Assemblies of Functional Peptides and Their Applications in Building Blocks for Biosensors

Abstract

We highlight our recent applications of functional peptide nanotubes, self-assembled from short peptides with recognition elements, as building blocks to develop sensors. Peptide nanotubes with high aspect ratios are excellent building blocks for directed assembly into device configurations, and their combining structures with the nanometric diameters and the micrometric lengths enables to bridge the nano-world and the micro-world.

Keywords: bionanotechnology; biosensor; electrochemistry; heavy metals; pathogens; peptide nanotube; self-assembly.

Figure 1

(a) Structural illustration of the template nanotube self-assembled from bolaamphiphile peptide monomers via 3D intermolecular hydrogen-bonding. (b) TEM image of the template nanotube in (a). Scale bar = 100 nm.

Figure 2

(a) Peptide nanotubes are injected onto the electrode-patterned platform while applying an AC field (left), and then peptide nanotubes are trapped at the gap between adjacent electrodes by positive dielectrophoresis (right in an optical micrograph). Scale bar = 2 μm. (b) (left) Scheme to assemble anti-mouse IgG-coated nanotubes and anti-human IgG-coated nanotubes onto their antigen-patterned substrates via biomolecular recognition; Location-specific immobilization of Alexa Fluor 546-labeled anti-mouse IgG nanotubes onto the mouse IgG trenches and FITC-labeled anti-human IgG nanotubes onto the human IgG trenches. (right) Fluorescence image of anti-mouse IgG nanotubes (in red) and anti-human IgG nanotubes (in green), attached onto four upper trenches filled with mouse IgG and four bottom trenches filled with human IgG, respectively, scale bar = 2 μm. (a, reproduced with permission from ref. , copyright Wiley-VCH Verlag GmbH & Co. KGaA. b, reprinted with permission from ref. , copyright 2005 American Chemical Society)

Figure 3

(a) The distribution of the electric field lines and currents is confined within a few micrometers around the electrodes in this device geometry. The presence of dielectric bioparticles in this region where the electric field strength is at maximum results in a decrease of the capacitance between the electrodes. (b) Free-flowing antibody-conjugated peptide nanotubes recognize and bind cells and then fast sedimentation of these complexes onto interdigitated electrodes generates an impedimetric signal for pathogen detection.

Figure 4

(a) Impedance spectra of peptide nanotube-assembled sensing platform. Hollow circles are impedance modulus values before incubating HSV-2, and filled circles are impedance modulus values after incubating HSV-2. Hollow triangles are phase angles before incubating HSV-2, and filled triangles are phase angles after incubating HSV-2. Impedance data was fitted to the equivalent electric circuit in the inset. R_c is the resistance of the contacts, R_sol is the resistance of the solution, and C_sol is the capacitance of the solution, which is proportional to the permittivity of the solution. (b) Correlation between capacitance and the concentration of HSV-2 in the sample solution. ΔC_sol is the corrected capacitance value by subtracting the blank measurement. (reproduced with permission from ref. , copyright Wiley-VCH Verlag GmbH & Co. KGaA)

Figure 5

Strategy for the detection of ultra-low levels of Pb^II with the peptide nanotube detection platform; (a) in the absence of Pb^II nanowires are not templated by the nanotubes and no conductance is measured between the electrodes; (b) in the presence of Pb^II the peptide nucleate the crystallization of Pb; after signal enhancement by Ag reduction, the metallic Pb/Ag coating on the nanotube that bridges the electrodes appears as a resistor in the circuit and the conductance between the electrodes is detected as the signal for Pb^II. (c) Conductance (G) of the peptide nanotube between the electrodes after the incubation with different heavy metal ions with the concentration indicated on the bars. “Control” is the experiment in the presence of 100 nM Pb (II) without the TAR-2-Asp peptide conjugated with the peptide nanotube. (reproduced with permission from ref. , copyright Wiley-VCH Verlag GmbH & Co. KGaA)

Figure 6

Label-free detection of pathogens with antibody-modified peptide nanotubes; a) bacteria agglutinated by the interaction with antibodies on peptide nanotubes sediment fast, and the increased number of the insulating cells on the transducer via the sedimentation increases the impedance at 316 kHz; b) control nanotubes modified with rabbit IgG that do not interact specifically with E. coli do not sediment these cells fast enough to generate the impedance signal; c) Multiplexed detection of pathogens with the peptide nanotube biochip; variations of the real part of the impedance (Z′) of samples containing E. coli and S. typhi in various concentrations was converted into a color chart. (reproduced with permission from ref. , copyright Wiley-VCH Verlag GmbH & Co. KGaA)

Figure 7

Distribution of forward light scattering (FSC) intensity and fluorescence intensity of (a) anti-HSV nanotubes with 10⁶ pfu/mL HSV-2 in solution. (b) Integrated fluorescence intensities inside the gates in (a). (c) Linear correlations and fittings between the integrated fluorescence intensities of the antibody nanotube-virus aggregates and the concentrations on a log scale (R² = 0.9010). (Reproduced by permission of The Royal Society of Chemistry).