Battery-free radio frequency identification (RFID) sensors for food quality and safety.

Market demands for new sensors for food quality and safety stimulate the development of new sensing technologies that can provide an unobtrusive sensor form, battery-free operation, and minimal sensor cost. Intelligent labeling of food products to indicate and report their freshness and other conditions is one important possible application of such new sensors. This study applied passive (battery-free) radio frequency identification (RFID) sensors for the highly sensitive and selective detection of food freshness and bacterial growth. In these sensors, the electric field generated in the RFID sensor antenna extends from the plane of the RFID sensor and is affected by the ambient environment, providing the opportunity for sensing. This environment may be in the form of a food sample within the electric field of the sensing region or a sensing film deposited onto the sensor antenna. Examples of applications include monitoring of milk freshness, fish freshness, and bacterial growth in a solution. Unlike other food freshness monitoring approaches that require a thin film battery for operation of an RFID sensor and fabrication of custom-made sensors, the passive RFID sensing approach developed here combines the advantages of both battery-free and cost-effective sensor design and offers response selectivity that is impossible to achieve with other individual sensors.

Combinatorial screening of polymeric sensing materials using RFID sensors: combined effects of plasticizers and temperature.

Recently, we have developed battery-free, passive RFID chemical and biological sensors that are attractive in diverse applications where sensor performance is needed at a low cost and when battery-free operation is critical. In this study, we apply this attractive low-cost sensing platform for the combinatorial screening of formulated sensing materials. As a model system, a 6 x 8 array of polymer-coated RFID sensors was constructed to study the combined effects of polymeric plasticizers and annealing temperature. A solid polymer electrolyte Nafion was formulated with five different phthalate plasticizers: dimethyl phthalate, butyl benzyl phthalate, di-(2-ethylhexyl) phthalate, dicapryl phthalate, and diisotridecyl phthalate. These sensing film formulations and control sensing films without a phthalate plasticizer were deposited onto 9-mm diameter RFID sensors, exposed to eight temperatures ranging from 40 to 140 degrees C using a gradient temperature heater, and evaluated for their response stability and gas-selectivity response patterns. This study demonstrated that our RFID-based sensing approach permits rapid cost-effective combinatorial screening of dielectric properties of sensing materials.

Multianalyte chemical identification and quantitation using a single radio frequency identification sensor.

We demonstrate an approach for multianalyte chemical identification and quantitation using a single conventional radio frequency identification (RFID) tag that has been adapted for chemical sensing. Unlike other approaches of using RFID sensors, where a special tag should be designed at a much higher cost, we utilize a conventional RFID tag and coat it with a chemically sensitive film. As an example, we demonstrate detection of several vapors of industrial, health, law enforcement, and security interest (ethanol, methanol, acetonitrile, water vapors) with a single 13.56-MHz RFID tag coated with a solid polymer electrolyte sensing film. By measuring simultaneously several parameters of the complex impedance from such an RFID sensor and applying multivariate statistical analysis methods, we were able to identify and quantify several vapors of interest. With a careful selection of the sensing film and measurement conditions, we achieved parts-per-billion vapor detection limits in air. These RFID sensors are very attractive as ubiquitous multianalyte distributed sensor networks.