Sandwich-Type DNA Micro-Optode Based on Gold–Latex Spheres Label for Reflectance Dengue Virus Detection

A DNA micro-optode for dengue virus detection was developed based on the sandwich hybridization strategy of DNAs on succinimide-functionalized poly(n-butyl acrylate) (poly(nBA-NAS)) microspheres. Gold nanoparticles (AuNPs) with an average diameter of ~20 nm were synthesized using a centrifugation-based method and adsorbed on the submicrometer-sized polyelectrolyte-coated poly(styrene-co-acrylic acid) (PSA) latex particles via an electrostatic method. The AuNP–latex spheres were attached to the thiolated reporter probe (rDNA) by Au–thiol binding to functionalize as an optical gold–latex–rDNA label. The one-step sandwich hybridization recognition involved a pair of a DNA probe, i.e., capture probe (pDNA), and AuNP–PSA reporter label that flanked the target DNA (complementary DNA (cDNA)). The concentration of dengue virus cDNA was optically transduced by immobilized AuNP–PSA–rDNA conjugates as the DNA micro-optode exhibited a violet hue upon the DNA sandwich hybridization reaction, which could be monitored by a fiber-optic reflectance spectrophotometer at 637 nm. The optical genosensor showed a linear reflectance response over a wide cDNA concentration range from 1.0 × 10−21 M to 1.0 × 10−12 M cDNA (R2 = 0.9807) with a limit of detection (LOD) of 1 × 10−29 M. The DNA biosensor was reusable for three consecutive applications after regeneration with mild sodium hydroxide. The sandwich-type optical biosensor was well validated with a molecular reverse transcription polymerase chain reaction (RT-PCR) technique for screening of dengue virus in clinical samples, e.g., serum, urine, and saliva from dengue virus-infected patients under informed consent.

Fabrication of Coatings with Structural Color on a Wood Surface

A facile method for the fabrication of colloidal photonic crystal coatings with tunable structural color on a wood surface was presented. The photonic crystal coatings were formed from monodisperse latex spheres composed of poly(styrene-methyl methacrylate-acrylic acid) (P(St-MMA-AA)). The latex spheres with a hard PSt core and elastomeric P(MMA-AA) shell were prepared using the emulsion polymerization method. The sessile drop method, a rapid single-step self-assembly method through simple evaporation of emulsion, was used to form three-dimensional colloidal crystals. Coatings with brilliant colors and uniform Bragg’s diffraction covering the entire visible region were fabricated by controlling the sphere size. This simple method provided new insight into the development of wood color embellishment.

Characterization of steady-state fluorescence properties of polystyrene latex spheres using off- and online spectroscopic methods

Fluorescent dyed polystyrene latex spheres (PSLs) are commonly used for characterization and calibration of instruments detecting fluorescence signals from particles suspended in the air and other fluids. Instruments like the Ultraviolet Aerodynamic Particle Sizer (UV-APS) and the Waveband Integrated Bioaerosol Sensor (WIBS) are widely used for bioaerosol research, but these instruments present significant technical and physical challenges requiring careful characterization with standard particles. Many other research communities use flow cytometry and other instruments that interrogate fluorescence from individual particles, and these also frequently rely on fluorescent PSLs as standards. Nevertheless, information about physical properties of commercially available PSLs provided by each manufacturer is generally proprietary and rarely available, making their use in fluorescence validation and calibration very difficult. This technical note presents an overview of steady-state fluorescence properties of fluorescent and non-fluorescent PSLs, as well as of polystyrene-divinylbenzene (PS-DVB) particles, by using on- and offline spectroscopic techniques. We show that the “fluorescence landscape” of PSLs is more complex than the information typically provided by manufacturers may imply, especially revealing multimodal emission patterns. Furthermore, non-fluorescent PSLs also exhibit defined patterns of fluorescent emission originating from a mixture of polystyrene and detergents, which becomes a crucial point for fluorescence threshold calibrations and qualitative comparison between instruments. By comparing PSLs of different sizes, but doped with the same dye, changes in emission spectra from bulk solutions are not immediately obvious. On a single-particle scale, however, fluorescence intensity values increase with increasing particle size. No significant effect in the fluorescence signatures was detectable by comparing PSLs in dry vs. wet states, indicating that solvent water may only play a minor role as a fluorescence quencher. Because information provided by manufacturers of commercially available PSLs is generally very limited, we provide the steady-state excitation–emission matrices (EEMs) of PSLs as open-access data within the Supplement. Detergent and solvent effects are also discussed in order to provide information not available elsewhere to researchers in the bioaerosol and other research communities. These data are not meant to serve as a fundamental library of PSL properties because of the variability of fluorescent properties between batches and as a function of particle aging and agglomeration. The data presented, however, provide a summary of spectral features which are consistent across these widely used fluorescent standards. Using these concepts, further checks will likely be required by individual researchers using specific lots of standards.

Technical note: Characterization of steady-state fluorescence properties of polystyrene latex spheres using off- and on-line spectroscopic methods

Fluorescent dyed polystyrene latex spheres (PSLs) are commonly used for characterization and calibration of instruments detecting auto-fluorescence signals from particles suspended in the air and other fluids. Instruments like the Ultraviolet Aerodynamic Particle Sizer (UV-APS) and the Waveband Integrated Bio-aerosol Sensor (WIBS) are widely used for bioaerosol research, but these instruments present significant technical and physical challenges requiring careful characterization with standard particles. Many other research communities use flow cytometry and other instruments that interrogate fluorescence from individual particles, and these also frequently rely on fluorescent PSLs as standards. Nevertheless, information about physical properties of commercially available PSLs provided by each manufacturer is generally proprietary and rarely available, making their use in fluorescence validation and calibration very difficult. This technical note presents an overview of steady-state fluorescence properties of fluorescent and non-fluorescent PSLs, as well as for polystyrene-divenylbenzene (PS-DVB) particles, by using on- and off-line spectroscopic techniques. We show that the fluorescence landscape of PSLs is more complex than the information typically provided by manufacturers may imply, especially revealing multimodal emission patterns. Furthermore, non-fluorescent PSLs also exhibit defined patterns of fluorescent emission originating from a mixture of polystyrene- and detergents, which becomes a crucial point for fluorescence threshold calibrations and qualitative comparison between instruments. By comparing PSLs of different sizes, but doped with the same dye, changes in emission spectra from bulk solutions are not immediately obvious. On a single-particle scale, however, fluorescence intensity values increase with increasing particle size. No significant effect in the fluorescence signatures was detectable by comparing PSLs in dry- vs. wet states, indicating that solvent water may only play a minor role as a fluorescence quencher. Because information provided by manufacturers of commercially available PSLs is generally very limited, we provide the steady-state excitation-emission matrices (EEMs) of PSLs as open access data. Detergent and solvent effects are also discussed in order to provide information not available elsewhere to researchers in the bioaerosol and other research communities. These data are not meant to serve as a fundamental library of PSL properties, because of the variability of fluorescent properties between batches and as a function of particle aging and agglomeration. The data presented, however, provide a summary of spectral features which are consistent across these widely used fluorescent standards. Using these concepts, further checks will likely be required by individual researchers using specific lots of standards.

Coordination-bond-driven fabrication of crack-free photonic crystals

Centimeter-scale crack-free opal PC films are prepared in which the latex spheres are bound together through coordination bonds.