Browsing by Author "Zhang, Qiang"
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- ItemGraphene oxide films prepared using gelatin nanofibers as wearable sensors for monitoring cardiovascular health(2019) Liu, Y.; Meng, F.; Zhou, Y.; Mugo, Samuel; Zhang, QiangA gelatin nanofiber film that shows a failure tensile stress of 35 MPa, much stronger than conventional polyacrylamide hydrogels (<0.2 MPa), tough double network hydrogels (0.2–1.0 MPa), some engineering plastics such as polyethylene films (16 MPa) and polysulfones (1–10 MPa), is prepared by electrospinning. It is processed into a graphene oxide film, which exhibits high conductivity, via a high‐temperature treatment. A simple approach to prepare graphene oxide films using gelatin is provided. A highly sensitive and responsive wearable sensor is fabricated using the graphene oxide film, which is capable of sound recognition, apexcardiogram recording, and pulse spectrum measurement. The apexcardiogram is strongly associated with hemodynamic cardiac health, which reflects the cardiac process of ventricular contraction, blood ejection, diastole, semilunar valve open/close, atrioventricular valve valve open/close, etc. The developed cardiac sensor could be used to measure arterial stiffness index, a derivative of pulse spectrum, useful to evaluate artery walls stiffness and health status. Using the developed sensor, the detection result can be wirelessly relayed to mobile devices for personal cardiac health monitoring.
- ItemLipase-modified pH-responsive microgel-based optical device for triglyceride sensing(2015) Zhang, Qiang; Berg, Darren; Mugo, Samuel; Serpe, MichaelLipase-modified pH-responsive poly(N-isopropylacrylamide)-based microgels were synthesized. An optical device was subsequently fabricated by sandwiching the enzyme loaded responsive microgels between two thin Au layers, and their response to triolein, a model triglyceride, was investigated. The device's response depended on the triglyceride concentration, demonstrating its potential application as a triglyceride biosensor.
- ItemMechanistic investigation on copper-arylacetylide polymerization and sensing applications(2021) Liang, Quanduo; Chang, Xiaoyong; Su, Ya-qiong; Mugo, Samuel; Zhang, QiangExploration of new polymerization reactions is very intriguing in fundamental and practical research, which will advance reaction theories and produce various functional materials. Herein, we report a new polymerization method based on the reaction of CuI and arylacetylide, which generates linear polymers with high molecular weight and low polydispersity index of molecular weight. The Cu–arylacetylide polymerization exhibits different characteristics with traditional polymerizations such as mild reaction temperature, air atmosphere reaction, high molecular weight, fast polymerization rate, and imprecise molar ratio between monomers. The bond formation path and activation energy of each step was investigated by density functional theory calculations to understand the reaction mechanism. The poly(Cu-arylacetylide)s exhibit strong fluorescence emission and inherent semiconductive properties, which have been used to fabricate an electronic device for streptavidin sensing.
- ItemMolecularly imprinted carbon based electrodes for tetrahydrocannabinol sensing(2019) Zhang, Qiang; Berg, Darren; Mugo, SamuelTetrahydrocannabinol (THC) sensors were fabricated using carbon nanotubes (CNT) or carbon beads and poly(methyl acrylic acid-co- ethylene glycol dimethacrylate) (poly(MAA-Co-EGDMA)) with molecularly imprinting technology in micropipette tubes. The carbon materials allow the electrode high sensitivity due to high surface area, and the cavities of THC temples will enhance selectivity of the electrode toward THC because of molecular recognition of THC cavities. These electrodes exhibit high THC detection selectivity over caffeine and acetaminophen. The limit of THC detection for CNT-MIP electrodes is as low as 0.18 ± 0.02 ng/mL, which is much lower than that of electrodes with nonimprinted polymers (NIP) which is 12.5 ± 0.5 ng/mL. The morphology was characterized using scanning electron microscope (SEM), which exhibited the presence of polymers on the surface of carbon materials in the electrodes. The thermal stability of polymers was also tested using thermogravimetric analysis (TGA).
- ItemResponsive microgels-based wearable devices for sensing multiple health signals(2022) Xia, Xiangjiao; Mugo, Samuel; Zhang, QiangFlexible and wearable sensors have recently found wide applications in health monitoring and human-machine interaction. Desirable features in wearable sensors are high sensitivity and multi-targets detection capability in non-invasive manners. The sensitivity and multi-analyte detection capabilities are a function of the sensing material and sensor structures. Herein, we utilize a single-layer microgels structure integrated into a wearable capacitive sensor to realize both high sensitivity and multi-targets detections. We established a responsive sensing chain of analytes-the conformational changes of polymer chains-the morphology changes of the single-layer microgels structure-device capacitive signals. The conformational changes of microgel polymer chains due to physiological signals and metabolites in body fluids induce measurable capacitive signals generated by the sensors. This work provides mechanistic insight into a stimuli-responsive chain of analytes induced molecular conformation and thus morphology changes that induce the capacitive signal in the wearable sensors. This multipurpose sensor platform demonstrates the ability to detect bacteria such as E. coli and B. subitilis, metabolites such as uric acid in sweat, and physiological signals such as sound recognition, respiration, and pulse beat.