Jeong, H.; Jeon, S. Determination of Dopamine in the Presence of Ascorbic Acid by Nafion and Single-Walled Carbon Nanotube Film Modified on Carbon Fiber Microelectrode. Sensors 2008, 8, 6924-6935

Carbon fiber microelectrode (CFME) modified by Nafion and single-walled carbon nanotubes (SWNTs) was studied by voltammetric methods in phosphate buffer saline (PBS) solution at pH 7.4. The Nafion-SWNTs/CFME modified microelectrode exhibited strongly enhanced voltammetric sensitivity and selectivity towards dopamine (DA) determination in the presence of ascorbic acid (AA). Nafion-SWNTs film accelerated the electron transfer reaction of DA, but Nafion film as a negatively charged polymer restrained the electrochemical response of AA. Voltammetric techniques separated the anodic peaks of DA and AA, and the interference from AA was effectively excluded from DA determination. Linear calibration plots were obtained in the DA concentration range of 10 nM - 10 μM and the detection limit of the anodic current was determined to be 5 nM at a signal-to-noise ratio of 3. The study results demonstrate that DA can be determined without any interference from AA at the modified microelectrode, thereby increasing the sensitivity, selectivity, and reproducibility and stability

Freestanding 3D-interconnected carbon nanofibers as high-performance transducers in miniaturized electrochemical sensors

3D-carbon nanomaterials have proven to be high-performance transducers in electrochemical sensors but their integration into miniaturized devices is challenging. Herein, we develop printable freestanding laser-induced carbon nanofibers (f-LCNFs) with outstanding analytical performance that furthermore can easily allow such miniaturization through a paper-based microfluidic strategy. The f-LCNF electrodes were generated from electrospun polyimide nanofibers and one-step laser carbonization. A three-electrode system made of f-LCNFs exhibited a limit of detection (LOD) as low as 1 nM (S/N = 8) for anodic stripping analysis of silver ions, exhibiting the peak at ca. 100 mV vs f-LCNFs RE, without the need of stirring. The as-described system was implemented in miniaturized devices via wax-based printing, in which their electroanalytical performance was characterized for both outer- and inner-sphere redox markers and then applied to the detection of dopamine (the peak appeared at ca. 200 mV vs f-LCNFs RE) with a remarkable LOD of 55 pM. When modified with Nafion, the f-LCNFs were highly selective to dopamine even against high concentrations of uric and ascorbic acids. Especially the integration into closed microfluidic systems highlights the strength 3D porous structures provides excellent analytical performance paving the way for their translation to affordable lab-on-a-chip devices where mass-production capability, unsophisticated fabrication techniques, transfer-free, and customized electrode designs can be realized

Bioelectroanalysis in a Drop: Construction of a Glucose Biosensor

This lab experiment describes a complete method to fabricate an enzymatic glucose electroanalytical biosensor by students. Using miniaturized and disposable screen-printed electrodes (SPEs), students learn how to use them as transducers and understand the importance SPEs have acquired in sensor development during the last years. Students can also revise concepts related to enzymatic assays, with glucose oxidase and horseradish peroxidase involved in subsequent reactions. Moreover, they learn the trends that current analytical chemistry follows presently such as miniaturization, portability, and low cost. At the same time, this experiment serves to teach basic analytical concepts (accuracy, precision, sensitivity, and selectivity) in a practical way. The high clinical interest of glucose, due to a large number of diabetes patients around the world, and the application of the sensor to analysis of real food samples make this experiment very attractive to students. The questions set out along this experiment help students to acquire skills for solving analytical problems from the very beginning

Stretchable Phase Change Composites

Currently phase change materials (PCMs) are widely used to store thermal energy and control the temperature by dissipating heat. Without simply embed PCMs into construction, more researchers are focus on utilizing PCMs into clothing and electronics, since the heat dissipation is always a problem of human body and electronic devices. However, different from utilizing PCMs in construction, the applications of clothing and electronics are requiring PCMs should be stretchable so that they can fit the motion of human body and the complex shapes of electronics. But PCMs are not capable to be stretchable, thus, some stretchable matrix materials should be used to form composites with PCMs. The purpose of this essay is to fabricate stretchable phase change composites with PCMs, with the highly-stretchable material PDMS used as the matrix of composites. And the paraffin is used as PCMs in composites since paraffin is safe, cheap, have high latent of heat and proper phase change temperature range which is close to human body. Three different kinds of composites are fabricated in this essay, a) simple PDMS-based phase change composites, b) reinforced phase change composites and c) modified phase change composites. From a) to b), carbon nanotubes are added into composites to reinforce the tensile strength and thermal conductivity. Also, trying have high heat capacity for reinforce composites, the content of microcapsules is fixed at 35 wt.%. From b) to c), surface modification is applied to improve both tensile strength and thermal stability of composites. The results of thermal and mechanical characterizations of composites demonstrates that both thermal and mechanical properties are improved by reinforcement and modification. Based on the stress-strain curves, the strains of all composites are higher than 0.7 (mm/mm), which means the sample will elongate 70% of its original length and demonstrates the composites have high stretchability. With the reinforcement and modification, composites have high heat capacity, stretchability and tensile strength. This makes composites potentially useful in applications requiring materials with complex shapes and high strength such as cooling of human body and electronics