Quantum Dot‐Based Thermal Spectroscopy and Imaging of Optically Trapped Microspheres and Single Cells

Abstract

Laser‐induced thermal effects in optically trapped microspheres and single cells are investigated by quantum dot luminescence thermometry. Thermal spectroscopy has revealed a non‐localized temperature distribution around the trap that extends over tens of micrometers, in agreement with previous theoretical models besides identifying water absorption as the most important heating source. The experimental results of thermal loading at a variety of wavelengths reveal that an optimum trapping wavelength exists for biological applications close to 820 nm. This is corroborated by a simultaneous analysis of the spectral dependence of cellular heating and damage in human lymphocytes during optical trapping. This quantum dot luminescence thermometry demonstrates that optical trapping with 820 nm laser radiation produces minimum intracellular heating, well below the cytotoxic level (43 °C), thus, avoiding cell damage.

Gold nanorod assisted intracellular optical manipulation of silica microspheres

“…Ashkin and associates also proposed and demonstrated the potential use of optical traps for biological applications [4,7,8]. From these studies, it was determined that near infrared (700 nm < λ < 1070nm) laser traps had the lowest detrimental effect on cell viability, compared to using lasers sources in the visible region [11]. From these studies, it was determined that near infrared (700 nm < λ < 1070nm) laser traps had the lowest detrimental effect on cell viability, compared to using lasers sources in the visible region [11].…”

“…Since these pioneering studies, various biological objects, including viruses, bacteria, and single cells have been trapped successfully, using the single-beam configuration and a great variety of laser sources (with different trapping wavelength, λ) [9,10]. This feature of nearinfrared optical traps has been explained in the past in terms of the reduction in the laserinduced thermal loading (water does not absorb to a significant extent in the 700-980 nm range) and also by the fact that certain wavelengths in the infrared do not promote harmful intracellular reactions [11][12][13][14]. This feature of nearinfrared optical traps has been explained in the past in terms of the reduction in the laserinduced thermal loading (water does not absorb to a significant extent in the 700-980 nm range) and also by the fact that certain wavelengths in the infrared do not promote harmful intracellular reactions [11][12][13][14].…”

“…From these studies, it was determined that near infrared (700 nm < λ < 1070nm) laser traps had the lowest detrimental effect on cell viability, compared to using lasers sources in the visible region [11]. Recent results have concluded that almost damage-free single cell manipulation can be achieved by using trapping wavelengths close to 800 nm [11]. Recent results have concluded that almost damage-free single cell manipulation can be achieved by using trapping wavelengths close to 800 nm [11].…”

“…The viscosity of the intracellular medium has been estimated to be as large as 137.05 Pa·s for 1µm sized bead Murine Macrophage [25]. Increasing the trapping power may be impractical since it may lead to absorption by the medium, causing significant heating and subsequent thermal damage [11]. Therefore, the larger intracellular viscosity particle manipulation would make the optical forces required for intracellular manipulation to be larger than those required in a low viscosity medium at moderate/low laser powers [23,26].…”

Microgels and Nanoparticles: Where Micro and Nano Go Hand in Hand

“…Therefore, Au NPs have been extensively studied in nanoscale thermometry, i. e. temperature measurements by nanometric objects that provide information from individual entities, such as cells. In this context, the characterization of single nanostructures allows understanding and controlling processes at the nanoscale such as membrane or DNA melting, drug release or protein denaturation [46][47][48][49]. Nanoscale thermodynamics of a single Au NP heated by a laser source has gained attention from both experimental and theoretical points of view [50][51][52].…”