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A hydro-thermophoretic trap for microparticles near a gold-coated substrate.

ABSTRACT: Optical tweezers have revolutionised micromanipulation from physics and biology to material science. However, the high laser power involved in optical trapping can damage biological samples. In this context, indirect trapping of microparticles and objects using fluid flow fields has assumed great importance. It has recently been shown that cells and particles can be turned in the pitch sense by opto-plasmonic heating of a gold surface constituting one side of a sample chamber. We extend that work to place two such hotspots in close proximity to each other to form a very unique configuration of flow fields forming an effective quasi-three-dimensional 'trap', assisted by thermophoresis. This is effectively a harmonic trap confining particles in all three dimensions without relying on other factors to confine the particles close to the surface. We use this to show indirect trapping of different types of upconverting particles and cells, and also show that we can approach a trap stiffness of 40 fN μm^-1 indicating a weak confinement regime without relying on feedback.

SUBMITTER: Nalupurackal G

PROVIDER: S-EPMC7613615 | biostudies-literature | 2022 Sep

REPOSITORIES: biostudies-literature

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A hydro-thermophoretic trap for microparticles near a gold-coated substrate.

Nalupurackal Gokul G Gunaseelan M M Roy Srestha S Lokesh Muruga M Kumar Sumeet S Vaippully Rahul R Singh Rajesh R Roy Basudev B

Soft matter 20220921 36

Optical tweezers have revolutionised micromanipulation from physics and biology to material science. However, the high laser power involved in optical trapping can damage biological samples. In this context, indirect trapping of microparticles and objects using fluid flow fields has assumed great importance. It has recently been shown that cells and particles can be turned in the pitch sense by opto-plasmonic heating of a gold surface constituting one side of a sample chamber. We extend that wor ...[more]

PMID: 36040245

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Project description:As biospectroscopy techniques continue to be developed for screening or diagnosis within a point-of-care setting, an important development for this field will be high-throughput optimization. For many of these techniques, it is therefore necessary to adapt and develop parameters to generate a robust yet simple approach delivering high-quality spectra from biological samples. Specifically, this is important for surface-enhanced Raman spectroscopy (SERS) wherein there are multiple variables that can be optimised to achieve an enhancement of the Raman signal from a sample. One hypothesis is that "large" diameter (>100 nm) gold nanoparticles provide a greater enhancement at near-infrared (NIR) and infrared (IR) wavelengths than those <100 nm in diameter. Herein, we examine this notion using examples in which SERS spectra were acquired from MCF-7 breast cancer cells incubated with 150 nm gold nanoparticles. It was found that 150 nm gold nanoparticles are an excellent material for NIR/IR SERS. Larger gold nanoparticles may better satisfy the theoretical restraints for SERS enhancement at NIR/IR wavelengths compared to smaller nanoparticles. Also, larger nanoparticles or their aggregates are more readily observed via optical microscopy (and especially electron microscopy) compared to smaller ones. This allows rapid and straightforward identification of target areas containing a high concentration of nanoparticles and facilitating SERS spectral acquisition. To some extent, these observations appear to extend to biofluids such as blood plasma or (especially) serum; SERS spectra of such biological samples often exhibit a low signal-to-noise ratio in the absence of nanoparticles. With protein-rich biofluids such as serum, a dramatic SERS effect can be observed; although this might facilitate improved spectral biomarker identification in the future, it may not always improve classification between control vs. cancer. Thus, use of "large" gold nanoparticles are a good starting point in order to derive informative NIR/IR SERS analysis of biological samples.

Dataset Information

A hydro-thermophoretic trap for microparticles near a gold-coated substrate.

Publications

A hydro-thermophoretic trap for microparticles near a gold-coated substrate.

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