Abstract
Silica nanoparticles (SNPs) have been used as favoured platforms for sensor, drug delivery and biological imaging applications, due to their ease of synthesis, size-control and bespoke physico-chemical properties. In this study, we have developed a protocol for the synthesis of size-tuneable SNPs, with diameters ranging from 20 nm to 500 nm, through the optimisation of experimental components required for nanoparticle synthesis. This protocol was also used to prepare fluorescent SNPs, via covalent linkages of fluorophores, to the nanoparticle matrix using 3-aminopropyltriethoxysilane (APTES). This enabled the fabrication of ratiometric, fluorescent, pH-sensitive nanosensors (75 nm diameter) composed SNPs covalently linked to two pH-sensitive fluorescent dyes Oregon Green (OG) and 5(6)-carboxyfluorescein (FAM) and a reference fluorescent dye 5-(6)-carboxytetramethylrhodamine (TAMRA), extending the dynamic range of measurement from pH 3.5 to 7.5. In addition, size-tuneable, core–shell SNPs, covalently linked to a fluorescent TAMRA core were synthesised to investigate distance-dependant fluorescence quenching between TAMRA and black hole quencher 2 (BHQ2®) using nanometre-sized silica shells as physical spacers. The results showed a significant fluorescence quenching could be observed over greater distances than that reported for the classical distance-dependent molecular fluorescence quenching techniques, e.g. the Förster (fluorescence) resonance energy transfer (FRET). The methods and protocols we have detailed in this manuscript will provide the basis for the reproducible production of size tunable SNPs, which will find broad utility in the development of sensors for biological applications.
Highlights
We have developed a protocol optimising the amounts of each reactant and catalyst required for nanoparticle synthesis to produce size-controlled and tuneable silica nanoparticles (SNPs)
The primary aim in our study was to develop a protocol to optimise the synthesis of size-tuneable SNPs that can be used in applications where nanoparticle size-control is important
The results showed that this two-step synthesis protocol produced monodisperse SNPs with diameters ranging from 200 to 500 nm (PDI < 0.10), Fig. 4D
Summary
Nanoparticle-based techniques have opened new horizons towards the development of smart tools for many applications, including drug delivery, biological imaging and intracellular measurements.[1]. It is important to note previously reported studies[12,16] do not agree with the ndings reported by Stober These contradicting ndings indicate the need for further studies to develop and optimise a valid protocol that can be readily followed for the synthesis of size-tuneable SNPs, especially for applications where nanoparticle size control is critical, e.g. intracellular measurements. Surface plasmon resonance (LSPR), excluding any potential role that silica could exhibit This re ects the fact that further research is required to investigate uorescence transfer/ quenching between a uorescent donor and a quencher over distances using silica shells as spacers. Fluorescence quenching between 5-(6)carboxytetramethylrhodamine (TAMRA) and black hole quencher 2 (BHQ2®), separated by silica shells with different thickness was observed and quanti ed
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