A rigid conjugated pyridinylthiazole derivative and its nanoparticles for divalent copper fluorescent sensing in aqueous media

AIE active fluorescent organic nanoparticles based optical detection of Cu2+ ions in pure water: a case of aggregation-disaggregation reversibility

An AIE-active pyrene-terpyridine derivative, (4'-(pyren-1-yl)-2,2':6',2''-terpyridine) (1) was found to form nanoaggregate in an aqueous medium. The probe involved hydrogen bonding with solvent molecules that modulated the charge transfer behavior and consequently resulted in different spectroscopic behavior due to the formation of fluorescent organic nanoparticles (FONs). In the presence of Cu2+ ions, FONs displayed a ratiometric red shift of the absorption band (360 to 420 nm) accompanied by a prominent naked-eye color change from colorless to light yellow. With a gradual increase in water content, 1 displayed a huge red shift of the emission band (430 to 475 nm) denoting its switching from monomer to FONs. In the presence of Cu2+, the 475 nm emission band of FONs gradually diminished, facilitating the micromolar scale detection of Cu2+ (LOD = 8.57 μM) in a 100% aqueous medium with a fluorogenic color change from cyan to dark. The SEM and DLS data indicated the cation-induced disaggregation of FONs, which was further confirmed by mass spectral analysis and electron paramagnetic resonance measurement. In addition, the high selectivity of FONs towards Cu2+ ions over other potential cations and the 2 : 1 (1-Cu2+) binding stoichiometry were also determined. Moreover, the spectroscopic behavior of the monomeric amphiphilic probe was well supported by extensive DFT study. Such detection of Cu2+ ions in pure aqueous medium denoting an aggregation-disaggregation event is very rare in the literature.

Fluorescent organic nanoparticles (FONs) as convenient probes for metal ion detection in aqueous medium

Fluorescent organic nanoparticle (FON)-based chemosensors are emerging as a valuable tool for the fast and accurate detection of metal ions in aqueous media. In this review, we highlight the recent developments in this field.

Carbazole based nanoprobe for selective recognition of Fe3+ ion in aqueous medium: Spectroscopic insight

A simple carbazole based nanoprobe prepared by reprecipitation method shows selective sensing behavior for Fe³⁺ ion in aqueous medium. The prepared SDS capped 9-phenyl carbazole nanoparticles (9-PCzNPs) has narrower particle size distribution with an average diameter 35nm and zeta potential of -34.3mV predicted a good stability with negative surface charge over the nanoparticles. The Field Emission Scanning Electron Microscopy (FE-SEM) image showed cubic shape morphology of nanoparticles. The aqueous suspension of SDS capped 9-phenyl carbazole nanoparticles exhibited aggregation induced enhanced red shifted intense emission in comparison with the emission arising from dilute solution of 9-phenyl carbazole in DCM. The cation recognition test based on fluorescence change shows Fe³⁺ ion induce significant fluorescence quenching, however remaining cations responds negligibly. The obtained quenching data fit into Stern-Volmer relation in the concentration range of 0.0-1.0μg·mL^-1 of Fe³⁺ ion solution and the detection limit is 0.0811μg·mL^-1. The probable mechanism of fluorescence quenching of SDS capped 9-PCzNPs is because of adsorption of Fe³⁺ ion over the negatively charged surface of NPs through electrostatic interaction. Thus the proposed method was successfully applied for the detection of Fe³⁺ ion in environmental water sample.

Fluorimetric detection of Sn(2+) ion in aqueous medium using Salicylaldehyde based nanoparticles and application to natural samples analysis

The fluorescent 2-[(E)-(2-phenylhydrazinylidene)methyl]phenol nanoparticles (PHPNPs) were prepared by a simple reprecipitation method. The prepared PHPNPs examined by Dynamic Light Scattering show narrower particle size distribution having an average particle size of 93.3nm. The Scanning Electron Microphotograph shows distinct spherical shaped morphology of nanoparticles. The blue shift in UV-absorption and fluorescence spectra of PHPNPs with respect to corresponding spectra of PHP in acetone solution indicates H- aggregates and Aggregation Induced Enhanced Emission (AIEE) for nanoparticles. The nanoparticles show selective tendency towards the recognition of Sn(2+) ions by enhancing the fluorescence intensity preference to Cu(2+), Fe(3+), Fe(2+), Ni(2+), NH4(+), Ca(2+), Pb(2+), Hg(2+) and Zn(2+) ions, which actually seem to quench the fluorescence of nanoparticles. The studies on Langmuir adsorption plot, fluorescence lifetime of PHPNPs, DLS-Zeta sizer, UV-visible and fluorescence titration with and without Sn(2+) helped to propose a suitable mechanism of fluorescence enhancement of nanoparticles by Sn(2+) and their binding ability during complexation. The fluorescence enhancement effect of PHPNPs induced by Sn(2+) is further used to develop an analytical method for detection of Sn(2+) from aqueous medium in environmental samples.

Fluorescent organic nanoparticles (FONs) for selective recognition of Al3+: application to bio-imaging for bacterial sample

(a) Changes in fluorescence upon successive addition of Al³⁺ ions to salpn-ONPs; (b) titration profile of fluorescence; (c) recognition of Al³⁺ through bio-fluorescence Staphylococcus aureus bacterial cells.

Nanoparticles made of π-conjugated compounds targeted for chemical and biological applications

This feature article summarizes the recent applications of nanoparticles made of π-conjugated compounds in bio/chemo-sensing, disease therapy, and photoacoustic imaging.

Highly selective colorimetric sensing of Cu(II) ions in aqueous solution via modulation of intramolecular charge transfer transition of aminonaphthoquinone chemosensor

An aminonaphthoquinone based colorimetric chemosensor has been developed and demonstrated for the highly selective detection of Cu(II) ions in aqueous solution. The intramolecular charge transfer (ICT) transition exits in amine moiety directly attached to the quinone ring is modulated by the d-d transition of a square planar Cu(II)-receptor complex resulting in a change of color from yellow to blue. No significant color change was observed upon addition of other selected metal ions. The sensing property has been investigated using various spectral techniques (UV-Vis, fluorescence) and product analysis (Elemental analysis, magnetic moment, UV-Vis, FT-IR, EPR).