A 'Plug and Play' Method to Create Water-dispersible Nanoassemblies Containing an Amphiphilic Polymer, Organic Dyes and Upconverting Nanoparticles

Summary

Organic dye molecules and oleic acid coated upconverting nanoparticles are not water-soluble. This protocol describes a ‘plug and play’ method that enables the transfer of organic dye molecules and upconverting particles from their initial hydrophobic solvent to water.

Abstract

In this protocol, we first describe a procedure to synthesize lanthanide doped upconverting nanoparticles (UCNPs). We then demonstrate how to generate amphiphilic polymers in situ, and describe a protocol to encapsulate the prepared UCNPs and different organic dye molecules (porphyrins and diarylethenes) using polymer shells to form stable water-dispersible nanoassemblies. The nanoassembly samples containing both the UCNPs and the diarylethene organic dyes have interesting photochemical and photophysical properties. Upon 365 nm UV irradiation, the diarylethene group undergoes a visual color change. When the samples are irradiated with visible light of another specific wavelength, the color fades and the samples return to the initial colorless state. The samples also emit visible light from the UCNPs upon irradiation with 980 nm near-infrared light. The emission intensity of the samples can be tuned through alternate irradiation with UV and visible light. Modulation of fluorescence can be performed for many cycles without observable degradation of the samples. This versatile encapsulation procedure allows for the transfer of hydrophobic molecules and nanoparticles from an organic solvent to an aqueous medium. The polymer helps to maintain a lipid-like microenvironment for the organic molecules to aid in preservation of their photochemical behavior in water. Thus this method is ideal to prepare water-dispersible photoresponsive systems. The use of near-infrared light to activate upconverting nanoparticles allows for lower energy light to be used to activate photoreactions instead of more harmful ultraviolet light.

Introduction

Today there is still an urgent need to develop new types of bio-imaging agents. Many novel fluorescent probes have been well documented.^1-6 However, substantial improvements in the image resolution remains a challenge.⁷ One practical method is to directly modulate the fluorescence probes between a ‘light’ emissive state and a ‘dark’ quenched state.^8-12 This particular method has been applied to develop technologies such as stimulated emission depletion (STED) microscopy¹³ and stochastic optical reconstruction microscopy (STORM).¹⁴

Another approach to modulate flu....

Protocol

1. Synthesis of the NaYF₄/Yb³⁺/Er³⁺ Upconverting Nanoparticles (UCNP)

1. Set up the apparatus as followed:
   1. Place a 250 ml heating mantle on a regular stirring plate and plug the mantle onto the thermal couple.
   2. Place a 250 ml round bottom flask equipped with a magnetic stir bar onto the heating mantle with proper clamping.
   3. Attach an air adapter to the left neck of the round bottom flask and connect this air adapter to the Schlenk line with plastic tubing.
   4. Attach a glass adapter to the right neck of the round bottom flask and fix a thermometer adapter onto the glass adapter. Insert th....

Results

Absorption spectra and photoluminescence spectra were collected for sample DAE-UCNP. The absorption spectra are used for comparing the spectral overlap between the closed diarylethene chromophores and the upconverting nanoparticles. Photographs of the samples (both TPP-UCNP and DAE-UCNP) were also included to demonstrate successful encapsulation of organic dye molecules and upconverting nanoparticles, which are located within the amphiphilic polymer shells in the aqueous phase. The modulation of photochemistry and fluore.......

Discussion

The nanoparticles synthesized according to this protocol have a size distribution from 20 to 25 nm centered at around 22.5 nm.^26,27 They can be classified as spherical particles with a α-NaYF₄ host lattice structure. There are two critical steps in this protocol. In the UCNP synthesis, it is crucial to maintain the heating temperature and time as precise as possible to assure a narrow distribution of particle size. Simultaneous addition of NaOH and NH₄F along with the addition of lan.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Yttrium acetate	Sigma	326046	Yttrium(III) acetate hydrate
Ytterbium acetate	Sigma	544973	Ytterbium(III) acetate hydrate
Erbium acetate	Sigma	325570	Erbium(III) acetate hydrate
Oleic acid	Sigma	75096	analytical standard
Octadecene	Sigma	O806	Technical grade
NaOH	Sigma	S5881	reagent grade
NH4F	Sigma	216011	ACS reagent
Poly(styrene-co-maleic anhydride)	Sigma	442399	Average Mn = 1700
JeffAmine 2070	Huntsman	M-2070
Varian Carry 300	Agilent
JDSU NIR laser	JSDU	L4-9897510-100M	980 nm diode laser