## 2 Methodology  
The proof-of-concept stages described herein include multiple components that rely on air sampling and pathogen capture, a pathogen dataset, and a decision tree designed to assist in rapid identification and characterization of airborne pathogens. The pathogen dataset (described below) includes only airborne bacterial pathogen identifying features that are compatible with microscopy. Bacteria were chosen because of their large size, easily identifiable characteristics, and slower mutation rates. They also have the largest number of pathogenic species for humans. Electrospray Air Sampling: Traditional air filtration technology requires significant fan power. In addition, these systems require manual servicing that involves filter cleaning and exchange. Alternative filtration systems based on impaction require even greater fan power to accelerate the gas flow to speeds necessary for inertial deposition on a collecting surface. For nearly 100 years, \"electrostatic precipitation\" (EP) has been used in the industry to remove large quantities of smoke, mist, and dust from exhaust streams. EP's characteristics consist of a few moving parts and very low-pressure drops; hence they require very modest levels of power consumption while still exhibiting high single-pass particle removal efficiencies of 99% [2]. Electrostatic precipitators typically work in two steps: applying either a positive or negative charge to the particles via an electrostatic discharge and deposition of the charged particles on collecting electrodes biased with a high voltage of opposite polarity. Although the voltages are large, the currents are small, resulting in 50-500 watt of power consumption to clean 1000 CFM (Cubic Feet per Minute) of air while filter or impaction based techniques can require thousands of watts to process the same amount of air [3]. Among the primary drawbacks of traditional EP is the possibility of toxic ozone production by corona discharge. An additional limitation is associated with the build-up of particle deposits with high electrical resistivity that can impede performance due to space charge effects. Electrospray particle capture technology is a superior variant of electrostatic precipitation that eliminates the current drawbacks of conventional EP. This technology replaces a corona discharge with a mist of highly charged micro-droplets generated by electrospray ionization as the mechanism by which incoming particles are charged. In electrospray a very low flowrate (1 microliter/minute) of liquid, typically ordinary tap water, made conductive with trace amounts of dissolved salts such as NaCl, is fed from the tip of a needle held at several kilovolts (1-2 kV) relative to a counter electrode. At sufficient field strength, a sharp liquid meniscus forms, emitting millions of highly charged droplets that drift through the surrounding gas and are collected on the counter electrode. Particles in the gas have a high probability of interaction with the droplets, either adhering to them or otherwise acquiring a high level of charge. This causes droplets to be captured on the collecting electrode. The spray acts as a filtration material that is continuously introduced and removed from the gas flow. The primary advantage of using electrospray particle  
Figure 1: A strategy for an airborne detection system that couples air sampling, pathogen capture, and analysis via visualization technologies and decision analysis platforms. capture for droplet charging over EP is that ozone is not generated. Additional benefits include the reduction of space charge on the collected deposit, which is maintained in a conductive and cohesive state by the spray. In addition, there is zero pressure drop in the filtration process, which in of itself consumes only milliwatts of power [4]. Importantly, biological species, such as bacteria and viruses, can be captured and nondestructively charged for manipulation using electrostatic fields.