Food QC and nutritional testing

Into the real world: CE microchips for food analysis

The complexity of food matrices is one of the primary challenges in terms of improving the selectivity and sensitivity of food analysis.  Capillary electrophoresis (CE) microchips have emerged as a promising solution to this challenge, with new strategies to simplify sample preparation.  In a recent review in Electrophoresis, new advances and examples of real-world applications of CE microchips are examined, providing a good overview of the potential of this technology for food QC in the near future.

The CE microchip report was published in the December 2008 issue of Electrophoresis by group of Spanish researchers led by Alberto Escarpa, with the Department of Analytical Chemistry and Chemical Engineering of the University of Alcala in Madrid.

Various strategies can be used with CE microchips to increase both the selectivity and sensitivity of food analysis either avoiding sample preparation, or simplifying it as much as possible.  These techniques include (1) enhancing the peak capacity in order to carry out direct injection; (2) measuring one type of analyte, or group of analytes, without necessarily separating related interferences; (3) integrating various sample preparation steps on the microchip platform itself; and (4) integrating new, nanotechnology-based analytical tools for the detection stage.

Although the majority of applications to date involve the use of simple microchip designs, there are a number of new, sophisticated designs that have recently been reported as well.

In the past few years, CE microchips have been used successfully for the detection of a growing variety of analytes from a number of different food sources.  With an average separation time of a few minutes (or less than one minute, in the case of a DNA analysis of genetically modified maize), CE microchip-based analysis has been applied to measure biogenic amines (in beverages such as wine and beer), vanillin, food dyes (in soft drinks, syrups, and candies), alkaloids (including colchinine, aconitine, strychnine, and nicotine).

Two studies described in this report are worth mentioning in further detail.  In the first example, researchers at Pusan National University in South Korea used a total integration approach for the analysis of food dyes in juice, alcoholic beverages, fish, and noodles.  This involved a sophisticated microchip layout that integrated several different steps, including pre-concentration, separation, and electrochemical detection (ED).  The microchip was designed with three parallel channels – two for the field-amplified sample stacking (FASS) and subsequent field-amplified sample injection (FASI), and one for micellar EKC with ED (MEKC-ED). Compared with a conventional MEKC-ED analysis, the microchip CE method was over 10,000-fold more sensitive.  For the food dyes tested, LODs were estimated to be between 1 and 5 nM.

Using another example – in this case, from the group of Escarpa at the University of Alcala – a nanotechnology approach was highlighted.  By employing carbon nanotubes in CE microchips, Escarpa's team was able to carry out real detection of natural antioxidants, vitamin A, flavours and isoflavones in various foods and supplements, with LODs in the single-digit micromolar range.

As illustrated by these and several other examples of real-world applications, such clever combinations of "lab-on-a-chip" designs and nanotechnology elements are enabling an entirely new, “second generation” of microfluidic chips for food QC. The world is indeed getting smaller.

Article by Escarpa and colleagues on carbon nanotube-based detection in CE microchips, Electrophoresis, July 2008

Article by Shim and colleagues on microchip detection of food dyes, Electrophoresis, May 2008

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