Comparison of electrical properties of viruses studied by AC capacitance scanning probe microscopy.
Capacitances of five types of viruses, adenovirus type 5 (AV5), herpes simplex virus type 1 (HSV1), simian virus 40 (SV40), vaccinia (MVA), and cowpea mosaic virus (CPMV), were compared by AC capacitance scanning probe microscopy. This technique, using a Pt-coated AFM tip as an electrode to probe capacitance of materials between the tip and a bottom electrode, has been applied to study surface structures of semiconductors and polymers with nanometer spatial resolution; however, biological samples at the nanoscale have not been explored by this technique yet. Because most biological cells are poor conductors, this approach to probe electric properties of cells by capacitance is logical. This scanning probe technique showed that each virus has distinguishable and characteristic capacitance. A series of control experiments were carried out using mutant viruses to validate the origin of the characteristic capacitance responses for different viruses. A mutation on the capsid in HSV1 with green fluorescence proteins increased capacitance from 9 x 10(-6) to 1 x 10(-5) F/cm2 at the frequency of 10(4) Hz. Herpes simplex virus type 2 (HSV2) decreased capacitance when its envelope and glycoproteins were chemically extracted. These control experiments indicate that dielectric properties of capsid proteins and envelope glycoproteins significantly influence overall dielectric constants of viruses. Because those capsid proteins and glycoproteins are characteristic of the virus strain, this technique could be applied to detect and identify viruses at the single viron level using their distinct capacitance spectra as fingerprints without labeling.
MacCuspie
Robert I
RI
Department of Chemistry, Hunter College, and The Graduate Center, The City University of New York, 695 Park Avenue, New York, New York 10021, USA.
Nuraje
Nurxat
N
Lee
Sang-Yup
SY
Runge
Anne
A
Matsui
Hiroshi
H
D002213:Capsid / Q000737:chemistry; D036022:Capsid Proteins / Q000737:chemistry / Q000235:genetics; D025802:Electric Capacitance; D049452:Green Fluorescent Proteins / Q000737:chemistry; D008839:Microelectrodes; D018625:Microscopy, Atomic Force / Q000379:methods*; D020527:Microscopy, Scanning Probe / Q000379:methods*; D009154:Mutation; D010984:Platinum / Q000737:chemistry; D014780:Viruses / Q000737:chemistry* / Q000235:genetics
D036022:Capsid Proteins; D049452:Green Fluorescent Proteins; D010984:Platinum