Learning-based automatic sensing and size classification of microparticles using smartphone holographic microscopy.

The accurate and fast size classification of microparticles is important in environmental monitoring and biomedical applications. Conventional methods for sensing and classifying microparticles require bulky optical setups and generally show medium performance. Accordingly, the development of a portable and smart platform for accurate particle size classification is essential. In this study, we propose a new sensing platform for automatic identification of microparticle types through the synergistic integration of smartphone-based digital in-line holographic microscopy (DIHM) and machine-learning algorithms. The smartphone-based DIHM system consists of a coherent laser beam, a pinhole, a sample holder, a three-dimensional printed attachment, and a modified built-in smartphone camera module. The portable device has a physical dimension of 4 × 8 × 10 cm3 and 220 g in weight. Holograms of various polystyrene microparticles with different sizes (d = 2-50 µm) were recorded with a wide field-of-view and high spatial resolution. To establish a proper classification model, tens of features including geometrical parameters and light-intensity distributions were extracted from holograms of individual particles, and five machine-learning algorithms were used. After examining the performance of several classifiers, the resulting support vector machine model trained by using three geometrical parameters and three extracted parameters from light-intensity distributions shows the highest accuracy in the particle classification of the training and test sets (>98%). Therefore, the developed handheld smartphone-based platform can be potentially utilized to cope with various imaging needs in mobile healthcare and environmental monitoring.

Preparation and infrared/raman classification of 630 spectroscopically encoded styrene copolymers.

The barcoded resins (BCRs) were introduced recently as a platform for encoded combinatorial chemistry. One of the main challenges yet to be overcome is the demonstration that a large number of BCRs could be generated and classified with high confidence. Here, we describe the synthesis and classification of 630 polystyrene-based copolymers prepared from the combinatorial association of 15 spectroscopically active styrene monomers. Each of the 630 copolymers displayed a unique vibrational fingerprint (infrared and Raman), which was converted into a spectral vector. To each of the 630 copolymers, a vector of the known (reference) composition was assigned. Unknown (prediction) vectors were decoded using multivariate data analysis. From the inner product of the reference and prediction vectors, a correlation map comparing 396 900 copolymer pairs (630 x 630) was generated. In 100% of the cases, the highest correlation was obtained for polymer pairs in which the reference and prediction vectors correspond to copolymers prepared from identical styrene monomers, thus demonstrating the high reliability of this encoding strategy. We have also established that the spectroscopic barcodes generated from the Raman and infrared spectra are independent of the copolymers' morphology (beaded versus bulk polymers). Besides the demonstration of the generality of the polymer barcoding strategy, the analytical methods developed here could in principle be extended to the investigation of the composition and purity of any other synthetic polymer and biopolymer library, or even scaffold-based combinatorial libraries.

Nanoscale effects leading to non-Einstein-like decrease in viscosity.

Nanoparticles have been shown to influence mechanical properties; however, transport properties such as viscosity have not been adequately studied. This might be due to the common observation that particle addition to liquids produces an increase in viscosity, even in polymeric liquids, as predicted by Einstein nearly a century ago. But confinement and surface effects provided by nanoparticles have been shown to produce conformational changes to polymer molecules, so it is expected that nanoparticles will affect the macroscopic viscosity. To minimize extraneous enthalpic or other effects, we blended organic nanoparticles, synthesized by intramolecular crosslinking of single polystyrene chains, with linear polystyrene macromolecules. Remarkably, the blend viscosity was found to decrease and scale with the change in free volume introduced by the nanoparticles and not with the decrease in entanglement. Indeed, the entanglements did not seem to be affected at all, suggesting unusual polymer dynamics.

Nanoparticles of latexes from commercial polystyrene.

Nanoparticles of polystyrene (PS) (Mw = 1.0-3.0 x 10(6) g/mol) latexes have been successfully prepared from their respective dilute PS (commercial) solutions in cyclohexane, toluene/methanol, or cyclohexane/toluene at each theta temperature. The cationic surfactant cetyltrimethylammonium bromide (CTAB) was used to stabilize the formed PS latex particles. By varying different concentrations of CTAB and PS solution of various Mw, we have successfully produced, for the first time, stable bluish-transparent latex particles ranging from about 10 to 30 nm in diameter (Dw). The number of polymer chains per latex particle (np) is directly proportional to the volume occupied by each latex particle and hence associated to its Dw. The characteristics of these preformed PS latex particles are quite similar to those obtained from the microemulsion polymerization of styrene as reported in literature. These PS latex particles could be further grown by seeding polymerization of styrene to about 50 nm (Dw) with a monodisperse size distribution of Dw/Dn = 1.08.

Interaction of bacterial endotoxine (lipopolysaccharide) with latex particles: application to latex agglutination immunoassays.

The latex agglutination immunoassay technique uses polymer colloids as carriers for antibodies or antigens to enhance the immunological reaction. In this work, the interaction of a lipopolysaccharide (LPS) of Brucella Melitensis with two conventional latexes has been studied. Some experiments on the physical adsorption of the LPS onto these polystyrene beads have been performed and several complexes with different coverage degrees were obtained by modifying the incubation conditions. Regarding the application in the development of diagnostic test systems, it is advisable to study the latex-LPS complexes from an electrokinetic and colloidal stability point of view. The complexes were electrokinetically characterized by measuring the electrophoretic mobility under different redispersion conditions. The colloidal stability was determined by simple turbidity measurements. Experimental and theoretical data have been employed to study the molecular disposition of the LPS in the latex particle surface to compare with the outer membrane of bacterial cells. Latex complexes covered by different LPS amounts showed high colloidal stability and adequate immunoreactivity that remains for a long time period.