Abstract
In modern biosensing and imaging, fluorescence-based methods constitute the most diffused approach to achieve optimal detection of analytes, both in solution and on the single-particle level. Despite the huge progresses made in recent decades in the development of plasmonic biosensors and label-free sensing techniques, fluorescent molecules remain the most commonly used contrast agents to date for commercial imaging and detection methods. However, they exhibit low stability, can be difficult to functionalise, and often result in a low signal-to-noise ratio. Thus, embedding fluorescent probes into robust and bio-compatible materials, such as silica nanoparticles, can substantially enhance the detection limit and dramatically increase the sensitivity. In this work, ultra-small fluorescent silica nanoparticles (NPs) for optical biosensing applications were doped with a fluorescent dye, using simple water-based sol-gel approaches based on the classical Stöber procedure. By systematically modulating reaction parameters, controllable size tuning of particle diameters as low as 10 nm was achieved. Particles morphology and optical response were evaluated showing a possible single-molecule behaviour, without employing microemulsion methods to achieve similar results.Graphical abstractWe report a simple, cheap, reliable protocol for the synthesis and systematic tuning of ultra-small (< 10 nm) dye-doped luminescent silica nanoparticles.
Highlights
A fundamental requirement for highly responsive optics-based biosensors is to have enough signal-tonoise ratio (SNR) to reveal the presence of analytes at very low concentrations (Banica 2012)
The integration of fluorescein isothiocyanate (FITC) within inorganic silica frameworks is usually conducted by the addition aminopropyl triethoxysilane (APTES) to FITC (Enrichi et al 2009a, 2010; Riccò et al 2011)
Fluorescein-doped silica nanoparticles with a diameter down to 10 nm or less could be produced in an environmentally friend fashion, by a simple modification of the classical Stöber technique without the needs of microemulsion systems, avoiding the use of organic solvents and surfactants
Summary
A fundamental requirement for highly responsive optics-based biosensors is to have enough signal-tonoise ratio (SNR) to reveal the presence of analytes at very low concentrations (Banica 2012). The use of dye-doped silica NPs was demonstrated to improve significantly the detection limit of a microarray device (Enrichi et al 2010), permitting the implementation of this fluorescent nanosystem in the in vitro DNA microarray detection of human papilloma virus (HPV) single-strand sequences (Riccò et al 2011). All these studies suggest the use of dye-doped silicon oxide nanoparticles (ddSiONPs) as a promising strategy to overcome the drawbacks of fluorescent molecule labels. Small size is a key requirement for this new class of fluorescent labels,
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