## 2 Methodology
The manipulation capability of charged aerosol biologicals is crucial to potential airborne pathogen identification and monitoring. Electrospray Pathogen Capture: Fundamental processes involved in electrospray ionization were predicted by [PERSON] in 1883 and further characterized by other researchers, [5; 6; 7], that culminated in definitive work by [PERSON] [8] that yielded a coherent description of the end-to-end process that has served as the foundation for further application studies including those described herein. While the aforementioned research is the foundation of electrospray as applied to mass spectrometry, where an unknown analyte is introduced in the needle solvent for electrospray conversion to individual intact ions with multiple charges, the present use for electrospray stems from an accidental discovery in [PERSON]'s lab at Yale [9] where desorbing electrospray droplets were discovered to also capture ambient polar or polarizable chemical species, as well as bacteria, viruses, and aqueous-based droplets containing bacteria and viruses. The basic mechanism of electrospray captures of polar or polarizable trace species from air, including pathogens, is depicted in Figure 2.  
The electrostatic field created as a result of the applied voltage to a conductive fluid exerts a force on the surface of the fluid, which when increased, a threshold is reached where the force due to the field equals the cohesive properties of the fluid, known as the \"Rayleigh Limit\" [10]. A subsequent increase in the field then yields a rapid transition to form a \"Taylor Cone\" coupled with a subsequent emission of a \"jet\" of fluid. This jet ultimately breaks up into a plurality of droplets, which undergo fission due to the increase in droplet surface charge density [11]. Ambient particles such as polar or polarizable molecules and pathogens are attracted to, and captured by, these desorbing droplets with high efficiency using only milliwatts of power and microliters of solvent, which can be water or an organic solvent. Figure 2: Mechanism for electrospray pathogen capture from ambient air. A conductive needle containing a polar solvent and a conductivity enhancer is subjected to an electric field that produces a Taylor Cone. An emerging jet fragments into fine highly charged desorbing solvent droplets that attract and capture ambient respiratory droplets containing pathogens. Charged droplets with pathogens are then deposited onto the electrode target. Electrospray Concentration and Collection Capability: [8] stated that sensors should not be referred to as detectors, but \"identifiers\", and that a \"detector\" is really composed of a collection device and an identifier. If more analyte is collected from the surrounding air-diluent, a less sensitive identifier is needed and vice-versa. It is therefore ideal if the collection device captures and concentrates only the class of materials of interest while ignoring the background. This is incredibly beneficial as it offers a mechanism that has small size, low power consumption, reliability, ease of use, and low cost. It is appropriate to note here the reasons for transforming neutral molecules into ions before attempting characterization. These include the ability to control the trajectories and destinations of charged species by appropriate combinations of electric and magnetic fields. Additionally, detectability is generally much greater for ions than for neutral molecules because each ion gives rise to at least one electron in a primary signal current that can be greatly amplified by well-established techniques such as using an electron multiplier. Multipliers can produce millions of electrons in signal current for each incident ion, coupled to a picoammeter.