Microscale direct measurement of localized photothermal heating in tissue-mimetic hydrogels

Abstract

Photothermal hyperthermia is proven to be an effective diagnostic tool for cancer therapy. The efficacy of this method directly relies on understanding the localization of the photothermal effect in the targeted region. Realizing the safe and effective concentration of nano-particles and the irradiation intensity and time requires spatiotemporal temperature monitoring during and after laser irradiation. Due to uniformities of the nanoparticle distribution and the complexities of the microenvironment, a direct temperature measurement in micro-scale is crucial for achieving precise thermal dose control. In this study, a 50 nm thin film nickel resistive temperature sensor was fabricated on a 300 nm SiN membrane to directly measure the local temperature variations of a hydrogel-GNR mixture under laser exposure with 2 mK temperature resolution. The chip-scale approach developed here is an effective tool to investigate localization of photothermal heating for hyperthermia applications for in-vitro and ex-vivo models. Considering the connection between thermal properties, porosity and the matrix stiffness in hydrogels, we present our results using the interplay between matrix stiffness of the hydrogel and its thermal properties: the stiffer the hydrogel, the higher the thermal conductivity resulting in lower photothermal heating. We measured 8.1, 7.4, and 5.6 °C temperature changes (from the room temperature, 20 °C) in hydrogel models with stiffness levels corresponding to adipose (4 kPa), muscle (13 kPa) and osteoid (30 kPa) tissues respectively by exposing them to 2 W/cm 2 laser (808 nm) intensity for 150 seconds.

In-Line Observation of Laser Cladding Processes via Atomic Emission Spectroscopy

“…In addition, the number of measurable peaks is also increasing. Such behaviour is also quite typical for laser-induced heating where the surface temperature of irradiated metal increases linearly with increasing incident laser power [ 41 , 42 ]. Thus, it can be assumed that the observed increase in peak intensity is—to a certain extent—simply caused by the temperature rise of the irradiated powder material.…”

Plasmonic optical fiber for bacteria manipulation—characterization and visualization of accumulation behavior under plasmo-thermal trapping

“…We note here that, due to the highly localized heating and the low thermal diffusivity of the surrounding medium, there is a considerable mismatch in time constants between plasmonic structures in dry states (< 1 ms) and submerged in fluids (approx. 40 s) [ 56 ]. This can lead to an increase in the local temperature gradient over time, as observed here.…”

Localized Dielectric Loss Heating in Dielectrophoresis Devices

“…The electrodes and the RTD are made of a 25 nm thick nickel film. The device is fabricated with a standard micromachining technique, and the detailed fabrication method is described elsewhere 43–46 . In brief, the inlet, outlet, and channel are formed by 30% w/w KOH etch at 60 °C bath temperature.…”

“…The RTD is biased with 0.1 mA DC current. The RTD has 0.002 K temperature resolution 46 . All the electronics and data acquisition are controlled and collected by a LabView program.…”