Selective microwave sensors exploiting the interaction of analytes with trap states in TiO₂nanotube arrays

Abstract

Sensing of molecular analytes by probing the effects of their interaction with microwaves is emerging as a cheap, compact, label-free and highly sensitive detection and quantification technique. Microstrip ring-type resonators are particularly favored for this purpose due to their planar sensing geometry, electromagnetic field enhancements in the coupling gap and compatibility with established printed circuit board manufacturing. However, the lack of selectivity in what is essentially a permittivity-sensing method is an impediment to wider adoption and implementation of this sensing platform. By placing a polycrystalline anatase-phase TiO2 nanotube membrane in the coupling gap of a microwave resonator, we engineer selectivity for the detection and differentiation of methanol, ethanol and 2-propanol. The scavenging of reactive trapped holes by aliphatic alcohols adsorbed on TiO2 is responsible for the alcohol-specific detection while the different short chain alcohols are distinguished on the basis of differences in their microwave response. Electrodeless microwave sensors which allow spectral and time-dependent monitoring of the resonance frequency and quality factor provide a wealth of information in comparison with electrode-based resistive sensors for the detection of volatile organic compounds. A high dynamic range (400 ppm-10,000 ppm) is demonstrated for methanol detection.

Screen-Printed f-EM Sensors Based on Two Chelating-Polymers and a Metal Oxide for the Continuous Detection of Cu Ions in Surface Water

“…The response of the sensor manifests itself as a resonant frequency change, alteration in the signal amplitude or a resonant peak shift. The sensitivity and selectivity toward a specific pollutant is then increased by the integration of functional materials [4,5].…”

TiO2-Based Nanoheterostructures for Promoting Gas Sensitivity Performance: Designs, Developments, and Prospects

“…In the past decades, it has been discovered that TiO 2 could be employed in many promising fields including photovoltaics [ 21 ], photocatalysis [ 22 , 23 ], sensors, etc. [ 24 , 25 , 26 ]. In particular, because of its high stability, harsh environmental tolerance, and environmentally-friendly properties, TiO 2 has been widely investigated and is regarded as one of sensing materials for gas detection with the most potential [ 27 , 28 , 29 , 30 ].…”

Selectivity Enhancement in Electronic Nose Based on an Optimized DQN

“…Data from this device, when used with a pattern recognition method that utilizes temporal information and the large data set, the e-mucosa system improves the discrimination power of this instrument compared to conventional e-noses. One of the promising techniques is a microwave transduction technique [ 19 , 20 ], which is based on the change of electromagnetic properties of gas sensitive layer in the microwave range. Abdolrazzaghi et al [ 21 ] developed a robust and fault-tolerant approach to microwave based sensitive measurements using Fuzzy Neural Network.…”