The application of metal-organic frameworks (MOFs) as a sensing layer has been attracting great interest over the last decade, due to their uniform properties in terms of high porosity and tunability, which provides a large surface area and/or centers for trapping/binding a targeted analyte. Here we report the fabrication of a highly sensitive humidity sensor that is based on composite thin films of HKUST-1 MOF and carbon nanotubes (CNT). The composite sensing films were fabricated by spin coating technique on a quartz-crystal microbalance (QCM) and a comparison of their shift in resonance frequencies to adsorbed water vapor (5 to 75% relative humidity) is presented. Through optimization of the CNT and HKUST-1 composition, we could demonstrate a 230% increase in sensitivity compared to plain HKUST-1 film. The optimized CNT-HKUST-1 composite thin films are stable, reliable, and have an average sensitivity of about 2.5×10−5 (Δf/f) per percent of relative humidity, which is up to ten times better than previously reported QCM-based humidity sensors. The approach presented here is facile and paves a promising path towards enhancing the sensitivity of MOF-based sensors.
Ahmad, Rafiq; Majhi, Sanjit Manohar; Zhang, Xixiang; Swager, Timothy M.; Salama, Khaled N.(Advances in Colloid and Interface Science, Elsevier BV, 2019-05-22)[Article]
Vertically oriented zinc oxide (ZnO) nanomaterials, such as nanorods (NRs), nanowires (NWs), nanotubes (NTs), nanoneedles (NNs), and nanosheets (NSs), are highly ordered architectures that provide remarkable properties for sensors. Furthermore, these nanostructures have fascinating features, including high surface-area-to-volume ratios, high charge carrier concentrations, and many surface-active sites. These features make vertically oriented ZnO nanomaterials exciting candidates for gas sensor fabrication. The development of efficient methods for the production of vertically oriented nanomaterial electrode surfaces has resulted in improved stability, high reproducibility, and gas sensing performance. Moving beyond conventional fabrication processes that include binders and nanomaterial deposition steps has been crucial, as the materials from these processes suffer from poor stability, low reproducibility, and marginal sensing performance. In this feature article, we comprehensively describe vertically oriented ZnO nanomaterials for gas sensing applications. The uses of such nanomaterials for gas sensor fabrication are discussed in the context of ease of growth, stability on an electrode surface, growth reproducibility, and enhancements in device efficiency as a result of their unique and advantageous features. In addition, we summarize applications of gas sensors for a variety of toxic and volatile organic compound (VOC) gases, and we discuss future directions of the vertically oriented ZnO nanomaterials.
Biosensor development includes the deposition of (nano)materials onto a conductive electrode surface, which is a crucial step for obtaining improved performance from the constructed biosensors. Various methods have been used to create a successful matrix of (nano)materials that ensures proper contact between the material and electrode surface. The purpose of (nano)material deposition is to provide a high surface area to improve the electroanalytical performance of biosensors by supporting the stable immobilization of enzymes in a more significant quantity as well as enhancing the catalytic or bioaffinity features. For decades, researchers have been using increasingly advanced methods not only for improving sensing performance, but also for improving stability, reproducibility, and mass production. In this review, we summarized the methods used for (nano)material deposition onto an electrode surface for efficient biosensor fabrication. An enhanced and optimized (nano)material deposition method is crucial for the mechanical stability and fabrication reproducibility of electrodes when designing a suitable biosensing device. In addition, we discussed the problems faced during biosensor application as well as the present challenges and prospects for superior deposition methods.
Morphology, nanoscale features, and tunable properties are the fundamentals of nanomaterials to many applications in use nowadays. Exciting approaches are utilized for developing and exploring new nanomaterials that enable broader impact on a variety of application areas. In this study, we synthesized thin nickel oxide (NiO) nanosheets using wet chemistry process and modified their surface with gold (Au) nanoparticles (NPs) via reduction method to obtain new hybrid (Au NPs-NiO nanosheets) nanomaterial. The morphological analysis of NiO and Au NPs-NiO nanosheets revealed small, uniform, thin, and smooth surface of NiO nanosheets formation, which become rough and decorated with small Au NPs uniformly over the NiO nanosheets surface. The synthesized NiO nanosheets and hybrid (Au NPs-NiO nanosheets) nanomaterials were further utilized to modify the glassy carbon electrode for the fabrication of electrochemical-based hydrazine sensors. The fabricated sensors were applied to detect hydrazine using cyclic voltammetry (CV). And the obtained sensing properties of the hybrid nanomaterial-based sensor were comparatively better than the only NiO nanosheets based sensors. Further, hybrid nanomaterial-based sensors characterized in detail, which showed an excellent sensitivity of 31.75 μAnM cm. The lower detectable limit of hydrazine sensor was as low as ˜0.05 nM, which is considerably better than the other metal oxide-based hydrazine sensors. Better sensing performance of hybrid nanomaterial-based sensor likely stems from nanosheets small size, tiny thickness, and Au modification that significantly improve the surface area and lead a positive synergistic effect (an effect arises between two or more materials that produce an enhanced effect compared to their individual effects) for electrocatalytic reaction. We believe that this hybrid nanomaterial with excellent catalytic properties could be utilized as an efficient electrode material to design other chemical and biological sensors.
In this work, ultrathin Ti3C2-MXene nanosheets were synthesized by minimally intensive layer delamination methods, and uniformly functionalized with aminosilane (f-Ti3C2-MXene) to provide a covalent binding for the immobilized bio-receptor (anti-CEA) for label free, ultrasensitive detection of cancer biomarker (carcinoembryonic antigen, CEA). The effect of different redox probes on the electrochemical behavior of f-Ti3C2-MXene was investigated and found that hexaammineruthenium ([Ru(NH3)6]3+) is the preferable redox probe for biosensing. The fabricated biofunctionalized Ti3C2-MXene exhibits a linear detection range of 0.0001–2000 ngmL−1 with sensitivity of 37.9 µAng−1mLcm−2 per decade. The wider linear detection range of our f-Ti3C2-MXene is not only higher than previously reported pristine 2D nanomaterials, but is even comparable to other hybrid 2D nanomaterials. We believe that this work opens a new window for development of MXene-based highly sensitive DNA, aptamer, enzyme, antibody, and cell based biosensors, and could be further used in drug delivery application.
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