Polystyrene Latex Beads Research Articles

A Size‐Exclusion Nanocellulose Filter Paper for Virus Removal

This is the first time a 100% natural, unmodified nanofibrous polymer-based membrane is demonstrated capable of removing viruses solely based on the size-exclusion principle, with a log10 reduction value (LRV) ≥ 6.3 as limited by the assay lower detection limit and the feed virus titre, thereby matching the performance of industrial synthetic polymer virus removal filters.

Influence of external calcium and thapsigargin on the uptake of polystyrene beads by the macrophage-like cell lines U937 and MH-S

BackgroundMacrophages are equipped with several receptors for the recognition of foreign particles and pathogens. Upon binding to these receptors, particles become internalized. An interaction of particles with macrophage surface receptors is accompanied by an increase in cytosolic calcium concentration. This calcium is provided by intracellular stores and also by an influx of external calcium upon activation of the calcium channels. Nevertheless, the role of calcium in phagocytosis remains controversial. Some researchers postulate the necessity of calcium in Fc-receptor-mediated phagocytosis and a calcium-independent phagocytosis of complement opsonized particles. Others refute the need for calcium in Fc-receptor-mediated phagocytosis by macrophages.MethodsIn this study, the influence of external calcium concentrations and thapsigargin on the phagocytosis of polystyrene latex beads by the macrophage-like cell lines MH-S (murine) and differentiated U937 (human) was analyzed. The phagocytosis efficiency was determined by flow cytometry and was evaluated statistically by ANOVA test and Dunett’s significance test, or ANOVA and Bonferroni’s Multiple Comparison.ResultsAcquired data revealed an external calcium-independent way of internalization of non-functionalized polystyrene latex beads at free calcium concentrations ranging from 0 mM to 3 mM. The phagocytosis efficiency of the cells is not significantly decreased by a complete lack of external calcium. Furthermore, the presence of thapsigargin, known to lead to an increase of cytosolic calcium levels, did not have a significant enhancing influence on bead uptake by MH-S cells and only an enhancing effect on bead uptake by macrophage-like U937 cells at an external calcium concentration of 4 mM.ConclusionThe calcium-independent phagocytosis process and the decrease of phagocytosis efficiency in the presence of complement receptor inhibitor staurosporine lead to the assumption that besides other calcium independent receptors, complement receptors are also involved in the uptake of polystyrene beads. The comparison of the phagocytosis efficiencies of both cell types in bivalent cation-free HBSS buffer and in cell medium, leads to the conclusion that it is more likely that other media ingredients such as magnesium are of greater importance for phagocytosis of non-functionalized polystyrene beads than calcium.

Flat Flow Profiles Achieved with Microfluidics Generated by Redox-Magnetohydrodynamics

Horizontal flow profiles having uniform velocities (3-13% RSD) at fixed heights across 0.5, 2.0, and 5.6 mm widths, with magnitudes of ≤124 μm/s, can be sustained along a ∼25.0 mm path using redox-magnetohydrodynamics (MHD) microfluidic pumping in a small volume (14.3 mm wide × 27.0 mm long × 620 μm high) on a chip. Uniform velocity profiles are important in moving volume elements without shape distortion for assays and separations for lab-on-a-chip applications. Fluid movement resulting from the MHD force (FB = j × B) was monitored with video microscopy by tracking 10 μm, polystyrene latex beads mixed into the solution. The ionic current density, j, was generated in 0.095 M K3Fe(CN)6, 0.095 M K4Fe(CN)6, and 0.095 M KCl by applying a constant current across a 0.5, 2.0, or 5.6 mm gap between an anode-cathode pair of electrodes, consisting of one to four shorted parallel, coplanar gold microbands [each 25.0 mm × 98 μm × ∼100 nm (thickness), and separated by 102 μm] fabricated on an insulated silicon substrate. By shorting the increasing numbers of microbands together, increasing currents (118, 180, 246, and 307 μA) could be applied without electrode damage, and the impact of ionic current density gradients on velocity profiles over the anodes and cathodes could also be investigated. The magnetic field, B, was produced with a 0.36 T NdFeB permanent magnet beneath the chip. Data analysis was performed using particle image velocimetry software. A vertical flow profile was also obtained in the middle of the 5.6 mm gap.

Study on steric transition in asymmetrical flow field-flow fractionation and application to characterization of high-energy material

In field-flow fractionation (FFF), there is the ‘steric transition’ phenomenon where the sample elution mode changes from the normal to steric/hyperlayer mode. Accurate analysis by FFF requires understanding of the steric transition phenomenon, particularly when the sample has a broad size distribution, for which the effect by combination of different modes may become complicated to interpret. In this study, the steric transition phenomenon in asymmetrical flow FFF (AF4) was studied using polystyrene (PS) latex beads. The retention ratio (R) gradually decreases as the particle size increases (normal mode) and reaches a minimum (Ri) at diameter around 0.5μm, after which R increases with increasing diameter (steric/hyperlayer mode). It was found that the size-based selectivity (Sd) tends to increase as the channel thickness (w) increases. The retention behavior of cyclo-1,3,5-trimethylene-2,4,6-trinitramine (commonly called ‘research department explosive’ (RDX)) particles in AF4 was investigated by varying experimental parameters including w and flow rates. AF4 showed a good reproducibility in size determination of RDX particles with the relative standard deviation of 4.1%. The reliability of separation obtained by AF4 was evaluated by transmission electron microscopy (TEM).

Principal component and causal analysis of structural and acute in vitro toxicity data for nanoparticles

Structure toxicity relationship analysis was conducted using principal component analysis (PCA) for a panel of nanoparticles that included dry powders of oxides of titanium, zinc, cerium and silicon, dry powders of silvers, suspensions of polystyrene latex beads and dry particles of carbon black, nanotubes and fullerene, as well as diesel exhaust particles. Acute in vitro toxicity was assessed by different measures of cell viability, apoptosis and necrosis, haemolytic effects and the impact on cell morphology, while structural properties were characterised by particle size and size distribution, surface area, morphology, metal content, reactivity, free radical generation and zeta potential. Different acute toxicity measures were processed using PCA that classified the particles and identified four materials with an acute toxicity profile: zinc oxide, polystyrene latex amine, nanotubes and nickel oxide. PCA and contribution plot analysis then focused on identifying the structural properties that could determine the acute cytotoxicity of these four materials. It was found that metal content was an explanatory variable for acute toxicity associated with zinc oxide and nickel oxide, while high aspect ratio appeared the most important feature in nanotubes. Particle charge was considered as a determinant for high toxicity of polystyrene latex amine.

Assessment of penetration through vacuum cleaners and recommendation of wet cyclone technology

In many commercial vacuum cleaners, the captured aerosol particles contained in the dust collector may accidentally release from the exhaust filtration owing to leakage or penetration. Vacuum cleaners may cause dust to become airborne by exhausting air that is not completely filtered. This may cause the operator to inhale dust, in turn causing health problems. This study aimed to investigate the dust penetration rates from three commercial vacuum cleaners and suggest the best technique for completely filtering exhaust air using a combination of cyclonic separation and water filtration. The commercial vacuum cleaners were tested inside a custom-built hood, and the exhausted particles were monitored using a sampling probe in conjunction with an aerosol particle sizer. Quartzose mineral dusts were added to each vacuum cleaner through the dust transport line. A 2400 L/min wet cyclone was employed as the proposed vacuum cleaner. It was designed using Stokes scaling, and its collection characteristics were evaluated using polystyrene latex beads. Surprisingly, the conventional vacuum cleaners failed to capture an overall average of ˜14% of the particles in the given size range. However, only ˜3.8% of the collected particles escaped from the vacuum cleaner that used the wet cyclone technology. Thus, the proposed vacuum cleaner should potentially be an effective method for vacuuming household dust. Implications: The successful investigation of conventional vacuum cleaners is useful for both manufacturers and users. As an effective vacuum cleaning mechanism, household dust is able to migrate along the thin water film that forms on the inner walls of the cyclone vacuum cleaner. It collects dust in a small water inflow (3 mL/min), which allows it to capture a higher percentage of contaminants than most of the currently available vacuum cleaners. The significantly low accidental exposure rates achieved by this new vacuum cleaner enable healthy conditions in various environments, including indoors.

A crossflow filtration system for constant permeate flux membrane fouling characterization

Membrane fouling is often characterized using a crossflow filtration apparatus. Typically, the transmembrane pressure (TMP) difference is fixed, and the flux is allowed to decline as the membrane fouls and the resistance to mass transfer increases. However, as flux varies, so too does the rate at which foulants are brought to the membrane surface, so the observed fouling behavior is not solely the result of membrane∕foulant interactions. Constant flux experiments, where the permeate flux is fixed and the TMP difference varies, minimize such variations in the hydrodynamic conditions at the membrane surface, but constant TMP difference experiments dominate the fouling literature because they are more straightforward to execute than constant flux experiments. Additionally, most industrial water purification membrane installations operate at constant flux rather than at constant TMP. Here, we describe the construction and operation of a constant flux crossflow fouling apparatus. System measurement accuracy was validated by comparison of pure water permeance measurements to values specified by the membrane manufacturer, reported elsewhere, and measured by another technique. Fouling experiments were performed with two membrane∕foulant systems: polysulfone ultrafiltration membranes with a soybean oil emulsion foulant and PVDF microfiltration membranes with a polystyrene latex bead suspension foulant. Automatic permeate flux control facilitated flux stepping experiments, which are commonly used to determine the threshold flux or critical flux of a membrane∕foulant pair. Comparison of a flux stepping experiment with a literature report yielded good agreement.

Development of a foam flotation system for harvesting microalgae biomass

The lack of efficient and cost-effective technologies for harvesting bulk quantities of microalgae biomass is a major obstacle to commercialisation of algae-derived biofuels. This article demonstrates the efficacy of a foam harvester that combines dispersed air flotation with foam fractionation to allow harvesting, concentration, and physical separation of particles in suspension. Fractional factorial experiments using polystyrene latex beads were combined with trials using microalgae to determine the relative importance of key design and operational variables (air flow rate, batch run time, foam column height, surfactant concentration, and surfactant type) on the particle concentration factor. The model revealed that highest concentration factors were gained using the following variables and variable interactions: cationic cetyl trimethylammonium bromide (CTAB), lower surfactant concentrations, and CTAB combined with high column heights. Variables that increased foam residence time produced the greatest concentration factors. Analyses of the harvest economics revealed that foam flotation consumes only 0.015kWh/m3 providing an advantageous cost–benefit relationship, and outcompeting many commonly used bulk harvesting technologies.

Effect of Surfactant on Retention Behaviors of Polystyrene Latex Particles in Sedimentation Field-Flow Fractionation: Effective Boundary Slip Model Approach

A retention theory in sedimentation field-flow fractionation (SdFFF) was developed by exploiting the effective slip boundary condition (BC) that allows a finite velocity for particles to have at the wall, thereby alleviating the limitations set by the no-slip BC constraint bound to the standard retention theory (SRT). This led to an expression for the retention ratio R as R = (R(o) + v*(b))/(R(o) + v*(b)), where R(o) is the sterically corrected SRT retention ratio and v*(b) is the reduced boundary velocity. Then, v*(b) was modeled as v*(b) = v*(b,o)/[1 + (7K*S(o))(1/2)], where S(o) is the surfactant (FL-70) concentration and K* is the distribution coefficient associated with the langmuirian isotherm of the apparent effective mass against S(o). We applied this to study the surfactant effect on the retention behaviors of polystyrene (PS) latex beads of 170-500 nm in diameter. As a result, an empirical relation was found to hold between v*(b,o) and d(o) (estimated from R(o) at S(o) = 0) as v*(b,o) - v*(o,o)[1 - (d(c)/d(o))], where v*(o,o) is the asymptotic value of v*(b,o) in the vanishing d(c)/d(o) limit and d(c) is the cutoff value at which v*(b,o) would vanish. According to the present approach, the no-slip BC (v*(b,o) = 0) was predicted to recover when d(o) ∼ d(c), and the boundary slip effect could be significant for S(o) ≤ 0.05%, particularly for large latex beads.

The effect of initial parameters on particle size distribution inverted using the laser diffraction technique and a non-linear iterative method

The Twomey non-linear iteration (NLI) method is known by the simple algorithm. However, the performance of the inversion is strongly depended on parameters of the NLI algorithm. Major parameters in the algorithm are the initial size distribution, weight parameter, and the number of iteration. In the study, we show how values of initial parameters affect to the result of size distribution in the algorithm by the laser diffraction scattering method. Computer simulations and experimental method are carried out to observe the influence of the parameters in the algorithm. Scattering pattern is calculated by Mie scattering model in the range of 5.0×10−4−2.5rad. Experimental results were measured mono-distribution polystyrene latex (50μm) and poly-distribution glass beads (3–30μm, and 10–100μm). The number of iteration is a most influence parameter in the NLI algorithm. If the number of iteration is too high for calculation, calculated result will lose the smoothness. We also introduced a new parameter C (combination of the sum of residual squares of scattering signals and sum of secondary differentiation of size distribution) to monitor the suitable stop criterion for the NLI method. The parameter C is a useful index for the poly dispersion sample to find the suitable stop criterion.

Characterizing the effects of cell settling on bioprinter output

The time variation in bioprinter output, i.e. the number of cells per printed drop, was studied over the length of a typical printing experiment. This variation impacts the cell population size of bioprinted samples, which should ideally be consistent. The variation in output was specifically studied in the context of cell settling. The bioprinter studied is based on the thermal inkjet HP26A cartridge; however, the results are relevant to other cell delivery systems that draw fluid from a reservoir. A simple mathematical model suggests that the cell concentration in the bottom of the reservoir should increase linearly over time, up to some maximum, and that the cell output should be proportional to this concentration. Two studies were performed in which D1 murine stem cells and similarly sized polystyrene latex beads were printed. The bead output profiles were consistent with the model. The cell output profiles initially followed the increasing trend predicted by the settling model, but after several minutes the cell output peaked and then decreased. The decrease in cell output was found to be associated with the number of use cycles the cartridge had experienced. The differing results for beads and cells suggest that a biological process, such as adhesion, causes the decrease in cell output. Further work will be required to identify the exact process.

Infectious disease aerobiology: miasma incarnate

Infectious disease aerobiology: miasma incarnate

Experimental study of dielectrophoresis and liquid dielectrophoresis mechanisms for particle capture in a droplet

This work presents a microfluidic system that can transport, concentrate, and capture particles in a controllable droplet. Dielectrophoresis (DEP), a phenomenon in which a force is exerted on a dielectric particle when it is subjected to a non-uniform electric field, is used to manipulate particles. Liquid dielectrophoresis (LDEP), a phenomenon in which a liquid moves toward regions of high electric field strength under a non-uniform electric field, is used to manipulate the fluid. In this study, a mechanism of droplet creation presented in a previous work that uses DEP and LDEP is improved. A driving electrode with a DEP gap is used to prevent beads from getting stuck at the interface between air and liquid, which is actuated with an AC signal of 200 V(pp) at a frequency of 100 kHz. DEP theory is used to calculate the DEP force in the liquid, and LDEP theory is used to analyze the influence of the DEP gap. The increment of the actuation voltage due to the electrode with a DEP gap is calculated. A set of microwell electrodes is used to capture a bead using DEP force, which is actuated with an AC signal of 20 V(pp) at a frequency of 5 MHz. A simulation is carried out to investigate the dimensions of the DEP gap and microwell electrodes. Experiments are performed to demonstrate the creation of a 100-nL droplet and the capture of individual 10-μm polystyrene latex beads in the droplet.

Effect of Carrier Fluid Viscosity on Retention Time and Resolution in Gravitational Field-Flow Fractionation

Gravitational field-flow fractionation (GrFFF) is a useful technique for fast separation of micrometer-sized particles. Different sized particles are carried at different velocities by a flow of fluid along an unobstructed thin channel, resulting in a size-based separation. They are confined to thin focused layers in the channel thickness where force due to gravity is exactly opposed by hydrodynamic lift forces (HLF). It has been reported that the HLF are a function of various parameters including the flow rate (or shear rate), the size of the particles, and the density and viscosity of the liquid. The dependence of HLF on these parameters offers a means of altering the equilibrium transverse positions of the particles in GrFFF, and hence their elution times. In this study, the effect of the viscosity of the carrier fluid on the elution behavior (retention, zone broadening, and resolution) of micrometer-sized particles in GrFFF was investigated using polystyrene (PS) latex beads as model particles. In order to change the carrier liquid viscosity without affecting its density, various amounts of (hydroxypropyl) methyl cellulose (HPMC) were added to the aqueous carrier liquid. It was found that particles migrate at faster rates as the carrier viscosity is increased, which confirms the dependence of HLF on viscosity. At the same time, particle size selectivity decreased but peak shape and symmetry for the more strongly retained particles improved. As a result, separation was improved in terms of both the separation time and resolution with increase of carrier viscosity. A theoretical model for plate height in GrFFF is also presented, and its predictions are compared to experimentally measured values.

Caffeine, dibutyryl cyclic-AMP and heparin affect the chemotactic and phagocytotic activities of neutrophils for boar sperm in vitro

The objective was to examine the effects of caffeine, dibutyryl cyclic AMP, and heparin on the chemotaxis and/or phagocytosis of PMNs for porcine sperm. The chemotactic activity of PMNs, determined in a blind well chamber, increased (P < 0.05) when fresh serum was added to the medium (control containing BSA, 1109.5 cells/mm2 vs serum, 1226.3 cells/mm2), regardless of the presence of sperm (control, 1121.1 cells/mm2 vs serum, 1245.8 cells/mm2), whereas heat-inactivated serum did not affect activity (without sperm, 1099.4 cells/mm2 and with sperm, 1132.6 cells/mm2). Regardless of live and dead sperm and of the origin of PMNs (boars vs sows), the phagocytotic activity of PMNs, as determined by co-culture of PMNs with sperm for 60 min, increased (P < 0.05) in the presence of fresh serum containing active complement (46.7 and 43.0%, respectively), but stimulation was decreased (P < 0.05) when 1 mM or higher concentrations of caffeine was added to the medium (from 40.7 to 20.8–31.6%). The origin of PMNs (sows vs boars) did not significantly affect phagocytotic activity. The percentage of PMNs that phagocytized polystyrene latex beads decreased when 2 mM caffeine was added to the medium containing porcine serum (from 43.7 to 21.5%). Serum-stimulated chemotactic activity of PMNs (1089.9 cells/mm2) was also reduced (P < 0.05) with 2 mM caffeine (942.5 cells/mm2). Furthermore, dibutyryl cAMP at ≥ 0.1 mM or heparin at ≥ 100 μg/mL decreased phagocytotic activity, in a concentration-dependent manner (P < 0.05). Supplementation of PMNs with heparin at 100 or 500 μg/mL decreased (P < 0.05) chemotactic activity in the presence of serum (from 1137.1 cells/mm2 to 1008.8–1026.3 cells/mm2). We inferred that opsonization in the presence of active complement stimulated phagocytotic and chemotactic activities of PMNs, whereas supplementation with caffeine and dibutyryl cAMP (which could be associated with the intracellular cAMP level of PMNs) or adding heparin decreased serum-stimulated phagocytotic and chemotactic activities.

Evaluating a composite cartridge for small system drinking water treatment

A pilot-scale evaluation was conducted at the U.S. Environmental Protection Agency (EPA) Test & Evaluation (T&E) Facility in Cincinnati, Ohio, on a multi-layer, cartridge-based system that combines physical filtration with carbon adsorption and ultraviolet (UV) light disinfection to serve as a home-base water treatment security device against accidental or intentional contaminant events. The system was challenged with different levels of turbidity, a number of biological contaminants including Bacillus subtilis, Escherichia coli, MS2 bacteriophage and Polystyrene Latex (PSL) beads as a surrogate for Cryptosporidium and a number of chemical contaminants including super-chlorination, methyl tertiary butyl ether (MTBE), water chlorination disinfection byproducts (DBPs) and diazinon. The results demonstrated that the performance of the system varies as a function of the specific contaminant or surrogate. The overall performance indicated the potential of the system to improve the quality and safety of household water and to serve as an additional treatment barrier in circumstances where there is little or no treatment or where the quality of treated water may have deteriorated during distribution. The results also demonstrated that B. subtilis spore can serve as a more conservative surrogate for Cryptosporidium than PSL beads.

Highly Scattering, Surface-Enhanced Raman Scattering-Active, Metal Nanoparticle-Coated Polymers Prepared via Combined Swelling−Heteroaggregation

We report on a combined swelling−heteroaggregation (CSH) method for preparation of highly scattering, metal nanoparticle(NP)-coated polystyrene (PS) latex beads. This methodology is a facile and relatively benign single-step process for preparation of metal-coated dielectrics for applications in biomedical imaging, sensors, photonics, electronics, and surface-enhanced Raman scattering (SERS). A range of NPs with different sizes (30, 60, and 80 nm), chemistries (gold and silver), and shapes (sphere and cube) were successfully coated on the PS beads by using the CSH procedure. Homogeneous and dense metal coatings on the PS beads were obtained by the addition of tetrahydrofuran (THF) to an aqueous cosuspension of polyvinyl pyrrolidone (PVP) capped-metal NPs and 10 μm PS beads. Composite beads were stable with no loss of the NP coating during long-term (15 months) deionized (DI) water storage. The coating morphology, metal coverage, and optical properties of the composite beads were tunable by simple adjustme...

Visualization of multiprotein complexes by flow cytometry.

Multiprotein complexes and other protein-protein interactions play important roles in virtually all cellular processes. Analysis of coimmunoprecipitation of protein complexes by flow cytometry (IP-FCM, or "the fly-p" method) provides a sensitive means to measure these interactions in the native/nondenatured state. First, immunoprecipitating antibodies are covalently coupled to polystyrene latex beads whose low autofluorescence is compatible with flow cytometry. These antibody-coupled beads are used to immunoprecipitate a specific protein (primary analyte) present in cell lysates. Finally, the protein complexes associated with the beads are probed with fluorochrome-conjugated antibodies specific for interaction partners, or secondary analytes, that may be associated with the primary analyte. The use of quantitative flow cytometric methodology can allow the semiquantitative fluorescence data generated to be converted into estimated numbers of co-associated molecules on the beads. The method represents a robust technique to assess native protein-protein interactions without requiring genetic engineering or large sample sizes.

Collection characteristics of a batch-type wetted wall bioaerosol sampling cyclone

The collection efficiency and sample retention of a batch-type wetted wall bioaerosol sampling cyclone (BWWC) were experimentally characterized. The BWWC is designed to sample air at 400 l/min and concentrate the particles into 12 ml of water. Aerosol is transported into a cylindrically-shaped axial flow cyclone through a tangential slot and the particles are impacted on the inner wall, which is wetted by air shear acting on a liquid pool at the base of the cyclone. The retention of collected particles and the aerosol collection efficiency of the BWWC were evaluated with polystyrene latex beads (PSL), sodium fluorescein/oleic acid droplets, and Bacillus atrophaeus (aka BG) spores. The retention of particles was determined by adding hydrosol directly into the device, running the BWWC for a pre-set period of time, and then determining the amount of particulate matter recovered relative to the initial amount. For 1-μm diameter PSL, 90% of the particles were recoverable from the cyclone body immediately after their introduction; however, only 10% were retained in the collection liquid after 8 h of operation. The aerosol sampling efficiency was determined by comparing the amount of particulate matter collected in the liquid with that collected by a reference filter. The collection efficiency was 50–60% for 1- and 3-μm polystyrene (PSL) particles, and 1.5% for 10-μm oleic acid particles. The efficiency for 3-μm oleic acid droplets was 35%. Explanations are provided for the difference between liquid and solid particle behavior, and for the low efficiency for the large liquid particles. The collection efficiency for single spore BG was slightly lower than that for 1-μm PSL.

Electrochemical nitrite nanosensor developed with amine- and sulphate-functionalised polystyrene latex beads self-assembled on polyaniline

Aniline doped with polyvinyl sulphonate (PV-SO 3 −) was electropolymerised on screen printed carbon (SPCE) and glassy carbon (GCE) electrodes. Then nano-structured polystyrene (PS NP) latex beads functionalised with amine (PS NP-NH 2) and sulphate (PS NP-OSO 3 −) were self-assembled on the modified SPCE and GCE. The resultant polyaniline nanocomposites (PANI|PS NP-NH 2 or PANI|PS NP-OSO 3 −) were characterised by cyclic voltammetry (CV), UV–vis spectroscopy and scanning electron microscopy (SEM). Brown–Anson analysis of the multi-scan rate CV responses of the various PANI films gave surface concentrations of the order of 10 −8 mol cm −2. UV–vis spectra of the PANI films dissolved in dimethyl sulphoxide showed typical strong absorbance maxima at 480 and 740 nm associated with benzenoid π–π* transition and quinoid excitons of polyaniline, respectively. The SEM images of the PANI nanocomposite films showed cauliflower-like structures that are <100 nm in diameter. When applied as electrochemical nitrite sensor, sensitivity values of 60, 40 and 30 μA/mM were obtained for electrode systems containing PANI|PS NP-NH 2, PANI and PANI|PS NP-SO 3 −, respectively. The corresponding limits of detection of the sensors were 7.4, 9.2 and 38.2 μM NO 2 −.