the developing fetus.
• There is no level of exposure to lead that is known to be without harmful effects.
• Lead exposure is preventable.

 

Impact of lead:

• Young children are particularly vulnerable to the toxic effects of lead and can suffer profound and permanent adverse health effects, particularly affecting the development of the brain and nervous system.
• Lead also causes long-term harm in adults, including increased risk of high blood pressure and kidney damage.
• Exposure of pregnant women to high levels of lead can cause miscarriage, stillbirth, premature birth and low birth weight.
• The neurological and behavioural effects of lead are believed to be irreversible.

 

 

Sources and routes of exposure

People can become exposed to lead through occupational and environmental sources. This mainly results from:

• inhalation of lead particles generated by burning materials containing lead, for example, during smelting, recycling, stripping leaded paint, and using leaded gasoline or leaded aviation fuel; and
• ingestion of lead-contaminated dust, water (from leaded pipes), and food (from lead-glazed or lead-soldered containers).

 

 

WHO Response:

• The phasing out of lead paint by 2020 is one of the priority actions for governments included in the WHO Road map to enhance health sector engagement in the Strategic Approach to International Chemicals Management towards the 2020 goal and beyond.
• This road map was approved by the Seventieth World Health Assembly in decision WHA70(23). 
• WHO has identified lead as 1 of 10 chemicals of major public health concern, needing action by Member States to protect the health of workers, children and women of reproductive age.
• WHO has made available through its website a range of information on lead, including information for policy-makers, technical guidance and advocacy materials.

The elimination of lead paint will contribute to the achievement of the following Sustainable Development Goal targets:

• 3.9: By 2030 substantially reduce the number of deaths and illnesses from hazardous chemicals and air, water, and soil pollution and contamination; and
• 12.4: By 2020, achieve the environmentally sound management of chemicals and all wastes throughout their life cycle, in accordance with agreed international frameworks, and significantly reduce their release to air, water and soil in order to minimize their adverse impacts on human health and the environment.

 

 

Preventive measures:

Preventive measures include:

• Environmental standards that remove lead from petrol/gasoline, paint and plumbing.
• If lead pipes cannot be removed, water (cold should be flushed through in the morning before drinking).
• Enforcement of occupational health standards.
• Surveillance of potentially exposed population groups, especially the vulnerable ones (small children, pregnant women, workers).
• Water treatment.
• Removing lead solder from food cans.
• Use of lead-free paint in homes.
• Screening of children for blood levels over acceptable limit and referral for medical care as necessary.

 

 

Source)

https://www.thehindu.com/todays-paper/tp-features/tp-sci-tech-and-agri/iit-jodhpur-fabricates-highly-sensitive-device-to-detect-lead/article29748088.ece