Label-free identification of single dielectric nanoparticles and viruses with ultraweak polarization forces

Abstract

Label-free detection of the material composition of nanoparticles could be enabled by the quantification of the nanoparticles' inherent dielectric response to an applied electric field. However, the sensitivity of dielectric nanoscale objects to geometric and non-local effects makes the dielectric response extremely weak. Here we show that electrostatic force microscopy with sub-piconewton resolution can resolve the dielectric constants of single dielectric nanoparticles without the need for any reference material, as well as distinguish nanoparticles that have an identical surface but different inner composition. We unambiguously identified unlabelled ~10 nm nanoparticles of similar morphology but different low-polarizable materials, and discriminated empty from DNA-containing virus capsids. Our approach should make the in situ characterization of nanoscale dielectrics and biological macromolecules possible.

Nanoscale dielectric microscopy of non-planar samples by lift-mode electrostatic force microscopy

“…The use of lift mode imaging ensures the maximum sensitivity in all positions of the sample, and our analysis ensures the results are free from topographic crosstalk artefacts. We would like to highlight, however, that for planar samples or low dimensional non-planar samples (like nanoparticles, nanotubes, etc,) the use of constant height imaging mode can be preferred since the accuracy required (very often in the sub-1zF/nm) [26,27,29] cannot be offered by the reconstruction procedure presented here.…”

“…As explained above, given that the substrate is metallic-like we do not need to include these effects in the present work, so we take L = 0 µm. The explicit tip geometry used in the calculations is determined by means of the tip calibration procedure described elsewhere [8,26]. Briefly, theoretical approach curves calculated for the tip on the bare substrate are least square fitted to an experimentally recorded approach curve on the metal, with the tip radius, R, and cone angle, θ, as fitting parameters (other probe geometric parameters are fixed to nominal values: H=12.5 µm, W=3 µm, L=0 µm).…”

“…Among them, we can cite nanoscale capacitance microscopy [1][2][3], electrostatic force microscopy (EFM) [4][5][6][7][8][9][10], nanoscale impedance microscopy [11,12], scanning polarization force microscopy [13][14][15][16], scanning microwave microscopy (SMM) [17,18] and nanoscale non-linear dielectric microscopy [19]. These techniques have allowed measuring the electric permittivity with nanoscale spatial resolution on planar samples, such as thin oxides, polymer films and supported biomembranes [2][3][4]8,10], and on non-planar ones, such as, single carbon nanotubes, nanowires, nanoparticles, viruses and bacterial cells [20][21][22][23][24][25][26][27][28][29][30].…”

Nanoparticles charge response from electrostatic force microscopy

“…This technique has been used for discriminating insulating from metallic nanotubes, 1,2 measuring their charging capacity, [3][4][5] and measuring the dielectric coefficient of insulating nanoparticle (NP) and viruses. 6 EFM is also of fundamental interest as it could be used to measure the charge compressibility j ¼ dn=dl of conducting nanomaterials. The charge compressibility is a fundamental thermodynamic property of electronic systems whose determination requires measurements of the charge response on the scale of the screening length (k / 1=e 2 j).…”

Band excitation Kelvin probe force microscopy utilizing photothermal excitation

“…KPFM has been particularly useful for characterizing materials and devices ranging from metals, 1 semiconductors, 8,9 and ferroelectrics, 10,11 to self-assembled monolayers, 12 polymers, 13 and biomolecules. 14,15 The continued success of KPFM necessitates both the advancement of the technique in terms of accuracy and resolution 16,17 across all imaging environments, 18,19 as well as improved capabilities to distinguish and correlate different electronic parameters (i.e., dielectric properties, [20][21][22][23] dissipation 24,25 ) beyond that currently attainable with conventional KPFM.…”