The development of a simple paper based assay was studied to find an inexpensive and easy way to analyze different food components. This technique was observed to be used in the food industry for qualitative control purposes. The authors used dehydrogenase enzymes along with dye and NAD+ to observe a colored reaction on the paper. It was demonstrated to be compatible with food sample analysis as well. Chromatography paper was cut into 3x3 and 6x6 cm^2 and divided into 1x1 cm^2 with lines to observe (L) glutamate, (L) and (D) lactate, ethanol, and dehydrogenase. A coupled reaction was used with diaphorase in the presence of NAD+ and MTT. A solution of 3 microliters of enzyme, gelatine, MTT, NAD+, selected dehydrogenase and diaphorase was pipetted onto the chromatography paper. Food samples were set up by being dissolved in water and centrifuged. The supernatant was diluted with enzyme. Other food samples that were too dark in color were decolorized using PVPP. Color was observed after 10 minutes using the naked eye. Images were taken using a smartphone and imported into a computer were analyzed by ImageJ Freeware in RGB mode. The strip was further analyzed by placing the paper into phosphate buffer and gelatine for 5 minutes and left to dry. The reaction was able to be seen better using the naked eye after being submerged in the phosphate buffer. Dipstick detection used 3x0.5 cm2 strips. The reaction mixture was pipetted near an orientation line that was drawn at the shorter end of the strip.This method was analyzed by submerging the end in standard solution and observed using the naked eye. A calibration curve was plotted using the concentration of glutamate (x-axis) and the intensity of the strip (y-axis). The main advantage of this method is that only colorimetric paper test strips are used and can be observed with the naked eye.
Article 2: Advances in developing rapid, reliable and portable detection systems for alcohol.
This article discusses different types of detection systems that are small, portable and reliable that can be used in different types of industries such as the alcoholic beverage, pharmaceuticals, and also food and clinical industries. Microfluidics and micro sensors are being tested to separate sample contaminants for rapid and specific detection of alcohol. Ethanol determination was set up by using smart membranes of microchips, developed by in-situ fabrication of microchannel. Chitosan membrane with PNIPAN nanogels were used as a semi permeable membrane. Colorimetric techniques were used to monitor ethanol distribution in microfluidic channels using layers of cholesteric liquid crystal. Electrochemical micro-paper-based analytical devices combined with glucometers can detect alcohol in bodily fluids such as urine or blood. Organic electrochemical transistors can be printed on paper, makes this a great concept for a disposable paper breathalyzer. Fluidic operation such as particle separation, mixing, and liquid metering with fully automated and integrated complex assay protocols could be done with lab-on-a-disc (LabCD). No calibration curve was made for this experiment. Portable alcohol sensors still need a lot more research due to the fact that they are not as accurate as large instruments such as gas chromatography, or infrared analysis.
Article 3: Evaluation of portable near-infrared spectroscopy for organic milk authentication
Using Micro-NRS, conventional milk and organic milk displayed the largest separation between the groups of samples at 1220-1390 nm. Organic milk has a higher (slightly) absorbance at this wavelength. The peaks are strongly related to the concentration of different fatty acids. The three most abundant fatty acids in mils are C16:0 (palmitic acid), C181n9c (oleic acid) and C14:0 (myristic acid). Conventional milk has significantly higher concentrations of these fatty acids. FT-NIRS shows that organic milk has higher absorbance at 1500-2000 nm because the concentration of these three fatty acids are lower. Different detection methods such as micro-NIRS was able to distinguish between organic milk and conventional milk but not for other types of pasture milk samples. Fatty acid analysis by gas chromatography remains the best way to distinguish between the different types of milk because of its high specificity. Micro NIRS was shown to have potential and the authors stated that more research can be beneficial to aid in producing a portable and reliable detection method in not only milk, but in other industries as well.