Nanofiber Sensor Research Articles

Sensitive liquid refractive index sensors using tapered optical fiber tips

An optical fiber sensor based on the change of optical confinement in a subwavelength tip is presented. The optical spot is substantially increased when the environmental refractive index (RI) increases from 1.3 to 1.4. By measuring the intensity of low angular spectral components, an intensity sensitivity up to 8000% per RI unit is achieved. The fiber tip sensors take advantage of the small detection volume and real-time responses. We demonstrate the application of the nanofiber sensors for measuring concentrations of acids and evaporation rates of aqueous mixtures.

Low temperature high sensor response nano gas sensor using ITO nanofibers

Indium Tin Oxide (ITO) nanofibers were fabricated by the electrospinning process. Sensors based on these nanofibers were fabricated by applying silver paste as electrode. The morphology and crystal structure of ITO nanofibers were studied by Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD), respectively. The optimal working temperature and sensor response of ITO nanofiber sensors were investigated. All results showed that ITO nanofiber sensors have good sensor response for NO 2 at temperatures as low as 50 °C.

Electrospun Composite Nanofibers for Sensor Applications

AbstractElectrospun polymer nanofiber materials have attracted tremendous interest in sensor applications as their effective sensing surface area dramatically increases with decreasing fiber diameter. The highly tunable polymer composite chemistry and surface functionality of the nanofiber material provides a wide platform for exploring different applications, such as filtration media, sound isolation materials, and sensor components. This paper presents a nanofiber sensor platform device composed of electrospun polymer/carbon composite nanofibers combined with electrodes directly printed onto the surface of the electrospun fiber mat. This structure forms an integrated sensor system for detecting various chemical vapors including volatile organic compounds (VOCs) and oxidative gases. In this sensor, the composite polymer nanofibers form a chemo-resistor sensing material, and the conductivity of these composite sensing materials varies with chemical vapor exposure. The sensor performance exhibits very stable baselines with dramatically reduced noise levels compared to conventional interdigitated electrodes. Furthermore, the sensor response to different vapors shows a linear relationship between conductivity change and vapor concentration in the range of ppb – ppm for some analytes, including methanol, chloroform and ozone. The sensitivity and selectivity of these sensors to different vapor analytes will also be discussed.

Electric response of isolated electrospun polyaniline nanofibers to vapors of aliphatic alcohols

Electrospun isolated camphor sulfonic acid-doped polyaniline nanofiber sensors were fabricated and tested in the presence of various aliphatic alcohol vapors. Due to the large surface to volume ratio, uniform diameter and small quantity of active material used in the construction, these sensors are comparable to or faster than those prepared from nanofiber mats of the same polymer. Sensors made from individual fibers exhibit larger responses, especially for bigger alcohol molecules, and also show true saturation upon exposure and removal of the alcohol vapor. Interestingly, the response of sensors made from electrospun nanofibers to small alcohol molecules is opposite to that observed for cast nanofiber mats and could be related to the doping process used in the preparation of the polymer in either case. The results indicate that the size of the alcohol and the dopant counterion determine whether alcohol molecules are allowed to penetrate polyaniline and lead to an extended coil configuration. A faster response and the ability to selectively deposit isolated nanofibers using electrospinning makes this technique attractive in the fabrication of low cost and low power consumption rapid response sensors.

Fabrication of Functional Nanofibrous Ammonia Sensor

A nanofibrous sensor for ammonia gas is fabricated by electrospinning the composite of poly(diphenylamine) (PDPA) with poly(methyl methacrylate) (PMMA) onto the patterned interdigit electrode. The composite electrospun membrane shows interconnected fibrous morphology. Functional groups in PDPA and the high active surface area of the fibrous membrane make the device detect a lower concentration of ammonia with a good reproducibility. The sensing capability of the device is studied by monitoring the changes in resistance of the membrane with different concentrations of ammonia. The changes in resistance of the membrane shows linearity with the concentration of ammonia in the limit of 10 and 300 ppm. UV-visible spectroscopy reveals the mechanism of sensing ammonia by the membrane.

Doped and dedoped polyaniline nanofiber based conductometric hydrogen gas sensors

Template-free, rapid polymerisation was employed to synthesize polyaniline nanofibers using chemical oxidative polymerisation of aniline, with HCl as a dopant. The doped and dedoped nanofibers were deposited onto conductometric sapphire transducers for gas sensing applications. The sensors were exposed to various concentrations of hydrogen (H 2) gas at room temperature. The sensitivity was measured to be 1.11 for doped and 1.07 for dedoped polyaniline nanofiber sensors upon exposure to 1% H 2. Fast response times of 28 and 32 s were observed for dedoped and doped sensors, respectively. The dedoped nanofiber sensor outperforms the doped sensor in terms of baseline stability and repeatability. Due to its room temperature operation, the gas sensor is promising for environmental applications.

Ultrasensitive Chemiresistors Based on Electrospun TiO2 Nanofibers

Nanostructured semiconducting metal oxides and particularly single nanowire devices offer exceptional gas sensitivity but at the expense of statistical variations and excessive noise levels. In this study TiO2/poly(vinyl acetate) composite nanofiber mats were directly electrospun onto interdigitated Pt electrode arrays, hot pressed at 120 degrees C, and calcined at 450 degrees C. This resulted in a novel multiple nanowire network composed of sheaths of 200-500 nm diameter cores filled with readily gas accessible approximately 10 nm thick single-crystal anatase fibrils. TiO2 nanofiber sensors tested for NO2, in dry air, exhibited exceptional sensitivity showing with, for example, a 833% increase in sensor resistance when exposed to 500 ppb NO2 at 300 degrees C, consistent with a detection limit estimated to be well below 1 ppb. Unusual response patterns were observed at high NO2 concentrations (> 12.5 ppm), consistent with n to p inversion of the surface-trap limited conduction facilitated by the high surface-to-volume ratio of this material.

Electrospun polymer nanofiber sensors

Using the electrospinning technique, we have prepared lithium perchlorate (LiClO 4) doped-polyethylene oxide (PEO) electrospun nanofibers for humidity sensing and camphosulfonic acid (HCSA) doped-polyaniline (PANI)/polystyrene (PS) electrospun nanofibers for sensing hydrogen peroxide (H 2O 2) and glucose. The diameters of these as-prepared polymeric nanofibers are in the range of 400–1000 nm. Owing to the large surface area and good electrical properties intrinsically associated with these nanoscale functional polymer fibers, we achieved significantly enhanced sensitivity for the nanofiber sensors in respect to their corresponding film-type counterparts. While scanning electron micrographs showed some distortions for the LiClO 4 doped-PEO nanofibers after the humidity measurements, no observable morphological change was seen for the HCSA doped-PANI/PS nanofiber sensors after the measurements of H 2O 2 and/or glucose.

Polyaniline Nanofiber Gas Sensors: Examination of Response Mechanisms

Using a new interfacial polymerization method for the synthesis of polyaniline nanofibers, we have developed nanofiber sensors and compared them to conventional polyaniline sensors. Five different response mechanisms are explored: acid doping (HCl), base dedoping (NH3), reduction (with N2H4), swelling (with CHCl3), and polymer chain conformational changes (induced by CH3OH). In all cases, the polyaniline nanofibers perform better than conventional thin films. Their high surface area, porosity and small diameters enhance diffusion of molecules and dopants into the nanofibers.

SYNTHESIS AND ELECTROSPINNING OF A NOVEL FLUORESCENT POLYMER PMMA-PM FOR QUENCHING-BASED OPTICAL SENSING

ABSTRACT This work presents the synthesis of a new fluorescent polymer and its applicability for optical sensing using the electrospinning technique for the fabrication of nanofibrous membrane sensors. A new fluorescent monomer was first synthesized by coupling reactions between methacryloyl chloride and a pyrene derivative, 1-pyrene butanol. Fluorescent polymers containing different ratios of pyrene were then obtained by the copolymerization of this monomer with methylmethacrylate using 2,2′-azobisisobutyronitrile as the initiator. These polymers show distinct and well-defined fluorescence that is characteristic of the pyrene chromophores. Quenching-based optical chemical sensors were then fabricated by the electrospinning technique. The preliminary results show that these sensors have an order of magnitude higher sensitivity to the target analyte 2, 4-dinitro toluene than sensors formed from continuous thin films. This is believed to be due to the higher surface area to volume ratio of the electrospun nanofibrous membranes. The quenching behavior follows Stern-Volmer bimolecular quenching kinetics. The synthesis, characterization, electrospinning fabrication, and sensing capability of these polymers are discussed.