Employed by dates - assume that perishable products like milk are transported and stored at four degrees Celsius but aspects do not always work-out in such a manner. Power cuts, employee error or a round-about trip home from the shop, then the milk can often warm-up which inadvertently speeds the growth of bacteria that can spoil it. Typically expensive electronic time-temperature indicators are available to monitor the temperature history of a product, but are more useful for shops monitoring entire shipments than shoppers worried about individualproducts. Plasmonic crystals that change colour over time could be an inexpensive alternative, according to a team of researchers from Peking University and The Chinese University of Hong Kong.
Previously suspension of plasmonic crystals have been employed to create colours well before people understood the science behind the phenomenon. Most famously, Gold nanoparticles (AuNP) are what give stained glass their ethereal ruby reds. Such strong, easily distinguishable colours, is what make photonic crystals ideal for displays on food packaging. Therefore, when Gold (Au) nano-rods suspended in agar gel are red, but adding silver nitrate (Ag ) and acid to the gel will gradually turn it green as the Ag coats the nano-rods. Adjusting ratios of the two allowed the team to calibrate the colour change to the growth rates of bacteria, and because Ag deposition is a kinetic process the colour change speeds-up as the gel gets warmer proportional to microbial growth.
In 2010, Younan Xia'a group at the Georgia Institute of Technology, USA - published a related approach that employed suspensions of triangular Ag nano-crystals which changed colour as the edges dulled. However, Xia had subsequently shelved his research. Unfortunately, the problem, he states, is that - "we have to make sure the etching or growth will follow exactly the same path-way when the nanoparticles are subjected to different conditions. Otherwise, the indicator might provide some wrong information." Also, he states that this will also be a problem for the Chinese group.
Of course, Au and Ag is not cheap and Xia cautions that Au is too expensive for such a "low-end" approach. Xia adds - "I believe our approach, purely based on Ag, should have a better chance for commercialisation if there is any," However, Jianfang Wang, who also worked on the milk monitor, disagrees, and explains that "we have estimated that most of the expense comes from the "auxiliary ingredients" like the stabilising and reducing agents, rather than the "main ingredients" - Au and Ag." Not least, Jianfang Wang states, because so little of the metals are needed. Original article available here and Similar article available here
In summary, the Chinese team are now looking to improve their approach by collaborating with a commercial company, and, therefore, could DCN Corp be that company? If so, we encourage the Chinese researchers to be in touch with the company as soon as practicably possible.