Tethered Bilayer Lipid Membranes to Monitor Heat Transfer between Gold Nanoparticles and Lipid Membranes

Summary

This work outlines a protocol to achieve dynamic, non-invasive monitoring of heat transfer from laser-irradiated gold nanoparticles to tBLMs. The system combines impedance spectroscopy for the real-time measurement of conductance changes across the tBLMs, with a horizontally focused laser beam that drives gold nanoparticle illumination, for heat production.

Abstract

Here we report a protocol to investigate the heat transfer between irradiated gold nanoparticles (GNPs) and bilayer lipid membranes by electrochemistry using tethered bilayer lipid membranes (tBLMs) assembled on gold electrodes. Irradiated modified GNPs, such as streptavidin-conjugated GNPs, are embedded in tBLMs containing target molecules, such as biotin. By using this approach, the heat transfer processes between irradiated GNPs and model bilayer lipid membrane with entities of interest are mediated by a horizontally focused laser beam. The thermal predictive computational model is used to confirm the electrochemically induced conductance changes in the tBLMs. Under the specific conditions used, detecting heat pulses required specific attachment of the gold nanoparticles to the membrane surface, while unbound gold nanoparticles failed to elicit a measurable response. This technique serves as a powerful detection biosensor which can be directly utilized for the design and development of strategies for thermal therapies that permits optimization of the laser parameters, particle size, particle coatings and composition.

Introduction

The hyperthermic performance of irradiated gold nanomaterials offers a new class of minimally invasive, selective, targeted treatment for infections and tumors¹. The employment of nanoparticles that can be heated by a laser has been used to selectively destroy diseased cells as well as providing a means for selective drug delivery^2,3. A consequence of the photothermolysis phenomena of heated plasmonic nanoparticles is damage to the cell membranes. The fluid lipid bilayer membrane is considered a particularly vulnerable site for cells undergoing such treatments because denaturation of in....

Protocol

1. tBLMs electrodes preparation

1. Preparation of first monolayer coating
   1. Immerse a freshly sputtered gold patterned electrode microscope slide in an ethanolic solution comprised of a 3 mM 1:9 ratio of benzyl-disulfide-tetra-ethyleneglycol-OH "spacer" molecules (benzyl disulfide comprised a four oxygen-ethylene glycol spacer, terminated with an OH group) and benzyl-disulfide (tetra-ethyleneglycol) n=2 C20-phytanyl "tethered" molecules. This creates the first laye.......

Discussion

This protocol describes the use of tBLM model with a coplanar electrode substrate in conjunction with a horizontal laser alignment set up that enables the real-time electrical impedance recording in response to laser irradiation of gold nanoparticles. The method of EIS recording presented here constructs a minimal list of experiments necessary to provide recording of ion current changes across the membrane, which corresponds to the heat generated by the coupled laser and gold nanoparticle.......

Materials

Name	Company	Catalog Number	Comments
30 nm diameter streptavidin-conjugated gold nanoparticles	Cytodiagnostics	AC-30-04-05	This is a streptavidin-conjugated GNPs product ready for use
30 nm diameter bare gold nanoparticles	Sigma-Aldrich	753629	This is a bare GNPs product ready for use
Cholesterol-PEG-Biotin (MW1000)	NANOCS	PG2-BNCS-10k	Dissolved in highly pure ethanol
C20 Diphytanyl-Glycero-Phosphatidylcholine lipids	SDx Tethered Membranes Pty. Ltd.	SDx-S1	1 ml glass vial containing 70% C16 diphytanyl phosphatidylcholine (DPEPC) and 30% C16 diphytanyl glycerol (GDPE) in 99.9% ethanol
Benzyl-disulfide-tetra-ethyleneglycol-OH	SDx Tethered Membranes Pty. Ltd.	SDx-S2	Spacer molecules
Benzyl-disulfide (tetra-ethyleneglycol) n=2 C20-phytanyl	SDx Tethered Membranes Pty. Ltd.	SDx-S2	Tethered molecules
532 nm green laser continuous light	OBIS LS/OBIS CORE LS, China	ND-1000	The power of this laser was ~135 mW
tethaPod EIS reader	SDx Tethered Membranes Pty. Ltd.	SDx-R1	A reader of conductance and capacitance on six channels simultaneously
tethaPlate cartridge assembly	SDx Tethered Membranes Pty. Ltd.	SDx-BG	Materials to attach the slide with electrodes to the flow cell cartridge
Clamp and slide assembly jig	SDx Tethered Membranes Pty. Ltd.	SDx-A1	Materials to attach the slide with electrodes to the flow cell cartridge
Lipid coated coplanar gold electrodes	SDx Tethered Membranes Pty. Ltd.	SDx-T10	Coplanar  gold electrodes are made from 25 mm x 75 mm x 1 mm polycarbonate base substrate with patterned gold arrays layout, then coated with benzyldisulphide, bis-tetraethylene glycol C16 phytanyl half membrane spanning tethers in a tether ratio of 10%
tethaQuick software	SDx Tethered Membranes Pty. Ltd.	SDx-B1	Software for use with tethaPod to process data and display conductance, impedance and capacitance measurements from the tethaPlate electrodes
99.9% Pure ethanol	Sigma-Aldrich	34963	Absolute,  99.9%
Phosphate buffered saline (PBS)	Sigma-Aldrich	P4417	pH 7