10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Real-time Characterization of Airborne Bacteria Using Optofluidic Surface-Enhanced Raman Spectroscopy (SERS) Platform
JAE HEE JUNG, Jungan Choi, Korea Institute of Science and Technology
Abstract Number: 640 Working Group: Bioaerosols
Abstract Bioaerosols such as viruses, bacteria, and fungal spores are closely related to human health problem both indoor and outdoor places. Their size distribution ranges from 20 nm to 100 μm which is easy to be aerosolized into the air. Due to their low settling velocities, they are suspended in the air for a long time and have the potential for spread over a wide area within a short period. Also, these properties increase the possibility of inhalation, which can amplify the potential for adverse human health effects, infectious diseases, pneumonia, asthma, and allergies. Therefore, for active disease control and to minimize bioaerosol exposure risk, there is a requirement for effective bioaerosol monitoring systems, including continuous bioaerosol sampling and rapid analysis
Recently, micro-fluidics based devices with portability and high sensitivity for detecting microorganism and fine particle have been widely developed. A new diagnostics for real-time single-cell detection based on flow cytometry technic have been introduced using target aptamer-conjugated fluorescent nanoparticles for specific cell counting methods (Chung et al., 2015). The micro-optofluidic platform was developed for quantitative analysis of bioaerosol by Choi et al. (2015). However, there is no integrated optofluidic system for qualitative measurement of bioaerosol using Raman spectroscopy with continuous aerosol sampling. Raman spectroscopy is label-free and non-destructive analysis method. Therefore, it is the proper way for molecular detection and cellular analysis.
Here, we demonstrate a micro-optofluidic platform for real-time detection and quantitative analysis of airborne microorganisms using Raman microspectroscopy. In general, the Raman signal has intrinsically weak intensity with the order of 1 photon per 106 incident photons which means very low sensitivity compared to Rayleigh scattering. To overcome low intensity, we employed the surface-enhanced Raman Spectroscopy (SERS) techniques using silver nanoparticles to improve Raman signal up to ~1011 times amplifying using plasmonic resonance effects.
In our study, the optofluidic platform involves the following three steps: (1) sampling of airborne microorganisms; (2) mixing and reacting in a microchannel for staining; and (3) real-time detection and analysis of microorganism using Raman signal. Numerical simulations were conducted for the design of micro-optofluidic platform and estimation of particle collection efficiency before the experiment. Five different microorganisms and polystyrene latex particles were introduced for the performance evaluation.
In the curved-microfluidic channel, the two-phase fluid (sampling air and collecting liquid) stably forms a stratified flow. The collecting liquid including silver colloid covers the outer wall of the channel during bioaerosol sampling. For collection, the particles are transferred from air to the liquid phase by centrifugal and drag forces by passing fluids through the curved region. The cut-off diameter of particle collection was selected controlling the air flow velocity (microfluidic air flow of 1.2 L/min showed a particle collection efficiency of ~98% at a particle diameter of 1 μm), and continuous enriched particle sampling was possible for real-time SERS measurement to identify sampled particle.
Our results indicated that the developed system represents a significant step forward as an inexpensive, simple, portable and continuous bioaerosol monitor based on the optofluidic platform.
This research was supported by the KIST Institutional Program. This research was also supported in part by the Ministry of Environment (2016000160008), Republic of Korea.