One-step fabrication of a polyaniline nanofiber vapor sensor

A single-step, bottom-up technique has been used to fabricate sensors, based on conducting polymer nanofibers. A small amount of an aqueous solution containing aniline, a dopant, and an oxidant was placed on an interdigitated electrode array. Ultraviolet (UV)-irradiation of the solutions affected polymerization, yielding a highly porous film of polyaniline nanofibers with a mean diameter of around 100 nm and a length on the order of 1 μm. Solutions that were not irradiated formed bulk-like polyaniline (PANI) films. Nanofibers and bulk polyaniline sensors were exposed to chloroform, a weak proton donor; to toluene, a vapor that causes polymer swelling; and to triethylamine, which alters the doping level. Because of their higher surface areas, the response times of the fiber sensors were about a factor of 2 faster, with the current variations up to 4 times larger than those of the bulk polyaniline sensors. These results suggest methods for the advancement of simple and environment-friendly production of organic nanofiber-based sensors and electronic devices.     

电纺PANI/PEO纳米纤维传感器制备与应用

采用静电纺丝法制备了聚苯胺/聚环氧乙烷（ PANI/PEO）纳米纤维,研究了电压、接收距离对电纺PANI/PEO纳米纤维直径的影响,对电纺参数进行了优化。通过对电纺接收端的控制,制备了平行纳米纤维阵列,实现了纳米纤维的定向排布;通过对电纺射流沉积次数的控制,制备了PANI/PEO纳米单纤维传感器,并对NH3进行了气敏性测试。结果表明：当电纺电压为20 kV且接收距离为20 cm时,获得的PA-NI/PEO纳米纤维直径为105 nm,且形貌较佳,在此优化参数条件下制备的单纤维PANI/PEO纳米传感器在常温下对低浓度的NH3有良好的线性响应输出。     

Piezoelectricity of wet drawn cellulose electro-active paper

Piezoelectricity is one major actuating mechanism of cellulose-based electro-active paper (EAPap). In order to increase the piezoelectricity of EAPap, wet drawing method with different stretching conditions was introduced in the fabrication process of cellulose film. Structural and mechanical characterizations of wet drawn and stretched cellulose film were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), high voltage electron microscope (HVEM) and mechanical pulling test setup. From the piezoelectric charge constant measurement, it was revealed that the performance of EAPap was sensitive to the drawing ratio of cellulose film and its material orientation. We found that optimized alignment direction along the cellulose fibers and drawing ratio during wet drawing process were very critical parameters to improve electro-mechanical properties of EAPap. Also we conclude that the simple wet drawing method is a very effective fabrication method to enhance the mechanical stiffness and the piezoelectricity of EAPap.     

Electro-mechanical behavior and direct piezoelectricity of cellulose electro-active paper

This study focuses on investigating the piezoelectric effects of cellulose-based electro-active paper (EAPap) using quasi-static direct piezoelectricity. Mechanical properties were investigated first and then electro-mechanical behavior was studied by applying electric field during the pulling test. In-plane piezoelectric charge constant (d₃₁) of EAPap was quantified by the quasi-static relation between induced charge and applied stress. Strong shear electro-mechanical coupling was observed and 45° sample provided the largest in-plane piezoelectric charge constant. The measured piezoelectric charge constant was in the range of 8–28.2 pC/N, which are similar to those of piezo polymer. Cellulose EAPap provides promising potential as biodegradable and cheap piezoelectric polymer material.     

Fabrication of novel chitosan nanofiber/gold nanoparticles composite towards improved performance for a cholesterol sensor

A novel amperometric cholesterol biosensor was fabricated by the immobilization of ChOx (cholesterol oxidase) onto the chitosan nanofibers/gold nanoparticles (designated as CSNFs/AuNPs) composite network (NW). The fabrication involves preparation of chitosan nanofibers (CSNFs) and subsequent electrochemical loading of gold nanoparticles (AuNPs). Field emission scanning electron microscopy (FE-SEM) was used to investigate the morphology of CSNFs (sizes in the range of ∼50-100 nm) and spherical AuNPs. Cyclic voltammetry, hydrodynamic voltammetry and amperometry were used to examine the performance of CSNF-AuNPs/ChOx biosensor. The CSNF-AuNPs/ChOx biosensor exhibited a wide linear response to cholesterol (concentration range of 1-45 μM), good sensitivity (1.02 μA/μM), low response time (∼5 s) and excellent long term stability. The combined existence of AuNPs within CSNFs NW provides the excellent performance of the biosensor towards the electrochemical detection of cholesterol.     

DC humidity sensing properties of BaTiO3 nanofiber sensors with different electrode materials

Barium titanate (BaTiO₃) nanofibers were synthesized by electrospinning and calcination techniques. Two direct current (DC) humidity sensors with different electrodes (Al and Ag) were fabricated by loading BaTiO₃ nanofibers as the sensing material. Compared with the Al electrode sensor, the Ag electrode sensor exhibits larger sensitivity and quicker response/recovery. The current of Al electrode sensor increases from 4.08 × 10⁻⁹ to 1.68 × 10⁻⁷ A when the sensor is switched from 11% to 95% relative humidity (RH), while the values are 2.19 × 10⁻⁹ and 3.29 × 10⁻⁷ A for the Ag electrode sensor, respectively. The corresponding response and recovery times are 30 and 9 s for Al electrode sensor, and 20 and 3 s for Ag electrode sensor, respectively. These results make BaTiO₃ nanofiber-based DC humidity sensors good candidates for practical application. Simultaneously, the comparison of sensors with different electrode materials may offer an effective route for designing and optimizing humidity sensors.     

羧甲基纤维素交联缩合反应的动力学研究

本文研究了羧甲基纤维素和水溶性酚醛树脂的交联缩合动力学的测试方法并得到了该反应的动力学方程。因为水溶性酚醛树脂是多种活性中间体的混合物,羧甲基纤维素是受羧甲基取代度和聚合度影响的大分子,两者的交联缩合反应可以同时发生在多点、多分子之间,动力学研究较为复杂,所以本文分别采用Borchardt-Daniels模型和Kissinger模型方法,根据差示扫描量热仪(DSC)测定不同升温速率下的羧甲基纤维素和水溶性酚醛树脂交联缩合反应的热流曲线数据,计算得到反应动力学方程。利用非等温单一扫瞄速率法的Borchardt-Daniels模型得到的动力学参数为:反应级数n 1.05,反应活化能E 93.86kJ/mol,指前因子InA16.23。采用非等温多加热扫描速率法的Kissinger模型计算得到的动力学参数为:反应级数n 1.04,反应活化能E 94.37 kJ/mol,指前因子InA15.96。3个热力学参数值分别相差0.55%、1.71%和1.14%,证明2种模型计算结果较一致。水溶性酚醛树脂与羧甲基纤维素缩合交联缩合反应的动力学方程为(dα)/(dt)=e~(-16.24E/(RT))(1-α)~(1.05)。     

纤维素类高分子玻璃化温度的QSPR研究

玻璃化温度是表征聚合物性能的一个重要的物理化学参数,研究玻璃化温度对聚合物分子设计和改性具有重要意义.本文采用密度泛函论在B3LYP/6-31G(d)水平上优化22种纤维素结构单元,得到分子总能量EHF、热力学能ETHERMAL、最高占据轨道能EHOMO、最低空轨道能ELUMO、最大净负电荷q-、偶极距μ、取代基长度L等7个量子化学参数,并用逐步线性回归方法探讨这些参数与纤维素玻璃化温度(Tg)的关系,建立定量结构-性质模型(QSPR):Tg=94.343-581.544q+0.114EHF-309.152ELUMO.该模型判定系数R2=0.940,表明所选自变量与因变量相关性很高,各参数方差膨胀因子VIF均远小于10,不存在多重共线性问题.最后,用留一法(LOO)检测模型的可信度,结果表明,预测值和实验值吻合较好,交叉验证相关系数为0.888,说明本文所得模型可靠,可用于研究纤维素类聚合物的玻璃化温度,为设计和改性纤维素分子提供理论指导.     

Conductometric glucose biosensor made with cellulose and tin oxide hybrid nanocomposite

This paper reports the feasibility study of glucose oxidase (GO_x) immobilized cellulose-tin oxide (SnO₂) hybrid nanocomposite as a glucose biosensor. Porous SnO₂ layer was grown on regenerated cellulose films via liquid phase deposition technique with varying deposition time. Tin oxide was crystallized in the solution and formed nanocrystal coatings on the cellulose films. Enzyme (GO_x) was immobilized into cellulose-SnO₂ hybrid nanocomposite by physical absorption method. X-ray photoelectron spectroscopy analysis revealed the successful immobilization of GO_x into the cellulose-SnO₂ hybrid nanocomposite via covalent bonding between GO_x and SnO₂. The glucose biosensor under study is displayed linear response in the range of 0.5-12 mM with correlation coefficient of 0.96, which can cover the clinical region of glucose concentration. These results indicate that the cellulose-SnO₂ hybrid nanocomposite can be an inexpensive, flexible and disposable glucose biosensor.     

Flexible humidity and temperature sensor based on cellulose–polypyrrole nanocomposite

Recently, cellulose has been re-discovered as a smart material that can be used as sensor and actuator materials, which is termed as electro-active paper. In this work we demonstrate the application of cellulose as a flexible humidity and temperature sensor. Nanoscaled polypyrrole (PPy) as a humidity and temperature sensitive layer was introduced onto cellulose surface via in situ polymerization technique without disrupting cellulose structure. Atomic force microscopy, UV–visible spectroscopy, transmission electron microscopy and secondary ion mass spectroscopic analysis revealed the successful deposition of polypyrrole nanolayer onto cellulose surface, which is referred as a cellulose–PPy nanocomposite. Effect of polymerization time on sensing behavior of cellulose–PPy nanocomposite was investigated, experimental results revealed that cellulose–PPy nanocomposite with 16 h polymerization time suitable for suitable for humidity and temperature sensor.     

Prediction and optimization of electrospinning parameters for polymethyl methacrylate nanofiber fabrication using response surface methodology and artificial neural networks

Since the fiber diameter determines the mechanical, electrical, and optical properties of electrospun nanofiber mats, the effect of material and process parameters on electrospun polymethyl methacrylate (PMMA) fiber diameter were studied. Accordingly, the prediction and optimization of input factors were performed using the response surface methodology (RSM) with the design of experiments technique and artificial neural networks (ANNs). A central composite design of RSM was employed to develop a mathematical model as well as to define the optimum condition. A three-layered feed-forward ANN model was designed and used for the prediction of the response factor, namely the PMMA fiber diameter (in nm). The parameters studied were polymer concentration (13–28 wt%), feed rate (1–5 mL/h), and tip-to-collector distance (10–23 cm). From the analysis of variance, the most significant factor that caused a remarkable impact on the experimental design response was identified. The predicted responses using the RSM and ANNs were compared in figures and tables. In general, the ANNs outperformed the RSM in terms of accuracy and prediction of obtained results.     

Fabrication of three-dimensional microfluidic channels in a single layer of cellulose paper

Three-dimensional microfluidic paper-based analytical devices (3D-μPADs) represent a promising platform technology that permits complex fluid manipulation, parallel sample distribution, high throughput, and multiplexed analytical tests. Conventional fabrication techniques of 3D-μPADs always involve stacking and assembling layers of patterned paper using adhesives, which are tedious and time-consuming. This paper reports a novel technique for fabricating 3D microfluidic channels in a single layer of cellulose paper, which greatly simplifies the fabrication process of 3D-μPADs. This technique, evolved from the popular wax-printing technique for paper channel patterning, is capable of controlling the penetration depth of melted wax, printed on both sides of a paper substrate, and thus forming multilayers of patterned channels in the substrate. We control two fabrication parameters, the density of printed wax (i.e., grayscale level of printing) and the heating time, to adjust the penetration depth of wax upon heating. Through double-sided printing of patterns at different grayscale levels and proper selection of the heating time, we construct up to four layers of channels in a 315.4-μm-thick sheet of paper. As a proof-of-concept demonstration, we fabricate a 3D-μPAD with three layers of channels from a paper substrate and demonstrate multiplexed enzymatic detection of three biomarkers (glucose, lactate, and uric acid). This technique is also compatible with the conventional fabrication techniques of 3D-μPADs, and can decrease the number of paper layers required for forming a 3D-μPAD and therefore make the device quality control easier. This technique holds a great potential to further popularize the use of 3D-μPADs and enhance the mass-production quality of these devices.     

Surface interactions of oxidized cellulose with fibrin(ogen) and blood platelets

Hemostatic effects of oxidized cellulose are well known but the mechanism of its action is far from being well understood. Hemostatic (hemostyptic) biomaterials with their ability to initiate or accelerate thrombus formation belong to surgical sealants. Thrombus formation is a surface phenomenon. The exploitation of surface plasmon resonance sensing principle for the examination of interactions of oxidized cellulose with fibrinogen, fibrin and blood platelets is reported. Cellulose decreased and slowed down the interaction of immobilized fibrin monomer with fibrinogen as observed by surface plasmon resonance. Only weak interactions of cellulose with plasma proteins albumin and fibrinogen were observed. Delayed gelation and slower increase in turbidity occurred in fibrinogen–thrombin solutions in the presence of the cellulose. Platelets in plasma but not washed platelets in a buffer were activated in the presence of cellulose. We suppose that activation of the coagulation contact system of blood plasma initiated very likely by the negatively charged surface of the oxidized cellulose leads to the fibrin formation and activation and adhesion of blood platelets. The direct interactions of platelets and fibrinogen with the cellulose seem to play a secondary role.     

High toluene sensing properties of NiO–SnO2 composite nanofiber sensors operating at 330 °C

NiO–SnO₂ composite nanofibers are synthesized by electrospinning of a poly(vinyl pyrroridone) (PVP)/SnCl₂·2H₂O/NiCl₂ solution. Indirect-heated sensors are fabricated by coating the nanofibers on ceramic tubes with signal electrodes. The obtained nanofibers are analyzed by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The sensors are tested at different temperatures to various gases. High toluene sensing properties are observed at 330 °C, and the corresponding response value (Ra/Rg), response time, and recovery time are about 11.2 s, and 4 s to 50 ppm toluene at this condition. Good selectivity and excellent stability are also observed based on the sensors at this temperature. These high sensor performances are explained by the sensing enhancement brought about by NiO addition and the one-dimensional nanostructure of nanofibers.     

Formaldehyde sensors based on nanofibrous polyethyleneimine/bacterial cellulose membranes coated quartz crystal microbalance

A novel formaldehyde sensor based on nanofibrous polyethyleneimine (PEI)/bacterial cellulose (BC) membranes coated quartz crystal microbalance (QCM) has been successfully fabricated. The nanoporous three-dimensional PEI/BC membranes are composed of nanofibers with diameter of 30-60 nm. The sensor showed high sensitivity with good linearity and exhibited a good reversibility and repeatability towards formaldehyde in the concentration range of 1-100 ppm at room temperature. Moreover, the results showed that the sensing properties were mainly affected by the content of PEI component in nanofibrous membranes, concentration of formaldehyde and relative humidity. Additionally, the nanofibrous PEI/BC membrane coated QCM sensors exhibited a good selectivity to formaldehyde when tested with competing vapors. The simple and feasible method to prepare and coat the PEI/BC sensing membranes on QCM makes it promising for mass production at a low cost.     

Highly stable and sensitive humidity sensors based on quartz crystal microbalance coated with bacterial cellulose membrane

A novel highly stable and sensitive humidity sensor based on bacterial cellulose (BC) coated quartz crystal microbalance (QCM) has been successfully fabricated. The results showed that the sensors possessed good sensing characteristics by increasing more than two orders of magnitude with increasing relative humidity (RH) from 5 to 97%, and the Log(Δf) showed good linearity (20-97% RH). The sensitivity of sensors coated with BC membranes was four times higher than that of the corresponding cellulose membranes at 97% RH. In addition, the sensor sensitivity is greatly enhanced by increasing the coating load of the BC membranes with more absorption sites in the sensing membranes. Moreover, the experimental results prove that the resultant sensors exhibited a good reversible behavior and good long term stability. Herein, not only a novel and low-cost humidity sensor material was exploited, but also a new application area for BC nanofibrous membranes was opened up.     

乙基纤维素修饰的超高交联吸附树脂对四环素的吸附行为

通过Friedel-Crafts反应和化学修饰反应制备了乙基纤维素修饰的超高交联吸附树脂ECMR,采用傅里叶变换红外光谱和比表面及孔径分析对树脂结构和表面参数进行分析表征。通过静态吸附.脱附、吸附动力学和小柱吸附-脱附实验探讨了ECMR树脂对四环素的吸附行为。结果表明:ECMR树脂的BET比表面积为1083.9m~2/g,微孔面积为885.7 m~2/g。与NDA150相比,ECMR树脂对四环素具有更好的吸附性能,2种树脂对四环素的吸附量均随着温度升高而增加,吸附过程存在着较强的不可逆的化学吸附作用。2种树脂对四环素吸附动力学过程符合准一级方程,颗粒内扩散是吸附过程的主要控制步骤。小柱吸附-脱附结果表明ECMR:树脂对四环素的饱和吸附量较大,Methanol/4%NaOH(V_1/V_2=1/1)的溶液能够很好的使ECMR树脂再生。     

A microfluidic gel valve device using reversible sol–gel transition of methyl cellulose for biomedical application

We have fabricated a microfluidic gel valve device that used reversible sol–gel transition of methyl cellulose (MC). A microheater and a microtemperature sensor were implemented in each microchannel in the gel valve device. Before evaluating the performance of the gel valve device, various properties of the MC solution were investigated using viscometer, spectrophotometer, and NMR. Gelation temperature was increased as the MC concentration was increased. Clear gel, an intermediate state between clear sol and turbid gel, was found at the temperature range from 30–40°C to 50–60°C. Temperature at each microchannel of the device was measured and the effect of the temperature difference on the valve operation was elucidated. In order to have normal operation of the gel valve, it was important to keep the temperature of the heated microchannel around 60°C while keeping the temperature of the flowing microchannel below 35°C. The temperature difference between two microchannels was about 23 K when fan forced cooling (FFC) method was used. For normal performance of the gel valve device, a temporary pause of fluid flow for at least 5 s was required to complete the local gelation in the microchannel. Stable gel valve performance was obtained at the flow rates larger than 5 μl/min. The gel valve device showed no leakage up to 2.07×10⁴ Pa.