K.M. Mohibul Kabir

A silver electrode based surface acoustic wave (SAW) mercury vapor sensor: a physio-chemical and analytical investigation

We developed for the first time a silver electrode-based surface acoustic wave (SAW) elemental mercury (Hg0) vapor sensor and carried out detailed physio-chemical and analytical studies to better understand Hg–Ag interaction as well as to assess the sensor’s feasibility for real world applications. The mercury sorption and desorption rates on the Ag surface were calculated by differentiating the sensor’s dynamic response which indicated that fast adsorption process occurred at the initial stage of the 30 minute Hg0 exposure before the relatively slower diffusion process started to take place. Furthermore, the sensor’s dynamic response magnitudes and maximum sorption/desorption rates were found to follow the Langmuir extension isotherm at all tested operating temperatures indicating that relatively small concentrations of Hg0 vapor interacting with Ag surface can be detected. Moreover, the operating temperature was found to have little effect on the maximum sorption rate of the sensor while the maximum desorption rate was found to increase at elevated operating temperature. Following extensive testing and analysis, the developed Ag based SAW Hg0 vapor sensor was found to have a limit of detection (LoD) as low as 0.5 ppbv (at 35 °C), which is comparable with the LoD reported for an Au-electrode based SAW sensor (0.7 ppbv). Further investigation indicated that the low concentrations (<400 ppbv) of Hg0 vapor can be detected selectively at various operating temperatures between 35 and 105 °C even when common industrial gases (i.e. ammonia, acetaldehyde, ethylmercaptan, dimethyl disulphide, methyl ethyl ketone and humidity) are present without showing spurious artifacts, significant response degradation or unmanageable memory effects.

A Nanoengineered Conductometric Device for Accurate Analysis of Elemental Mercury Vapor

We developed a novel conductometric device with nanostructured gold (Au) sensitive layer which showed high-performance for elemental mercury (Hg(0)) vapor detection under simulated conditions that resemble harsh industrial environments. That is, the Hg(0) vapor sensing performance of the developed sensor was investigated under different operating temperatures (30-130 °C) and working conditions (i.e., humid) as well as in the presence of various interfering gas species, including ammonia (NH3), hydrogen sulfide (H2S), nitric oxide (NO), carbon mono-oxide (CO), carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen (H2), methane (CH4), and volatile organic compounds (VOCs) such as ethylmercaptan (EM), acetaldehyde (MeCHO) and methyl ethyl ketone (MEK) among others. The results indicate that the introduction of Au nanostructures (referred to as nanospikes) on the sensors surface enhanced the sensitivity toward Hg(0) vapor by up-to 450%. The newly developed sensor exhibited a limit of detection (LoD) (∼35 μg/m(3)), repeatability (∼94%), desorption efficiency (100%) and selectivity (∼93%) when exposed to different concentrations of Hg(0) vapor (0.5 to 9.1 mg/m(3)) and interfering gas species at a chosen operating temperature of 105 °C. Furthermore, the sensor was also found to show 91% average selectivity when exposed toward harsher industrial gases such as NO, CO, CO2, and SO2 along with same concentrations of Hg(0) vapor in similar operating conditions. In fact, this is the first time a conductometric sensor is shown to have high selectivity toward Hg(0) vapor even in the presence of H2S. Overall results indicate that the developed sensor has immense potential to be used as accurate online Hg(0) vapor monitoring technology within industrial processes.

Determining the Optimum Exposure and Recovery Periods for Efficient Operation of a QCM Based Elemental Mercury Vapor Sensor

In recent years, mass based transducers such as quartz crystal microbalance (QCM) have gained huge interest as potential sensors for online detection of elemental mercury (Hg0) vapor from anthropogenic sources due to their high portability and robust nature enabling them to withstand harsh industrial environments. In this study, we determined the optimal Hg0 exposure and recovery times of a QCM based sensor for ensuring its efficient operation while monitoring low concentrations of Hg0 vapor (<400 ). The developed sensor was based on an AT-cut quartz substrate and utilized two gold (Au) films on either side of the substrate which functions as the electrodes and selective layer simultaneously. Given the temporal response mechanisms associated with mass based mercury sensors, the experiments involved the variation of Hg0 vapor exposure periods while keeping the recovery time constant following each exposure and vice versa. The results indicated that an optimum exposure and recovery periods of 30 and 90 minutes, respectively, can be utilized to acquire the highest response magnitudes and recovery rate towards a certain concentration of Hg0 vapor whilst keeping the time it takes to report an accurate reading by the sensor to a minimum level as required in real-world applications.

Development and experimental verification of a finite element method for accurate analysis of a surface acoustic wave device

Accurate analysis of surface acoustic wave (SAW) devices is highly important due to their use in ever-growing applications in electronics, telecommunication and chemical sensing. In this study, a novel approach for analyzing the SAW devices was developed based on a series of two-dimensional finite element method (FEM) simulations, which has been experimentally verified. It was found that the frequency response of the two SAW device structures, each having slightly different bandwidth and center lobe characteristics, can be successfully obtained utilizing the current density of the electrodes via FEM simulations. The two SAW structures were based on XY Lithium Niobate (LiNbO3) substrates and had two and four electrode finger pairs in both of their interdigital transducers, respectively. Later, SAW devices were fabricated in accordance with the simulated models and their measured frequency responses were found to correlate well with the obtained simulations results. The results indicated that better match between calculated and measured frequency response can be obtained when one of the input electrode finger pairs was set at zero volts and all the current density components were taken into account when calculating the frequency response of the simulated SAW device structures.

Silver/gold core/shell nanowire monolayer on a QCM microsensor for enhanced mercury detection

The formation of a silver nanowire monolayer (Ag NWML) galvanically replaced with gold (Au) directly on the electrodes of a quartz crystal microbalance (QCM) transducer for non-spectroscopic based elemental mercury (Hg0) vapor sensing is reported in this study. The modification of Ag NWML to Ag/Au alloyed (Ag/Au NWML) structures through galvanic replacement (GR) reaction was found to enhance the sensitivity and selectivity of the sensors. Following GR reaction, the morphology of the Ag nanowires was found to change without deforming the monolayer packing arrangement. Interestingly, the selectivity of the sensor toward Hg0 vapor was increased by increasing the Au concentration during the GR reaction. The Ag/Au NWML based sensor which was modified using a 2 mM Au solution was found to produce 3 times higher sensitivity compared to the Au control QCM as well as having more than 95% accuracy and >90% repeatability. This was found to be due to the formation of Ag/Au alloys (Ag/Au NWML) with active sites that had a high affinity toward Hg0 vapor.

Tips for reading patents: a concise introduction for scientists

ABSTRACT Many commercial and academic institutions protect their commercially valuable research information using patents, making the patent literature a rich and early source of cutting-edge research. While scientists and students often create the data that finds its way into patents, some rarely read the patent literature. Here, we provide an informal and brief collection of hints and tips that may assist scientists and students who do not regularly read the patent literature to locate the key scientific findings that are disclosed by patentees. These tips will introduce the reader to: (i) the general structure of patents and the sections of the patents that scientists and students may find particularly helpful; and (ii) a few factors to keep in mind when using data disclosed in the patent literature, such as patent lifespans, jurisdictions and the patent review processes. Although this is not a comprehensive and complete guide to reading patents, the accessible nature of this informal introduction to patent reading should assist scientists and students to make more effective use of the cutting-edge research disclosed in patent specifications.

Cancer breath testing: a patent review

ABSTRACT Introduction: Human breath can contain thousands of volatile organic compounds (VOCs) and semi-volatile compounds that are related to metabolism and other biochemical processes. The presence of cancer cells can affect the identity and abundances of chemicals in breath when compared to those in healthy control subjects, which can be used to indicate the likelihood of a patient having cancer. Recently, the chemical analysis of exhaled breath from patients has been shown to be promising for diagnosing many different types of cancers, including lung, breast, colon, head, neck, and prostate, along with pre-cancerous conditions (dysplasia). Areas covered: Here, we reviewed the sampling, analytical and data analysis methods reported in the recent patent literature related to cancer breath testing (2014–2017). In addition, the different types of cancer biomarkers that were disclosed are discussed. Expert opinion: The major advantages of breath testing compared to conventional X-ray and imaging based methods includes simplicity of use, non-invasiveness, and the potential to detect cancer at a relatively early stage. Such methods are also suitable to perform population screening because of their non-invasiveness. However, the establishment of standard sampling, detection and quantification methods for breath testing is required before the methods can be employed for clinical diagnosis.

A QCM-based ‘on–off’ mechanistic study of gas adsorption by plasmid DNA and DNA–[Bmim][PF6] construct

The study of the adsorption behavior of disease markers such as ammonia (NH3) and acetaldehyde (CH3CHO) with biomaterials is important, as it will improve our understanding of their interaction behavior and enable the development of self-diagnosis technologies, among others. In this study, three types of DNA-based biomaterials were synthesized (pGFP plasmid DNA isolated from E. coli DH5α, a DNA–ionic liquid construct (DNA–IL) and DNA–ionic liquid–gold chloride (DNA–IL–Au)) and their adsorption capacities for NH3 and CH3CHO were tested by utilizing a gravimetric transducer, namely, a quartz crystal microbalance (QCM). Pristine DNA itself displayed high sensitivity towards both gases, with a pristine DNA-based QCM displaying magnitudes of response of ∼3.74 and 2.62 ng cm−2 μg−1 following 10 minutes of exposure to 600 ppm NH3 and CH3CHO, respectively. Interestingly, no response was observed when these gases were exposed to the DNA–IL complex, which comprised DNA modified with the hydrophobic IL [Bmim][PF6]. However, when the DNA–IL complex was further treated with HAuCl4, the biomaterial (DNA–IL–Au) regained its adsorption capacity, exhibiting magnitudes of adsorption/response up to 140% and 36% higher than its DNA counterpart toward NH3 and CH3CHO, respectively. It was also observed that the utilization of DNA–IL–Au significantly reduced the sensitivity of the QCM device to humidity content, which indicates that the developed biomaterial can be readily employed to detect NH3 and CH3CHO in humid environments. Further study showed that the magnitudes of the QCM response of the DNA and DNA–IL–Au materials toward the different concentrations of NH3 and CH3CHO that were tested follow the loading ratio correlation (LRC), which thus indicates that the developed materials can potentially be utilized as sensitive layers for the detection of biomarker gases that are produced in the body as a result of biomedical disorders. In addition, a plausible sorption mechanism has also been proposed on the basis of the interaction of DNA with the ionic liquid and HAuCl4 (experimentally proved by XPS and FTIR), which strongly indicates the role of the phosphates and nucleobases of DNA for the electrostatic binding of NH3 and CH3CHO, respectively.

Simultaneous multi-mode analysis of surface acoustic wave device temperature stability utilizing time-frequency methods

Perturbations in the boundary conditions of Surface Acoustic Wave (SAW) devices are typically quantified through the use of frequency-domain methods, where the device is incorporated as the feedback element in a closed-loop oscillator. While simple in implementation, this method is inherently limited to tracking a single acoustic mode, and discards potentially useful information from the time-domain. In this work an alternative approach utilizing time-frequency methods to extract meaningful information from SAW device transient responses are considered. The advantages of the proposed method are experimentally demonstrated by varying the operating temperature of an XY-cut LiNbO3 SAW device. The location in time and frequency of multiple acoustic modes was monitored simultaneously as temperature was varied between 30°C and 150°C. Data from the time-frequency domain demonstrates good agreement with conventional analysis techniques.