Absorption and scattering microscopy of single metal nanoparticles

Abstract

Several recently developed detection techniques opened studies of individual metal nanoparticles (1-100 nm in diameter) in the optical far field. Eliminating averaging over the broad size and shape distributions produced by even the best of current synthesis methods, these studies hold great promise for gaining a deeper insight into many of the properties of metal nanoparticles, notably electronic and vibrational relaxation. All methods are based on detection of a scattered wave emitted either by the particle itself, or by its close environment. Direct absorption and interference techniques rely on the particle's scattering and have similar limits in signal-to-noise ratio. The photothermal method uses a photo-induced change in the refractive index of the environment as an additional step to scatter a wave with a different wavelength. This leads to a considerable improvement in signal-to-background ratio, and thus to a much higher sensitivity. We briefly discuss and compare these various techniques, review the new results they generated so far, and conclude on their great potential for nanoscience and for single-molecule labelling in biological assays and live cells.

A flow cytometric method to assess nanoparticle uptake in bacteria

“…Transmission electron microscopy [TEM; (4)], scanning electron microscopy 1 backscattered electron 1 energy-dispersive X-ray spectroscopy [SEM 1 BSE 1 EDS (5)], confocal and fluorescence microscopy (6), reflection-based imaging (7)(8)(9), and dark field imaging (10,11) are the commonly used methods to detect ENMs presence in the cell. Although these techniques have the advantage of tracking ENMs in the cell as well as cellular organelles, there are certain drawbacks, for example, in electron microscopy, the samples have to be fixed, hence, uptake in live cells cannot be monitored.…”

Chemometric determination of the length distribution of single walled carbon nanotubes through optical spectroscopy

“…When a particle's radius (r) is comparable to the wavelength of light (λ), the Mie theory [21] indicates that C sca varies in the order of r 6 , while C abs varies in the order of r 3 only. Therefore, for nano-scale particles, absorption is predominant over scattering [22]. This has been reported in both experimental and theoretical studies [22].…”

“…Therefore, for nano-scale particles, absorption is predominant over scattering [22]. This has been reported in both experimental and theoretical studies [22]. For instance, the C sca /C abs ratio of gold nanospheres with radius of 10 nm under 521 nm light is only 0.01 [23].…”

Photothermal Methods for Single Nonluminescent Nano-Objects

“…However, because the polarizability of an NP is proportional to its volume, the intensity scattering cross section of the particle varies as D 6 , whereas its absorption cross section varies as D 3 and dominates for small sizes. For example, for gold spheres in water probed by 532 nm laser light, absorption is more important than scattering for D < 100 nm.…”

“…Because of the amplification by the reference wave, such interferometric techniques not only result in high sensitivity but also can provide the amplitude and the phase of the scattered wave. A review dedicated to these scattering-and absorption-based methods was published recently (6).…”