It has been almost two years since my fellow FoodSmartphone colleagues, and I have started developing our state of art biosensors for food analysis. For those who might not know what a biosensor is, it is an analytical device to detect and measure the amount of the analyte in a sample based on different sensing strategies. Some use the interaction of antibody and antigen, and some are based on the aptamer, DNA, or enzyme. They have been designed to detect the trace and ultra-trace amount of food contaminants with the highest sensitivity. Now, it is time for us to test our biosensors in real food samples. For this, sample preparation is considered to be a critical step. Therefore, in this blog, I would like to write about sample preparation step for Food analysis.
Sample preparation is one of the biggest challenges when testing food samples. First of all, food samples are not consistent. The designed biosensors usually require a minimal amount of sample, about a few milligrams should suffice for a test. If we consider testing Muesli, which is a mixture of rolled oats and ingredients like grains, nuts, seeds, and dried fruits, we might end up with testing just fruits and no grains. Therefore, the samples need to be homogenized to have reliable and accurate test results. That’s why the samples must be ground to fine particles (less than 0.5 millimeters) and then appropriately mixed. Once, we made sure that our test sample is an accurate representation of the original food sample, we need to isolate the target analyte and get rid of the matrix interferences.
The main goal of the sample preparation step is to extract and isolate the target analyte (mycotoxins, pesticides, and antibiotics) from food samples. The extraction method is based on the contaminants solubility and usually is done using organic solvents such as methanol and acetonitrile, particularly in case of my target analyte aflatoxins. The issue here is that the biorecognition interaction of the antibody or aptamer with target analyte in a biosensor is adversely affected by the organic solvents. Moreover, the protein, fat, and starch content of the extract promotes nonspecific interactions and affects the biorecognition as well. One way to get rid of these adverse effects is to dilute the extract. However, this means lowering the target analyte concentration needs to be detected. Another way is to evaporate the organic solvent and reconstitute the analyte in a water-based solution.
No matter which extraction method we choose, we should consider the automation and miniaturization capability in mind. The solid-phase microextraction method seems to be a perfect choice since it provides simple extraction using a lower volume /no extraction solvent. In this method, the analyte is extracted by being adsorbed on the fibers coated with the sorbent or polymer. The coatings type and its polarity, thickness, and surface area depend on the target analyte characteristics and the sample matrix. Then these fibers will be transferred for detection, and the analyte will be desorbed. The advantageous of this extraction method includes being fast, simple, and no need for solvents. Moreover, it can be efficient for onsite sampling by non-experts. However, the commercial solid-phase microextraction cartridges are expensive and can increase the test cost for the end-user.
To conclude, the sample preparation for food analysis is a multifaceted challenge. The ideal solution needs to be a fast, simple, and efficient extracting cartridge with the minimum additional cost for the test. That’s the goal we all working so hard to achieve, hopefully very soon. Till my next blog with even more exciting news and discussion on our FoodSmartphone biosensors