Capture of airborne nanoparticles in swirling flows using non-uniform electrostatic fields for bio-sensor applications

Abstract

Collection of biological particles is the first and critical step for any biological agent detection system. Towards our goal of capturing and detecting airborne biological entities in real time, here we investigate on the design of an electrostatic particle capture system. We report on the capture of airborne 100 nm diameter polystyrene nanoparticles as a model system, in swirling flows under non-uniform electrostatic fields with an electrospray aerosol generator and a homemade particle collector. The particle collector has five positive electrodes on the bottom and one large grounded electrode on the top. The nanoparticles coming into the collector were slowed down during their swirling and stayed in the collector long before leaving the collector. Silicon chips were placed on the bottom electrodes and the electrostatically captured particles were counted as a function of flow rates, electrode positions, bias voltages, and capture times by epifluorescent images and scanning electron micrographs (SEMs). Particles captured in the electrode at the center of the collector were much less than those on the surrounding four electrodes and 10-25% of the particles with negative charges entering the collector were captured on the bottom electrodes at a flow rate of 1.1 l/min and an applied potential of 2 kV. Particle capture increased with decreasing flow rates. We also simulated flow and electrical fields separately, and found the positional trends to be in good agreement with the measurements. This collector is well adaptable to integration with micro resonator devices and can be used for real-time monitoring of bioaerosols.

Widely Tunable and Highly Efficient 2.3-µm-Band Difference Frequency Generation in Direct-Bonded Quasi-Phase-Matched LiNbO3 Ridge Waveguide

“…Particle generator, neutralizer and particle collector Figure 1 shows a schematic of a particle generation system and the particle collector (Jang et al 2007), and its top view, which shows the three different inlet/outlet configurations, FO (i), BO (ii) and SO (iii) (Jang et al 2006). This collector has five metal sheets (12 × 12 mm 2 ) on its bottom, acting as the positive electrodes to capture negatively charged airborne nanoparticles or microorganisms, and a large grounded electrode on the top (see figure 1(c)).…”

“…In the current simulation, both flow and electric fields were obtained separately and particles were traced from flow fields without considering the effects of electric fields on the particles. These particle tracks give important information on the relationship between the particle velocities, the distance from the electrodes to the particles and the captured particle counts with the electrode position when the electrostatic forces are almost constant with the electrode positions (Jang et al 2007). Particle trajectories in the collector were numerically computed with the discrete phase model of a CFD code FLUENT 6.2.…”

“…We presented a flow-swirling-based electrostatic particle collector without a corona discharger (Jang et al 2006(Jang et al , 2007. The advantage of this particle collector is that flow swirling makes particles stay long and slow down in the collector, which gives rise to many particles to be captured.…”

Real-time detection of airborne viruses on a mass-sensitive device

“…17 The current detection limit can be further improved by higher flow rates in combination with secondary amplification techniques such as gold nanoparticle conjugation 18 and/or the use of electric fields to attract the viruses. 16 In conclusion, we presented the capture of airborne Vaccinia viruses in real-time using a mass sensitive device. We showed that the capture rate of airborne viruses measured by a QCM was linear with virus concentrations and that it had the potential for quantitative detection of airborne viruses.…”

“…The concentration of airborne viruses generated at the capillary tip of the aerosol generation system can be approximated by dividing the product of the concentration of the starting virus suspension in fluid ͑viral particles/ml͒ and the suspension feed rate ͑432 nl/ min͒ by the gas mixture flow rate ͑l/min͒. 16 Considering that only a small fraction of the particles ͑ϳ9.5% ͒ out of those generated at the capillary tip can reach the QCM crystal, 16 the minimum detectable airborne virus concentrations over the quartz crystal are calculated as around 40 and 210 particles/ ml at a flow rate of 2.0 and 1.1 l / min, respectively, which are close to the detection limit ͑10 particles/ ml͒ by BAMS. 17 The current detection limit can be further improved by higher flow rates in combination with secondary amplification techniques such as gold nanoparticle conjugation 18 and/or the use of electric fields to attract the viruses.…”