Data on the concentration of urea in blood and urine helps in diagnosing renal and liver diseases. In a development that can enhance this, researchers at the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam, near Chennai, have now developed an inexpensive, highly sensitive optical probe that can almost instantaneously detect the presence of urea across a very broad range (0.003 to 334 grams per litre).
Analytical approaches currently available cannot measure urea in a large concentration range, and some methods need pre-treatment of the sample.
How it works
The two-member team, led by Dr. John Philip from the Metallurgy and Materials Group, used a magnetic nanofluid emulsion (oil droplets finely dispersed in water) attached with certain macromolecules (polymers) for detecting urea. The polymer attached to the oil droplets appears like a ball with a shock of hair in all directions and keeps the droplets well separated. It is the attached polymer that interacts with urea. The nanoemulsion also contains superparamagnetic nanoparticles that remain suspended in the oil phase. These nanoparticles make the nanoemulsions magnetically responsive.
In the presence of a magnetic field, the emulsion forms a one-dimensional array due to the presence of superparamagnetic nanoparticles. The oil droplets in the array remain separated with a certain amount of spacing between them. “The distance of separation between the droplets is determined by the macromolecules used for functionalisation,” says Dr. Philip.
When urea is added to the emulsion, the spacing between the droplets changes and causes the droplets to move closer to each other. “There is a direct correlation between the concentration of urea present in the sample and the change in distance between the droplets,” says A.W. Zaibudeen, first author of the paper. The results of the study have been published in the journal, Sensors and Actuators B: Chemical .
The urea in the sample interacts with the polymer causing it to change shape; the hair-like structure of the polymer bends or collapses. The change in shape, in turn, reduces the net repulsion between the droplets, leading to a change in the spacing between the droplets. It takes less than a second for the spacing between the droplets to change when urea is added to the emulsion.
“The change in the spacing can be detected using a miniature optical spectroscopy. In principle, we can bring about a colour change in the presence of urea that is easily discernible to the naked eye by using a proper functional molecule,” says Dr. Philip.
A wide range
“We have calibrated the detection range of urea by using a known concentration of urea. We attempted different macromolecules for functionalisation to achieve the best sensitivity and to cover a large range of urea concentration,” he adds.
The researchers used three different polymers in order to measure urea in a large concentration range — very minute concentration range of 0.003-0.6 grams per litre which covers the normal range of urea in human serum, mid concentration range of 0.18-33.3 grams per litre, and large concentration range of 2.4-334 grams per litre.
To mimic urine and serum samples, the researchers added sodium, potassium and iron to the emulsion. “The probe was still able to detect urea but at a slightly reduced sensitivity,” says Dr. Philip.
In the next phase, they will try and identify appropriate polymers that will exhibit specificity to urea so that even in the presence of other ions, sensitivity is unaffected.
