Advanced Compositional Analysis of Nanoparticle-polymer Composites Using Direct Fluorescence Imaging

Summary

Here we present a reliable method to monitor the incorporation of nanoparticles into a polymer host matrix via swell encapsulation. We show that the surface concentration of cadmium selenide quantum dots can be accurately visualized through cross-sectional fluorescence imaging.

Abstract

The fabrication of polymer-nanoparticle composites is extremely important in the development of many functional materials. Identifying the precise composition of these materials is essential, especially in the design of surface catalysts, where the surface concentration of the active component determines the activity of the material. Antimicrobial materials which utilize nanoparticles are a particular focus of this technology. Recently swell encapsulation has emerged as a technique for inserting antimicrobial nanoparticles into a host polymer matrix. Swell encapsulation provides the advantage of localizing the incorporation to the external surfaces of materials, which act as the active sites of these materials. However, quantification of this nanoparticle uptake is challenging. Previous studies explore the link between antimicrobial activity and surface concentration of the active component, but this is not directly visualized. Here we show a reliable method to monitor the incorporation of nanoparticles into a polymer host matrix via swell encapsulation. We show that the surface concentration of CdSe/ZnS nanoparticles can be accurately visualized through cross-sectional fluorescence imaging. Using this method, we can quantify the uptake of nanoparticles via swell encapsulation and measure the surface concentration of encapsulated particles, which is key in optimizing the activity of functional materials.

Introduction

The application of nanomaterials has long served as an area of increasing interest for novel technologies.^1-3 This has included the growing use of nanoparticles in everyday items, including cosmetics, clothes, packaging and electronics.^4-6 A major drive toward using nanoparticles in functional materials stems from their higher reactivity relative to the materials, in addition to the ability to tune properties by variation in particle size.⁷ One further advantage is the capability to easily form composite materials, introducing crucial properties to the host matrix, such as catalytic functionality, material strengthening and tu....

Protocol

1. Preparation of CdSe/ZnS Core/Shell Quantum Dots

1. Preparation of the trioctylphosphine (TOP)-Se solution
   1. Prepare a 0.5 M solution of selenium in TOP by mixing the appropriate amount of Se into TOP in a Schlenk flask under nitrogen or in a glovebox (8 ml required per reaction, typically 0.4 g dissolved in 10 ml of TOP).
   2. Stir the mixture to dissolve the Se for 1 hr, resulting in a grey solution of the TOP-Se complex.
   3. Ensure the solution is then freeze-pump-thaw degassed 5 times. The resulting stock solution can be stored under nitrogen for 3 months.
2. Preparation of the CdSe Co....

Results

The quantum dots exhibited red fluorescence, with a lambda max of approximately 600 nm.^22,28 The red emission was due to the confinement of the exciton by the quantum rod whose size dimensions are within the strong confinement regime. Li et al. showed that for quantum rods, the emission shifts to lower energy with an increase in either width or length of the rod. They further showed that the emission mainly determined by the lateral confinement, which plays an importan.......

Discussion

Cross-sectional fluorescence imaging allows for direct visualization of nanoparticles during swell encapsulation. The kinetics of encapsulation has been shown, with the drive toward a high nanoparticle surface concentration demonstrated. The extent of nanoparticle incorporation is shown to vary with swell encapsulation time (described in section 2.3), with the total amount of incorporated nanoparticles increasing as this time is extended, with the particle concentration localized at the surface if the polymer samples are.......

Materials

Name	Company	Catalog Number	Comments
Polydimethylsiloxane sheets	NuSil	-	Medical Grade
Oleylamine	Sigma Aldrich	O7805	Technical Grade
Trioctylphosphine	Sigma Aldrich	117854	Technical Grade
Trioctylphosphine oxide	Sigma Aldrich	346187	Technical Grade
1-Octadecene	Sigma Aldrich	O806	Technical Grade
Zinc diethyldithiocarbamate	Sigma Aldrich	329703	-
Oleic acid	Sigma Aldrich	364525	Technical Grade
Triethylamine	Sigma Aldrich	471283	-
Cadmium oxide	Alfa Aesar	33235	-
Hexadecylamine	Alfa Aesar	B22459	Technical Grade
1-Dodecylphosphonic acid	Alfa Aesar	H26259	-
Selenium powder	Acros	19807	-
Chloroform	Sigma Aldrich	366919	-
n-Hexane	Sigma Aldrich	208752	-
Microscope slides	VWR	631-0137	Thickness No. 1