Carbon nanotube electric immunoassay for the detection of swine influenza virus H1N1

Abstract

A low-cost, label-free, ultra-sensitive electric immunoassay is developed for the detection of swine influenza virus (SIV) H1N1. The assay is based on the excellent electrical properties of single-walled carbon nanotubes (SWCNTs). Antibody-virus complexes influence the conductance of underlying SWCNT thin film, which has been constructed by facile layer-by-layer self-assembly. The basic steps of conventional immunoassay are performed followed by the electric characterization of immunochips at the last stage. The resistance of immunochips tends to increase upon surface adsorption of macromolecules such as poly-L-lysine, anti-SIV antibodies, and SIVs during the assay. The resistance shift after the binding of SIV with anti-SIV antibody is normalized with the resistances of bare devices. The sensor selectivity tests are performed with non-SIVs, showing the normalized resistance shift of 12% as a background. The detection limit of 180 TCID(50)/ml of SIV is obtained suggesting a potential application of this assay as point-of-care detection or monitoring system. This facile CNT-based immunoassay also has the potential to be used as a sensing platform for lab-on-a-chip system.

Fig. 1

The fabricated carbon nanotube thin film immunochips: (a) schematic of an individual immunochip with close-up hierarchy of SWCNT multilayer, (b) an optical image of the individual chip, SEM images of metal (Cr/Au) electrode pattern (c) and SWCNTs multilayer thin film between two electrodes (d), and (e) sorted immunochips in a 24-well plate for use in immunoassay. Conductance of SWCNT thin film changes due to antibody–virus complex.

Fig. 2

Titers for serial 10-fold dilutions of FCV, TGEV, and SIV stocks used for the assay: the concentration exhibited a good linear relationship with the dilution.

Fig. 3

The electrical characterization of SWCNT immunochips: (a) the resistance of layer-by-layer assembled SWCNT resistor with the width of 1 mm and thickness of 38 nm at variable channel lengths, and (b) the effect of surface adsorption on the resistance of chips with channel lengths of 10, 20, and 50 μm. Resistances significantly increase upon surface adsorption of PLL. Error bars indicate standard error from 10 devices in a batch.

Fig. 4

Resistance shift upon immunobinding of SIV on channel lengths of 10, 20, and 50 μm: binding tends to increase with the concentration of SIVs. This suggests controllable detection range and detection limit in terms of sensing area.

Fig. 5

The normalized resistance shift with the resistance of bare chips (R_chip), PLL coated (R_PLL), and anti-SIV antibody assembled chips (R_Ab) in 10 μm channel: the sensitivity increased significantly upon normalization with bare chips while the plateau is observed from undiluted to 10²-fold dilution in the normalization with (R_PLL) and (R_Ab). The error bars indicate standard error from 5 sets of assays.

Fig. 6

Sensor selectivity tests of 10 μm channel immunochips against TGEV and FCV based on normalization with the resistance of bare chips (R_chip). The error bars indicate standard error from 5 sets of assays.