The ability to detect and size individual nanoparticles with high resolution is crucial to understanding behaviours of single particles and effectively using their strong size-dependent properties to develop innovative products. We report real-time, insitu detection and sizing of single nanoparticles, down to 30 nm in radius, using mode-splitting in a monolithic ultra-high-Q whispering-gallery-mode (WGM) microtoroid resonator. Particle binding splits a WGM into two spectrally shifted resonance modes, forming a self-referenced detection scheme. This technique provides superior noise suppression and enables extracting accurate size information in a single-shot measurement. Our method requires neither labelling of the particles nor apriori information on their presence in the medium, providing an effective platform to study nanoparticles at single particle resolution.
The ability to analyze and identify large macromolecular complexes whose molecular weight is beyond the analyzable range of mass spectrometry is of great interest. The size of such complexes makes them suitable for analysis via mobility size spectrometry. In this work, charge reduced electrospray size spectrometry was used for the analysis of bacteriophage viruses with total molecular masses ranging from 3.6 MDa up to the gigadalton range. The electrospray source used was operated in "cone jet" mode with a mean droplet diameter of 170.56 nm. Bacteriophage MS2 was found to have a mobility diameter of 24.13 +/- 0.06 nm and remain highly viable after the electrospray process. Larger bacteriophages T2 and T4 have lengths greater than the diameter of the electrospray jet and droplets; thus, they could not be completely enclosed and were found to fragment at the virus capsid head-tail noncovalent interface during either the jet formation or jet breakup process. No viable T2 or T4 virions were detectable after being electrosprayed. While the exact mechanism of fragmentation could not be determined, it is proposed here that macromolecular fragmentation at noncovalent interfaces occurs due to mechanically and electrically induced stresses during jet formation and jet breakup. Bacteriophage T4 capsid heads were found to be statistically significantly larger than bacteriophage T2 capsid heads, with a mean peak diameter of 88.32 +/- 1.02 nm for T4 and 87.03 +/- 0.18 nm for T2. While capsid head fragments were detectable, tail and tail-fiber fragments could not be detected by size spectrometric analysis. This is attributed to the fact that the contractile tails of bacteriophage T2 and T4 virions mechanically deform to a varying degree while confined within the smaller jet and droplets. Further evidence of contractile tail deformation during the electrospray process was found by measuring the size spectrum of bacteriophage lambda, which has a noncontractile tail. Bacteriophage lambda had two distinct peaks in its size spectrum, one corresponding to the capsid head and the other corresponding to the tail fragment. Size spectrometry was also used for rapid quantification of virus concentrations, thus demonstrating its full capabilities in the analysis of large macromolecular complexes.
Detecting and characterizing single nanoparticles and airborne viruses are of paramount importance for disease control and diagnosis, for environmental monitoring, and for understanding size dependent properties of nanoparticles for developing innovative products. Although single particle and virus detection have been demonstrated in various platforms, single-shot size measurement of each detected particle has remained a significant challenge. Here, we present a nanoparticle size spectrometry scheme for label-free, real-time and continuous detection and sizing of single Influenza A virions, polystyrene and gold nanoparticles using split whispering-gallery-modes (WGMs) in an ultra-high-Q resonator. We show that the size of each particle and virion can be measured as they continuously bind to the resonator one-by-one, eliminating the need for ensemble measurements, stochastic analysis or imaging techniques employed in previous works. Moreover, we show that our scheme has the ability to identify the components of particle mixtures.
The antimicrobial activity of ZnO nanoparticles (NPs) was investigated under aquatic and aerosol exposure modes. ZnO NPs in aquatic media aggregated to micrometer-sized particles and did not interact with microorganisms effectively. Hence, the inhibition of microbial growth by nano-ZnO NPs (e.g., Mycobacterium smegmatis and Cyanothece 51142) in aquatic media was mainly attributable to dissolved zinc species. Shewanella oneidensis MR-1 and Escherichia coli were able to produce large amounts of extracellular polymeric substances, and their growth was not inhibited by ZnO NPs in aquatic media, even at high concentrations (>40 mg/L). On the other hand, when ZnO NPs were electrosprayed onto an E. coli biofilm so that NPs could be directly deposited onto the cell surface, the aerosol exposure dramatically reduced cellular viability. For example, an electrospray of ZnO NPs (20 nm) reduced the total number of viable E.coli cells by 57% compared to the control case, in which we electrosprayed only the buffer solution. However, electrospraying large-sized ZnO particles (480 nm) or nonsoluble TiO(2) NPs (20 nm) caused much less lethality to E. coli cells. The above observation implies that the aerosol method of exposing ZnO NPs to biological systems appears to have a much higher antimicrobial activity, and thus may lead to practical applications of employing a novel antimicrobial agent for airborne disease control.
A numerical model has been developed to optimize the design of pleated filter panels. In this model, the fluid flow is modeled by a steady laminar flow and the filter media resistance is governed by the Darcy-LapwoodBrinkman equation. A finite element method with a nine-node Lagrangian element is used to solve the governing equations. For the rectangularly pleated filter panel, the numerical results agree well with the analytical model of Yu and Goulding (1992) and with his experimental data. The pressure drop increases a t small pleat count due to increased media face velocity, and a t large pleat count due to increased viscous drag in the pleat spacings. Therefore, an optimal pleat count for minimum pressure drop exists at a certain pleat height for each filter media type. The optimization of rectangular pleated filters, e.g., mini-pleated filter panels, has been performed for six commercial filter media. The optimal pleat count is shown to increase with decreasing media permeability of the filter media. A generalized correlation curve has been found for the six filter media by using a nondimensional parameter analysis. The results can be used to design pleated filter panels with minimum pressure drop.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.