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RFID Chemical Sensor: toward the RFID Lab-on-tag
by Cecilia Occhiuzzi
The possibility to use UHF RFID technology for sensing applications in addition to
the more traditional logistic purposes is well established nowadays: university laboratories
around the world have proposed many different devices in the last ten years, able to
contemporarily label objects and provide information about their state and evolution. By
properly loading the tag with sensitive materials or by using the bare antenna as a sensor of
the surrounding environment, many different employments have been already envisaged and
experimented: the rationale relies on the fact that the RFID signal is affected by the
surrounding environment and by the antenna operative conditions, and hence it is possible to
retrieve sensing information by just evaluating the variation of the power received and
backscattered from the tags along with time.
Among the two sensing approaches, the possibility to load the tag by means of sensitive
materials appears extremely effective, especially for chemical sensors. The sensitive material
can be either lumped into the device, connected in some part of the tag’s antenna or instead
distributed all over the antenna surface, for instance as a receptor painting. The sensor is
hence considered as a lumped or distributed impedance load, whose variations, caused by the
change of the environment, will accordingly produce a change of the tag’s gain and
impedance, wirelessly detectable by any commercial reader.
From the first experiments done by Siden et al in 2007[Siden, Zeng, Unander,
Koptyug, and Nilsson 2007], with a blotting paper covering an RFID tag such to obtain a
simple moisture sensor, many improvements have been made, with the aim to integrate even
more sensitive materials and to control and optimize the tag’s sensing response.
In the January 2014 issue of the IEEE Transactions on Antennas and Propagation , Manzari et
al [Manzari and Marrocco 2014] proposed an effective way to control the sensing response of
RFID passive gas sensors by properly optimizing the amount of chemical interactive
materials (CIM) deposited on the tag. For this purpose, an open-circuit shielded slot-line
layout has been proposed as a general purpose tunable RFID radiator, suitable to directly host
small amounts of CIM in proper loading niches carved out of the radiating-slot. The sensor
has been optimized by means of a hybrid distributed-lumped model and a sensitivity threetimes higher than those achieved by the current state of the art RFID devices has been
obtained by integrating in the tag just a 3x3mm of the conductive polymer Pedot:PSS.
As suggested by the authors, the next step of the research is to arrange such class of RFID
sensors loaded with different CIMs within a sensor array forming a radio-chemical nose or a
more futuristic RFID lab-on-tag selective to different environmental and biological chemical
parameter.
In this perspective, an early contribution by Yuan et al on the April 2014 issue of IEEE
Sensor Journal [Yuan, Alocilja, Chakrabartty 2014], envisages the possibility to use RFID
passive technology for biosensing applications, by loading the tag with conductive selfassembling elements properly placed in gaps carved out of the antenna structure. In the
presence of the target analytes or pathogens, a silver-enhancement process self-assembles a
chain of conductive elements. As the size of the silver-enhanced particles grows, the
conductive chain fills the entire gap and restores the original tag structure. To react with the
analytes, the gap has to be functionalized by immobilizing on its surface target specific
antibodies (in this case anti-IgG). Since different parts of the antenna could be functionalized
with types of different detection probes, the authors suggested that the proposed approach
could be easily extended to multi-analyte detection.
The proof-of-concept has been validated for IgG detection, and the authors demonstrated that
different concentrations of rabbit IgG can be detected by means of COTS UHF reader.
The possibility to implement RFID passive chemical sensors seems to open
extremely interesting perspectives. However, beside the promising results, the optimization of
this class of chemical-doped RFID tags is still prone to considerable improvements mainly
related to the technology process to produce and deposit the load and its robustness in term of
reproducibility. Depending on the load preparation technique and process, in fact, the
properties and the behavior of the radio-sensors can vary significantly, and this is a very
crucial issue for the large-scale production of chemical-based sensor devices. Furthermore,
the CIMs are mostly characterized only in DC and hence the design of these antennas suffers
from the lack of information about the CIM’s electromagnetic parameters in the UHF RFID
band.
True applications are however not so distant: to completely fulfill the vision of RFID lab-ontag, the understanding and application of the electromagnetism must be opened to broader
and longer-term perspectives and become the convergence of a number of heterogeneous
medical and engineering disciplines and expertise, such as chemistry, biology and material
science.
Remote Moisture Sensing utilizing Ordinary RFID Tags
Siden, J. ; Xuezhi Zeng ; Unander, Tomas ; Koptyug, A. ; Nilsson, Hans-Erik
Sensors, 2007 IEEE
Digital Object Identifier: 10.1109/ICSENS.2007.4388398
Publication Year: 2007 , Page(s): 308 - 311
Modeling and Applications of a Chemical-Loaded UHF RFID Sensing Antenna With
Tuning Capability
Manzari, S. ; Marrocco, G.
Antennas and Propagation, IEEE Transactions on
Volume: 62 , Issue: 1
Digital Object Identifier: 10.1109/TAP.2013.2287008
Publication Year: 2014 , Page(s): 94 - 101
A Novel Biosensor Based on Silver-Enhanced Self-Assembled Radio-Frequency
Antennas
Mingquan Yuan ; Alocilja, E.C. ; Chakrabartty, S.
Sensors Journal, IEEE
Volume: 14 , Issue: 4
Digital Object Identifier: 10.1109/JSEN.2013.2296155
Publication Year: 2014 , Page(s): 941 - 942