Filipino scientists and researchers have developed molecular imprinting technology and surface plasmon resonance spectroscopy for fast, highly specific, and sensitive detection method for chemical contaminants in consumer products.

Food contamination caused by leaching of harmful contaminants from food containers such as milk packages, baby bottles, and porcelain mugs is one of the health threats that we face. The immediate detection of these contaminants is necessary before the products are placed on the market. However, the amount of a contaminant that leaks from container is not detectable by sight.

Thus, a fast, highly specific and sensitive method is needed to detect the leaks. Traditional analytical methods are available to detect these chemical contaminants. However, they are known to be slow and require tedious sample preparations and extractions. In this article, a procedure that uses the technology of molecular imprinting is introduced to provide a faster and sensitive alternative method.

The method of detection of chemical contaminants from food containers and food packaging materials is done in two phases – the use of a sensing element and the use of the detector.

For the sensing element, the technology of molecular imprinting in introduced. The principle of molecular imprinting can be explained simply by using the “lock-and-key” model. The “lock” represents the molecular imprint while the “key” represents the chemical contaminant that may leak from food containers and food packaging materials. The chemical contaminant is also called the template molecule.

For the detector, a technique called surface plasmon resonance (SPR) spectroscopy is used. SPR spectroscopy detects changes on top of a molecular imprint film.

Molecular imprinting can be done using a technique called cyclic voltammetry (CV). The properties of the film can be controlled by CV to fit the requirements for the sensing element. These properties are the thickness of the film and the number of molecules in the film that can interact with one another.

In general, molecular imprinting involves the pre-organization of the functional monomers and template of the “key” molecules on top of a metal substrate. This will be followed by polymerization or the association of the monomers to create a very thin plastic called polymers.

The polymers will be washed with solvents to remove the template or the “key” molecules creating holes or cavities in the polymer film. This polymer that now contains holes is what we call the “lock” or the molecular imprints. The “lock” or the molecular imprints can be described by the properties of the “key” or the template that was removed from it.

The second part of the method is the detection of the incoming “analytes”. Analyte is the term used to describe a substance of unknown amount in a sample. In this study, the analytes of interest are the chemical contaminants.

To detect the analytes, SPR spectroscopy is used. This technique is sensitive to changes on a surface of a film. The surface of interest for this study is the molecular imprints on top of the metal substrate.

The figure shows how the SPR curve changes with and without the presence of the analyte in the molecular imprint. When the analyte is detected, the SPR curve shifts to the right in comparison with the SPR curve without the analyte. The extent of this shift is dependent on the amount of the analyte detected in the sample. If there is a great amount detected, the shift will be more dramatic.

The main advantage of this process is that it lessens the time dedicated to the experiment compared with the current methods for chemical contaminant detection. Another advantage is that it is more sensitive than the traditional methods.

The interaction of light with the surface of the film is the basis of SPR. This interaction produces a signal that is dependent on the thickness of the film and how the molecules in the film interact. The SPR instrument can also show that the molecular imprinting is successful and that the imprints can sense the templates.

Some of the analytes tested using this technique are melamine, bisphenol A, bisphenol AF, and bisphenol S.

Melamine is a chemical contaminant commonly found in fertilizers, insecticides, and pet food. However, melamine is commonly used as an impurity to cereal flours to create an apparent increase in the protein content of the flour. The reason for such action is to increase the premium prices of cereal flours in the market.

Other than this, the contaminant can also migrate from plastic tableware to liquids like coffee, juices, and milk. Generally, melamine is non-toxic. However, recent studies showed that excess melamine in the body can cause nephrolithiasis or the formation of calculi in the kidneys.

Other researchers also showed that melamine can cause urolithiasis and bladder cancer. Bisphenol A (BPA) and Bisphenol S (BPS) are industrial chemicals.

These man-made chemicals are commonly used in the manufacture of plastic-based items. These are studies showing that both chemicals can leach out when used as plastic linings for food containers, baby bottles, plastic tableware, white dental filling and sealants.

The leaching rate of bisphenol A and bisphenol S increases with increasing acidity, temperature, and duration of contact with the packaging.

The results of this study demonstrate the combination of molecular imprinting with SPR to be a powerful technique for fast screening of any potential chemical contaminant candidates and the monitoring of known ones. Such data can be made available to the public and can have large impact towards safer products and protecting environment. It can help in the policy and decision making of the government.

Written by: 
Clarisse Buensuceso, Frances Hubilla and Florian R. del Mundo
University of the Philippines Diliman

Published by:
Department of Science and Technology-Science and Technology Information Institution (DOST-STII