β-Cyclodextrin grafted gold nanoparticles with short molecular spacers applied for nanosensors based on plasmonic effects

Abstract

The detection and quantification of organic molecules is of vital importance in many areas as Biochemistry, Medicine, Environmental Chemistry, etc. The Supramolecular systems as macrocycles form host guest complexes that they can be applied to the design of Nanosensors due to their capabilities of molecular recognition. In this work it was used β-CD that it is a very well-known host for organic molecules. The βCD was attached by covalent linking over gold nanoparticle surface modified with molecular spacers. The guest studied was Rhodamine B (RhB) as a typical organic molecule that absorbs at the interval 500–600 nm that it overlaps perfectly with the gold Nanoparticles Plasmon. By this manner the selectivity of this Nanosensor works by a Supramolecular interaction and a Plasmonic complementarity. The βCD Nanoparticles grafted interact and form Nanoaggregates and depending of the state of development it was the effect obtained on the fluorescence emission. Nanoaggregates sizes below 500 nm, due to the short distances of the molecular spacers the guest emission was quenched. With higher Nanoaggregates it was measured an enhanced fluorescence emission effect based on Enhanced Plasmonics (EP) and Metal Enhanced Fluorescence (MEF). These Nanoaggregates were applied as Nanoplatforms for molecular detection. Based on these Nanoarchitectures it was possible to estimate the number of molecules detected per Nanoaggregate by NanoImaging with fluorescence microscopy. The sensitivity (m) of the Nanosensor allowed to arrive to limit of detections (LOD) close to 0.98 nM. From Fluorescence NanoImaging it was possible to detect two distribution of Nanoaggregates; the first one smaller than 500 nm and the second one higher aggregates, from where it was possible to detect at the best of the cases a minimal and a maximal number of molecules of 15 and 400 respectively per Nanoaggregate unit. In order to validate the sensitivity of the Nanosensor, it was tested in real samples of soil and water.