PHOTOSENS developed nano-structured, large-area multi-parameter sensor arrays using Photonic Crystal (PC) and Surface Enhanced Raman Scattering (SERS) methodologies.
Using SERS, multiple molecular targets can be detected simultaneously or through functionalisation using molecularly imprinted polymers (MIPs), a pre-set molecule can be detected – the project model was melamine in milk products.
MIPS are suitable for chemical contamination but not for bacterial/viral issues, for example, the technology would not work if looking for E.coli in milk powder.
Build on knowledge
Dr David Eustace, commercial business manager at Renishaw Diagnostics, said the project built on previous work in SERS detection.
“The use of SERS with advanced Raman instrumentation is a developing technology that has previously demonstrated trace level detection of contaminants in a variety of foodstuffs, but the technique is still some way short of full scale adoption,” he told FoodQualityNews.com.
“The aim of the PHOTOSENS project was to produce technology and manufacturing techniques which would overcome the market barriers preventing wider implementation of SERS technology, such as high cost per test, test robustness and regulatory requirements.”
The project team, co-ordinated by Finnish research centre VTT, created high-throughput nanophotonic sensor structures using polymer materials with roll-to-roll (R2R) nanoimprinting methods.
This reduces substrate manufacturing costs when compared to existing silicon based technology.
Reduction in analysis time
Current detection techniques for melamine in milk include High Performance Liquid Chromatography (HPLC), Gas Chromatography Mass Spectrometry (GCMS) and Enzyme-Linked Immunosorbent Assay (ELISA).
However, these methods require time-consuming sample preparation steps and must be done by trained personnel in a centralized laboratory setting.
The method developed by PHOTOSENS allows for rapid analysis times (a matter of minutes) and for testing to be carried out using portable Raman instrumentation.
Experiments were designed to determine whether the polymer SERS substrates are a viable candidate for use in food monitoring applications, said Eustace.
“The sensors can be an inspection tool for imports on the border or at a customs site. The test involves the simple deposition of the test material on the SERS substrate followed by rapid scanning with a Raman spectrometer,” he said.
“The use of MIPs enables the development of a dip stick test as melamine binds into the cavities in the MIP and the additional components present in the test sample are excluded from the surface.
“The portable nature of the test allows, for example, a food safety inspector to carry out tests in the field, instead of taking samples of food products and sending these to a centralised lab.”
Currently, utilization of nanophotonic sensor structures is hindered by the lack of low-cost and highly reproducibility fabrication methods for nano-structured surfaces.
The three-year project, which finished last month, developed three sensing platforms: roll-to-roll printed free-form SERS substrates, proof-of-principle Photonic Crystal (PC) sensors and roll-to-roll printed waveguide sensors.
For the SERS sensor the gold metallization is the main cost factor but with suitable development of a R2R metallisation method (not considered within the project), the price can be less than €3 per sensor.
The PC sensor is potentially low-cost when the fabrication processes and materials are developed further. The waveguide sensor does not require metallization, so can be processed in the roll-to-roll process.
Eustace said there were still barriers to overcome to see the technology used in industry.
“There are regulatory barriers and more testing needs to be done but we have proof of concept and a strong technology baseline - we now need a partner with experience in the industry to help develop the PHOTOSENS outcomes into a final product.”
Project partners included VTT Technical Research Centre of Finland, University of Southampton (UK), Momentive (Germany), TNO (the Netherlands), University of Vienna (Austria), Nanocomp (Finland), 3D AG (Switzerland), Philips (the Netherlands) and Renishaw Diagnostics (UK).