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Posted: May 20, 2014

Nanotechnology in food quality control: Preventing food from biting back (page 3 of 4)

An inexpensive colorimetric method using label-free AgNPs with detection limit of 2.32 mM has been developed by Chinese researchers for rapid on-site detection of melamine adulteration in raw milk without any costly instrument14. In the experiment, presence of melamine induces the aggregation of AgNPs, which leads to the colour change as yellow to red and the adulteration can be measured by UV-Vis spectrophotometer or even with the naked eyes. Also, to measure the glucose concentration in commercial beverages, scientists have utilized glucose sensitive enzymes and PtNPs-based polymer nanocomposite immobilizing matrix to develop a biosensor with unprecedented sensitivity, a response time as fast as 3 sec and a lower detection limit of 0.7 µM15.
Pork is a common adulterant in beef food items as it looks similar in texture and colour while being much cheaper. A species-specific hybrid nano-bioprobe based on pork-DNA fragment bound AuNPs (3nm) has been developed by Malaysian scientists to detect pork adulterant in ready-to-eat pork-spiked beef burgers and can detect very short length foreign nucleic acid targets, which cannot be detected by conventional methods in forensic testing and food analysis16.
Food allergen gliadin in wheat is the main reason for gluten intolerance in celiac disease and its detection in consumables is extremely necessary to prevent allergic reaction in celiac patients.
Researchers from China have developed an anti-gliadin antibody labelled AuNPs based quartz crystal microbalance biosensor to detect gliadin in food and tested it on many commercial products. Results obtained were consistent with those of Association of Analytical Communities (AOAC) approved gliadin kit17.
Most of the conventional methods used for detecting various food colorants include HPLC and MS, which are quite expensive, complicated and time consuming. Detection and quantification of soft drinks colorants (Allura Red, Ponceau 4R) using a simple CNTsbased colorimetric assay with higher sensitivity have been developed18.
Also, a rapid and low-cost electrochemical detection method of another food colorant Sudan IV in chilli powder and tomato sauce has been developed by Chinese scientists at Heze University using graphene-modified glassy carbon electrodes. The method proposed a wide range of detection limit (2×10-7M – 8×10-5M) and sample recovery as high as 96.8%-99.2%19.
A non-instrumental, immuno-dipstick based gold nanosensor with high detection limits to measure vitamin B12 amount in fruit and labelled energy drinks has been developed by Indian scientists at CFTRI, Mysore 20.
Biosensors research group at Sabah University of Malaysia has developed a cholesterol oxidase immobilized MWCNT/AuNPs/chitosan composite matrix-based nanosensor for the determination of total cholesterol in food especially in meat samples with good sensitivity and selectivity21.
Detection of Microbial Contaminants
Most of the conventional immunological assays to detect microbial contamination in food are lengthy (with longer incubation period) and unsuitable at times when immediate clinical measurements have to be taken. Nanoscale devices can detect food pathogens at various stages of food production chain and are fast, inexpensive, and suitable for ‘point of care’ (non-laboratory) settings. Also, the sensitivity of conventional biosensors is approximately in the range of 103 to 104 CFUmL-1 whereas the superior surface properties of nanomaterials render them as an obvious choice to detect even ~ 1 CFUmL-1 in samples.
NanoScience Technology Center of University of Central Florida, USA has developed a magnetic nanosensor using bacteria specific antibody conjugated dextran-coated iron oxide NPs to detect milk bacteria (Mycobacterium avium spp. paratuberculosis - MAP) within 30 minutes and with detection limits as low as 1-10 CFU22.
German scientists from University of Regensburg have developed a pH nanosensors based on fluorescent NPs (∼12 nm) to monitor bacterial growth in packaged foods (Fig. 4). This nanosensor does not interfere with the growth of the bacteria and can be adapted to detect CO2 and O2 or incorporated into the barcodes to monitor food freshness in packaged foods23.
Growth of E. coli in medium containing pH-sensitive nanoparticles
Fig. 4: Growth of E. coli in medium containing pH-sensitive nanoparticles. The first row displays controls with a homogeneous green fluorescence whereas due to the bacterial growth colour of the medium changes with respect to variation in pH values, shown in 2nd row. (Image courtesy: Dr. Xu-dong Wang, Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, Germany)
Detection of viable Salmonella typhimurium, Escherichia coli O157:H7 and Listeria monocytogenes simultaneously in food samples (lettuce, tomato and ground beef) has been done by Chinese scientists. Researchers used magnetic nano-beads based separation to isolate bacterial cells and amplified the target genes by using the multiplex PCR assay. Then a photoreactive DNA-binding dye (propidium monoazide-PMA) was used to detect the viable bacteria in food sample24.
A novel mycotoxin (aflatoxin B1 and zearalenone) purification system in feed using anti-fungal monoclonal antibodies and magnetic NPs (100 nm) with remarkable purification efficiency (>90 %) has been developed by Korean scientists, which takes approximately 5 minutes for detection and may replace the lengthy conventional immunoaffinity columns methods25. Several strains of the marine pathogen Vibrio parahaemolyticus (present in seafood) were detected by using unique quasi-3D (Q3D) plasmonic nanostructure arrays as SERS-active substrates, where individual strains could be identified in both blind samples and mixtures26.
Researchers from University of Calofornia, LA, USA have developed a QD enabled detection of Escherichia coli and other pathogens in complex food matrices using a cell phone based fluorescent imaging and sensing platform in resource limited environments. They used bacterial antibody functionalized glass capillaries as substrates for QD-based sandwich assay in combination with inexpensive LEDs and imaged the emission on the cell-phone camera, using an additional lens between the capillary and the phone to detect the bacterial concentration as low as ∼5 to 10 CFUmL-1 27.
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