Suspension Of Polystyrene Microspheres Research Articles

Anomalous scattering of polystyrene microparticles revealed by evanescent wave coupled cavity ringdown spectroscopy.

Forward scattering is an essential tool for investigating the colloidal suspension of polystyrene microspheres (PSMs). Evanescent wave coupled cavity ringdown spectroscopy (EW-CRDS) shows the anomalous extinction behavior in the limit of PSM particles that is much larger than the wavelength. EW-CRDS is a highly sensitive technique that improves weak absorption signals by enhancing the absorption path length, allowing for probing a range of processes at the solid/liquid interface by assessing the extinction properties. Additionally, it possesses the ability to sense a minimum absorbance of 1.2 × 10-6. EW-CRDS provides sufficient accuracy to detect correlation effects for PSMs in water at the interfacial region and their influence on forward scattering or extinction. In this work, we discuss the impact of volume fraction on the extinction of scatterers composed of microparticles in aqueous media. The findings of this study will contribute to a deeper understanding of the scattering dynamics in colloidal suspensions, with potential applications in various fields, including biology and metrology.

Reflectance calibration of multimode optical fiber probes by probe-to-target distance reflectance profile modeling

Reflectance acquired with a multimode optical fiber probe can be related to optical properties of an investigated turbid medium by utilizing a light propagation model. During this step, a calibration of the light propagation model is required, as the modeled reflectance is normalized to the light energy of the source fiber, while the experimentally acquired reflectance is normalized to a reflective standard. Since currently established calibration methods based on liquid and solid turbid phantoms suffer from drawbacks such as low stability and dependence on other characterization methods, we propose a new method for reflectance calibration that is based on modeling and acquisition of probe-to-target distance reflectance profiles from first surface mirrors. We show that the spectrally resolved calibration factors can be estimated with a repeatability of 2% and agree within 10% with the reference values obtained by using turbid phantoms based on aqueous suspensions of polystyrene microspheres.

Species-dependent response of food crops to polystyrene nanoplastics and microplastics

This study investigated the early responses of four common food crops (Italian lettuce, radish, wheat and corn) by exposing their seeds to suspensions of polystyrene nanoparticles (nano-PS) and microspheres (micro-PS). We found that the crop responses to exposure to nano-PS and micro-PS at different doses were dependent on the plant species. Among the four species, Italian lettuce was the most sensitive crop in terms of seed germination and its germination index after polystyrene exposure for 7 days was inhibited by 18.2%–36.0% compared with that of the control (p < 0.05). The root growth (root dry weight, root/shoot ratio and root length) of Italian lettuce and corn was significantly inhibited by the exposure treatment (p < 0.05), whereas that of radish and wheat was hardly affected. Analyses of antioxidant enzymatic activities, lipid peroxidation, and integrated biomarker indexes confirmed that the toxic effects of nano-PS and micro-PS on crops are likely due to oxidative stress. The observed distribution of fluorescent nano-PS in the roots or germs of the tested crops suggests that nanoplastics can be taken up by plants even at a very early growth stage (<7 days after sowing). Future research is needed in order to obtain more insights into their implications for agricultural sustainability and food safety.

Penetration capability of near infrared Laguerre-Gaussian beams through highly scattering media.

The higher capability of optical vortex beams of penetrating turbid media (e.g., biological fluids) with respect to the conventional Gaussian beams is, for the first time to our knowledge, demonstrated in the 1.3 µm wavelength range which is conventionally used for optical coherence tomography procedures in endoscopic intravascular scenarios. The effect has been demonstrated by performing transmittance measurements through suspensions of polystyrene microspheres in water with various particulate concentrations and, in reflection, by using samples of human blood with different thicknesses. The reduced backscattering/increased transmittance into such highly scattering media of Laguerre-Gaussian beams with respect to Gaussian ones, in the near infrared wavelength region, could be potentially exploited in clinical applications, leading to novel biomedical diagnoses and/or procedures.

Determination of polystyrene microsphere suspension concentration by optical coherence tomography and artificial neural network

In order to accurately determine the concentration of turbid samples, we compare two optical measurement systems at near-infrared wavelengths, one is optical coherence tomography(OCT) and the other is beam analyzer(BA). The back-scattering and transmitted light were measured and analyzed to determine the concentration of turbid solution prepared with polystyrene microsphere and water. The research shows that the concentration is strongly correlated with both depth-dependence coherent optical signal and beam expansion of transmitted light. By exploiting a suitable model of artificial neural network and dozens of training data, the concentration of sample was determined with an uncertainty of 8% and 7.5 % for OCT and BA respectively. After averaging the results of the two methods, the relative error can be reduced to 6% or better. Although the study focused on particular solution of polystyrene microsphere, the results of the two independent methods represent consistency and effectiveness for determination of optical properties.

Determination of refractive index, size, and solid content of monodisperse polystyrene microsphere suspensions for the characterization of optical phantoms.

Monodisperse polystyrene microspheres are often utilized in optical phantoms since optical properties such as the scattering coefficient and the scattering phase function can be calculated using the Mie theory. However, the calculated values depend on the inherent physical parameters of the microspheres which include the size, refractive index, and solid content. These parameters are often provided only approximately or can be affected by long shelf times. We propose a simple method to obtain the values of these parameters by measuring the collimated transmission of polystyrene microsphere suspensions from which the wavelength-dependent scattering coefficient can be calculated using the Beer-Lambert law. Since a wavelength-dependent scattering coefficient of a single suspension is insufficient to uniquely derive the size, refractive index and solid content by the Mie theory, the crucial and novel step involves suspending the polystyrene microspheres in aqueous sucrose solutions with different sucrose concentrations that modulates the refractive index of the medium and yields several wavelength-dependent scattering coefficients. With the proposed method, we are able to obtain the refractive index within 0.2% in the wavelength range from 500 to 800 nm, the microsphere size to approximately 15 nm and solid content within 2% of their respective reference values.

Self-assembly of polystyrene microspheres into two-level hierarchical structures

Two-level arrays of colloidal particles have been obtained using the method based on an intermittent, ‘‘stick–slip’’ motion of the meniscus during colloidal suspension evaporation. The ethanol suspension of monodisperse polystyrene microspheres of about 1 μm in size was prepared by emulsifier-free emulsion polymerization of styrene with potassium persulphate as an initiator. The resulting structures consist of parallel monolayer stripes of deposited microspheres, repeated with a period of 140–150 μm, and empty spaces between them. The microspheres are packed into a hexagonal structure inside the stripes. Laser diffraction patterns have been demonstrated for both levels of ordering, i.e., for the hexagonal structure at the first level and for the parallel stripes at the second level.

Depolarization of an Ultrashort Pulse in a Disordered Ensemble of Mie Particles

We study propagation of an ultrashort pulse of polarized light through a turbid medium with the Reynolds-McCormick phase function. Within the basic mode approach to the vector radiative transfer equation, the temporal profile of the degree of polarization is calculated analytically with the use of the small-angle approximation. The degree of polarization is shown to be described by the self-similar dependence on some combination of the transport scattering coefficient, the temporal delay and the sample thickness. Our results are in excellent agreement with the data of numerical simulations carried out previously for aqueous suspension of polystyrene microspheres.

Efficient filtration of micron and submicron particles by ascidians from oligotrophic waters

AbstractSuspended food particles in oligotrophic waters are scarce and the planktonic community is dominated by minute picoplanktonic (&lt; 2 μm) cells. Consequently, suspension feeders inhabiting such environments are faced with the dual challenge of capturing extremely small particles and efficiently processing large volumes of water. We used direct in situ techniques to characterize the size‐dependent capture efficiency curve of four solitary ascidian species (Chordata, Tunicata) from the ultra‐oligotrophic East‐Mediterranean, and two species from the oligotrophic Gulf of Aqaba (Northern Red‐Sea). To control for confounding factors such as particle surface chemistry, we used a suspension of artificial polystyrene microspheres with a wide range of sizes (from 0.3 μm to 10 μm) but identical surface chemistry. This suspension was introduced into the inhalant siphon while the water inhaled and exhaled by the otherwise undisturbed ascidian was cleanly sampled. All the investigated ascidian species captured ≥ 1 μm microspheres at 95% ± 8% efficiency (mean ± 95% Confidence Interval) with no significant difference between species. Moreover, and in contrast to reports from eutrophic waters, both in situ and laboratory experiments revealed an efficient capture of submicron 0.3 μm microspheres at close to 50% efficiency. For most of the species tested, the capture efficiency of microspheres dropped below optimum between 1 μm and 0.5 μm providing an estimation of their mucus mesh pore size. We suggest that ascidians from oligotrophic waters are adapted for capturing submicron particles picoplankton and other. Such adaptation enables “oligotrophic” ascidians to access a much larger food source and facilitates the transfer of planktonic C, N, and P from the water column to the benthos.

Multi-allele dipstick assay for visual genotyping of four novel SIRT1 gene variant alleles as candidate biomarkers for sporadic Parkinson disease

The authors describe a visual genotyping assay for the rapid and simultaneous detection of four novel variant alleles within the SIRT1 promoter region. These alleles may be considered as a risk biomarker for the onset of Parkinson disease. An amplified DNA fragment, flanking the four SIRT1 polymorphisms, is subjected to a multiplex primer extension reaction in the presence of biotin-dUTP. Extension of primers and, consequently, incorporation of the biotin-dUTP occurs only if primers are perfectly complementary to the target sequence. Detection of the extension products is achieved by a DNA biosensor that functions in a lateral-flow mode and carries multiple test spots. Each spot comprises a suspension of polystyrene microspheres functionalized with capture probes. The primer extension reaction products hybridize, through specific sequence tags, to the capture probes of the biosensor. Biotinylated extended primers are visualized by means of anti-biotin-conjugated gold nanoparticles. The genotype is simply read out by observing the formation of red test spots. The method was optimized and evaluated by analyzing three recombinant DNA fragments carrying the novel polymorphisms and 48 clinical samples from patients with sporadic Parkinson disease and from healthy individuals. The proposed genotyping method is accurate, sensitive, and cost effective. As low as 6 fmol of amplified genomic DNA was found to be sufficient to generate detectable spots for correct genotyping. The total time required for the accumulation of genotyping results takes ∼2 h.

Study of a shear thickening fluid: the suspensions of monodisperse polystyrene microspheres in polyethylene glycol

ABSTRACTThe monodisperse polystyrene (PS) microspheres were prepared by dispersion polymerization. The rheological properties of shear thickening fluid (STF) based on PS microspheres dispersing in polyethylene glycol with different concentrations were studied through the steady and oscillatory shear at different temperatures, respectively. All suspensions successively present the first shear thinning, the shear thickening, and the second shear thinning. The experimental results indicate that the shear thickening behavior of STF is controlled by the concentration of PS microspheres and temperature, as changed from continuous shear thickening (CST) to discontinuous shear thickening (DST) with increasing solid content or decreasing temperature. The STF is affected by shear rate, temperature, and the viscosity of the dispersed medium, and it is reversible absolutely and presents transient response ability. Both CST and DST behave as dilatancy. The PS microsphere aggregations formed under shear stress may result in the shear thickening in STFs.

High temperature behavior of monodisperse porosity in alumina films

Understanding the sintering behavior of tailored porosity in thin-film ceramics is essential for applications in photonics, thermal coatings, catalysis, and electrodes. Alumina films exhibiting a random distribution of templated pores with monodisperse size were produced by spin coating from suspensions of alumina powder and polystyrene microspheres. The microstructural evolution, grain size, pore size, and their respective distributions were determined as a function of the initial volume fraction of templated pores, sintering temperature, and time. The behavior between grains and pores at the surface and in the bulk was evaluated and compared to other disordered and ordered porous alumina systems. Above a pore fraction threshold of ∼9vol%, increasing pore fractions retarded grain growth, with smaller grains observed between close pores. While the average bulk pore size did not change with sintering temperature, time, or pore fraction, it did produce a broader pore size distribution with different pore geometries.

Wavefront analysis of the laser beam propagating through a turbid medium

Laser beam propagation through a scattering suspension of polystyrene microspheres in distilled water is studied theoretically and experimentally. The dependence of wavefront aberrations on the particle concentration is investigated. The existence of symmetric wavefront aberrations of the laser beam passed through a turbid medium is shown.

Gelation of large hard particles with short-range attraction induced by bridging of small soft microgels.

In this study, mixed suspensions of large hard polystyrene microspheres and small soft poly(N-isopropylacrylamide) microgels are used as model systems to investigate the static and viscoelastic properties of suspensions which go through liquid to gel transitions. The microgels cause short-range attraction between microspheres through the bridging and depletion mechanism whose strength can be tuned by the microgel concentration. Rheological measurements are performed on suspensions with the volume fraction (Φ) of microspheres ranging from 0.02 to 0.15, and the transitions from liquid-like to solid-like behaviors triggered by the concentration of microgels are carefully identified. Two gel lines due to bridging attraction under unsaturated conditions are obtained. Ultra-small angle neutron scattering is used to probe the thermodynamic properties of suspensions approaching the liquid-solid transition boundaries. Baxter's sticky hard-sphere model is used to extract the effective inter-microsphere interaction introduced by the small soft microgels. It is found that the strength of attraction (characterized by a single stickiness parameter τ) on two gel lines formed by bridging is very close to the theoretical value for the spinodal line in the τ-Φ phase diagram predicted by Baxter's model. This indicates that the nature of the gel state may have the same thermodynamic origins, independent of the detailed mechanism of the short-range attraction. The relationship between the rheological criterion for the liquid-solid transition and the thermodynamic criterion for the equilibrium-nonequilibrium transition is also discussed.

Macroporous Bismuth Film Screen‐Printed Carbon Electrode for Simultaneous Determination of Ni(II) and Co(II)

AbstractMacroporous bismuth film screen‐printed carbon electrode (mpBiF‐SPCE) was used for simultaneous measurement of Ni(II) and Co(II) at their trace concentration level by means of adsorptive cathodic stripping voltammetry with dimethylglyoxime as a complexing agent. The mpBiF‐SPCE was prepared on a screen printed carbon electrode by colloidal crystal templating using aqueous suspension of polystyrene microspheres which were self‐assembled onto the electrode by slow evaporation of solvent. Following the electrochemical deposition of bismuth film, the microspheres were dissolved with toluene providing the macroporous bismuth film structure. The mpBiF‐SPCE offered good electroanalytical performance with estimated limits of detection of 27 and 94 ng L−1 for Ni(II) and Co(II), respectively, in combination with an accumulation time of 180 s, and relative standard deviations of 3.3 % for Ni(II) and 5.2 % for Co(II). The effect of potentially interfering ions and the surface‐active compounds was also investigated. Both Ni(II) and Co(II) were assayed in the sample of sewer water with satisfactory recovery.

Measurement of the anisotropy factor with azimuthal light backscattering

The potential capability of low coherence backscattering (LBS) is explored to determine the anisotropy factor based on azimuthal light backscattering map. The scattering intensity signal measured at azimuthal angle φ=0° is extracted for analysis. By performing nonlinear regression fitting on the experimental signal to the Henyey-Greenstein phase function, the anisotropy factor is determined. The experiments with tissue phantom consisting of the aqueous suspension of polystyrene microspheres are carried out. The results show that the measured anisotropy factor is well described by Mie theory.

Synthesis and upconversion emission properties of Pb0·9La0·1TiO3:Yb, Tb inverse opals by sol–gel technique

Inverse opal photonic crystals of Yb3+, Tb3+ codoped Pb0·9La0·1TiO3 were synthesised by a sol–gel technique in combination with a self-assembly method. Opal template was self-assembled from suspensions of monodisperse polystyrene microspheres with a mean diameter of 400 nm via a vertical deposition process. After infiltrating the Yb3+, Tb3+ codoped Pb0·9La0·1TiO3 sol into the opal template, the polystyrene microspheres were removed by calcination at 670°C, and Yb3+, Tb3+ codoped Pb0·9La0·1TiO3 inverse opal photonic crystals were formed. The effect of photonic band gap on upconversion emissions was investigated in the Yb3+, Tb3+ codoped Pb0·9La0·1TiO3 inverse opals. Significant suppression of the upconversion emission was detected if the photonic band gap overlapped with the Tb3+ ions emission band, leading to colour tuneable upconversion photonic crystals with applications in solid state colour displays.

Measurement of Scattering and Absorption Cross Sections of Dyed Microspheres.

Measurements of absorbance and fluorescence emission were carried out on aqueous suspensions of polystyrene (PS) microspheres with a diameter of 2.5 µm using a spectrophotometer with an integrating sphere detector. The apparatus and the principles of measurements were described in our earlier publications. Microspheres with and without green BODIPY@ dye were measured. Placing the suspension inside an integrating sphere (IS) detector of the spectrophotometer yielded (after a correction for fluorescence emission) the absorbance (called A in the text) due to absorption by BODIPY@ dye inside the microsphere. An estimate of the absorbance due to scattering alone was obtained by subtracting the corrected BODIPY@ dye absorbance (A) from the measured absorbance of a suspension placed outside the IS detector (called A1 in the text). The absorption of the BODIPY@ dye inside the microsphere was analyzed using an imaginary index of refraction parameterized with three Gaussian-Lorentz functions. The Kramer-Kronig relation was used to estimate the contribution of the BODIPY@ dye to the real part of the microsphere index of refraction. The complex index of refraction, obtained from the analysis of A, was used to analyze the absorbance due to scattering ((A1- A) in the text). In practice, the analysis of the scattering absorbance, A1-A, and the absorbance, A, was carried out in an iterative manner. It was assumed that A depended primarily on the imaginary part of the microsphere index of refraction with the other parameters playing a secondary role. Therefore A was first analyzed using values of the other parameters obtained from a fit to the absorbance due to scattering, A1-A, with the imaginary part neglected. The imaginary part obtained from the analysis of A was then used to reanalyze A1-A, and obtain better estimates of the other parameters. After a few iterations, consistent estimates were obtained of the scattering and absorption cross sections in the wavelength region 300 nm to 800 nm.

Extraction of effective parameters of turbid media utilizing the Mueller matrix approach: study of glucose sensing

An analytical technique based on Stokes polarimetry and the Mueller matrix method is proposed for extracting the effective linear birefringence, linear dichroism, circular birefringence, circular dichroism, linear depolarization, and circular depolarization properties of turbid media. In contrast to existing analytical models, the model proposed extracts the effective parameters in a decoupled manner and considers not only the circular dichroism properties of the sample, but also the depolarization properties. The results show that the proposed method enables all of the effective parameters to be measured over the full range. Moreover, it is shown that the extracted value of the depolarization index is unaffected by the order in which the depolarizing Mueller matrix is decomposed during the extraction procedure. Finally, a method is proposed for calibrating the optical rotation angle of a polystyrene microsphere suspension containing dissolved D-glucose (C6H12O6) powder in accordance with the distance between the sample and the detector. The experimental results show that the sensitivity of the resulting D-glucose measurement is equal to approximately 1.73 deg/M.

Macrogel induced by microgel: bridging and depletion mechanisms

In this work, aggregation and gelation behaviour of mixed suspensions of polystyrene microspheres and poly(N-isopropylacrylamide) microgels were studied. In dilute microsphere suspensions, with increasing concentration of microgel (ϕMG), microspheres first aggregated with each other through the bridging of the microgels, then dispersed individually when saturated adsorption was achieved, and finally depletion clusters formed at even higher concentrations of microgel. The concentration of microgel for saturated adsorption (ϕ*MG) is in a linear relationship with the given concentration of microsphere (ϕMS). For given ϕMS, the largest bridging clusters formed at ϕMG ≅ 0.5 ϕ*MG. In concentrated microsphere suspensions, with increasing ϕMG, the mixed suspensions showed a liquid–“bridging gel”–liquid–“depletion gel” transition. The maximum modulus and yielding stress of the bridging gel are also obtained at ϕMG ≅ 0.5 ϕ*MG. The gelation of the microsphere can be explained by the percolation of the clusters and the elasticity of bridging gel arising from the mutual attractions between the microspheres.