FG Nanobiotechnologie
It has recently been shown that surface plasmon microscopy (SPM) allows single nanoparticles (NPs) on sensor surfaces to be detected and analyzed. The authors have applied this technique to study the adsorption of single metallic and plastic NPs. Binding of gold NPs (40, 60 and 100 nm in size) and of 100 nm polystyrene NPs to gold surfaces modified by differently ω-functionalized alkyl thiols was studied first. Self-assembled monolayers (SAM) with varying terminal functions including amino, carboxy, oligo(ethylene glycol), methyl, or trimethylammonium groups were deposited on gold films to form surfaces possessing different charge and hydrophobicity. The affinity of NPs to these surfaces depends strongly on the type of coating. SAMs terminated with trimethylammonium groups and carboxy group display highly different affinity and therefore were preferred when creating patterned charged surfaces. Citrate-stabilized gold NPs and sulfate-terminated polystyrene NPs were used as negatively charged NPs, while branched polyethylenimine-coated silver NPs were used as positively charged NPs. It is shown that the charged patterned areas on the gold films are capable of selectively adsorbing oppositely charged NPs that can be detected and analyzed with an ~1 ng⋅mL−1 detection limit.
Resistive gas sensors based on the composites of nanostructured carbonized polyaniline and Nafion
(2016)
Due to constant necessity to have reliable and sensitive gas sensors in many contemporary technologies, there is a permanent need for development of new sensing platforms with good sensing properties. Here, we demonstrate a novel type of resistive gas sensors based on carbonized polyaniline/Nafion composites. The sensing mechanism of such sensors is based on the sorption of gases by the composites which induce Nafion swelling and decreasing of conductivity. Chemosensitive properties can be tuned by the (i) choice of carbon materials with different conductivities, (ii) Nafion content in the composite, and (iii) thickness of the composite layer. We have shown that the sensors respond to water, acetone, ethanol, and ethanol vapors. For the last two cases, we have achieved high sensitivity, fast response, wide concentration range, and good recovery. The use of simultaneous two- and four-point techniques for these sensors provides an internal control of the sensor integrity.
A concept of virtual sensor array based on electrically controlled variation of affinity properties of the receptor layer is described. It was realized on the base of integrated electrochemical chemotransistor containing polyaniline as the receptor layer. Electrical control of the redox state of polyaniline was performed in five-electrode configuration containing four electrodes for conductivity measurements and one Ag/AgCl reference electrode. All the electrodes were integrated on the same glass chip. A room-temperature ionic liquid was used for the electrical connection between the reference electrode and chemosensitive material. Conductivity measurements demonstrated effective potential-controlled
electrochemical conversions of the receptor material between different redox states. Binding of trimethylamine at three different potentials, corresponding to the different states of the receptor material, was studied. Concentration dependencies and binding kinetics were analyzed. The results demonstrated that the kinetic as well as the equilibrium binding properties of the receptor layer can be controlled by electrical potential, thus
providing a possibility to form a virtual sensor array using only a single sensing element.
The increasing production and application of nanoparticles necessitates a highly sensitive analytical method for the quantification and identification of these potentially hazardous materials. We describe here an application of surface plasmon microscopy for the individual detection of each adsorbed nanoparticle and for visualization of its electrochemical conversion. Whereas the adsorption rate characterizes the number concentration of nanoparticles, the potential at which the adsorbed nanoparticles disappear during an anodic potential sweep characterizes the type of material. All the adsorbed nanoparticles are subjected to the potential sweep simultaneously; nevertheless, each of the up to a million adsorbed nanoparticles is identified individually by its electrochemical dissolution potential. The technique has been tested with silver and copper nanoparticles, but can be extended to many other electrochemically active nanomaterials.
Nanofibrous polyanilines (PANIs) were synthesized by several oxidative polymerization pathways that have in common the presence of excess oxidant(s) (ammonium peroxydisulfate and its mixture with hydrogen peroxide), the absence of added acid, and the absence of external template (self-assembly process). Conducting forms of the synthesized PANI nanofibers (re)doped with various acids were further used as precursors for carbonization process to obtain nanofibrous carbonaceous materials (Carb-PANIs). Morphology, molecular structure, surface properties and electrical characteristics of PANI nanofibrous precursors and their carbonized counterparts were studied by scanning electron microscopy, Raman spectroscopy, by measurements of ζ-potential and determination of isoelectric points, as well as by measurements of electrical conductivity.
Sensitive detection of engineered nanoparticles (NPs) in air and in liquid samples is an important task and still a major challenge in analytical chemistry. Recent work demonstrated that it can be performed using surface plasmon microscopy (SPM) where binding of single NPs to a surface leads to the formation of characteristic patterns in differential SPM images. However, these patterns have to be discriminated from a noisy background. Computer-assisted recognition of nanoparticles offers a solution but requires the development of respective tools for data analysis. Hereby a numerical method for automated detection and characterization of images of single adsorbing NPs in SPM image sequences is presented. The detection accuracy of the method was validated using computer generated images and manual counting. The method was applied for detecting and imaging of gold and silver NPs adsorbing from aqueous dispersions and for soot and NaCl NPs adsorbing from aerosols. The determined adsorption rate was in range 0.1–40 NPs per (s mm2) and linearly dependent on the concentration of nanoparticles. Depending on the type of NPs and signal to noise ratio, a probability of recognition of 90–95 % can be achieved.
An ultrasensitive analytical method for direct detection of single nanoparticles in complex environment is described. The method relies on the wide-field surface plasmon microscopy (SPM). The suppression of matrix effects is achieved by image analysis based on the template matching. First, characteristic SPM images of nanoparticles are collected in aqueous suspensions. Then the detection of nanoparticles in complex environment is performed using template matching.
Quantification and characterization of nanoparticles size was demonstrated at subppb level (∼ 100 pg/mL) in such complex media as wines, fruit juices, or cosmetic formulation. Visualization of the nanoparticles is performed in real time. The method does not require any sample pretreatment. If the minimally acceptable adsorption rate is defined as one nanoparticle to the whole sensor surface per few seconds, the working range of the method is ∼ 10 6 to 10 10
nanoparticles per mL.