Label-Free Optical Sensing on Hybrid Plasmonic-Nanobiosilica Platforms

ABSTRACT Diatoms are single-celled algaes that make photonic-crystal-like silica shells or frustules with hierarchical micro-& nano-scale features consisting of two-dimensional periodic pores. In this paper, we present an innovative label-free optical sensor based on a biological-plasmonic hybrid nanostructure by self-assembling silver (Ag) nanoparticles into diatom frustules. The photonic-crystal-like diatom frustules provide a spatially confined electric field with enhanced intensity that can form hybrid photonic-plasmonic modes through the optical coupling with Ag nanoparticles. The experimental results demonstrate 4-6× and 9-12× improvement of sensitivities to detect the Raman dye for resonance and nonresonance SERS sensing, respectively

Electron Microscopy and Optical Characterization of Cadmium Sulphide Nanocrystals Deposited on the Patterned Surface of Diatom Biosilica

Intricately patterned biosilica obtained from the shell of unicellular algae called diatoms serve as novel templates for fabrication of optoelectronic nanostructures. In this study, the surface of diatom frustules that possessed hierarchical architecture ordered at the micro and nanoscale was coated with a nanostructured polycrystalline cadmium sulphide (CdS) thin film using a chemical bath deposition technique. The CdS thin film was composed of spherical nanoparticles with a diameter of about 75 nm. The CdS nanoparticle thin film imparted new photoluminescent properties to the intricately patterned diatom nanostructure. The imparted photoluminescent properties were dependent on the CdS coverage onto the frustules surface. The intrinsic photoluminescent properties of the frustules were strongly quenched by the deposited CdS. The origin of PL spectra was discussed on the basis of the band theory and native defects

Photoluminescence detection of 2,4,6-trinitrotoluene (TNT) binding on diatom frustule biosilica functionalized with an anti-TNT monoclonal antibody fragment

A selective and label-free biosensor for detection of the explosive compound 2,4,6-trinitrotoluene (TNT) in aqueous solution was developed based on the principle of photoluminescence quenching of upon immunocomplex formation with antibody-functionalized diatom frustule biosilica. The diatom frustule is an intricately nanostructured, highly porous biogenic silica material derived from the shells of microscopic algae called diatoms. This material emits strong visible blue photoluminescence (PL) upon UV excitation. PL-active frustule biosilica was isolated from cultured cells of the marine diatom Pinnularia sp. and functionalized with a single chain variable fragment (scFv) derived from an anti-TNT monoclonal antibody. When TNT was bound to the anti-TNT scFv-functionalized diatom frustule biosilica, the PL emission from the biosilica was partially quenched due to the electrophilic nature of the nitro (-NO₂) groups on the TNT molecule. The dose-response curve for immunocomplex formation of TNT on the scFv-functionalized diatom frustule biosilica had a half-saturation binding constant of 6.4±2.4·10⁻⁸ M and statistically-significant measured detection limit of 3.5·10⁻⁸ M. The binding and detection were selective for TNT and TNB (trinitrobenzene) but not RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) or 2,6-DNT (2,6-dinitrotoluene).Keywords: Antibody, Biosensor, Diatom, Trinitrotoluene, Biosilica, Photoluminescenc

Limits to biomass productivity during fed-batch cultivation of Laminaria saccharina female gametophyte cells in a stirred-tank photobioreactor

This study compared the growth of Laminaria saccharina female gametophyte filamentous cell suspension cultures in a stirred-tank photobioreactor under batch and fed-batch nutrient addition modes over a 48-day cultivation period. Cultures were grown on GP2 artificial seawater medium (0.75 mM nitrate, N:P = 16:1) at pH 8.3 without iron or copper. Total equivalent nutrient loadings ranged from 0.5X to 9.1X GP2 for batch cultivation and 1.3X to 10.4X GP2 for fed-batch cultivation at delivery rates of 0.0067–0.16 mmol N L⁻¹ day⁻¹ based on nitrate. The multicellular, L. saccharina filamentous clumps were dispersed to nominal size of 100 μm by mechanical blending (~ 16,000 rpm, 5 s) prior to inoculation. Fed-batch addition of all nutrients enhanced biomass productivity by a factor of two over a batch cultivation process at equivalent total nutrient loadings in a stirred-tank photobioreactor. Peak productivity through fed-batch cultivation was 57 mg DCW L⁻¹ day⁻¹, and average final biomass densities exceeded 1800 mg DCW L⁻¹, vs. 30 mg DCW L⁻¹ day⁻¹ and 800–900 mg DCW L⁻¹ for batch cultivation. However, there was a limit to biomass productivity enhancement at cumulative nutrient loadings greater than 3X GP2 that was not the result of insufficient CO2 or light delivery. It is suggested that the formation of large, multicellular clumps approaching 1-mm diameter during stirred-tank cultivation may have ultimately reduced biomass productivity during fed-batch cultivation under nutrient-replete conditions. Therefore, future bioreactor processing strategies might consider mechanical blending to disperse the filament clumps during the cultivation process

Metabolic Insertion of Nanostructured TiO2 into the Patterned Biosilica of the Diatom Pinnularia sp by a Two-Stage Bioreactor Cultivation Process

Diatoms are single-celled algae that make silica shells or frustules with intricate nanoscale features imbedded within periodic two-dimensional pore arrays. A two-stage photobioreactor cultivation process was used to metabolically insert titanium into the patterned biosilica of the diatom Pinnularia sp. In Stage I, diatom cells were grown up on dissolved silicon until silicon starvation was achieved. In Stage II, soluble titanium and silicon were continuously fed to the silicon-starved cell suspension (similar to 4 x 10(5) cells/mL) for 10 h. The feeding rate of titanium (0.85-7.3 mu mol Ti L-1 h(-1)) was designed to circumvent the precipitation of titanate in the liquid medium, and feeding rate of silicon (48 mu mol Si L-1 h(-1)) was designed to sustain one cell division. The addition of titanium to the culture had no detrimental effects on cell growth and preserved the frustule morphology. Cofeeding of Ti and Si was required for complete intracellular uptake of Ti. The maximum bulk composition of titanium in the frustule biosilica was 2.3 g of Ti/100 g of SiO2. Intact biosilica frustules were isolated by treatment of diatom cells with SDS/EDTA and then analyzed by TEM and STEM-EDS. Titanium was preferentially deposited as a nanophase lining the base of each frustule pore, with estimated local TiO2 content of nearly 80 wt %. Thermal annealing in air at 720 degrees C converted the biogenic titanate to anatase TiO2 with an average crystal size of 32 nm. This is the first reported study of using a living organism to controllably fabricate semiconductor TiO2 nanostructures by a bottom-up self-assembly process

NPE modeling of a laboratory bleach filtrate recycle experiment

"December 1999.""Submitted to AICHE meeting 1999 Tappi Pulping Conference, October 31-November 3 Orlando, Florida.