Detection and Characterization of Individual Nanoparticles in a Liquid by Photothermal Optical Diffraction and Nanofluidics

Abstract

Detection and characterization of individual nanoparticles less than 100 nm are important for semiconductor manufacturing, environmental monitoring, biomedical diagnostics, and drug delivery. Photothermal spectroscopy is a light absorptiometry and promising method for detection and characterization because of its high sensitivity and selectivity compared with light scattering or electrical detection methods. However, the characterization of individual nanoparticles in liquids is still challenging for conventional photothermal detection methods. Here, we report a method for the ultrasensitive detection and accurate characterization of individual nanoparticles in liquids by photothermal optical diffraction, which utilizes enhancement of optical diffraction by a nanochannel after light absorption and heat generation of individual nanoparticles in the channel. Our method realized individual 20 nm Au nanoparticle detection with almost 100% detection efficiency by utilizing nanochannels, leading to concentration determination without a calibration curve. Furthermore, we measured individual nanoparticle size and discriminated 20 and 40 nm Au nanoparticles from their photothermal signals. Our photothermal-based nanoparticle detection method in nanochannels has a potential for a wide range of applications such as on-site evaluation of synthesized plasmonic nanoparticles and drug delivery particles.

Nanofluidic Detection Platform for Simultaneous Light Absorption and Scattering Measurement of Individual Nanoparticles in Flow

“…We simultaneously measured both absorption and scattering signals from individual nanoparticles flowing within a nanochannel by the integration of two recently developed detection methods utilizing the optical diffraction phenomena of a single nanochannel: photothermal optical diffraction (POD) and nanofluidic optical diffraction interferometry (NODI). The detailed detection principle was described in our previous papers. , Briefly, the POD measures the light absorption of individual nanoparticles by the photothermal effect. The diffracted light intensity depends on the refractive index difference between water and the glass substrate.…”

“…Herein, we describe a novel nanofluidic detection platform that enables simultaneous measurement of absorption and scattering signals from individual nanoparticles in flow. Recently, we developed photothermal optical diffraction (POD) detection method that utilizes optical diffraction from a single nanochannel as a readout for the photothermal effect of individual nanoparticles flowing within the nanochannel. , Furthermore, we also developed nanofluidic optical diffraction interferometry (NODI) that utilizes optical diffraction from a single nanochannel as a reference light for interferometric detection of individual nanoparticles in flow . The combination of these detection methods offers a promising approach for the simultaneous measurement of light absorption and scattering of nanoparticles through a simple experimental system and workflow.…”

Lab-on-Valve Automated and Miniaturized Assessment of Nanoparticle Concentration Based on Light-Scattering

“…9,16 Considering the above-mentioned challenges, improved, alternative, and orthogonal procedures to the currently available strategies for NPs concentration measurements have been pursued. 17,18 Nevertheless, label free, simpler, and fit for purpose methods suitable to characterize the number of organic NPs in formulation batches for routine quality control operations are yet required. In this context, an automated, miniaturized and simple method to quantify NPs resorting to the sequential injection lab-on-valve (SI-LOV) system 19,20 is proposed.…”

Concentration Determination at a Countable Molecular Level in Nanofluidics by Solvent-Enhanced Photothermal Optical Diffraction

“…Different from other photothermal detection methods, the POD enables molecule/nanoparticle detection in 10 2 nm channels because thermal diffusion to substrates also contributes to the signal. For example, we demonstrated the detection and characterization of individual Au nanoparticles (20 nm in diameter) flowing in nanochannels . We also realized chromatographic separation and concentration determination of nonfluorescent molecules in 10 2 nm channels .…”

“…For example, we demonstrated the detection and characterization of individual Au nanoparticles (20 nm in diameter) flowing in nanochannels. 28 We also realized chromatographic separation and concentration determination of nonfluorescent molecules in 10 2 nm channels. 29 The advantage of concentration determination in nanochannels over microchannels is accurate detection volume regulation from the diameter of an excitation beam spot and the cross-section area of a nanochannel, which enables accurate estimation of the number of molecules contributing the signal at a countable molecular level.…”