The effect of gold nanoparticles on the impedance of microcapsules visualized by scanning photo-induced impedance microscopy

Abstract

Abstract:Polyelectrolyte microcapsules have attracted great interest in drug delivery applications, and microcapsules modified with gold nanoparticles have been used in this way with triggered release when a laser can be used to remotely open shells through light-induced local heating. The electrical impedance of unmodified microcapsules has been studied due to its implications for their permeability, however, the impedance of functionalised microcapsules has not yet been investigated. Herein, the impedance of microcapsules modified with gold nanoparticles was studied for the first time. It was shown that the modification of microcapsules with gold nanoparticles leads to a much greater impedance than would be expected from the increase in the thickness caused by the presence of a layer of gold nanoparticles alone. The impedance of gold nanoparticle modified capsules was measured using scanning photo-induced impedance microscopy 2 (SPIM), which is based on photocurrent measurements at an electrolyte-insulatorsemiconductor (EIS) field-effect structure. High resolution and good sensitivity were achieved using a two-photon effect for charge carrier excitation and organic monolayer modified silicon on sapphire (SOS) as the SPIM substrate. SPIM allowed impedance imaging of collapsed microcapsules with unprecedented detail. SPIM images of capsules labelled with gold nanoparticles (AuNPs) showed a good agreement with the corresponding optical images, including the creases resulting from the collapse of the hollow shells. The significant increase in impedance caused by the impregnation with AuNPs was also verified by conductive Atomic Force Microscopy (C-AFM) measurements in the dry state.

Image detection of yeast Saccharomyces cerevisiae by light-addressable potentiometric sensors (LAPS)

“…The complex local impedance can be determined from the maximum photocurrent measured in inversion -a technique that has been termed SPIM [21][22][23]. The impedance data obtained from SPIM and from classical AC impedance measurements were compared.…”

“…All chemicals were purchased from Sigma-Aldrich without further purification unless noted. 1,8-Nonadiyne (98%) was redistilled before use as reported [23]. All samples and buffer solution were prepared using ultrapure water (18.2 MΩcm) from a Milli-Q water purification system (Millipore, USA).…”

“…The SOS substrate was modified with an ohmic contact and subsequently with 1,8-nonadiyne as described previously [23]. After modification, the SOS substrate was cut into 4 mm × 4 mm pieces before use.…”

“…To improve the sensitivity of the LAPS surface, the traditional insulator was replaced with a 1,8-nonadiyne monolayer that was bound to hydrogen terminated silicon on SOS [19,20]. The technique has been adapted to the imaging of the local impedance, which has been termed Scanning photoinduced impedance microscopy (SPIM) [21][22][23].…”

Copper Contamination of Self-Assembled Organic Monolayer Modified Silicon Surfaces Following a “Click” Reaction Characterized with LAPS and SPIM

“…Silicon-on-sapphire (SOS) wafers and double polished silicon wafers were cut into 7 mm × 7 mm pieces. In order to form an ohmic contact on SOS substrates for photocurrent measurements, 30 nm Cr and 150 nm Au were thermally evaporated onto one corner of the front-side silicon layer and subsequently heated to 300 °C for 5 min as previously reported 23,24,36 . The substrate was cleaned in a hot piranha solution (3:1 H 2 SO 4 (96%)/H 2 O 2 (30%), caution: highly corrosive) at 100 °C for 30 min and then rinsed copiously with ultrapure (Milli-Q) water.…”