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Thirumalai, Dinakaran,Subramani, Devaraju,Yoon, Jang-Hee,Lee, Jaewon,Paik, Hyun-jong,Chang, Seung-Cheol The Royal Society of Chemistry 2018 NEW JOURNAL OF CHEMISTRY Vol.42 No.4
<P>A new approach based on differential pulse voltammetry (DPV) was developed for the simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA) using a modified glassy carbon electrode (GCE). The sensor was constructed by a simple “one-step” technique, wherein de-bundled single-walled carbon nanotubes (SWCNTs) were drop-cast onto the GCE. Without de-bundling, the SWCNTs were poorly dispersed in aqueous solution and were ineffective for the one-step procedure. De-bundling of the SWCNTs was achieved using a small amount (0.1 wt%) of the synthesized polymer dispersant, sulfonated poly(ether sulfone) (SPES); the de-bundled SWCNTs had a high aspect ratio (length = 2.5 ± 1.0 μm; height = 2 ± 1 nm, as determined using transmission electron microscopy and atomic force microscopy). The de-bundled SWCNTs also led to enhanced electrocatalytic activity and selectivity of the modified sensor for the simultaneous determination of AA, DA, and UA in DPV measurements: the peak-to-peak separation values were 221, 119, and 340 mV (<I>vs.</I> Ag/AgCl) for DA-AA, UA-DA, and AA-UA, respectively. The dynamic linear ranges for AA, DA, and UA were 0.2-1.6 mM, 5.0-50 μM, and 5.0-60 μM, and the detection limits were 10.6 μM, 15 nM, and 113 nM (S/N = 3), respectively. The analytical performance of the developed sensor was demonstrated in the determination of AA and DA in commercial pharmaceutical samples (vitamin C tablets and DA injection). The characteristics of the modified sensor make it promising for the individual or simultaneous determination of AA, DA, and UA.</P>
Dinakaran Thirumalai,Devaraju Subramani,신보성,백현종,장승철 대한화학회 2018 Bulletin of the Korean Chemical Society Vol.39 No.2
A new metal-free, non-enzymatic electrochemical sensor system for the detection of glucose was developed in this study. The developed sensor uses a de-bundled single-walled carbon nanotube (SWCNT)-modified glassy carbon electrode (GCE). SWCNTs were de-bundled in aqueous solution by adding a synthesized polymer dispersant, sulfonated poly(ether sulfone). The de-bundled SWCNTs showed two significant characteristics: (1) improvement of the aspect ratio and dispersibility in aqueous solution and (2) suitability for use as a selective and sensitive sensing element in non-enzymatic glucose sensors. The experimental results clearly demonstrated that the SWCNTs/GCE possesses high electro-catalytic activity and efficient sensitivity with a stable and faster amperometric response production. Furthermore, interference by ascorbic acid, acetaminophen, uric acid, and dopamine is effectively avoided. Therefore, the proposed approach is favorable for the design and development of non-enzymatic glucose sensors.
Thirumalai Dinakaran,Subramani Devaraju,Bosung Shin(신보성),Hyun-jong Paik(백현종),Seung-Cheol Chang(장승철) 한국고분자학회 2017 폴리머 Vol.41 No.6
탄소섬유전극을 기반으로 효소가 불필요한 과산화수소(H₂O₂) 센서를 분산된 은 나노와이어와 단일벽 탄소나노튜브를 탄소섬유전극 표면에 드롭캐스팅법으로 고정화하여 제작하였다. 센서 제작에 사용된 탄소나노튜브는 고분자 분산제인 술폰화 폴리(에테르 술폰)에 의하여 효과적인 길이/직경의 종횡비를 나타낼 수 있도록 개별 분산되었으며 센서의 성능 향상을 위하여 은 나노와이어와 더불어 컴포지트 형태로 제작되어 새로운 센서 제작법에 활용되었다. 제작된 센서는 H₂O₂에 대하여 높은 전기촉매활성과 재현성, 빠른 분석 시간 및 우수한 감도를 나타냄을 확인하였다(센서 감도: 1.3 μA·mM<SUP>-1</SUP>, 검출 한계: 0.69 μM (S/N=3) 및 검출 시간: 3초 미만). 따라서 본 연구에서 개발된 고분자 분산제를 사용한 단일벽 탄소나노튜브의 수용액 내에서의 분산도 향상은 효소가 불필요한 H₂O₂ 센서의 설계 및 제작에 활용될 것으로 기대된다. A new non-enzymatic hydrogen peroxide (H₂O₂) sensor based on carbon fiber microelectrodes (CFMEs) has been developed. The CFMEs were modified using a simple drop casting procedure with effectively dispersed silver nanowires (AgNWs) and debundled single-walled carbon nanotubes (SWCNTs). In aqueous solution, the SWCNTs were debundled with a high length/diameter aspect ratio using a synthesized polymer dispersant, sulfonated poly(ether sulfone) (SPES). Enhanced electrocatalytic activity of the sensor for the reduction of H₂O₂ was obtained with the sensor sensitivity of 1.3 μA·mM<SUP>-1</SUP> and the detection limit of 0.69 μM (S/N=3) with a quick turnaround time (less than 3 s). The results clearly reveal that the AgNW-SWCNTs/CFMEs possess high electro-catalytic activity and efficient sensitivity with high reproducibility and fast amperometric response production. Therefore, the proposed debundling approach can be expanded to design and develop nonenzymatic hydrogen peroxide sensors.
Mohanty, Aruna Kumar,Devaraju, Subramani,Kim, Nowon,Paik, Hyun-jong Elsevier 2018 Solid state ionics Vol.314 No.-
<P><B>Abstract</B></P> <P>A class of poly(ether sulfone) (FPES) block copolymers containing pendent quaternary ammonium (QA) and imidazolium (IM) groups were prepared as anion exchange membranes by reaction involving nucleophilic substitution, benzylic bromination, quaternization and anion exchange with hydroxide ions. Highly reactive hexafluorobenzene (HFB) was utilized as a linkage group for relatively low temperature (e.g., 105°C) coupling between hydrophobic and precursor hydrophilic oligomer blocks. The phase separated morphology, water uptake, swelling ratio, conductivity, and chemical stability of the resultant copolymer membranes were also investigated. The hydroxide conductivity of the ionomer membranes (IEC~2.0 mequiv./g) was 21–22mS/cm and 56–63mS/cm at 30°C and 80°C respectively. The FPES-IM membrane showed relatively very good dimensional integrity in high pH solution, whereas under the similar condition the FPES-QA membrane broke into pieces. However, the degradation of the imidazolium cations in FPES-IM was relatively faster in comparison to the ammonium cations in FPES-QA.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Anion exchange membranes were prepared using hexafluorobenzene as a linkage group. </LI> <LI> Quaternary ammonium has better alkaline stability than imidazolium cations. </LI> <LI> Block copolymer anion exchange membranes exhibited nano-phase separation in AFM. </LI> <LI> Good hydroxide ion conductivity up to 63mS/cm at 80°C was observed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>